Aleph-X humming\buzzing - diyAudio
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Old 7th August 2012, 07:06 PM   #1
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Default Aleph-X humming\buzzing

Finalized and powered up my stereo Aleph-X (with single PSU, 800VA 12V sec, dual rect.bridge and 2xCRCRC with C=47,000uF and R=0.1ohm per side, given about 11.0-11.5 V rail, which is a bit low but acceptable for now). I used the PCB's from the 2003 group buy:PCB)
using this schematic: Schematic
with option: J1a, D1a, and jumper from pin 1 to 3 on Q12a. Used IRFP044 biased at about 2.25A each.

Aleph-x settles in quite nicely, with absolute DC of about 50mV and relative DC of about 4mV on both channels using RCA with input caps.

The problem I'm facing is this:
When using open RCA I hear a clear hum from the xformer through the speakers, seems 50Hz but I'm not sure. I also hear some noise in the tweeter and midrange. Fiddling with the wires doesn't help.
When shorting +input to ground gives me a completely quiet amp at the speakers not hearing any noise or humming.
When connecting the interconnects to the RCA also gives me a completely quiet amp.

Question is what is causing the noise? Could it simply be a floating +input? Cause it seems to me that it has nothing to do with ground loops or so since the shorting of the RCA solves the problem.

Luckily the noise is only present when the amp is connected, so I've already had the pleasure of listening to this amp and it sounds marvelous!

Hope someone can help here.

Cheers.
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Old 7th August 2012, 08:01 PM   #2
Zen Mod is offline Zen Mod  Serbia
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pics , please
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Old 8th August 2012, 05:33 AM   #3
h_a is offline h_a  Europe
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Hi there,

noise measurements are always done using shorted inputs as there might be garbage picked up otherwise.

Keep in mind the X-amps are typically sensitive to the DC-impedance at its inputs, so if you want the same small output offset for balanced and unbalanced inputs, you can try AC-coupling.
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Old 10th August 2012, 03:54 PM   #4
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Default Photo's

Took a while but here are some pictures of my stereo amp.

Hope this will help.

Cheers.
Attached Images
File Type: jpg IMG_20120810_173228.jpg (414.0 KB, 279 views)
File Type: jpg IMG_20120810_173244.jpg (417.2 KB, 248 views)
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Old 10th August 2012, 04:07 PM   #5
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Do you have oscillaiton problems with fets mounted that way?
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Old 10th August 2012, 04:20 PM   #6
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Not as far as I know. Amp is about dead quiet except for a very very slight hum when getting almost into the woofer.

Any reason to assume oscillation with this setup?
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Old 10th August 2012, 06:08 PM   #7
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Resistor on the gate is not very close. It is there for the purpose of preventing oscillation. IF you got a DMM, plug it up to outputs and see.
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Old 11th August 2012, 09:18 PM   #8
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Ah, I was under the impression that with this setup oscillations wouldnt be that big a problem. But who knows. Nevertheless, I doubt if a conventional dmm can measure any hf oscillation. But I'll try with C and t wo anti parallel leds at the outputs to see. But the very low level of output noise makes we wonder if it is actually oscillating. It might sound like a dc component on the xformer or perhaps some overloading of the xformer... although Im not sure if overloading can.actually result in output noise...
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Old 11th August 2012, 09:47 PM   #9
juma is offline juma  Germany
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jeekee, you are using a combination of star and bus ground in this amp (bus is a red wire from bridge rectifier through ElKos to half-star point). Make a clean star and shorten the red wires.
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Old 12th August 2012, 09:46 AM   #10
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Thanks for the advice. Before making a mess of things here's the proposed layout. Guess this would be the star ground layout you propose...
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