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Board for WA1GFZ MOSFET Audio Driver




 
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Author Topic: Board for WA1GFZ MOSFET Audio Driver  (Read 7880 times)
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K1JJ
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"Let's go sailing, Tommy!" - Yaz


« Reply #25 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
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Frank / WA1GFZ says when he's working near high voltage, as a warning he sings this song by Jay and the Americans: "Come a little bit closer, you're my kind of man, so big and so strong, come a little bit closer, I'm all alone and the night is so long."
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« Reply #26 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



 

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"What kind of Koolaid do they make you drink in the Physics Department?" Charlie Epps to Dr. Larry Fleinhardt, NUMB3RS   Smiley
K1JJ
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« Reply #27 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
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Frank / WA1GFZ says when he's working near high voltage, as a warning he sings this song by Jay and the Americans: "Come a little bit closer, you're my kind of man, so big and so strong, come a little bit closer, I'm all alone and the night is so long."
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« Reply #28 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.  Smiley


Phil - AC0OB
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"What kind of Koolaid do they make you drink in the Physics Department?" Charlie Epps to Dr. Larry Fleinhardt, NUMB3RS   Smiley
w9jsw
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« Reply #29 on: February 17, 2019, 08:21:34 AM »

Almost ready for Fab....

* PCB_DRIVER-PCB.pdf (41.11 KB - downloaded 44 times.)
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« Reply #30 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.
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« Reply #31 on: February 18, 2019, 05:41:51 PM »

You have a buyer for a board. See PM.
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Bob
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His fear was when I turned it on for the first time life on earth would come to a stand still.
K1JJ
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« Reply #32 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.    Grin

T
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Frank / WA1GFZ says when he's working near high voltage, as a warning he sings this song by Jay and the Americans: "Come a little bit closer, you're my kind of man, so big and so strong, come a little bit closer, I'm all alone and the night is so long."
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« Reply #33 on: February 18, 2019, 09:00:31 PM »

7 confirmed out of 10 so that is a go. Getting quotes now.



John
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w8khk
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« Reply #34 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!
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« Reply #35 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
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« Reply #36 on: February 19, 2019, 09:55:45 AM »

thanks for this, just making sure you got my PM.

Peter
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« Reply #37 on: February 19, 2019, 11:24:11 PM »

Sorry, I've been out of town on business.

Yes, put me down.

PayPal work?

--Shane
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w9jsw
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« Reply #38 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
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KB2WIG
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« Reply #39 on: February 20, 2019, 07:36:17 AM »



I'll go for one board.

KLC
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« Reply #40 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.
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« Reply #41 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.
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K1JJ
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« Reply #42 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...  ***  Wink

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:



* MOSFET AUDIO DRIVER BOTTOM.png (45.09 KB, 500x344 - viewed 79 times.)

* MOSFET DRIVER TOP.png (58.45 KB, 500x344 - viewed 85 times.)
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Frank / WA1GFZ says when he's working near high voltage, as a warning he sings this song by Jay and the Americans: "Come a little bit closer, you're my kind of man, so big and so strong, come a little bit closer, I'm all alone and the night is so long."
w8khk
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« Reply #43 on: February 22, 2019, 02:47:46 AM »



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

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!
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« Reply #44 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.  Grin

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

* BOM_WA1GFZ Mosfet Audio Driver.xls (11 KB - downloaded 44 times.)
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« Reply #45 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
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« Reply #46 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
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K1JJ
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« Reply #47 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


* GFZ MOSFET Audio Driver.jpg (311.5 KB, 1280x960 - viewed 95 times.)
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Frank / WA1GFZ says when he's working near high voltage, as a warning he sings this song by Jay and the Americans: "Come a little bit closer, you're my kind of man, so big and so strong, come a little bit closer, I'm all alone and the night is so long."
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« Reply #48 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.

* Design Notes - 20190223.pdf (1723.19 KB - downloaded 39 times.)
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K1JJ
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« Reply #49 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!   Wink  Grin

T

Audio file below:

* K1JJ Test.mp3 (1365.38 KB - downloaded 65 times.)
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Frank / WA1GFZ says when he's working near high voltage, as a warning he sings this song by Jay and the Americans: "Come a little bit closer, you're my kind of man, so big and so strong, come a little bit closer, I'm all alone and the night is so long."
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