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Board for WA1GFZ MOSFET Audio Driver




 
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February 19, 2019, 08:59:28 PM *
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Author Topic: Board for WA1GFZ MOSFET Audio Driver  (Read 1037 times)
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K1JJ
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« 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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« 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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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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« 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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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 10 times.)
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w9jsw
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« Reply #30 on: Yesterday at 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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W1RKW
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« Reply #31 on: Yesterday at 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: Yesterday at 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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« Reply #33 on: Yesterday at 09:00:31 PM »

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



John
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WWW
« Reply #34 on: Today at 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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Rick / W8KHK  ex WB2HKX, WB4GNR
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« Reply #35 on: Today at 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: Today at 09:55:45 AM »

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

Peter
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