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THE AM BULLETIN BOARD => Technical Forum => Topic started by: w9jsw on February 09, 2019, 11:27:08 AM



Title: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on February 09, 2019, 11:27:08 AM
I am generating a new board for this driver design. Attached are the original schematic and my copy of it into EasyEDA so that I can generate the PCB. Please look at it carefully (WA1GFZ ??) to see if I copied it correctly.

WA1GFZ - your PMs are blocked and there is no email address. I tried to respond to your PM. Hopefully you will want to contribute to this thread.

I have most of the footprints correct.

Questions -

50uf non-polorized caps are crazy expensive. I subbed two back to back 27uF electrolytics. Are there any special characteristics I should be looking at for the caps (low ESR, etc)?

The 1000uf at 450V Electrolytics are huge. Can I place them off board so that I can save space on the PCB? Should I add some smaller ones or more bypasses in addition to the off-board caps?

Are there any design updates that are not listed on the schematic?

BTW, found some nice 2.2uf coupling caps - Panasonic ECWFD2J1225J - in stock and $1.5 each...
Put a trimmer in place of R26/R27
NFB Ladder in rig

Comments please...

John W9JSW




Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: K1JJ on February 09, 2019, 12:41:31 PM
Hi John,

Maybe Frank will see this and comment. I'll send him an email too.

Yes, the beer can 1000uFd @ 450Vs can be off-board.  I did it that way. Just keep the leads as short as possible. If you build the +- 300V supply in the same enclosure, the filter caps should be enough by themselves.  I think the extra caps are a precaution against remote supplies having PS leads of several feet. This is more about suppressing glitches and spikes rather than AC hum filtering and regulation.   IIRC, there is no PS current variation during modulation being in class A, so dynamic regulation is not an issue.


Speaking of RF bypassing, etc:

Yes,  capacitor bypasses are always a good idea to sprinkle around.  I also added ferrite cores, #63, to all input and output leads on the MOSFET driver. The ones that snap on work well. In fact I have about 30 of them all around the shack in critical low level audio and RF leads just to have a more stable environment.   The old days of RF in the audio never plague me anymore. This can become a big problem when running a KW and using antennas with exposed antenna tuners, openwire or antennas in close proximity... as well as unbalanced antenna currents in coaxial  feedlines, etc.  Operating on the higher bands can also bring out issues.  Once we cross 40M and higher, it's a different, squirrely, RF whirl.

T


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KK7UV on February 09, 2019, 02:16:23 PM
John,   JustRadios.com has 47uF 100v NP caps for $2.99.

I am building the MOSFET driver too.  I will do mine point-to-point I think.   Just putting the order together today.

Steve - KK7UV


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: N0WEK on February 09, 2019, 03:15:10 PM
Two back to back series 27 uf caps equal 13.5 uf.  In parallel of course they'd be 54 uf. 


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on February 09, 2019, 03:40:02 PM
Two back to back series 27 uf caps equal 13.5 uf.  In parallel of course they'd be 54 uf. 

Right...

I switched it to a non-polarized one. Like it better.

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on February 09, 2019, 03:41:58 PM
John,   JustRadios.com has 47uF 100v NP caps for $2.99.


Thanks for the pointer! That is the type of cap I would prefer to use. Let me know how big it is i.e. how much space do I need between holes. No specs on that site for me to pick the correct footprint.

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on February 09, 2019, 03:47:41 PM
I have the board laid out now but have not yet added the traces.

Advice is welcomed.

I was planning to use a 1oz copper board, 1.6mil thick. Traces at 20Mil for signals, more for power. Was going to do a ground plane on the bottom. Minimize vias. Grounded mounting holes on all 4 corners.

Fets mounted under the board with access holes to allow them to be screwed to a heatsink. I have done this before and it works quite well. Easy to install.

Feel free to comment on the above.

Overall board looks like 100mm by around 175mm. A 2 layer board from Taiwan for Qty of 10 is $40. Plus shipping on a slow boat for $15 and DHL for $26.

Not a bad price!

John



Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KC2ZFA on February 09, 2019, 04:16:34 PM
John, in case you open this project to the public,
I am interested in 2 or 3 boards (so I can manage
populating one that works  :) )

Please let me know when the time comes.

Peter


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: K1JJ on February 09, 2019, 04:29:07 PM
I have the board laid out now but have not yet added the traces.

Overall board looks like 100mm by around 175mm. A 2 layer board from Taiwan for Qty of 10 is $40. Plus shipping on a slow boat for $15 and DHL for $26.
Not a bad price!

John


Hi John,

$40 + shipping for ten is a tremendous price. It's not even worth it to do point-to-point anymore. Wish they were available when I built mine.

Anyway, they will sell out quickly.  This is the breakthru step between having average audio to transparant pristine audio.  Especially when the audio negative feedback is added.

I was talking to Frank WA1GFZ and he said he will send you an email. He will answer your questions and also wants a board for his new heavily-modified Valiant project.  Frank even wound his own FB mod xfmr.

Thanks for the excellent effort, John!    " Chirp-chirp -   AMers were only waiting for this moment to arrive..."


BTW, your Easy EDA schematic is MUCH easier to read than the original.  Use that one only - once it is perfected.    (Posted below)


It's important to point out that this driver uses only the famous and inexpensive 11N90 900 volt MOSFET as used in most class E rigs.  A well-proven device.

T


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on February 09, 2019, 05:16:38 PM
Latest schematic - use this one for comments -

Tom - the one you posted is identical to my first one. Did you have any comments for it? If it has annotations I did not get them.

Changes -

NP input cap
Fuse clip components for glass fuses (to get the footprint correct)
Removed beer can caps. Still need to add a few more coupling caps after I do the traces.

Still quite a bit of open real estate. I can go to 100mmx200mm at the same cost and no need to get it smaller/cheaper. I may stretch it out a bit to give more space between the 10W resistors.

Should have a picture of the board in the morning.

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: K1JJ on February 09, 2019, 05:46:50 PM
OK John -

I would keep the beer cans on the schematic since Frank intended that much capacitance there. You could make a note that these caps are not physically on the board but should have short leads to the board. They can be mounted on the power supply to double as filter caps - as long as the leads are short.  Short means = 6-8" or less to the audio driver PCB?  

Keep the board comfortably big enough to work on parts, remove them, etc. Also, sometimes parts change size in the future, so plan on roomier than too tight.  And remember we are dealing with 600VDC. (+ - 300V)  So keep the trace spacing wider rather than too narrow so not to end up with charred boards.

BTW, I used a Variac on my + - 300V supply. I found I could reduce it somewhat to just what was required to drive the tube modulators. Same results in class A, less heat. Still, the 11N90s barely get warm.  In my case using tetrode configured 4-1000A modulators, I was able to back it down to +- 260 volts.  Big low-mu triode modulators like 833As will require the most voltage.

Important: The driver board's MOSFET gate bias resistors are optimized for +- 300V. When the power supply voltage is changed too low, some of the FET gate bias resistors need to shift in value to get back to maximum output capability. So watch the scope carefully when reducing voltage.

How it works, simplified: The + - 300V supplies basically center tap  and produce  0 volts to the tube grids thru the FETS. You set this DC offset that sets the negative bias and adjusts the idle current for the tubes. Then the audio signal comes thru push-pull and swings the grids up and down around this DC bias point.  So if you need less than  +- 300V of audio swing to fully drive the tubes, you can back down the overall supply somewhat.  Put an audio tone thru at full RF and audio power and you can easily see this + - 300V voltage Variac adjustment threshold on the scope.


I don't have any more comments at this point. Let Frank look over the final schematic and PCB to see what he thinks...

T


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KD6VXI on February 09, 2019, 09:28:20 PM
If you have extra space, may I suggest that you include the qix negative peak limiter.

Of course, switch by passable.

I used it in my own processor design.  Works FB after an all pass rotator and 3 band compressor!

--Shane
KD6VXI



Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KK7UV on February 10, 2019, 07:34:51 AM
How much current does the driver need?   I am trying to design a power supply for it.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on February 10, 2019, 09:07:37 AM
40-60ma on each leg. Tom has a variac on his supply and runs it slightly reduced.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KK7UV on February 10, 2019, 10:07:04 AM
Thanks John.    Is a regulated supply needed?  or perhaps just rectified, cap filter, and perhaps a current limiting resistor?


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: Opcom on February 10, 2019, 11:02:33 AM
Is it done in LTspice? I would like to play around with it a little. I really like the design and the evolutions.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on February 10, 2019, 11:37:55 AM
Thanks John.    Is a regulated supply needed?  or perhaps just rectified, cap filter, and perhaps a current limiting resistor?

I would like to see a PS proposal as well.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: K1JJ on February 10, 2019, 12:29:21 PM
Thanks John.    Is a regulated supply needed?  or perhaps just rectified, cap filter, and perhaps a current limiting resistor?


FB, Steve -

The more help the better.

The driver board runs class A, a steady ~40 mA draw per leg, (two legs) so any brute force type power supply will work fine.   I believe the PS continuous rating should then be at least  100 mA since the two class A legs are running together.  Let me axe Frank about his rating opinion.  No need for voltage regulation.    

I have just one meter on the audio driver board panel monitoring the drain current of R4... a 50 mA meter in series with R4.  This is a steady state current of 40 Ma or so.   I read the modulator tube's grid current separately in the mod deck, since this is a dynamic measurement with audio fluctuation.

Just a heads-up to those ordering parts: Frank, John and I have been emailing and making some minor value changes. A few errors were found in the transition from the prototype to the schematic.... The C12  0.47 uF NFB cap is now 300 pF.  That's what I had in mine all along.

I am using the NP 20 uF cap in the audio input, so that still stands.  John is considering different pot wattage ratings too.

John will be posting an updated schematic.


BTW, yes, the QIX negative peak limiter would be a nice addition. It's really only a few parts, so worth adding.   The circuit can be found within his PWM modulator board. (We should ask for Steve's permission, of course)

** Another point:  I noticed that I never employed a way to key the driver board on and off for T/R. I just leave it running and a step start relay disconnects the audio drive. I probably didn't want to have power supply pops by keying the +- 300V.  Maybe we can find a way to bias the whole circuit off during receive to kill (or greatly reduce) class A current without causing audio pops.


*** UPDATE:  It was decided to keep any negative peak limiting circuitry off the driver board. This would require low level op amps, low voltage and other complications.  Keep NPL with the low level processing and leave the driver board as is...


T  
 


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on February 10, 2019, 02:01:53 PM
Preliminary look-see

BTW - found bi-polar elecrolytics at Digikey for a buck. Fets are $4 due to the tariffs.

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KD6VXI on February 10, 2019, 11:51:03 PM
I bought my NP caps from capacitorworld.net

Was prescribed by someone here, and I've purchased from them a few times.

--Shane
KD6VXI


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: DMOD on February 11, 2019, 12:20:59 PM
You might want to increase C1's value to C9's value (47 uF) since you are working into the same low impedance of about 1.9k.


Phil


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on February 13, 2019, 06:59:20 AM
I have a day job, so slow progress during the week.

Frank or Tom - can you respond to Phil's comment?

We are doing some finalization on the board footprints and making sure the tracks and vias are large enough and well spaced enough to handle +/- 300V. Also adding off board pots to allow for fine tuning adjustment of bias on the final mosfets. Frank is re-running the models to insure we have this right for various voltage applications.

What we will probably do is a small run to build some prototypes then a larger run with errata changes applied from the prototypes to get the final boards right. With the low costs for PCB runs in China we don't have to be perfect on the first run, just close. Takes the pressure off. It is a different world WRT PCB manufacturing than when this was tried back in 2010/2011.

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KD6VXI on February 13, 2019, 09:23:32 AM
It is a different world.

And realize.  These boards will be in ebay, alibaba and the rest of the sales sites within a couple days of being produced.

The big 3.5 inch bird meters square you see in ebay?  I had those made up.  And was told I had to come up with 10k dollars for an initial run or they would be in ebay.

They are now sold direct by China and n2yck.

The price we pay for below cost production.

--Shane
KD6VXI


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KB2WIG on February 13, 2019, 10:53:35 AM



Hmmmm    what would happen if a few lands were direct shorts to ground on the chicom boards?   Could someone with an exacto knife or a dremmel fix the short?


KLC


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on February 13, 2019, 01:11:30 PM
Don’t know if this is an issue so I asked Frank since he owns the copyright. I can get USA boards for around $12 each


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: K1JJ on February 13, 2019, 08:58:08 PM
You might want to increase C1's value to C9's value (47 uF) since you are working into the same low impedance of about 1.9k.
Phil


Hi Phil,

We'll have to axe Frank on that one...

Frank optimized everything in simulation so I imagine all is well.    He's gone a step further and is now using IMD simulation results to fine tune the board, looking for over -40 dB 3rd.  

It should be quite the design when he's finished.  

T


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: DMOD on February 13, 2019, 09:36:32 PM
Hi Phil,

My guess is that the large input cap will allow for most any low impedance, one volt audio driver.

Frank optimized everything in simulation so I imagine all is well.    He's gone a step further and is now using IMD simulation results to fine tune the board, looking for over -40 dB 3rd.  

It should be quite the design when he's finished.  

T

As did I, I simulated the stages as well in MatLab/Simulink.

I would assume one would want consistent -3dB down frequency responses at each stage so there are no bumps or dips in the overall response.

Addendum: The actual 3dB down plots show the following. What I had quoted earlier was the "breakpoint" frequencies:

According to the latest schematic - in the first stage, the low frequency 3-dB down frequency response is 7Hz, the low frequency frequency response of the second stage is 3dB down at 92Hz, and the low frequency frequency response of the third stage has a 3dB down point of 4.5Hz. So one could use C9 = C1 = 2.2 uF and C4 = 0.1 uF if one wanted a lowest frequency response of ~ 100Hz for the the first three voltage amplifiers.


The audio input impedance (resistive part) at P1, with the R47 4.7k, is 1.4k. 


Phil - AC0OB



 



Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: K1JJ on February 14, 2019, 12:17:07 AM
Now I see what you mean, Phil.

That's something I never noticed not having seen the sim myself.  I'll axe Frank and see if he's aware of it. Could be part of his current changes.

Tnx.

T


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: DMOD on February 14, 2019, 11:28:44 AM
Now I see what you mean, Phil.

That's something I never noticed not having seen the sim myself.  I'll axe Frank and see if he's aware of it. Could be part of his current changes.

Tnx.

T

I know sometimes if I have a bunch of capacitors that meet my lowest LF requirements I'll just use those instead of specifying a different value.  :)


Phil - AC0OB


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on February 17, 2019, 08:21:34 AM
Almost ready for Fab....


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on February 18, 2019, 05:27:09 PM
Missed that there is a $100 tooling charge. This puts the board at $25-$30 my cost and I have to front the full amount and hope I can sell all of them. Are these still interesting at that ballpark price? I see why folks use China so much.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: W1RKW on February 18, 2019, 05:41:51 PM
You have a buyer for a board. See PM.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: K1JJ on February 18, 2019, 05:54:30 PM
OK John -

FB!!

Frank has done a lot of thinking and optimization on the board behind the scenes. The IMD and flat response look heavenly. He's also looking into balanced input. It's his best effort to date.

You too have done an outstanding job laying it out and rounding up the perfect parts.  The pads are big and the traces are spaced wide for +- 300VDC.  There's a lot to like.

I will also order a board even though I have the old point to point prototype running FB. The opportunity to get a board may not happen again, so hey, even if I build another 813 rig or give it to someone else later on, it will get used.

I see my prodding enticed you to build one too, Bob!  You will be as happy as a clam, especially after adding in NFB to your 813 rig.    ;D

T


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on February 18, 2019, 09:00:31 PM
7 confirmed out of 10 so that is a go. Getting quotes now.



John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w8khk on February 19, 2019, 01:39:04 AM
Me Too... I sent a PM and email.....

How about Push-Pull 304TLs modulated by a pair?  That should not be too PW.....

 I have three of the tubes, maybe find one more at the Dalton Hamfest this Saturday. Anybody know of some spares floating around?

The board will be put to good use!


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on February 19, 2019, 06:33:20 AM
8 are spoken for now, 9 if Shane re-confirms. I will likely bump the order to 15 to insure some extras are available. Have not received the quotes yet, other than Oshpark which is always high.

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KC2ZFA on February 19, 2019, 09:55:45 AM
thanks for this, just making sure you got my PM.

Peter


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KD6VXI on February 19, 2019, 11:24:11 PM
Sorry, I've been out of town on business.

Yes, put me down.

PayPal work?

--Shane
KD6VXI


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on February 20, 2019, 06:36:32 AM
Here is the list I have that want boards -

confirmed 2 – John W9JSW
confirmed 2 - Frank WA1GFZ
Confirmed 1 - Shane KD6VXI
confirmed 1 – Tom K1JJ
confirmed 1 – Pete KC2ZFA
confirmed 1 – Bob W1RKW 
confirmed 1 – Rick W8KHK

Second quote came in $20 higher than Oshpark. Awaiting one more quote.

If anyone has a suggestion on US based FABs to try, I am game. I used 4pcb and Oshpark so far.

Thinking about a 50% deposit on the boards to help me defray the lump sum cost to kick off the process.

Comments? Also, this is a first pass board. No guarantees that there won't be a bypass or other type of mod to get them running. My boards usually come back clean and don't have any defects, but it can happen in a first pass effort. Take a close look and if you see anything, speak up.

John

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KB2WIG on February 20, 2019, 07:36:17 AM


I'll go for one board.

KLC


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: M0VRF on February 20, 2019, 10:24:35 AM
OSHPARK

NO TOOLING CHARGES

If you buy over 100sq inches is $1 sq inch

It's in the US too.

JB.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on February 21, 2019, 07:17:41 PM
Will place order in the morning. 15 day cycle to get best price. I will post sales price after I know the full cost including shipping.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: K1JJ on February 21, 2019, 08:44:37 PM
(Thanks to both Frank/GFZ - circuit design......  and John/JSW - board layout)


*** Hold off one more day, John.  I have a feeling there are a few more takers...  ***  ;)

Last call guys!

This is the critical part to building the ultimate tube modulator.  Even if it sits for a year, you will have something that may not be available again.

It's a great design, top quality and above all, cheap.   No transformers in your audio negative feedback loop. Rock solid IMD specs and ultra-
flat performance!   Just use a decent mod xfmr and robust tube modulators and youse gots it all.

Operators are standing by...  

T

Knock it out in one evening:



Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w8khk on February 22, 2019, 02:47:46 AM


*** Hold off one more day, John.  I have a feeling there are a few more takers...  ***  ;)

Last call guys!



Tom VU's crystal ball has been recapped and is working in splendid fashion.  My brother, W2WM, saw this thread and would like one too.  PM sent to John.  Thx!


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on February 22, 2019, 06:30:49 AM
Emails or PMs sent out to all folks that expressed an interest. Did not want to post my paypal info here. If I missed you then PM me or post here.

I ordered enough for the current needs plus about 10 more, so plenty for a while. I will need to sell a few more to break even but with Tom on the wagon hawking these wares, I am sure that will occur.  ;D

I set the price at $35 including free first class shipping (USA only). I am willing to ship international but shipping will be extra.

Here is the BOM. You should be able to import this at digikey and build your cart. I did not spec the external pots or the external large caps. I need to work with Frank to nail down those specs, so maybe wait a day or two if you are going to place an order. If you have trouble with the digi site, let me know. There is a feature where I can share a cart with you.

You will need to find a heat sink. Frank envisions that this board will be mounted very near the modulator and that the pots will be mounted so it is easy to fiddle with them for calibration but then not touched. So they need to be accessible but not on a front panel. I have 2 options for the NFB pot, one on board and it can also be substituted for a off board equivalent.

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KD6VXI on February 22, 2019, 09:02:45 AM
Money is sent, sorry I forgot to add that the Addy you have is correct.

--Shane
KD6VXI


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KD6VXI on February 22, 2019, 09:04:35 AM
Does it need an honest heat sink, or do you / Frank believe possibly chassis mounting the fets would be enough?

--Shane
KD6VXI


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: K1JJ on February 22, 2019, 12:42:39 PM
Does it need an honest heat sink, or do you / Frank believe possibly chassis mounting the fets would be enough?
--Shane
KD6VXI

Shane,

From my real experience with the prototype: I use a small 6" X 8" heatsink with 1/2" fins. (underneath - not shown here)    The FETs and sink barely get warm and I leave them keyed on all the time. (The 4-1000A modulator tubes get T/R keyed in the fil CT)   My guess is you could get away with just a 1/8" aluminum plate.  It will also depend on how hard you idle and bias it -   833As vs: smaller 811As, etc.

Big tubes, then use a heatsink - small tubes then just a plate will probably do.

T


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on February 23, 2019, 12:54:32 PM
While we are awaiting boards, I have started a design notes document. Feel free to suggest additions.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: K1JJ on February 23, 2019, 06:14:47 PM
They say the proof is in the pudding. For those of you wondering what the GFZ MOSFET  audio driver sounds like, well here it is.


This is a recording taken from on the air transmitted on 3885 and received thru an R-390 at Jeff/ W2NBC's QTH.   You're listening to my homebrew pair of 4-1000As -  plate modulated by a pair of tetrode-connected 4-1000As using regulated screen and grid supplies. It uses broadcash iron and heavy negative feedback. The transmit audio rolls off sharply at about 5.5 KHz so the signal bandwidth is reasonable.


I have just an average voice but must say this is my best building effort ever.   (To sound immodest)  I went to the ends of the Earth to get this rig running as cleanly as possible. Listen to the highs and lows.. balanced and clean. Not easy to do in a big rig like this. For once I am satisfied.   And, you can be too!!… with the World Famous WA1GFZ MOSFET audio driver!   ;)  ;D

T

Audio file below:


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on February 23, 2019, 08:06:45 PM
Wow! Never was able to hear you in the Midwest during this low solar cycle. Wow...


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on February 23, 2019, 09:37:31 PM

The FETs and sink barely get warm and I leave them keyed on all the time. (The 4-1000A modulator tubes get T/R keyed in the fil CT)

T

Tom,

Do you do anything with the audio into the driver? Or is your control entirely just cutting the HV to the mod tubes.

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: K1JJ on February 23, 2019, 09:59:00 PM
Tom,
Do you do anything with the audio into the driver? Or is your control entirely just cutting the HV to the mod tubes.
John


John,

Partly.  I use the sequencer unit using time delay key contacts going into the one volt audio input of the MOSFET driver.  Last thing coming on and first thing turning off. No audio spikes or key up noise. I have many relays in the shack and two are very loud HV supply step start contactors, so I need to delay the audio until the very end of the sequence.  Without sequencer keying, the audio clack! is ridiculous.

(I sequencer key the fil CT and the HV to the modulator tubes too, so three ways.)

The only other solution would be using vacuum relays which would cost a fortune to populate.

The reason you haven't heard me, I hate to say, is that I haven't been on the air for a few years... just testing here and there.  I'm focused solely on helping others build their rigs -  or I'm trading the Dow Index futures market. I'm a type A very focused person and have trouble spreading out my attention.  I'm hoping when these new rigs (like yours) get going, I will MAKE the time.

You will hear me. I run a 2-el delta loop at 190' beaming SW.     Calif is easy on 75M when the solar cycle is low.

T


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: VE3ELQ on February 24, 2019, 09:27:02 AM

This is a recording taken from on the air transmitted on 3885 and received thru an R-390 at Jeff/ W2NBC's QTH.  


That sounds incredible, just like a PWMod rig, (sorry). Hard to believe you did that with tubes running linear.  Very well done.

73s Nigel


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on February 24, 2019, 02:35:33 PM
Updates


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on March 12, 2019, 11:27:23 AM
Boards arriving today. Will send them out asap and will send an individual message when on the way.

Extra boards available.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KC2ZFA on March 12, 2019, 11:50:21 AM
thanks John,

is there a final BOM ?


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: steve_qix on March 12, 2019, 04:12:50 PM
I've layed out a LOT of boards.  Your price is definitely in-line, particularly for the low volume.

When I order boards for the class E PWM modulators, I tend to get at least 40 at a time to keep the price down.  So far, all that I've made have been sold.  I think I'm on my 5th run at this point.

What size is the board that you're having made and where did you finally go to have it done ?

I have used ExpressPCB for everything so far.  Good quality, but I think they're higher in cost than perhaps is out there.

Regards, Steve


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on March 13, 2019, 06:02:07 AM
Hi Steve,

The board is approximately 133mmx171mm. I used Precision Technologies or eproto.com. I did my layout on EasyEDA. I also use Elecrow for boards if I want to go to China Fab.

They had a $100 setup charge then a sliding scale based on number of boards and fab time. I chose my number based on how many solid orders I had at the time, a few more to sell to late comers and free ones to Frank and Tom for the immense help provided during layout. I also did not want to tie up my money on a huge order with doubts on if I would sell them all.

I then set my price accordingly. Won't get rich for sure but maybe $2 an hour wage for my time if I happen to sell all of them. But hey, when does a hobby ever break even?

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on March 13, 2019, 06:50:08 AM
Boards packed and shipping today. Here is the BOM.

WA1GFZ
K1JJ
KD6VXI
KC2ZFA
W1RKW
W8KHK
KB2WIG
W2WM
KC9LKE
W2XR
KA1SHU

Pending payment - WD5JKO

If I missed anyone, let me know...I tried to keep good records.

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: W1RKW on March 13, 2019, 04:07:52 PM
John,
Thank you for your work and sharing.
Looking forward to starting a new phase for my 813 rig.
Bob


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on March 13, 2019, 08:20:12 PM
I hear that there are some questions on how to mount the fets. I will work on that over the next few days. I don't yet have some of the larger FETs but i think I can show you using TO-220 fets and you will be able to figure it out. Here is a non-pic overview...

First step is to lay the board on the heat sink, and spot the six holes for the mounts. Once they are tapped or drilled, then you can mount it and spot the FET holes. If you are a good machinist, you can spot them all at the same time. I am not.

The FETs are mounted under the board, with the tabs flush to the heat sink. Don't forget silpads and insulators for the screws. Approx 18mm away from the hole, you bend the wires up 90 degrees. Then you poke them thru the board and bend them slightly. Then mount the board on the sink. You should see the fets thru the large holes. Screw them down. Then wiggle the pins to reduce stress on them and solder the 3 pins on the board.

From then on, you can take the screws out, remove the board, and remount it and it will fit just right.

Frank thinks 1/2 in or 3/8 in nylon spacers. I prefer 3/8 bit I don't have any fets to look at right now to see which one is best. The spacers should be available at any good hardware store.

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: K1JJ on March 13, 2019, 10:44:22 PM
Heathkit would be proud.  When stuffed, it will look as good as any commercial board.

Nice job, John!

I see Bruce, W2XR is building one too.   His 4-400A rig is one of the great sounding ones and I'm looking forward to him dropping the tube driver and pimping it out.

Yeah that's the ticket - everybody be pimping out their rigs!

T


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on March 14, 2019, 06:24:21 AM
7 boards left. $35 each includes shipping to lower 48.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on March 14, 2019, 01:23:50 PM
5 boards left.

Since most of the purchasers are from the east of the country, I think we can safely say that we are “Redefining East Coast Sound”!

Right, Tom?


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on March 14, 2019, 02:47:59 PM
3 boards left


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w8khk on March 14, 2019, 04:20:59 PM
They are going fast!  To the west coast or east???   If I didn't know better, I would think your name was Bill Cullen "The Price is Right"!  How many of us remember him?

Good job, and thanks for making these available. I have always  wanted to try the WA1GFZ driver circuit, but I did not want to wire point-to-point.  This should make a very professional looking implementation!


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: K1JJ on March 14, 2019, 04:24:00 PM
5 boards left.

Since most of the purchasers are from the east of the country, I think we can safely say that we are “Redefining East Coast Sound”!

Right, Tom?


Wow, 3 left. They will go fast now that that's that on that!

Well, you might say we are doing our best to help out and point the way to better audio.  :D    

A lot still depends on what the MOSFET board is driving. If a tube modulator has non-linearities and/or if the mod transformer is not of hi-fi quality, then we still have bottlenecks. At least we are removing SOME of the distorsion with a clean audio driver and overall NFB.

That said, I know of many big plate modulated rigs on the air that are built well and have high quality modulation components. They sound very good. Many use tube audio drivers with inter-stage transformers or 8 ohm hi-fi amplifiers driving backwards connected speaker/output transformers.  When these rigs receive the all-new, disco-duck GFZ driver board with audio negative feedback, they will sound even better.  Perhaps cleanly pass 50-100 Hz triangle waves that they could not before...  AND generate a cleaner signal on the air!
(lower IMD)

Over the next few months I hope we hear at least  1/2 of these boards on the air.   I'm sure there will be plenty of questions and optimizing work going on - here on the AM BB.

These group projects are the best!

T


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on March 14, 2019, 10:18:08 PM
1 board left


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: K6IC on March 14, 2019, 11:16:07 PM
John,   Thank you very much for laying out this board,   getting it fabbed,   shipped,  and for sharing your efforts to this AM community.

Thanks,  too,   to GFZ Frank,   JJ Tom,  and all of the others who contributed to getting this project designed and built.

This is eggziting !

73,  THANKS,    Vic


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on March 15, 2019, 06:43:32 AM
All boards sold, pending payment....

Here is a datasheet on the fuses. Tom says 100ma is normal for his rig. The actual value you use depends on the tube that the board is driving.

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: K1JJ on March 15, 2019, 09:15:06 PM
Now that we are officially into the construction phase, it's time to move on:

Taken from the board notes posted in this thread by John, the voltages on the MOSFETS below will give you a good idea if the board is operating correctly.

Connect two resistor loads to simulate the tube grids.  (Set the bias to -5 volts as the 300 volts is reached.)

When first built and tested, bring up the -+ 300VDC very slowly.  Sample the individual MOSFET voltage points below to make sure they are roughly tracking the 300VDC.  Once up to 300 VDC these voltage readings should be close.

Do a touchy-feely of all parts to be sure nothing is overheating. Be sure to respect the +- 300V supply when feeling around. Remember that - + 300V = 600 VDC when across them both.

Run some audio tones thru.  20 HZ triangles are a tough test and should easily pass.  Make sure everything is FB before hooking up the modulator tube grids.  

** As stated below, when connected to the real tube grids, be careful not to fry them since this is a low source impedance driver.  Be careful when applying negative feedback and the potential for the modulator and driver board to take off in audio oscillation when the NFB is overdone.  After 10 years of actual use with the prototype hand-wired version, I have never blown a grid fuse nor fried any grids.

The first person (guinea pig) to get one going should post his results since these boards have not been tested yet. You may be able to save others some time.   ;)

Refer to the notes for more details.

Thanks.

T



Additional info and WARNING:

“My design was modeled after the Gates quad 807 audio driver. The fifth stage was because Tom wanted a stage referenced to ground to make feedback easier. The 11N90 source impedance is a lot lower than an 807 cathode follower so you have to be careful not to fry the tube grids.”  

[The grid fuses will help if they are "fast-blo" and are sized right]


Frank / WA1GFZ:

Troubleshooting and pre test data - I recorded the operating voltages at each FET in simulation. This is assuming the output bias is set at -5 volts and the power supply is +/- 300 VDC.

M1: Gate = -.47 (set by bias pot ), Drain= +295.7, Source = -4.92

M2: Gate = -.47 (set by bias pot) , Drain +295.7, Source = -4.92

M3: Gate == -157.3, Drain = +160.7, Source = -161.7

M4: Gate = +5.86,  Drain = +135, Source = +1.5

M5: Gate = -292, Drain = -53, Source -296


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on March 16, 2019, 08:25:30 AM
Boards packed and shipping today. Here is the BOM.

WA1GFZ
K1JJ
KD6VXI
KC2ZFA
W1RKW
W8KHK
KB2WIG
W2WM
KC9LKE
W2XR
KA1SHU

Pending payment - WD5JKO

If I missed anyone, let me know...I tried to keep good records.

John

For this first shipment, you will either receive them today or got them yesterday. Please post your build progress!

Let me know if there were any issues with packaging. This is the first time I have tried the Mylar packing envelopes. They seem to be always good with stuff I get from China so decided to give them a try on boards.

A second shipment of 3 packs of 2 boards each went out on Friday for K3YA, W3GMS and KC9LKE. Should get them on Monday.

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: W3GMS on March 16, 2019, 10:54:20 AM
Thanks John!

Joe-W3GMS


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KC2ZFA on March 16, 2019, 11:10:00 AM
has the schematic implemented by the board been posted ?

a silly question: can the BOM, as posted above, be uploaded
to a parts vendor ?


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on March 16, 2019, 11:23:38 AM
Here are all the docs. You can upload the xls to digikey and use the quantity and the supplier part number to build your cart. I tested it. I did not try at mouser but you should be able to use the mfg part number. You may have to sub parts if they don't carry that exact part. I used the digikey parts to make sure the footprints were adequate. If you sub parts, you are on your own with respect to them fitting ok.

Mount the large 10W resistors slightly off the board. Also mount R14/R16 slightly off the board.

You will need to order the bias pots separate. They were crazy expensive at digikey. You can buy good pots at the surplus dealers for much less.

Good Building!

John



Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: W1RKW on March 16, 2019, 05:12:43 PM
John,
Received my board just now.  Looks good!
Thank you again.
Bob


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on March 17, 2019, 02:14:58 PM
Just bought a pair of these for the bias pots...

https://www.ebay.com/itm/Clarostat-140-6130-100K-Ohm-Pot-Potentiometer-5905-174-4794-2-Watt-New-Honeywell/252809317229

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: W1RKW on March 17, 2019, 03:21:51 PM
Updated the BOM for sourcing the caps and pots via Newark.

Priced out the unit cost for Digikey and Newark.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KB2WIG on March 17, 2019, 05:38:37 PM


J,

Rcvd da boards, FB OM.  They are as pretty as a fresh water clam.... ..

klc


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on March 18, 2019, 06:31:24 AM
Build pics from the maestro himself.

His needs are modest - using it in a Valiant, so not a big heatsink. For a larger tube driver, we suggest 1in fins.

Note how he drilled and tapped the sink to mount the FETs. Used 3/8 washers but 1/4 may also work if you keep your thru hole leads trimmed well.



Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on March 18, 2019, 06:58:01 AM
Updates on fusing and bias


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: W1RKW on March 18, 2019, 04:54:24 PM
with 5 FETs sharing a heatsink, is there any concern for one or more FETs heating up and changing bias and idling currents of other FETs on the same heatsink?


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: K1JJ on March 18, 2019, 05:48:43 PM
with 5 FETs sharing a heatsink, is there any concern for one or more FETs heating up and changing bias and idling currents of other FETs on the same heatsink?


Hi Bob,

I suppose anything could happen and produce a thermal runaway situation if taken to an extreme.

But in normal operation all the MOSFETS run pretty lukewarm and are very stable with capacitive coupling between stages.  Even if one FET were to create a problem I think the normal power supply fusing or the grid fusing might protect it from an extended heat up. But ya never know when it comes to voltage spikes, oscillations or other dangers to SS devices.

I have always been an extremist when it comes to circuit protection. My first class E rig before circuit boards were available had about 7 different sensors and shutdowns. It was foolproof even sensing input and output swr.  Also had a diode on the heatsink for temp sensing, etc.  Steve went on to build a nice all-inclusive protection design with Hall effect devices that did it all and more -  and is still available today.

So in the case of the GFZ driver board, there's no reason why you couldn't add a temperature probe on the heat sink to sound an alarm above a certain temp threshold. I have them sampling warm air above the finals in all of my bigs rigs. I use a digital/LED Kiln temp controller module that can be easily programed.

These are the type I use for $29.50. It would be easy to implement in the driver board. The top readout is the actual measured temp and the bottom is the preset trigger alarm limit. Easy as pie to use.  Comes with a sensor. (Our Chinese friends)

https://www.ebay.com/itm/12V-24V-32V-PID-SSR-TEMPERATURE-CONTROLLER-FURNACE-KILN/230399708125?epid=1448454664&hash=item35a4e48bdd:g:L7AAAMXQbcRQ6RbM


T


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w8khk on March 18, 2019, 06:10:53 PM
Another factor that determines thermal stability is the circuit topology.  If several stages are direct-coupled, (Direct Current) then a change in bias in the driving stage will likely cause a more dramatic bias change in the driven stage.

The board we are looking at here has resistive voltage dividers setting the bias for each individual stage, and the output push-pull stage has the bias individually set for each device.  All stages are capacitively coupled, passing only the AC audio signal, not the DC bias.  This results in a very stable design, and therefore thermal runaway due to the common heat sink should not be a concern.

The same device types are used for the amplifier, phase splitter, and the output stages.  The lower level input stages run at much less current with higher resistances than the output stages, further contributing to the reliability due to their conservative operation.  Tom's success with the design for a decade speaks volumes!


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on March 23, 2019, 08:23:32 PM
Build is progressing at Frank's place...


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w8khk on March 23, 2019, 08:28:01 PM
My second board arrived this afternoon.  Beautiful work...  Thanks, John!


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KD6VXI on March 24, 2019, 11:00:39 AM
I've been away from the house the last two weeks....  But, got home and my board is there.

Thanks a million.  One of these days I might get some time to out it together and transplant into the Viking!

--Shane
KD6VXI


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on April 02, 2019, 06:20:23 AM
Updated BOM.

I had the wrong fuse clips. Now corrected.

Integrated the part numbers for newark for the caps and pots.

Anyone other than Frank building?

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: W1RKW on April 02, 2019, 04:06:08 PM
 Not at this time.  Trying to wrap up my crystal radio project then with warmer weather around the corner will be outside.  probably won't start collecting parts until summer time.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on April 02, 2019, 08:23:47 PM
Me too,

Taxes done, finally,

Helping kids remodel a bath,

2 bedrooms to replace carpet with wood floor,

Going to be a while...

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KD6VXI on April 03, 2019, 05:27:43 AM
I wish.

Haven't seen home in almost 6 weeks, sans a day every week to do laundry and check that the house hasn't burned down.

Got into the IBEW, new job 150 miles away.  Finally out of Bakersfield and back to the 'coast of Cal'.

Signed papers on the new h ouse Monday.

Gonna be a couple more weeks, lol!

--Shane
KD6VXI


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: Opcom on April 04, 2019, 07:48:29 AM
That board sure has turned out beautifully. It's as tasteful as the table upon which it is shown.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KB2WIG on April 04, 2019, 05:22:03 PM


After I bite the bullet on the pot$, and waddle through the 4.2K listings of heat sinks on Mouser, then I'll start.... after the spring antenner work.

klc


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: K6IC on April 09, 2019, 04:05:12 PM
Updated BOM.

   ...   Anyone other than Frank building?
John

Hi John,

Spring has sprung here,   so  were back to trying to abate Fire Risk from weeds,   tree debris,   and general sloth  --  lotta rain this year,   so the WEEDs are getting ahead of us.

But hope to try to get to building a board,   this Summer.

Thank you again,   and to all others who have contributed to this project.

73,  Thanks,   Vic


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on April 14, 2019, 08:10:39 PM
Ordered parts for my board. Right at $100 from Digi including shipping and taxes. Did not order the pots (got on the 'bay) and the caps. Plan to place the supply on the modulator chassis right next to the board so the main caps on the supply should be enough. Going to use an Antek transformer for the supply and build it per the design in the design notes doc.  ;D

Modulator assy will be a 17 wide by 22 or 24 long piece of 3/4in plywood base with a 10x17 aluminum chassis for the mosfet board and the 813's. Hoping a 17x12-14 area is big enough for the mod trans, mod reactor and cap. That Gates iron is big and heavy. If not big enough, I will make it longer.  :o

John



Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on April 18, 2019, 07:06:49 AM
Trying a few parts for fit. Was some discussion off-line on fuse clips. Here are the proper clips as spec'ed in the BOM and a 5x20 100ma fuse. Fits just right. Also note the coupling cap in the background. It fits just right also...

Hopefully I can get some more parts placed this weekend. Going to be rainy so there is hope!

Wondering if my 15W pencil soldering Iron will have enough gas to solder this board. I bought it for SMT soldering, not this stuff. My alternative is a Weller Gun. What do you guys use? Perhaps a 30-50W pencil? Suggestions please...

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: steve_qix on April 19, 2019, 10:30:14 AM
Can't speak to wattage directly, but I use an adjustable soldering station.  Usually for components of this size, I run it quite high in temp (as high as it goes, usually).


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: W1RKW on April 19, 2019, 02:28:28 PM
Ordered the parts for my board.

found a suitable heatsink with a reasonable price.  Seller has a few more available.

https://www.ebay.com/itm/Heat-Sink-938SP-02000-A-200/121410536527?hash=item1c44a1c44f:g:0RwAAOSw7NNT7PBG:sc:USPSPriorityFlatRateBox!06415!US!-1


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on April 19, 2019, 05:08:54 PM
Nice Heatsink Bob. Looks like it was almost cut for your board. 6 more avail it appears. Inexpensive as well.

I picked up a 65W pencil iron on Amazon today. First time I have seen a product there with no negative comments. Hopefully it will work out. If not, was not that much $$.

I am going to drill and tap the heatsink before I start populating parts.

Strongly suggest to not skip the outboard filter caps. (C5/C6). You can fiddle with the values but we are seeing that they matter if your supply is away from the board. I plan to go with at least 470uf and my supply will be on the same chassis. The board has such a good audio passband that even minor 120Hz ripple is audible if not careful on filtering. This board provides really crisp/clean audio. We may have an errata on grounding as testing proceeds.

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: W1RKW on April 20, 2019, 06:55:02 AM
John, Good find on the soldering iron. 65w should be perfect for this building job.

Your plan is similar to mine with tapping, do that first before building the board. Some careful attention to detail is needed here.

And concur on the filter cap arrangement.  I will consider my options based on the email conversations with you and Frank. One of my issues will be how I'm going to shoehorn the board and heatsink into my modulator chassis.

One step at a time I guess.
 


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: W1RKW on April 23, 2019, 04:44:06 PM
Received all my parts.  Ordered them Saturday and they were in my mailbox on Monday, what a surprise.  Heatsink is on the way.  Should have that by end of this week and then I'll start drilling and blasting. 


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on April 24, 2019, 07:04:13 AM
I have 2 boards so will use one for the drilling and tapping and decided to go populate the other one. All parts fit just right as ordered from the BOM at Digikey. Agree with Frank that I should have made all of the R pads larger. Everything is fine but larger would have been better.

Here is a pic of all of the parts placed except for diodes and fets.

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KC2ZFA on April 24, 2019, 01:18:46 PM
just placed the order, everything from digikey...who cleaned out all the RES 50K OHM 10W 5% AXIAL ?
on backorder, estimated available 5/10...

John or anyone else who's building this, could you document the process of adding the heat sink ? I also
bought the one from eBay mentioned above.

Peter


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: W1RKW on April 24, 2019, 04:22:20 PM
Peter,
Allied Electronics has plenty of the 50kohm resistors.



Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KC2ZFA on April 24, 2019, 05:12:47 PM
yeah, but I got careless with the digikey online software that sucked
in the BOM...I can wait, should be done grading a mountain of exams
around that time.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: W1RKW on April 24, 2019, 06:44:23 PM
I had the same issue and unfortunately, I will end up with an extra set of resistors.  If I recall correctly, Digikey said the lead time was mid to end of May. I figured I didn't want to wait.

As far as prepping the heatsink, my plan is the following:

I'm going to tape the PC board to the heatsink.  I will carefully align it so I can minimize drilling into the heatsink fins.

Center punch the holes carefully to ensure they are well centered.

Remove the PC board then drill pilot holes. I'm going to use a drill press to make sure the holes are perpendicular to the heatsink surface.

Gradually increase drill hole size using the drill press to the desired size then  carefully tap the holes.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on April 25, 2019, 06:53:23 AM
I am going to try something new. I had a guy suggest to use an end mill to cut the holes. Lots less flex. I will use one to pilot the hole, then make it the right size with the correct numbered drill. I am also planning to just do two diagonally opposite holes, tap them, then screw the board down before marking the rest of the holes. That should get the rest of the mounting holes spot on. The fet holes are less critical but will do them the same way.

Tapping aluminum. I use WD-40 for a lube, and I go slow backing out the tap a lot to keep the threads clean. I use a hand tap.

You can get end mills from Enco or Grainger.

On the resistors, you can use 20J50K-ND as a substitute. They have 268 in stock at this time.

Mount those big resistors off the board a bit. They run warm.

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: W1RKW on April 25, 2019, 03:37:55 PM
Received my heatsink. >:(

Width was not as advertised.  The board over hangs the edges.  Waiting for a response from the seller.  Hopefully it's just a mix up and will be quickly rectified.  Keep you posted. 


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KC2ZFA on April 25, 2019, 06:47:12 PM
tell him I’m not happy either >:(

just saw the same issue...


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: W1RKW on April 26, 2019, 01:44:25 PM
Peter,
Seller said we can return it.  Unfortunately, he does not have any with the advertised dimensions. I might just keep it for another project, sell it and search for another heatsink, use it with an adapter plate and heatsink compound or return it. Have to think about it for a bit.   >:( >:(

Bob


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KC2ZFA on April 26, 2019, 02:10:14 PM
couldn't one fashion 4 Z brackets with the / of the Z as | to mount the board to this sink ?

I may not know what I'm talking about here but isn't it true that the only points of contact between the board and the sink are just the 4 corner holes ? with the transistors bolted to the sink and their legs bent to be soldered into their board holes ?


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: W1RKW on April 26, 2019, 02:58:15 PM
Peter,
Yes. That would work.  

Also, one could get away with just 2 brackets on one side of the heat sink.  One side of the board can mount to the heatsink and the other side of the board to the brackets which are fastened to the heatsink.

I was hoping to get away with the least amount of fuss and essentially have a symmetrical assembly and have a clean install so having not to worry about how  I'm going to fit and mount it into my modulator.  

But using your idea, I think I have in mind a variation of yours that could work in my situation.  I'll keep you posted.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on April 27, 2019, 09:00:22 AM
Bought a pair of these for the power supply.

https://www.ebay.com/itm/283384262755

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: W1RKW on April 27, 2019, 01:21:25 PM
I have 2 on the way also. Thanks for the tip, John.  Nice find and nice price!


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: W1RKW on April 28, 2019, 03:45:58 PM
Peter,
I took a piece of 1/2" x 3/4" aluminum angle stock and cut it to the length of the EBay heatsink. I drilled 3 holes for the mounting screws along it's length. Then drilled and tapped 3 holes in the heatsink.  The 3/4" side of the angle stock bolted to the heatsink.  The 1/2" side will be used to attach the PC board which is mounted so the surface is flush with the surface of the heatsink.  I attached the angle stock to the heatsink then proceeded to drill and tap the holes for mounting the board.  

Be aware of one thing, the fin spacing of this heatsink is not ideal.  When you drill and tap the holes for the transistors, only one transistor hole will line up between 2 fins if you align one side of the board mounting holes  to fall between 2 fins on an outer edge of the heatsink.  The other 4 transistor holes will graze a fin and there is risk of binding and breaking a drill bit.  I jammed a bit and broke it.  Go slow. Let the bit do the work. Highly recommend using a drill press with a new bit vice using a  hand drill.  Can be done with a hand drill if careful.

In the end, everything came out good.  


couldn't one fashion 4 Z brackets with the / of the Z as | to mount the board to this sink ?

I may not know what I'm talking about here but isn't it true that the only points of contact between the board and the sink are just the 4 corner holes ? with the transistors bolted to the sink and their legs bent to be soldered into their board holes ?


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KC2ZFA on April 28, 2019, 04:08:07 PM
hi Bob, can you snap a couple of pics ? something about pics and 1000s of words.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on April 28, 2019, 05:57:17 PM
Impossible to build a board to match unknown fin spacing unless this is a commercial operation where I can spec the heatsink as well. Best to go slow and worry your way thru it.  ;D

I finally got some time to go do some drilling and wouldn't you know it, not a 6-32 tap to be found. My plan is 6-32 on the mounting holes and 4-40 on the FETs. These fets are nice! They have a built in screw insulator. All you should need is the silpad.

Frank got his running for some QSOs. No smoke so the basic board is good to go. Of course, there may be some fine tuning of component values necessary depending on what you are driving.

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: W1RKW on April 28, 2019, 06:30:26 PM
hi Bob, can you snap a couple of pics ? something about pics and 1000s of words.


Peter, The pix are a little blurry but I think tell the story nonetheless.

John,  I expected that there might be issues with this but it is what it is.  So many different heatsink with various dimension, who would have known.  The key here was to go slow.  In retrospect, I think I would have aligned the transistor screws so that they would hit the spaces between the fins on the heatsink.  I think it was doable and not necessarily worry about 3 of the board mounting holes aligning between the fins.  The one thing I did not think of until after the fact was the transistor holes in the PC board left some wiggle room. I didn't take advantage of that.  It's possible I wouldn't have snap a bit had I thought of it.  But all in all, it worked out. Everything is tapped and ready to go.   



Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KC2ZFA on April 29, 2019, 09:37:20 AM
nice Bob ! and thanks for the pics.

Please let me know if this newby got this right:

The transistors are mounted on the heat sink
so that the mounting bolt is accessible through
the board hole and the transistor legs are bent
up and matched to their respective board solder
points. At the end of the day there is a separation
between the board and the sink of size equal to
the thickness of the transistor plus its silpad.

Peter


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: W1RKW on April 29, 2019, 04:29:34 PM
Peter, you describe what needs to be done perfectly, so a resounding yes.

Frank/GFZ is using 3/8" spacers to mount the board so that will give the transistors a little air gap between them and the PC board.  I will do the same.  I've ordered some nylon spacers for that purpose via Digikey.  If you need the part number, let me know.  I'll dig it up and send it along.

Bob


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KC2ZFA on April 29, 2019, 06:06:12 PM
excellent ! me no big dummy :-)

I've got tons of nylon spacers from Lowe's...thanks for the offer. And I need to get a
thread tap kit.

I have a drill press for my Dremmel, at highest speed if I go slow, would that suffice ?

all my past aluminum work is only with chassis and panels which I clamp between my
knees to drill or punch holes. I've never built anything with transistors...

Peter


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KD6VXI on April 30, 2019, 02:29:58 PM
In the electric world we now have combo tap drills.

Drills the hole and taps it for the correct screw all at the same time.

It may take some practice, but they do work.

--Shane
KD6VXI


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: W1RKW on April 30, 2019, 05:18:32 PM
Peter,
I'm not sure a Dremel will work well especially were torque may be required such as in my experience with the drill bit grazing the heatsink fin.  I suppose if you get the holes to line up in a manner where they don't hit a heatsink fin it will work.  It will take some drilling time.  If you have a hand drill you can do this. The key will be to make sure you're drilling as perpendicular as possible. Most important, have a nice sharp drill bit.  Get a new one if necessary.

When you get to tapping the threads for the screws, let us know. We can walk you through it but first if you can get yourself a scrap piece of aluminum that is 1/8" thick or so you can practice on that to get the feel for tapping.

Bob


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KC2ZFA on April 30, 2019, 07:18:03 PM
thanks for the tips Bob.

But why do we have to drill into the fins ?
The thickness of the sink plate, from flat to
the valley floor between fins, is 7/32”...
shouldn’t that be the drilling depth ?

Peter


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: K1JJ on May 01, 2019, 11:16:18 AM
thanks for the tips Bob.

But why do we have to drill into the fins ?
The thickness of the sink plate, from flat to
the valley floor between fins, is 7/32”...
shouldn’t that be the drilling depth ?

Peter



Hi Peter -

If the plate is thick enuff as you say, then no problem.   You will never hit a fin.

Just to be clear for other builders: In the case of thin plates, the problem is that the FET mounting holes in the PC board were not designed for any particular heatsink fin spacing, thus some holes will probably line up over fins.  If a standard heatsink was used for all projects, like for a commercial production run, then the designer would make sure no fins needed drilling...  ;)

If you have more than one heatsink, maybe one will match up with no hassles. Pot luck.  Though, tapping into fins is normally no problem other than a stuck drill.

BTW, right now there is a lot of email traffic going on about testing the board for performance and optimizing parts selection. These results will be posted in the future.


T


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KC2ZFA on May 01, 2019, 11:56:29 AM
thanks Tom.

to all, once completed can the board be tested using resistor loads to represent the tubes ?
If yes, how does one determine the resistor values for a given tube ?

And by tested I'm assuming it means putting in audio sigs from a generator and scoping various places to look for correct pk2pk, distortion, parasitics, etc...

Peter


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: W1RKW on May 01, 2019, 04:48:20 PM
Hi Peter,
Sorry for the late response.  I was saying you need to avoid grazing the fin as the drill bit penetrates the flat which is what I did with one hole and broke the bit because it jammed.  If you can get all the holes centered in a manner where a drill bit does not graze a fin that would be ideal.  If you drill straight into a fin that is OK too as Tom mentioned.  

Received the transformer and the 680uF caps today.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on May 05, 2019, 08:08:14 AM
BOM and schematic error - C11 needs to be .01uf.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: Opcom on May 05, 2019, 11:02:58 AM
An option for those who can't abide a fin in the way, or where it's half on and off the hole and difficult to drill for tapping, would be a Dremel tool. a 'worn down' cutting disc will slice off the fin base usually.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on May 10, 2019, 07:01:51 AM
Hot off the press - Frank's comments after the build and testing in his Valiant.

News is that the board has no errors and the components are all correct (after the C11 change to .01uf).

good stuff!

For demanding applications, a regulated supply is suggested. I am toying with the idea of making some regulator module PCBs based off a design that Phil posted on a thread a while ago. The concept would be to put all components on a board and use 2 of them for the two rails. The populated boards plus the transformer is all that would be needed. No other discrete parts.

The schematic of the full supply is probably not correct. I think the 230V trans will only do around 280V regulated. Probably need a 250V trans for a solid 300V regulated.

I did not change any values from Phil's schematic. I am sure some values will need change. This is all preliminary work on the concept of an easy regulated supply. Making PCBs is easy.

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: W1RKW on May 10, 2019, 04:51:57 PM
I was planning on doing a basic shunt regulator with zeners alone if some sort of regulator is needed. But I won't dive into that until the fall season.  I'm on hold for any radio projects other than the crystal set I'm still trying to get through.  

John, thanks for the new files. All is archived for future use.

Tom, I'll have some results in response your last question some time this weekend. Weather is supposed to suck so I'll be at the bench and operating position.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KK4YY on May 10, 2019, 06:25:43 PM
I think you need to revisit the way the bridge rectifiers are drawn on
"Schematic_WA1GFZ-Mosfet-Audio-Driver_Regulated-Supply.pdf"

Just sayin'. ;)


Don


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: K8DI on May 10, 2019, 09:33:52 PM
For your schematics, you've kept the resistors in front of the zener the same as the source schematic -- but it was dropping a hundred volts across the pair of resistors. That means several milliamps, most likely above the Izk specification of whatever diodes he was using. Izk is the minimum amount of current you need through a zener to have it regulate.  With dropping the ten volts shown in your schematic, the current is just under half a milliamp.  Typical diodes (On semi, part numbers chosen by sticking 'though hole', '100v', '5w', and 'in stock' on Digikey's website) have Izk values of 1mA. You'll want to lower the resistor values to get a couple mA through the diode stack, or raise the input voltage to at least 30-40 v above the zener voltage.

Ed


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: DMOD on May 11, 2019, 02:23:23 AM
For your schematics, you've kept the resistors in front of the zener the same as the source schematic -- but it was dropping a hundred volts across the pair of resistors. That means several milliamps, most likely above the Izk specification of whatever diodes he was using. Izk is the minimum amount of current you need through a zener to have it regulate.  With dropping the ten volts shown in your schematic, the current is just under half a milliamp.  Typical diodes (On semi, part numbers chosen by sticking 'though hole', '100v', '5w', and 'in stock' on Digikey's website) have Izk values of 1mA. You'll want to lower the resistor values to get a couple mA through the diode stack, or raise the input voltage to at least 30-40 v above the zener voltage.

Ed

If you are referring to the schematic below let's look at the numbers.

3X200V zeners  = 600 volts + 1X100V zener = 700 volts. Source voltage is 800 volts.

800-700 volts = 100 volts. 100 volts/20.2k = 5 mA.

So 5 mA is the current going through the series string of 2.2k, 18k, and the 4 zener diodes.

Look at this reference Page 6;

https://www.onsemi.com/pub/Collateral/1N5333B-D.PDF

The curves start at 0.1 mA and goes to some max current. This means the zener starts regulating (without excessive switching noise) at a minimum current of 0.1 mA. So Izmin = 0.1 mA.

Where is the curve the most linear? About 5 mA. What is the current flowing through the series combination of the 2.2k, 18k, and the 4 zener diodes?

5 mA.

The power dissipation of each 200 volt zener is 5e-3X200 V = 1 Watt. What is the maximum rated power of a 5 Watt zener? 5 watts. So we have about an 80% margin of safety in terms of power dissipation for the 200 volt zener.

The power dissipation of the 100 volt zener is 5e-3X100 V = 0.5 Watts. What is the maximum rated power of a 5 Watt zener? 5 watts. So we have about a 90% margin of safety in terms of power dissipation for the 100 volt zener.

Conclusion: One has to examine and study the device curves, whether it be solid-state or Thermionic-State, to see the whole picture.

Izt is NOT the minimum current at which a zener can regulate. Izt is the "Test" current for the zener specifications and Izt varies with zener voltage and power rating.


Phil - AC0OB

 

 



 



Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on May 11, 2019, 07:51:41 AM
Thanks Phil, I always appreciate your in-depth explanations of how a circuit works.

Thanks for all the comments on the regulator. Going to drop the zener to 280V. That gives me 1.5ma thru the zener. Looking at the 150 and 130V curves that is within the linear portion, I believe. 1K/9K would bump it up to 3ma.

And fixed the booboo on the bridges... Ignore the 1n4148 diode in the schematic - that was the default footprint. Will use 1N5408 or similar...

Forgot to add the new design notes.

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KK4YY on May 11, 2019, 09:33:44 AM
Phil,

I looked at those same graphs a few weeks ago when designing a dual voltage regulated supply. The log scale was hard to read, and I had to zoom in tight, to see it clearly. I found that figures 7,8, and 9 use three different log scales to cover the range of nominal zener voltages! Very deceiving.

I'm not trying to be nit-picky, really. But the way the data is displayed on that sheet is terrible.


Don


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on May 11, 2019, 11:17:37 AM
prelim pcb. Need to shrink it more.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KC2ZFA on May 11, 2019, 11:42:46 AM
constant load of 100 mA per 300vdc rail, why can't I regulate this with gas regulators ? 4 0D3's in each rail (two in parallel in series with two more in parallel). I think each 0D3 can handle 50 mA. Talking outa my behind here ?

Peter


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: KK4YY on May 11, 2019, 04:31:56 PM
John,

I bet your dual rail regulated power supply is going to look better than mine does! ::)


Don


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on May 11, 2019, 06:50:32 PM
This is what I will order. Will be able to fit a pair on a 100mmx200mm heatsink.

I use EasyEDA for the layout. They have an initial sales offer to build 10 of them for $5.00 plus free shipping. Going to give them a try.



Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: DMOD on May 11, 2019, 06:59:18 PM
Thanks Phil, I always appreciate your in-depth explanations of how a circuit works.

Thanks for all the comments on the regulator. Going to drop the zener to 280V. That gives me 1.5ma thru the zener. Looking at the 150 and 130V curves that is within the linear portion, I believe. 1K/9K would bump it up to 3ma.

And fixed the booboo on the bridges... Ignore the 1n4148 diode in the schematic - that was the default footprint. Will use 1N5408 or similar...

Forgot to add the new design notes.

John

Hi John, getting closer and lookin' good.

Below is my suggestion for the regulators with 310V in and 280V out.

Your 68k bleeder resistor would dissipate 1.2W so my suggestion would be to raise it to 220k 1W for a bleeder current of 1.3 mA and a power dissipation of 400 mW.


Phil - AC0OB  



Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on May 11, 2019, 07:04:55 PM
Thanks Phil!

I see that I forgot Cf.

Also, do you think it much better to include the fuse on the input to the FET after the diodes? I was planning on only fusing the primary.

Thanks for the revisions. You are welcome to have a few free boards when they arrive.

What does your model show for ripple?

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: DMOD on May 11, 2019, 07:30:45 PM
Thanks Phil!

I see that I forgot Cf.

Also, do you think it much better to include the fuse on the input to the FET after the diodes? I was planning on only fusing the primary.

Thanks for the revisions.

John

There advantages and disadvantages to each, but it would seem to require two fuses either way.

I think the main advantage of fusing each 310V PS section is in troubleshooting.


Phil


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on May 11, 2019, 08:23:43 PM
deleted - not adding a fuse per rail. If a fuse blows we don't want the other rail to still be driving the modulator. Best that both go away, per Frank.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: DMOD on May 12, 2019, 02:24:48 PM
deleted - not adding a fuse per rail. If a fuse blows we don't want the other rail to still be driving the modulator. Best that both go away, per Frank.

For the SS driver putting one fuse in the T3  primary IS probably the best way to implement protection.  8).

https://www.youtube.com/watch?v=pjW_z02EjaA   ;D


Phil


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on May 12, 2019, 10:11:53 PM
Phil, do you have any simulation data? What will the ripple look like?


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: Opcom on May 13, 2019, 12:21:52 AM
constant load of 100 mA per 300vdc rail, why can't I regulate this with gas regulators ? 4 0D3's in each rail (two in parallel in series with two more in parallel). I think each 0D3 can handle 50 mA. Talking outa my behind here ?

Peter

Gas regulators - 0D3 iIRC it is the Octal version - - can do 40mA maximum, and for good life is better to run lower. The obstacle you will face is that the firing voltage is higher than the regulating voltage, so in simple parallel they won't all fire. One will, then the regulation voltage across them all will be too low for the other(s) to fire.


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: DMOD on May 13, 2019, 02:37:48 AM
Phil, do you have any simulation data? What will the ripple look like?

Hi John,

On the regulator with the turn-on time constant R1, CTC? I did not run one but I did run one and implement the same type of circuitry shown below (for your implementation Sht. 1 ) for an EF Johnson modulator screen regulator in which the input voltage was 800 volts and the output voltage was 300 volts; the output ripple was less than 50 mV under load.

How much ripple can you tolerate? How much total gain do you have and how much will that gain amplify the ripple at the grids? Can the +, - power supply transformer secondaries be phased such that much of the ripple could be cancelled at the M3, M4, and M5 stages?

If you want the lowest ripple for a simple zener regulated "pass" implementation, you will have to dispense with the turn-on time constant circuit (which I thought you still wanted) because the time constant circuit R1, CTC will not allow the zener impedance to follow the input voltage excursions. You want the zener impedance to change in real time with the excursions of the input voltage waveform and not be delayed by a time constant circuit.

If you need a lower ripple voltage, then I think a regulator with a feedback amplifier (Sht. 2) would be needed and that would increase complexity.


Phil




 


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on May 16, 2019, 07:48:43 AM
I have extra boards on the way so I will build one of each to see. Yes, I did mention the desire for a soft start, however that may no longer be necessary.

50mv is quite good.

Transformer secondaries can be phased. They are completely independent.

Here is the final schematic/bom and the board that I ordered. I kept the 130V and 150V Zeners in the BOM as 140V Zeners were not available from Digikey.

John


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: DMOD on May 16, 2019, 02:18:08 PM
I have extra boards on the way so I will build one of each to see. Yes, I did mention the desire for a soft start, however that may no longer be necessary.

50mv is quite good.

Transformer secondaries can be phased. They are completely independent.

Here is the final schematic/bom and the board that I ordered. I kept the 130V and 150V Zeners in the BOM as 140V Zeners were not available from Digikey.

John

Considering the transformer secondary resistances in conjunction with the 470 uF filtering caps and the resulting time constant, I doubt the soft start circuit is going to buy you much.

Personally, unless there is some major criteria for safety or operation, I want my regulators to start regulating as soon as my raw power supply hits the regulation voltage threshold.


Phil


Title: Re: Board for WA1GFZ MOSFET Audio Driver
Post by: w9jsw on May 20, 2019, 08:00:33 PM
6 days from order to boards in my hands, from china. Unreal.
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