layout question

[lepomis]

The following is from Self's book...

Minimize radiation from the supply rails by running the V + and V– rails as close together as possible. Keep them away from the input stages of the amplifier and the output connections; the best method is to bring the rails up to the output stage from one side, with the rest of the amplifier on the other side. Then run tracks from the output to power the rest of the amp; these carry no half-wave currents and should cause no problems.

The part where his says to run tracks from the output... Does this simply mean to first run tracks to the emitter of the output transistor and from there to the rest of the amp (in the case of a CFP output stage) ?

 

[Ian Finch]

Usually, the placement of fuseholders determines the point of divergence for output and input stage power rails. Otherwise, it's clear as written. "..run tracks from the output to power the rest of the amp...". The point is that with a dual rail power feed, you make the path to the output stage the shortest, direct route and not vice versa. Let the routing of the small current required for the early stages take secondary importance. It is better, though, not to make this connection within the output stage where heavy switching currents may cause unnecessary noise.

Take a look at any PCBs posted on forum and you will see most people adopt this approach, even though they separate the supply rails and feed in from both sides. Visual symmetry is important to many, it seems.

 

[lepomis]

Thank you. I understand your explanation a little bit easier. I think I got hung up on the word output. It also makes the specific grounding track rules more understandable.

 

[Ian Finch]

Yes, it's just the abbreviation "Then run tracks from the output (stage)....." which threw you. Well, I guess you didn't want to connect the output to the power rails any more than Mr Self intended. Unfortunately, adopting an informal or conversational style might have eased the rigidity of the written advice here, but not without problems.