ELTIM Voltage Controlled Amplifiers
Normally and mostly volume is controlled by a logarithmic (stereo) potentiometer. More and more we see all kinds of digital "special" IC's, doing similar. However, they are NOT meant for use in serious audio gear actually.
In the Voltage Controlled Amplifier/buffer modules as write about here in short, we "just" adjust the gain/attenuation of a very high quality buffer circuit(s). A buffering circuit is required in serious gear anyway, so combining it could be a smart move.
Perhaps it is clarifieed best what we are doing and what the differences are with some block diagrams:
VCA-2161 VCA-2180x VCA-2181x
Basically al three setups are equal, but we use more or less separated components.
At the same time, the quality of the VCA-type used is better as well.
All VCA modules in our program are pin-compatible.
All three models can be controlled by a 0 - 5Vdc signal (f.e. from a single, LINEAR potentiometer), and/or
by feeding an SPI datastream into the built-on D/A converters. Step sizes 256 - 4096 depending the model.
Since we are working with DC signals already, we implemented an opamp circuit which is doing what
it was meant to do originally: CALCULATE analog signals, acting as the first "computers".
Today by a computer this blackbox om your bureau is meant, but officially it only means calulator.
Can you imagine that f.e. a Spaceshuttle and F16's "fly by wire" system are/were working like this? They DO/DID!
Sorry, lets go back: we recalculate in a plain, old school way the control voltage to values of -90 / +30mV,
so just hookup a cheap LED/LCD reading and you already have the attenuation/gain value visible.
Check under the > at left the specific type you want to know more about.