[sdiy] Op Amp Upgrades + Voltage Regs

[Ian Fritz]

Hi Rob --  (inline)

At 03:31 AM 1/21/06, Rob Keeble wrote:
>Hi
>I have been testing out various Op Amp upgrades over the last few weeks.

Lots of good info.  Thanks for posting!


>For CV's the OP177F and G and LT1012/1013 are low drift, low offset. Also
>good for CV generating DAC's.

OPA227, OPA277, and LT1055/1056 also useful here.


>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,

Digikey has the LM318 in stock (although I wouldn't argue with upgrading).


>  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...

Well, that kind of madness is routine nowadays.  :-)   As an example, my 
Tri VCO tracks accurately up to 40 kHz:
http://home.earthlink.net/~ijfritz/sy_cir4.htm


>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.

Yep.  However, it's easier sometimes to get HF oscs with the inexpensive 
devices.  Many of the newer devices have better stability designed in.


>Of course the 748 still has its uses, its so slow it used to create new
>waveforms....

Sure, and sometimes it's better than a filter for taking out switching 
glitches!


>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.

Yes, that has been much discussed here.  :-)

Many of us use voltage-reference sub-regulators for critical voltages, 
rather than highly regulated supplies.

Will be looking forward to your results.

   Ian