[sdiy] SSM2164 VCAs

[David G. Dixon]

Yes, I've gone through the datasheet again, and the Irwin paper and all that
follows, and I now have a very clear picture of the CV response.  There is
an example in the datasheet for hooking the 2164 up to a DAC which implies
that the 0 to 10V range of the DAC output would correspond to the 0 to
-100dB dynamic range of the VCAs.  This is what had me all confused.  That,
and the fact that I was running on about 3 hours' sleep and we had run out
of caffeinated coffee!

Now I'm wondering why I would want my envelopes to be 0 to 10V (the MFOS
standard, I guess).  Changing one resistor in the circuit shifts this level.
It might be more useful at 0 to 5V.  Either that, or I simply rely on the CV
attenuator to bring it down, but then I'd be riding the bottom 1/3 of the
knob swing all the time.  Alternatively, I could hardwire the CV summer for
1/3 gain.  I'll have to think about it.


> -----Original Message-----
> From: Tom Wiltshire [mailto:tom at electricdruid.net]
> Sent: Tuesday, June 09, 2009 2:41 AM
> To: David G. Dixon
> Cc: Synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] SSM2164 VCAs
> 
> David,
> 
> This confused the hell out of me at first too. The examples in the
> datasheet are very lax about what level the CV should be (Fig 24
> shows 0-5V CV used). However, the figures are quite clear:
>   -33mV/dB.
> Hence you need 3.3V for fully off -100dB, and -0.66V for 20dB gain. A
> 10V envelope is overdoing it quite a bit. This isn't too big an issue
> since you've probably got a CV summer in the circuit anyway, but you
> need to watch the levels and offsets.
> 
> Regards,
> Tom
> 
> 
> On 9 Jun 2009, at 01:50, David G. Dixon wrote:
> 
> > Also, the gain can
> > increase as much as +20dB or decrease as much as -100dB.  At one
> > point, the
> > datasheet mentions that a 0 to 10V CV range will give gains from 0
> > to -100
> > dB.  Hence, I'm presuming that a 0 to -2V CV range will give gains
> > from 0 to
> > +20dB, although this is never stated.