i built jack orman's opamp buffer on vero and it works fine but is very hissy and noisy. i'm powering it with a pp2 and it's on it's own plug, no sharing. the buffer sits in a true bypass looper. any ideas?
all I can say is that I asked this question once and the answer was runaway feedback.
In part of a buffered distortion I had an output that was too close to an input.
The problem could be a layout issue
The solution could be some shielded wire.
hope that helps
I see 3 variants of his opamp buffer. I advise getting intimate with them, especially the part under "miscellaneous" that talks about power supply noise rejection. :) What I mean is, what kind of PS filtering did you use? You still need it even with a good power supply. It's not about the supply, it's about the pedal. ;)
http://www.muzique.com/lab/buffers.htm
Oh my, I just realized I hit 1000!
Hi
choose your opamp carefully. The ME5532 is very quiet, but has low input impedance, so it's not an buffer (!), the 741s and 4558s* hiss a lot. In general, it's hard to beat a TL071/2/4. However, keep the input resistance low (resistor to Vref for a non-inverting confidguration) or you'll pick up RFI and other cable noise.
cheers
* 4558s are simply dual 741s. Popular opinion has it that they contain enormous amounts of mojo (esp as feedback clippers), while 741s contain none. I conclude that popular opinion is popular, not smart.
My buffers are a little noisy too but clean up when I put them on a real circuit board with proper grounding and stuff. Also 4558 are quieter than tl072. Look up the datasheet at mouser and look for the nV/Hz spec. Also, look at different brand 4558's. Some are quiter than others.
I put Jacks AMZ Simple Jfet Buffer on board my flying V. Very low noise and works quite well.
(http://i218.photobucket.com/albums/cc93/ftrock/fvbuf3.jpg)