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Old 10th May 2009, 11:17 PM   #231
Bigun is offline Bigun  Canada
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And now looking to the power supply. Updated to single board, Chokes mounted underneath. I've allowed two 2,700uF on each rail before the choke, another two after the choke + a third spot which can be populated with an extra 2,700 cap or a 1,800 / 1,200 / 560uF as they are all available in the same footprint.


Should be able to get this pcb made and populated this week. Then, if it works as planned, I have something to test the amp with
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Old 11th May 2009, 12:24 AM   #232
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And the updated PSU schematic.

(the Eagle eyed people will see that the pcb layout had two rectifiers the wrong way around).
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Old 11th May 2009, 01:22 AM   #233
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Hi Gareth,
You might want to consider splitting the ground as shown below. The 100 ohm resistor (with opposed diodes) isolate the audio ground from the chassis ground. Helps (I think) to eliminate ground loops and keeps some of the high frequency noise from the diodes and bypass caps out of the audio ground.
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Old 11th May 2009, 02:22 AM   #234
Bigun is offline Bigun  Canada
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This forum is good at keeping me honest - I had slipped in a little change to simplify the grounding but you are right, it's not the best approach.

Trouble is, I cut the raw pcb board, so now if I make changes it has to fit on the same board. A challenge I can meet no doubt.

How does this approach match up to the ground lift resistors on the signal inputs ?





** I am concerned about instability in the psu because of these chokes though. The L and total C produces some options for oscillations does it not ? - can anyone put my mind at ease on this point ?? **
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Old 11th May 2009, 02:45 AM   #235
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Quote:
Originally posted by Bigun
This forum is good at keeping me honest - I had slipped in a little change to simplify the grounding but you are right, it's not the best approach.

Trouble is, I cut the raw pcb board, so now if I make changes it has to fit on the same board. A challenge I can meet no doubt.

How does this approach match up to the ground lift resistors on the signal inputs ?

:
I just wire my audio input socket to the chassis which is earthed and dont get any problems.
The only equipment I connect to the amp are a cd player and a guitar effects pedal so its unlikely I will get two earths.
If it was a problem I would use a switched earth on the amp.
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Old 11th May 2009, 02:48 AM   #236
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Quote:
How does this approach match up to the ground lift resistors on the signal inputs ?

I used both in my 6 channel amp to good effect.

Oscillation shouldn't be a problem...
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Old 11th May 2009, 02:57 AM   #237
Bigun is offline Bigun  Canada
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Well I managed to fit it in on the same board
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Old 11th May 2009, 03:17 AM   #238
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C9 and C15 (bypass caps) would be better on the chassis ground side.
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Old 11th May 2009, 12:51 PM   #239
Bigun is offline Bigun  Canada
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Look cafefully, I've hidden a pair of decoupling caps on the chasis side too
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Old 11th May 2009, 10:48 PM   #240
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Aha! I'm blind...


I think a pair of your smoothing caps are backwards.
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