aleph3 built, but humming... - diyAudio
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Old 7th July 2004, 02:02 AM   #1
cowanrg is offline cowanrg  United States
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Default aleph3 built, but humming...

so, i finally have an aleph3 put together fully, but its got a hum to it. its pretty slight, but you can still hear it.

ive checked the DC offset, its at 6mv or something really low, and it plays sound just fine, and everything else appears to be working.

Magura suggested that its because i dont have a filter on my power supply. im an idiot and didnt realize you needed one. right now, i have outlet > fuse > transformer > rectifiers > caps > boards. i guess im supposed to have some sort of inductor or resistor? will this get rid of my hum?

i ask because when i was testing it outside of the case, i had no hum and it sounded fine. however, i was only using 2 caps, instead of the 8 im using in the power supply now. could it be a wiring issue?

any help anyone can offer would be greatly appreciated. Magura has helped me to better understand troubleshooting so i should be a bit better at following advice. i just want it to work so i can make the second mono block!

pictures are on my site if you want to see more of what's going on:

http://www.cowanrg.mesanetworks.net/projects/
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Old 7th July 2004, 02:34 AM   #2
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Offtopic, just HAD to make some smileys about your 800VA trannie for your BoSoZ

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Old 7th July 2004, 02:36 AM   #3
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Oh, and very nice projects there!

Like your volume pot.

800VA @ BoSoZ & 250VA @ Aleph 3

/Tobias
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Old 7th July 2004, 02:59 AM   #4
cowanrg is offline cowanrg  United States
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yeah, the 800va bosoz was a bit overkill, and the 250va aleph3 is slightly underkill, but both were easily available and the prices were right...

thanks for the comments. im learning a lot. its been a long road, but i at least feel comfortable building things now. the electronics are still a bit unknown.

anyone got ideas?

i downloaded duncan's PS designer, but i have NO idea how to use it. i dont know what the numbers mean. i can throw together what i have, and add resistors or whatever, but i dont know what the results tell me...
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Old 7th July 2004, 03:02 AM   #5
jwb is offline jwb  United States
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You have pictures of the interior but I can't tell from them how the power is connected. The star ground point should be on that huge copper bar which I assume is the ground, and the input connector should be grounded to that initially. You can try grounding the input to the chassis instead, sometimes it works out better that way.

Your assertion about that metal washer shielding the PCB is, as far as I can tell, unfounded. I think moving the transformer far, far away from the input amplifier is a good idea.
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Old 7th July 2004, 03:06 AM   #6
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Try moving your board a little further away from the toroid while it's on and see if it varies or goes away. I think a few traces on thew board may be acting as a partial wind on the transformer and inducing currents.
Also check to temp of the sinks with the case together. With the fins horizontal and encased, you may loose some of the majic smoke from the fets with it all closed up. But you may be ok as those sinks look like overkill for 2 fets each.
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Old 7th July 2004, 03:06 AM   #7
cowanrg is offline cowanrg  United States
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the metal washer isnt shielding the pcb... the pcb sits on a metal plate about 1/8th inch thick.
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Old 7th July 2004, 03:08 AM   #8
cowanrg is offline cowanrg  United States
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yeah, the sinks dont get all that hot, even when completely closed up. its bigger than it looks actually.

Quote:
Originally posted by Brian Donaldson
Try moving your board a little further away from the toroid while it's on and see if it varies or goes away. I think a few traces on thew board may be acting as a partial wind on the transformer and inducing currents.
Also check to temp of the sinks with the case together. With the fins horizontal and encased, you may loose some of the majic smoke from the fets with it all closed up. But you may be ok as those sinks look like overkill for 2 fets each.
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Old 7th July 2004, 03:14 AM   #9
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Is the plate magnetic? Aluminum won't corral the stray magnetic feilds. Also read about star ground. Does shorting the input stop the hum? if so, you may have a ground loop in the source chain.
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Old 7th July 2004, 03:22 AM   #10
cowanrg is offline cowanrg  United States
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hum, i didnt realize that. i thought metal stopped interference

i took some pics to give you all a better idea i hope.

so you dont think its the PS? its just bad wiring/grounding?

http://www.cowanrg.mesanetworks.net/...3/DSCF0033.JPG

http://www.cowanrg.mesanetworks.net/...3/DSCF0034.JPG

edit:

i ground the input by just connecting input to ground right?
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