[sdiy] Rail to Rail Op Amp or Voltage to Current converter

Michael Bachman bachmanm50 at gmail.com
Wed Nov 13 00:47:15 CET 2013

This may be a dumb question... but I will dare to ask it as I am about
to redo some significant portions of my sound card..

Presently I drive all the LM13700 gain pins with a +8 to -12v signal
though a 10K resistor (getting to -12v takes a rail to rail op-amp in
this case).   Every other circuit I have seen uses a op-amp/transistor
voltage to current converter to drive the gain pin.

In my case, I am not worried about slight non-linearities as every
note/pitch has its own tuning table and the cents between notes are
interpolated in 16 bit math.

Certainly a +/- 12v rail to rail op-amp is not cheap compared to a basic TL072.

What other issues might I be missing?
Could  there a "balance" problem in a 4 pole filter?
I don't see (hear) any issues
Is there temperature drift associated with the v-c circuit?

I plan to just try the difference and see, but thought I would ask first.


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