[sdiy] Op Amp Upgrades + Voltage Regs

[Rob Keeble]

Hi
I have been testing out various Op Amp upgrades over the last few weeks.

For CV's the OP177F and G and LT1012/1013 are low drift, low offset. Also
good for CV generating DAC's.
For audio I'm using OPA134/2134 with good results. Some of the modern fast
slew FET Op Amps are tricky to use because they can introduce distortion and
HF oscillation (Audiophiles also report this, as they search for the
ultimate sound).

There are useful reviews here (not mine):
http://tangentsoft.net/audio/opamps.html
http://www.dself.dsl.pipex.com/ampins/webbop/op275.htm

There are more esoteric and expensive Op Amps about with zero offset or very
fast slew. The only one I am trying out is the SMT AD825 as a possible
replacement for the hard to find LM318, its needed for the core of the E-mu
Systems VCO. The speed is needed to generate an accurate sawtooth, although
Dave Rossum went a bit mad with the upper frequency which is well over
30kHz...

I tend to use NE5534/TL082 for prototyping and then move onto more expensive
Op Amps once the circuit works, looking out for HF oscillation with a scope.
Of course the 748 still has its uses, its so slow it used to create new
waveforms....

Rather off topic... But I am also testing out precision voltage regulators.
The LM723 and REFxx type regulators give 1mV of drift, in some VCO cores
this causes frequency drift that is audible. So I am trying out some ultra
low drift regulators (6ppm) with E-mu VCO, SSM2030 VCO. I'll publish some
results on the web site , comparing frequency stability with the excellent
Oakley Mk 2 VCO and the "all on a chip" CEM3340. One immediate finding is
that the frequency control pot(s)s should be driven from a low drift power
supply.

Regards
rob
www.emulatorarchive.com