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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 12:57 PM

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 01:04 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 01:06 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 08:33 PM

I can't open your jpg image.

ddietz 8th January 2012 08:38 PM

Gootee, its a PDF and opened fin for me.

veteran 8th January 2012 08:46 PM

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

gootee 9th January 2012 12:11 AM

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 08:36 AM

Quote:

Originally Posted by gootee (Post 2852672)
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 12:18 PM

Quote:

Originally Posted by veteran (Post 2853181)
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 01:51 PM

Quote:

Originally Posted by veteran (Post 2851821)
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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