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-   -   Universal FET buffer / preamplifier (http://www.diyaudio.com/forums/analog-line-level/204013-universal-fet-buffer-preamplifier.html)

veteran 8th January 2012 11:57 AM

Universal FET buffer / preamplifier
 
For a long time I was looking for a good supplement for my input selector project (described in this thread) an here it is ;)

http://unisonus.com/PDF/unisonus-buf...buffer_pre.JPG

In the beginning I wanted to make modified Nelson Pass B1 buffer (which sounds quite good in my system) but then I decided to upgrade it a bit to make it more universal. I designed PCB which can be:
  • standalone FET buffer
  • op-amp preamplifier (for example LM4562)
  • op-amp preamplifier with FET output stage
  • op-amp preamplifier with FET output stage in the feedback loop
There is also dc-servo circuit so the output capacitors may be omitted.

Here is the schematic of one channel.

veteran 8th January 2012 12:04 PM

Measurements made with my e-mu 0202 shows that the THD+N is less than 0.001% for entire band.
This is how it looks for 1kHz, +-17V supply voltage, 10k load and 1.55V RMS (4.42V Pk-Pk) Vout.

E-mu 0202 loop:
http://unisonus.com/PDF/unisonus-buffer/loop.png

Standalone FET buffer:
http://unisonus.com/PDF/unisonus-buffer/loop_buffer.png

Op-amp preamplifier with FET output stage:
http://unisonus.com/PDF/unisonus-buffer/loop_pre.png

veteran 8th January 2012 12:06 PM

20kHz square wave from my GAG-810 generator:
http://unisonus.com/PDF/unisonus-buffer/scope_0.png

http://unisonus.com/PDF/unisonus-buffer/scope_1.png

gootee 8th January 2012 07:33 PM

I can't open your jpg image.

ddietz 8th January 2012 07:38 PM

Gootee, its a PDF and opened fin for me.

veteran 8th January 2012 07:46 PM

Schematic is in PDF, rest of the files are in PNG format.

gootee 8th January 2012 11:11 PM

Sorry, it was the JPG photo at the top that wouldn't open. But it's fine, now. Thanks.

I would be interested in seeing how you routed the grounding, and the signals and power, on the PCB. But if you don't want to post that I will understand.

veteran 9th January 2012 07:36 AM

Quote:

Originally Posted by gootee (http://www.diyaudio.com/forums/showthread.php?p=2852672#post2852672)
Sorry, it was the JPG photo at the top that wouldn't open. But it's fine, now. Thanks.

I would be interested in seeing how you routed the grounding, and the signals and power, on the PCB. But if you don't want to post that I will understand.

There are two separate grounds for signal and power connected in one point. I'll post more details later.

AndrewT 9th January 2012 11:18 AM

Quote:

Originally Posted by veteran (http://www.diyaudio.com/forums/showthread.php?p=2853181#post2853181)
There are two separate grounds for signal and power connected in one point. I'll post more details later.

Can you label the schematic to show the different grounds/returns?

Ken Newton 9th January 2012 12:51 PM

Quote:

Originally Posted by veteran (http://www.diyaudio.com/forums/showthread.php?p=2851821#post2851821)
Measurements made with my e-mu 0202 shows that the THD+N is less than 0.001% for entire band.
This is how it looks for 1kHz, +-17V supply voltage, 10k load and 1.55V RMS (4.42V Pk-Pk) Vout.

E-mu 0202 loop:
http://unisonus.com/PDF/unisonus-buffer/loop.png

Standalone FET buffer:
http://unisonus.com/PDF/unisonus-buffer/loop_buffer.png

Op-amp preamplifier with FET output stage:
http://unisonus.com/PDF/unisonus-buffer/loop_pre.png

I'm curious to know what measurement software you are using with your e-mu 0202? Also, how satisfied are you with that measurement solution?


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