[sdiy] Audio taper pots - shunt resistors and contact resistance

[Ove Ridé]

On 9 September 2012 01:13, David G Dixon <dixon at mail.ubc.ca> wrote:
>> Some people may worry about noise from a digital circuit (for
>> example through stray capacitance) and may want to keep them
>> apart. It may also be that the semiconductor processes used
>> for a typical DAC and a "high" voltage (as opposed to 3.3 V
>> or 5 V) VCA are incompatible or difficult to combine without
>> a lot of additional R&D. Feel free to prove me wrong.
>
> 2164 VCAs are at unity gain at 0V, and are more or less completely off (-110
> dB) at +3.3V.  Hence, the range is just about perfectly suited to a 0 to
> 3.3V digital circuit.

I'm not talking about the voltage range as such. I'm talking about the
semiconductor manufacturing process. For example, in a modern digital
circuit, you may want to use 0V as your ground reference. You may also
want to use a manufacturing process which allows small transistor
sizes. On the other hand, having +/-12 V on the same die, may
completely shatter parts of the VCA circuit, similar to what ESD would
do and/or cause latchup.

I'm not saying it's impossible, just that it isn't trivial and may
cost far more in R&D to put into production than it's worth, compared
to having two separate chips.

-- 
/Ove

Blog: <http://blog.gg8.se/>

"Here is Evergreen City. Evergreen is the color of green forever."