Universal FET buffer / preamplifier

[veteran]

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



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]

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:


Standalone FET buffer:


Op-amp preamplifier with FET output stage:

[veteran]

20kHz square wave from my GAG-810 generator:

[gootee]

I can't open your jpg image.

[ddietz]

Gootee, its a PDF and opened fin for me.

[veteran]

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

[gootee]

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]

Originally Posted by gootee

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]

Originally Posted by veteran

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]

Originally Posted by veteran

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:


Standalone FET buffer:


Op-amp preamplifier with FET output stage:

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?