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Old 20th February 2004, 08:41 AM   #1
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Default humming amp

Hi,
I have a 'Hum' problem with an aleph like cirquit.
when I connect a signal source I hear hum at the output.
it's the same when I connect the 2 inputs of R1 and R4 together.
I have a star like ground with 4mm˛ wire.
any ideas?

Christian
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Old 20th February 2004, 12:33 PM   #2
JCoffey is offline JCoffey  United States
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Maybe it doesnt know the words?
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Old 20th February 2004, 02:11 PM   #3
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Pumuckel,

First, did you check the power supply, with a scope take a look at the regulated rails
and tell us if ripple is present or not.

It's the first point to check. If there is no ripple on the supply's, go for grounds.
Look for the grounds, how are your grounds connected...
Is it to the same point... where is it situated...

Regards.

Alain.
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Old 20th February 2004, 04:22 PM   #4
Stabist is offline Stabist  Slovenia
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Something similar happened in my case with Zen v4 - and it was a ground loop - I have each channel on it's board - and for each channel the PS cables came direct from PSU - and there was the loop.
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Old 23rd February 2004, 01:21 PM   #5
gasjack is offline gasjack  Denmark
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Quote:
Originally posted by Stabist
Something similar happened in my case with Zen v4 - and it was a ground loop - I have each channel on it's board - and for each channel the PS cables came direct from PSU - and there was the loop.
So how did you solve it? I think I might have a similar problem with a six channel gainclone.
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Old 25th February 2004, 07:59 PM   #6
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sorry for not responding, I had to leave for a few days.

I isolated the problem, it's an induction loop. If I connect the 2 channels, there's a loop from the input to the ground point and back on the second channel. I think this can't be solved because I'm using a single transformer for both channels. If anybody has a solution for that, please tell me!
so I completely shielded the magnetic field from the transformer, and it was much better, but not gone. then I played around moving the power supply cables, and that was the second problem. The high load current spikes and the arch's of the cables also generate a magnetic field , wich inducts current to the loop on the input.
I think the only solution is to completely shield the psu, until after theCLC filter.

Christian
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Old 25th February 2004, 08:18 PM   #7
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Pumucket,

>> I think this can't be solved because I'm using a single transformer for both >>channels. If anybody has a solution for that, please tell me

Never say never, be positive:

I also have a single transformer 750 VA in my stereo A75, with a single output
of 2*37 volts and 2 rectifier bridges ; the center of the secondary goes directly to
the masses. I conduct the power cables for 120Volt primary always twisted
in the bottom of the chassis. and no humm at all... even at full power.

Do you have filtering caps at the arrival on the front end card ?

Could you make some pictures of the interior of your baby?

Regards.

Alain.
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Old 25th February 2004, 08:29 PM   #8
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Hi,

I join a picture of a Aleph like power Supply.

tell us what's different in your setup.

Regards.

Alain.
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Old 25th February 2004, 09:15 PM   #9
Stabist is offline Stabist  Slovenia
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Quote:
Originally posted by gasjack


So how did you solve it? I think I might have a similar problem with a six channel gainclone.
Well - after Zen was build - the hum was quite annoying ...

So I took these steps trying to solve the problem:
1.) I've noticed that the metal plate on which the boards are mounteds is "isolated" from the res of the chassis - so it was not grounded - connection was done ... It didn't help much - but it was a start ...
2.) in "original" design - both output signals were wired from PCB to the output conectors - now the (+) goes from the PCB but the (-) goes from central ground point.
3.) oh yes - central ground point - before it looked like this: cca 5cm long solid CU wire with wires connected to it - now it is a POINT - and that was very much solving the problem
4.) before - the input signal was connected to each board with 2 "independent" wires - now there is "kimber look like" - that also helped a lot
5.) finaly - each pcb had it's own PSU cable - which came straight from PSU rails - and that was the loop - now - one channel has a cables that come from PSU but the other one feeded from first PCB ... And the loop is gone ...

So - if I make a conclussion - 3.), 4.) and 5.) were the main solvers of mine problem ...

Hope it will help!
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Old 25th February 2004, 09:39 PM   #10
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@alain
no major differences, using 20000ufd-1mH-54000ufd common for both channels, and then 10mH-36000ufd for each channel
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