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Old 12th August 2012, 10:40 AM   #11
juma is offline juma  Germany
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You still have a bus between the rectifier and the first ElKo.
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Old 12th August 2012, 10:43 AM   #12
Zen Mod is offline Zen Mod  Serbia
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like this

in some cases you'll also need bridge directly between Audio gnd left and Audio gnd right , made of thick wire , laid out in shortest path
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Old 12th August 2012, 12:55 PM   #13
AndrewT is offline AndrewT  Scotland
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I think that hum is better suppressed if the first capacitor pair have their "ground" connection tied together before the common wire is brought to the output star.

I have not built a 3stage rCRCRC PSU, so I am not sure where the second pair of capacitors should be ground connected.
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Old 12th August 2012, 01:28 PM   #14
Zen Mod is offline Zen Mod  Serbia
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nope
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Old 14th August 2012, 07:56 PM   #15
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Guys, thanks for all the input. I've managed to rewire the bung and the hum improved nicely. It's still there but it's almost not audible anymore. Best guess is some ripple getting through to the output.

Perhaps changing the R's for L's might reduce ripple enough. On the other hand perhaps it's worth the effort to rewire the xformer to output 24V, this will give me room to reduce ripple rigorously and perhaps use an input choke to dampen input current swings. Might also benefit the xformer hum... when aiming for a 15V rail the only problem is the current rating for the choke. If I remember correctly the RMS current would be around 10A but the peak current at about 16A. Most if not all chokes will go to about 10A, so I'm not sure whether the 16A peak will be problem... Any ideas?

Thanks again for all the GOOD help and fast answers!
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Old 14th August 2012, 08:57 PM   #16
Zen Mod is offline Zen Mod  Serbia
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are you having hum with inputs grounded ?
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Old 15th August 2012, 06:45 PM   #17
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Zen Mod, good point. No hum with inputs grounded... so guess ripple isn't much of a problem. Any options left untouched to further reduce the last bit of hum?
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Old 15th August 2012, 06:58 PM   #18
Zen Mod is offline Zen Mod  Serbia
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I can bet that amp will be silent in case of using balanced inputs

try that fat bridge wire between two gnds as I wrote in post #12

it's role is solely to kill any possible potential difference between two (channel) star gnds
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