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Old 2nd May 2013, 03:10 PM   #1
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Default My Chip Amp PCB - Thoughts?

I'm working on a dual 3886-based chip amp; going for a simple design overall. It has nothing too fancy in the power supply, with 5600 uF caps on each rail and uses an Avel transformer with dual 25V outputs. I've started by laying out the power supply PCB, using dual bridges and the Elliott safety ground/ground loop preventer. I'm hoping to get some helpful advice before I etch the board.

The MUR860 diodes have heat sinks that are not outlined - but nearly touch between the diodes, cover the adjacent traces and come within a couple of 10ths of the capacitors.

What do you think?
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Old 2nd May 2013, 03:58 PM   #2
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Put the caps close together, put the diodes close together. Route the rest.
The GND of the caps should be close together, and the GND "out" should pass thru cap's pins, not "just connected" to the pins.

I'd put the PS on amp's board. PS per amp, or make a 2-channel single board, with PS - then you won't need to go dual-mono (separate trafos/separate trafo windings) to get the benefits of dual-mono thing.
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Old 3rd May 2013, 05:59 AM   #3
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Thanks s3tup - I'm working on moving the cap grounds closer together and onto the ground path as you suggest. The choice of a single power supply PCB and dual mono amp cards stems, mostly, from my design layout for the case - which will have the chipamps mounted to a 1/4" back aluminum back panel; each placed between its RCA and speaker jacks for a short signal path. The power PCB will go back and center on the bottom panel between the amp cards with the transformer center-front. Each amp card will have a stepped attenuator soldered onboard with a drive shaft running on either side of the transformer up to the front panel. There are probably better ways to do some of these things - but half the fun is making interesting physical design choices while avoiding really bad sonic design choices.
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Old 3rd May 2013, 09:56 AM   #4
AndrewT is offline AndrewT  Scotland
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PJ,
look at the trace feeding the Zero Volts to the output.
The in from the rectifiers meets the out to the Zero volts some distance from the capacitor PIN/PAD.
This is BAD !!!!
The IN trace must NOT share any route with the OUT trace.
You have this drawn correctly for the +ve voltage and the -ve voltage traces.

When you come to laying out your grounds in the amplifier. The same rule "never share" applies just as much.

The three output pads are close together = very good.
The input side is not as good. Aim for LOW LOOP AREA for every pair of Flow and Return. Again this applies to amplifier wiring and amplifier PCB layout.
The smoothing caps are too far apart. This has resulted in an excessively long Zero Volts trace. This trace can also be double sided for lower resistance. A pair of wide thin traces will be better than a single wide trace.
A single wide trace will be better than a group of wires.
Even better would be where the + & - traces (Flow & Return) are overlaid on each other on either side of a very thin double sided PCB. This is very much more laborious in laying out.
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Last edited by AndrewT; 3rd May 2013 at 10:04 AM.
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Old 4th May 2013, 10:48 PM   #5
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Thanks AndrewT & s3tup,

I've redrawn the circuit - trying to follow your advice and still create a board that has some symmetry - pleasing to the eye. Specifically - I've tried to bring the diodes and caps closer together, route the output from the diodes THROUGH the cap pins and move the safety ground bits to the periphery and route to them. Thoughts?
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