[sdiy] Free SSM2044, SSM2056 chips for pickup and one question about single supply VCAs

brianw brianw at audiobanshee.com
Thu Mar 7 01:25:11 CET 2024

Good point, but a ground reference isn't guaranteed to be a perfect solution. Not every "ground" reference is free from noise, because if enough current flows through that "ground" reference and if there's enough resistance along the path then the Voltage will rise above ground. If the current is both both substantial and has a noise component, then the error on the "ground" reference will show up as noise.

This basically means that you have to pay attention to layout so that the ground references aren't a problem.

Granted, many of the parts will only pull power from +12V and -12V, but if your circuit induces enough current through the "ground" then there can be noise.

The converse of this is that you can create a relatively noise-free -12V if you take the same amount of care, although the current will probably be higher. I understand that +12V almost always uses more current than -12V, depending upon the circuit.


p.s. Thanks for the link, René. I'll check that out. Such articles are always appreciated.

On Mar 6, 2024, at 6:31 AM, Mike Bryant wrote:
> And if you translate the control voltage to the -12V line you'll probably inject PSU noise as well.  Ground referencing is always best for control voltages if you can manage it.
>> The reason is that the Iabc (the control current) is created with a
>> resistor from a voltage referenced to GND.
>> The OTAs sinks this current into the negative supply terminal.
>> If you'd run them from +-12V then you need extra circuitry to translate
>> the voltage.
>> (If you want to read a bit more on OTAs there is an article at my
>> homepage, link below.)
>> Best,
>>   René

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