[sdiy] Quick query about 2164 VCAs

Tom Wiltshire tom at electricdruid.net
Sat Mar 16 22:06:13 CET 2019

Thanks David. I couldn’t see why not either. I think I’ll go ahead and try it.

Do you think I’ll need to adjust (double) I-to-V resistor values when I do eventually go back to a voltage since I’ll be driving two VCAs with the same current? Perhaps that saves me from the distortion you mention. I’ll have twice the current coming in (two VCAs being summed) but it’ll get divided out to two VCAs on the output, so I finish up back where I started. Lordy, it’d be lovely if it was that neat…;)


PS: If you’ve got a nice 2164 crossfader design, I’d be interested to see - ping me offlist. If I don’t finish up using such a thing here, I can see lots of places it could come in handy!

> On 16 Mar 2019, at 18:42, David G Dixon <dixon at mail.ubc.ca> wrote:
> Quick answer, without giving it too much deep thought:  I don't see why not.
> As long as you terminate all of the 2164s to a virtual then you should be
> golden.  Just be cognizant of how much current you are summing and putting
> through a single 2164 in the chain... you don't want to run it into
> distortion.
> If you are using two 2164 VCAs for things such as wet/dry balance, you might
> want to consider using a single-2164 crossfader instead.  If you want really
> accurate crossfading, it requires a trim, but it does save an entire
> linearized VCA circuit.  I can hook you up with a schematic if you're
> interested.
> -----Original Message-----
> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Tom
> Wiltshire
> Sent: Saturday, March 16, 2019 11:15 AM
> To: SDIY
> Subject: [sdiy] Quick query about 2164 VCAs
> Hi all,
> I know you can mix together the outputs of several 2164 VCAs direct into the
> input of another one, but can you mix together the outputs of several VCAs
> into the inputs of several VCAs simultaneously?
> The situation I've got is this: I have a wet and dry level controlled by a
> VCA each. These are brought back together at a single point (which will need
> to be a virtual ground node). I then have Main and Phones outputs, both
> controlled by a VCA each too. Can I connect the inputs of the two output
> VCAs together and mix the outputs of both the Wet and Dry VCAs into that
> same single point? Will the current divide equally between the two output
> VCAs? Will I need to adjust the output I-to-V stage resistors to compensate
> for the fact that each VCA only gets half the current?
> I love the fact that often with the 2164 VCA you can omit the following
> I-to-V stage and just feed the current direct into the next stage somewhere.
> There's often no need to go back to a voltage before turning things into
> currents again. I'm hoping that's the case here too! ;)
> Thanks,
> Tom
> ==================
>       Electric Druid
> Synth & Stompbox DIY
> ==================
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