Re: Groundplane in poweramplifier PCB design

In article <e1rcmb$2o3$1@xxxxxxxxxxxxxxxxxxxxxxx>,
Wiebe Cazemier <halfgaar@xxxxxxx> wrote:
Hi,

I've just about finished designing a PCB for a HiFi power amplifier, and now
I'm wondering something. Is it a good idea to fill up the unused space on the
board with ground copper (without orphans of course)? Or, is it best to keep
the ground clear of as much parts as possible, as you do with the supply
lines?

There can also be thermal reasons for putting copper in. You can't ignore
these.

You want the extra copper as shielding. If you can arrange to effectively
have a thick shorted turn around the whole circuit, this will help to keep
AC magnetic fields from going through the PCB.

Also remember that every bipolar transistor is an AM radio just waiting to
happen. The guy next dooor will buy a 1KW CB tomorrow.

There are other places in the design where you want the trace to be short
and thick. These are the places to look at. It is likely that you will
find that you want those traces so wide that they end up really being a
plane. ie:

Ascii art:


pin trace pin
O-------------------O

Becomes:


********************
********************
***O***********O****
********************
********************

If you have to, you can initially make the plane as a different net than
GND. It will flow around the GND traces. Then you can join it up using
whatever trick your layout tool allows.


The speaker returns go directly to the main power supply BTW, so the
groundplane is not necessary for that.

Thanks in advance,

I assume that this amplifier has feedback. Where are you picking off the
two sides of the speaker for feedback? These connections can also be
trouble makers.


--
--
kensmith@xxxxxxxxx forging knowledge

.

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