Humming DRV134 balanced output. - Page 2 - diyAudio
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Old 2nd March 2014, 01:31 PM   #11
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Thanks Andrew.
I have now re-tested first amp with identical lash-up to 2nd amp test - works fine.
Only difference between successful & unsucessful test is 1mtr of twisted speaker cable!
Can that cause a class D amp to oscillate?
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Old 3rd March 2014, 08:23 AM   #12
AndrewT is offline AndrewT  Scotland
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I don't know.
I have read a few ClassD posts here and the section in Cordell's book.
I still know nothing about ClassD design.
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Old 3rd March 2014, 08:24 PM   #13
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Andrew - Sorry to be a pain but I cannot find the grounding article you mention.
Can you direct me? Thanks.
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Old 3rd March 2014, 10:57 PM   #14
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It's hidden in the articles section:
Audio Component Grounding and Interconnection
David Davenport - 21st April 2010

Audio Component Grounding and Interconnection
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Old 4th March 2014, 06:48 PM   #15
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Thanks, got it. I have printed in full to study.
I have a lot to learn.
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Old 5th March 2014, 06:31 PM   #16
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Dumb question and I cannot see it in the Grounding Article:
I ground the xlr sockets pin 1 to chassis. I ground the power amp pcb to chassis star ground. I sort out the pre-amp grounds.
I have a short lengths of balanced screened cable from pcb to xlr chassis sockets. Do I ground these at pcb or at chassis socket?
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Old 5th March 2014, 06:55 PM   #17
AndrewT is offline AndrewT  Scotland
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Screens to Chassis at both ends.
Keep the audio on the PCBs.

H.Ott tells us that sometimes one end of the screen may need a capacitor coupling to Chassis. The other end is still to Chassis.
Quote:
I ground the power amp pcb to chassis star ground.
What does this mean?
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Old 5th March 2014, 07:08 PM   #18
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The Abletec amp is complete with power supply. The pcb has 6 mounting holes. 2 must be insulated. 4 are ground plane and have bright solder around the screw holes. I thought I was being smart mounting on insulated stand-offs. Now I know from the grounding article it should be connected to chassis. The mains cable earth wire is screwed to chassis (a star of 1 wire).
I could - a) run a short length of wire from pcb ground plane to this screw, b) replace the nearest stand-off (about 20mm away from earth screw) with a spacer and long screw thus grounding the pcb at 1 point or c) replace all 4 stand-offs with spacers and long screws.
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Old 6th March 2014, 07:43 AM   #19
AndrewT is offline AndrewT  Scotland
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Probably better to have all the standoffs making contact with the Chassis floor.
No need to take the Chassis connections to the Safety Earth.
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Old 9th March 2014, 10:26 AM   #20
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Grounding sorted. Zero hum. Success.
Thanks for all the help.
Preamp casework next - wooden mock-up before fabricating metal case.
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