On Thu, 24 Dec 2009 00:28:14 -0000, "fredbloggstwo"
wrote:

Hi All,

I was laying out a pcb tonight for a line amplifier using a tool called PCB
Wizard (a good little tool) and reminiscing to myself how I used to do it in
the past using black tape and a scalpel onto clear film.

Despite the ability of PCB Wizard to autoroute etc., I still prefer to lay
the track out myself. As well as the obvious topological challenge, I
was trying to wonder why and came to the conclusion that, instinctively, I
avoid the use of sharp edges such as right angle turns - I always use
rounded bends and avoid the obvious stuff of high-level and low level
signals being non parallel runs, star earthing etc. that I was trained to do
and that autorouting has no general concept of.

The line amp I am laying out is based on one from an EMI TG mastering
console where the boards were originally laid out at twice full size using
the tape and scalpel method as was the norm during the late 60s and 70s and,
as well as the low number of active devices in the signal path and good
electronic design, modern equipment seems incapable of equating in terms of
sound quality. The evidence of this is that these consoles are still
preferred when it comes to the audio mastering process at the likes of Abbey
Road studios for their 'sound' as well as their flexibility.

I suppose the ultimate in this is point to point wiring, but that is not
what I want to do in wiring up a line amp.

So my question is this: is there any evidence that the layout of pcbs does
affect audio quality? If so why? The type of evidence is things like the
use of rounded instead of right-angle corners. (For example, if I remember
my EM theory correctly, sharp points are the most effective for radiating an
electric field so could right angles could radiate and produce cross-talk)

Perhaps somewhat esoteric, but worth a few lines of discussion.

I would be interested in the references for hard evidence and not hearsay.

Best regards

Mike



The sharpness of corners does not matter for audio, though it does for
RF (for microwaves corners are carefully calculated).

For audio the most important thing is the star ground point. That will
have a real effect on pickup from power supply lines, and confer
invulnerability from external pickup.

Routing of tracks is also important. Power lines will be dirty and
should not go near low level signal lines. Tracks on opposite sides of
the boards should cross each other at right angles to minimize
capacitive coupling, but this is a secondary worry, and not likely
ever to be a problem..

d