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Old 19th August 2005, 11:21 PM   #1
PSz. is offline PSz.  United States
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Default My new mini Aleph

Hello all,

My little Aleph is up and running, and humming from the left channel. This only occurs when the rca signal cable is hooked to the amp and source, otherwise it is dead silent. The hum is independent of volume setting. The amp is single ended only and is showing very low dc offset. I have searched and read lots of posts. Iíve tried all that I can think of right now, includingÖ

1 switch rca input cable left to right, right to left.
Result- hum stays in left channel

2 connect to a different source component
Result- hum still there

3 rotate the toroid
Result- hum still there

4 re-route ground lines in chassis (every variation I could think of) including jumper across input rca grounds w/ one wire return to star ground
Result- hum still there

5 lift earth ground (then reconnected it after test)
Result- hum still there

6 other stuff I canít think of right now. Yup, hum still there.

Oh yeah, a little more background info. I have 3ohm resistors for R0. The pcbís are from BrianGT. Power supply is LT1083 regulated and star grounded. The amp will live in a biamp system powering compression drivers (where any hum is really annoying).

Perhaps try a serial ground instead of the star ground?

Any other suggestions or obvious things I missed?

Thanks in advance,
PSz.
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Old 20th August 2005, 06:35 AM   #2
winslow is offline winslow  United States
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You have any DC off set?
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Old 20th August 2005, 07:00 AM   #3
PSz. is offline PSz.  United States
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20 and 30 millivolts.

the shielded wire I just put in for the inputs helped, but the left channel is still humming. I have been reading up on toroid shielding, but my hum is low frequency (120Hz ?) and the shields I am reading about don't block those too well...

perhaps I am just being too picky about all this... every other amp I have built is run on batteries, and after all my hum (through horns) requires a silent room or an ear on the horn mouth to hear it.

am I being unreasonable?

I just have the impression that because the amp is silent when not connected to a source, that I should be able to get it to that level when a source is connected...

regards,
PSz.
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Old 20th August 2005, 07:09 AM   #4
Netlist is offline Netlist  Belgium
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Despite all your efforts I think you are left with a bad ground connection. Does the hum disappear when you short the input to ground? (Connect a shorted RCA)

/Hugo
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Old 20th August 2005, 07:40 AM   #5
PSz. is offline PSz.  United States
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I haven't tried that yet. I'll have to try in the morning because my wife is watching TV right now with that amp in the system. I just don't understand how a bad ground could have eluded me all day today. I've tried everything I can think of including the series ground. Nothing has helped except the shielded wire.

Could it be the transformer coupling such a low frequency into the circuit?

regards,
PSz.
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Old 20th August 2005, 07:51 AM   #6
Netlist is offline Netlist  Belgium
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I don't think it's the transformer because you said the amp is quiet with no input.
The idea of shorting the input is to make sure your input ground is well connected. If the amp still hums with shorted input the problem could be the female RCA connector or it's ground and grounding wire.

/Hugo
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Old 20th August 2005, 08:11 AM   #7
PSz. is offline PSz.  United States
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I'll try in the morning and report back, but I am skeptical because I went through so many permutations today.

Thanks for your input! I truly appreciate it. Sometimes I just need to be talked through the obvious!

regards,
PSz.
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Old 20th August 2005, 08:13 AM   #8
PSz. is offline PSz.  United States
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I just realized that I have neglected to give any impressions of how this little wonder sounds.

It's running on 13.8 volt regulated rails. Two IRFP044 output devices per channel. Caddock MK132 resistors. Cerafine 220uF caps except the Black Gate nonpolar feedback cap. It is built inside a Hafler DH120 chassis.

Back to the sound...
This little amp is INCREDIBLE.
I have heard detailed amps, and warm smooth amps. But somehow I have never experienced both together like this before. Tube or solid state.

During full range testing I was not disappointed by the bass as I had begun to expect.

I found that my heart would match time with the music being played! That is involvement! (or a serious medical problem)

more later,
PSz.
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Old 20th August 2005, 08:37 AM   #9
PSz. is offline PSz.  United States
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input short = hum.

regards,
PSz.
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Old 20th August 2005, 09:10 AM   #10
PSz. is offline PSz.  United States
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Insulating the rca jacks from the chassis just gave me a huge improvement! I can't believe that I didn't think of that sooner!

Thank you Netlist for getting my gears turning again!

regards,
PSz.
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