Tony (and all),
I built Tony's mixer with the plain old TL072s and was quite
pleased with the results. I was especially happy with the way reversing
was accomplished with only one op-amp. These actually zero out better in
the middle than anything else I have. As Tony said, it is not hugely
accurate for DC. 1% resistors are a must. Personally, I would take my
stack of 47K resistors used for the construction and measure all their
values. I would stick the highest value of the bunch in R72 and the lower
ones of the bunch in R69, 70 and 71. This would serve to cancel out the
effect of the 1K resistors on the outputs of the inputs attenuators being in
series with the summing resistors and bring the summing stage closer to
unity gain. Dave B's normalizing plans make this simple and small circuit
and very useful utility mixer/multiplier/reversing attenuator.
Larry H
----- Original Message -----
From: Tony Allgood <oakley@...>
OK I specify the TL072 in my multimix. Its OK for audio,
and less than perfect for CV. But still usable in most if not
all situations. I would be glad to hear of any problems that
people have had regarding the use of this unit.