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The AD712 in the VRG
MUFF WIGGLER Forum Index -> Oakley Sound Systems  
Author The AD712 in the VRG
terjewinther
The builders guide says that U2 should be a "good quality FET", and suggest using an AD712 op-amp.

- There are various versions of this to be found at my usual part sellers, with different extensions to the part number, like AD712JNZ and AD712KNZ. I have tried reading some differences in their specs, but can´t find any. Since the price difference is huge (one costs twice as much as the other one), is there a specific type to go for?

- If one should aim even higher than the AD712, which op-amp should that be?

I don´t mind using a bit of money on this particular part.
Synthbuilder
I used the cheapest AD712 that Farnell were selling at the time. This was perfectly good enough for my needs. I did have a full set of results showing output error voltages with different op-amps over different time settings and at different temperatures. Alas I threw it away in paper purge late last year - I only have a little workspace and it gets messy very quickly.

Anyway, with a FET op-amp it is the one with the lowest input offset voltage and input voltage drift (over temp) you are looking for. This is really only critical if you are to be using the VRG as a slew generator for pitch CVs, ie. voltage controlled portamento. For LFO and EG duties the offset voltage specification is less important.

Tony
terjewinther
Synthbuilder wrote:
Anyway, with a FET op-amp it is the one with the lowest input offset voltage and input voltage drift (over temp) you are looking for.


Thanks - then I know what to look for.
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