In article , David Looser
wrote:
"fredbloggstwo" wrote

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


It's my personal experience that good layout is vital. Poor layout can
result in instability and significantly increased noise levels, but I'm
afraid that I cannot offer "references for hard evidence".

Instead I can offer a simple experiment.

Take a power amp and set it delivering something like a few watts of a
20kHz sinewave. Monitor the output with a distortion or spectrum analyser.
Try wiggling/moving the wires that convey the dc lines/output so that their
relative locations and spacings and orientations change. If any components
can be moved, try also moving them. (Use some plastic pliers for safety.)
Watch how the distortion changes. Chances are this will be noticable unless
the level of distortion is high in the first place.

Note also any changes in ripple at the output if using the amps own PSU
rather than an excellent bench supply.

I've certainly in the past found that changes in wire looming and PCB
layout and tracking measurebly change performance in terms of
ripple/hum/distortion/stability/rf sensitivity. Reasons for this should be
obvious.

Also sometime the orientation of capacitors can matter. If they are 'swiss
roll' types for example, turning them around changes which pad is linked to
the 'outside' of the cap and directly exposed to coupling externally.

With something as simple as a line amp I'm suprised that you need
auto-routing. Most PCB layout software offers a manual routing option,
why not use that?

Perhaps worth adding one point.

People have sometimes chosen to make PCB 'tracks' by just etching away gaps
between areas of conductor. This saves money on the chemicals as it reduces
the area to be etched. The snag is that you get increased coupling between
'tracks' so may have more parasitic effects. This might help performance,
but can also cause any instability, etc, to be worse than if using the
traditional approach of 'lines of conductor of defined widths'.

No idea about references. I learned these things by experience. Have fun.
:-)

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html