Well, I cannot do the hard evidence stuff, but I've encountered some pigs in
my time.
Who recalls the Sinclair IC12, in which it was all too obvious that inside
the chip small and large currents came too close to each other making the
sound distorted by intermodulation, one assumes. The pcb was not much
better in this respect despite the advice on keeping input and output earths
apart, it seemed the pcb design had been made before this was written.
They also seemed to have some nicely tuned wiring designed to pick up radar
pulses as well.

On a similar note, one amplifier I encountered in the 70s, had a unique
feature on its balance control. as you got near the end of travel, the
opposite channel came up again with a very distorted version of the audio.
This seems to be once more, inappropriate earthing of the pcb mounted pot.


I'd have thought the sharp point problem you mention might matter more in rf
or in high impedance audio more myself. However long runs of audio near
other signals, particularly if they are not audio is to be avoided. Ref some
Cassette machines with inverters for the displays getting into the audio
chain. Did I say Techniques? grin.

Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
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"fredbloggstwo" wrote in message
...
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