JFET Buffer/Compressed Audio

[jaredcohen]

I built this very simple JFET Buffer done by IvIark (not posted on this site). I think I found it in a DIY Stompbox thread, but I can't be sure.  It's pasted below.



Everything works fine. But I notice as soon as the buffer is engaged there is a ton of compression on the audio. It actually doesn't make a half-bad compressor, but that's not really what I want it for. I tried a handful of J201's all with the same result. Just wondering if this is a natural consequence of the circuit, or if there might be something I'm missing here...

[IvIark]

I've never built that particular one, in fact I can't even remember doing the layout , but I don't see why you should get any compression.  There is no gain increase, it's a source follower and so just a unity gain buffer.  The only thing that is should do is provide a high input impedance and a low output impedance.  Maybe that change and the removal of any loading on your pickups is making an audible difference (although I would expect it to sound brighter if anything).

The reference voltage doesn't have any filtering.  Try adding a 47u cap from the bottom row to the second from bottom row below the 100n cap (negative to ground obviously), and just see if that alters anything.

That layout seems to be based on the third scheme shown on Jack's buffer page here:

http://www.muzique.com/lab/buffers.htm

so if there are any others you want to try I'm happy to knock up a quick layout for you.

[jaredcohen]

Thanks Mark. You've put too many layouts out in the world to keep track of them all!

Just for reference, here is an audio file.  First with bypassed signal, and then connected through the buffer. I figured it's worth posting since maybe someone will say "You're crazy, it's in your head. They sound the same."  For what it's worth: Fender Mustang (2 single coils) direct into an M-Audio Profire 2626 and then Garageband. No other effects, no virtual effects in Garageband.

http://www.jaredmcohen.com/storage/Test_JFET_Buffer.mp3

Anyway, I will try the 47uf cap and report back. Thanks for the help and amazing site. I do want to try a TL071/TL072 buffer, for comparison, but for that I will just try out one of the great Klon layouts you've already got here!