[sdiy] Any noise avantage to parallel 2164 VCAs?

[Mattias Rickardsson]

No no, separate input resistors and RC snubber networks for the two VCAs,
so you know what current each virtual-ground input pin gets - and then
summing their output current into one common op-amp just as you said.

30k for the Rin maxes out the input current capability for SSM2164/V2164
within +/-15 V supplies; with lower supplies you can handle lower input
resistances, and the SSI2164 even lower to reach lower noise.

/mr


Den sön 17 juni 2018 22:31Tom Wiltshire <tom at electricdruid.net> skrev:

> I don’t think it’s any extra C and Rs at all. Like Ian said, thew them
> together pin for pin. I don’t see the point of hanging two RC networks off
> one combined input, so there’s nothing extra there. I suppose you could use
> separate 30K input resistors and RC networks for the two inputs, but why?
>
> We know from the datasheet that the outputs can be tied together, so
> there’s no problem there.
>
> Control input impedance is a reasonable point - the 5K impedance isn’t
> high to start with, and will get lower, but it’s still at a manageable
> level. So I don’t see a problem there either.
>
> Tom
>
> > On 17 Jun 2018, at 15:28, Mattias Rickardsson <mr at analogue.org> wrote:
> >
> > Definitely, use them in parallel. The VCAs are easily the noisiest
> bottlenecks of your circuits and using two in parallel should lower it
> around 3 dB.
> >
> > I don't see how it wouldn't be worth the circuitry - what is it, an
> additional C and two additional R?
> >
> > Also, make sure to use the new improved SSI2164 for even better SNR
> and/or THD potential.
> >
> > /mr
> >
> > On Sun, 17 Jun 2018 at 13:49, Tom Wiltshire <tom at electricdruid.net>
> wrote:
> > Hi all,
> >
> > A quick query, if I may: Is there any noise advantage to using two 2164
> VCAs in parallel?
> >
> > I’ve got a circuit that uses two VCAs, so there are two others spare on
> the chip. And then it occurred to me that there might be a minor gain by
> using them in parallel pairs. It’s a case of “well, they’re there so we
> might as well use them” if there’s no reason not to.
> >  Or would it be better to simply disable the unused sections?
> >
> > Thanks,
> > Tom
> >
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> >        Electric Druid
> > Synth & Stompbox DIY
> > ==================
> >
> >
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