New proud owner of Aleph 5 freaking out 'cause of hum - diyAudio
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Old 23rd April 2004, 11:25 PM   #1
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Default New proud owner of Aleph 5 freaking out 'cause of hum

About a week ago I reported I have finished my Aleph 5, and I also told I don't have any hum. That's a big lie. Actually at first I did have some, then I messed around and it almost dissapeared. But I thought it dissapeared because it was less hum than the first try.
I tried moving away AC runs under the grounded aluminum plate, but it didn't help. I tried all the possible connections suggested in this forum, but no luck. I measured AC ripple on the PS caps and the meter showed around 80V. Is that possible? What is the next thing to try?
Please help, this hum issue can really make person feel frustrated and helpless.
For my grounding schemes please see this thread (page 1 & 2)
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Old 23rd April 2004, 11:52 PM   #2
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Measure the ripple with an oscilloscope if you have access to one. I think 80 volts ripple is impossible unless your diodes are shorted, but that makes no sense. Your meter may not have a capacitor in it on the AC range? Is it possible you have a bad or miswired filter capacitor? I still think grounding is the problem. Does the hum go away when disconnecting your preamp? Did you use the 10 ohm thermistor to isolate ground and chassis (earth gnd), if you did, make sure you measure 10 ohms between chassis and your power supply ground. I am no expert, I am just trying to give you some ideas.
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Old 24th April 2004, 03:48 PM   #3
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Default Nobody wants to help poor guy

OK I see nobody i interested in my problem, I guess thats because there were a lot of questions concerning the ground loop problem and lot of possible solutions. BUT I'WE TRIED IT ALL!!!!!!!!! Newest thing I did was disconecting AC plug earth completely from the chasis, but the hum is still there (when preamp is connected). What to do? I tried using rectifier bridge, resistors, thermistors and no luck.
Please advise something, I'm loosing my mind.

kilowattski thanks but I allready tried the thermistor and resistors and no luck.
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Old 24th April 2004, 04:01 PM   #4
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Is this a diagram of your grounding layout?

If so, did you try lifting the amp ground off of the chassis ground?
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Old 24th April 2004, 04:05 PM   #5
MBK is offline MBK  Singapore
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Firstly, some hum will remain because the power supply rejection is not infinite. It's a problem only if you hear it from the listening position. It's "normal" if you can hear it at say, 2 inches from the speakers only.

Grounding: from your scheme I see 2 things I would have done differently:

- chassis should go directly to the IEC ground wire with no resistances or diodes. This is for safety and also the point of earthing the chassis. The diode-resistor connection *then* connects from the chassis to the star ground for all other grounds, that you already have.

- the pin 1 (ground) of your XLR should not go anywhere. It should be connected to the chassis at the entry point of the XLR. Thinking of which, I hope your RCA input ground is isolated from the chassis...
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Old 24th April 2004, 04:19 PM   #6
fcel is offline fcel  United States
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Could it be that the additional length of cables to the mosfets is picking up noise from the surrounding equipments. Did you tried moving those additional wires & see if it makes any difference? Or even moving the amps away, say away from the TV?
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Old 24th April 2004, 05:29 PM   #7
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How much noise do you get if you disconnect the preamp and
short both inputs with shorting plugs?
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Old 24th April 2004, 05:49 PM   #8
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roddyama,
I tried to completely disconnect AC inlet earth pin from the chasis (if that's what you mean) and hum is still there.

MBK,
" chassis should go directly to the IEC ground wire with no resistances or diodes. This is for safety and also the point of earthing the chassis. The diode-resistor connection *then* connects from the chassis to the star ground for all other grounds, that you already have. "

Isn't that the same thing as I connected. I saw this type of connection in A75 article.
I completely disconnected XLR from the board and from the ground. Now I just have a jumper beetween XLR - and ground on the PCB.

fcel,
I did try moving all the internal wires but nothing changed. The thing is if Mosfet wires are making problems there would be some noise when premp is not connected. Am I right or not?

Nelson,
Do you mean shorting input RCA grounds with a wire while preamp is disconnected. If yes, I did try that and no noise with or without the shorting wire while preamp is disconnected. I tried using rectifier bridge as you used in one design, but no luck there. I tried to use 5.1R/1W resistor together with two diodes in antiparallel conection and it's not working. Do you have any other suggestions?
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Old 24th April 2004, 06:07 PM   #9
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If you have tried all of the suggestions so far the only thing I can think is that your rca jacks are touching your chassis or somehow your circuit ground and chassis are directly connected somewhere. A quick measurement with an ohm meter should verify that. If you read zero ohms that is your problem. You have verified you have a ground loop problem because the hum went away when you disconnected your preamp. Could the ground problem actually be in the preamp? What happens when you connect your source directly to the amp without the preamp?
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Old 24th April 2004, 10:12 PM   #10
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Hi to all..
I am also involved to this problem - boris and I know each other.
Attached is the latest grounding for his amplifier.
Kilowatski - do You suggest to disconnect signal grounds of the central point of the star ground that is on the chasis?

Another thing- could it be that he has some problems with his neutral, fase and grounding in main power supply that is coming to the amplifier. His preamplifier also has the same connector (live, neutral and ground) - it could be that there is the loup.
Unfortunatelly we did try to disconnect the grounding wire (only live and neutral remained connected) and the hum was still there. So it could be also that in his house the ground is not properly installed?????
We would try that tomorow- by connecting the amp in the house of my parents since I am sure that they have good power instalation in the house.

If that doesn't help than we must do the amplifier all over again checking every wire and every connection since everyone here really don't know what to do more.... (I mean here at his place- not on the forum)

The humming is from the grounding that is only for sure and it is gone when the amplifier is not connected with preamplifier. Also it is not humming but more like buzzing and it is not that loud. It can be heard from the point one is listening the music.
Oh, well we would be masters of the groundingness when we finish with that one.....
regards
daniel
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