[sdiy] Re: OTA nonlinearities

[Nils Pipenbrinck]

Thanks for your replies (especially thank you, Jim.. your OTA analysis was
very interesting to read!)

0.5% THD for a OTA based VCA is a bad performer (in my eyes).. It might be
ok to have such a distortion on mono synth-waves. I think the distortion
will be hearable as soon as I route a complete audio signal (read: music)
trough the OTA.

I wonder what options I have to build a better VCA... I looked up the
datasheet of the SSM 2024, and it's not that much better.. the THAT-Chips
look like a perfect choice, but they are a lot more expensive.

There are also a lot of 4-quadrant analog multiplier chips.. I never dealed
with them, but it shouldn't be that hard to turn them into VCA's..

I even considered dropping VCA's all together and go for digital
potentiometer chips.. Anyone has experiences with them? They are no VCA's,
but suitable for my application (some kind of mixer-matrix for hifi audio. I
want to control more than 2 channels with one pot, so stereo-pots won't do
the job). Of cause I would need some digital stuff around my module if I
choose the digi-pot way, but I would get midi-support and presets for free.
Stuff that's always nice to have, but not really required for me.

Does anyone has another idea how to control lots of audio channels with just
one pot?


Nils Pipenbrinck

BTW: I'll try out the asm-1 VCA, just to get a feeling how bad 0.5% THD
really is.. I mean.. I'm listening to my music with a self-build tranny
headphone amp, and I doubt, that it's THD is below 0.5% or so. I don't care
about that.. my amp somehow "flavours" the sound, and I like it that way..