[sdiy] Dirty vs. Clean Power (in modulars)

[Magnus Danielson]

From: "Greg James" <gjames at kddlab.com>
Subject: [sdiy] Dirty vs. Clean Power (in modulars)
Date: Sat, 26 May 2007 11:04:01 -0400
Message-ID: <CAEGKNANKJLNIBHOBLFMOEFOPDAA.gjames at kddlab.com>

> OK,
> 
> So I've read here and on some other lists about people moving certain
> modules on or off various power rails to isolate them from noise, etc. Is
> there anywhere I can find some good, comprehensive, guidelines for the what,
> why, how and when to do this?
> 
> For example, one recommendation I read is to isolate all CVAs from 'dirty'
> modules. Another is to isolate all modules with digital circuitry. And
> another person wrote about LEDs causing problems.
> 
> I'm just looking for "best practices" here. I understand that in the end,
> every system can have it's own quirks. But high-level rules of thumb would
> be helpful.

The issue is very simple. You want to protect your audio/precission paths from
noise sources which can polute your signals. Especially things that has abrupt
changes in power consumption (current) is potentially bad things. Among them
we find lamps, LEDs and just about anything which is or operate as digital
circuit. A first approach is to split the power-lines at the power-supply into
dirty and clean powerlines. The theory is that the poluting currents will not
cause a resistive and inductive voltage-swing also for the clean power. There
will be some of that, but that will be mainly handled closeup to the power
supply which should counteract it with capacitors and control-loop.

A better approach is to individually regulate the dirty and clean power lines.

An even better approach is to fine-regulate the clean power at each module.

There may also be things you can do in each module and especially directly at
each noise-maker to reduce the emission of signal. Decoupling capacitors is
among those methods. A series inductor with capacitors on each side is even
more effective. Dropping the current through a LED a bit can make quite a big
difference for its influence. Things like that.

Cheers
Magnus