[sdiy] Volume control help

[WeAreAs1 at aol.com]

In a message dated 7/6/05 12:37:30 PM, music.maker at gte.net writes:

<< One thing to try is to replace the one meg resistor (R14)
with a one meg pot used as a voltage divider.  That way, all
of the expected impedances are what the circuit expects.  >>

Hello Scott and Mikael,

I don't quite understand the purpose for R14 (the 1Meg resistor to ground at 
the output).  Can you explain?  Is it there to protect against potential DC 
voltages (pun unintended) the mixer might encounter in the nasty real world of 
DIY guitar stomp boxes?  It does form a mild high-pass filter with C5, but I'm 
not sure such a filter is even needed at that stage (and at that Fc).  Even 
with the 1Meg, the Fc of that highpass filter could be affected by plugging the 
mixer into an unexpectedly low-impedance destination.

BTW, I think a good solution to the master volume problem might be to wire 
that 10K pot as a voltage divider between the two opamps.  You would use the 
same kind of voltage divider that Mikael described before -- basically, just like 
those input volume controls at R1 through R4.  The pot would be connected 
between Pin 1 of ICa and R10 (100K resistor).  That way, the second opamp should 
be unaffected in its purpose as an inverter and output buffer amp, and that 1 
Meg resistor at the output can continue doing whatever it's supposed to do, 
unimpeded (OK, that one was intended).

Michael Bacich