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Old 7th January 2011, 10:01 PM   #1
Buhl is offline Buhl  Denmark
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Default Aleph P 1.7 problems

Hi all
First a happy new year to everyone!

Hope somebody has some experience to share on this one, because I am about to go sligthly crazy

I have built an P1.7, which plays really good I think, apart from quite a lot of hum! I have a stepped attenuator at the output, so it increases with the volume. The thing is that I am using KK's PCB, which has a lot of ground connections on it, and Im not sure I am connecting them correctly. I have done the wireing just as I did my BLS, which has no hum....

Basicly, I have a wire that go from the common input jack ground to the input ground which is shunted to negative input, as I am only using single ended. Then the output signal goes to the attenuator - ground for the attenuator connects at a "star point" at the input jacks, where the ground for the output jacks are also connected. Everything should be jolly!

But what about the negative output, should this also be shunted to ground?
And what about "all the other grounds on the board" - KK's P1.7 have 5(!) grounds pr. side: one power ground (unbalanced PSU design), then an ground for -out, one for +in, one for -in and one for +out. Should all these signal grounds meet at one point?

Hoping that someone has something to share on this one....?

Best regards
Hans
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Old 7th January 2011, 10:22 PM   #2
generg is offline generg  Germany
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I got only all hum free with the same boards when I left all output grounds open.

All devices seem to be connected already by the the third "Schutzkontakt". I do not know the english word....- the less connections I had inside. the less hum
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Old 7th January 2011, 11:12 PM   #3
Zen Mod is offline Zen Mod  Serbia
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besides any other solution ( please upload pictures of preamp ) - why don't you ask KK for recommended grounding scheme with his pcbs ?

I know - we'll help you as much we can , but I have repetitive impression of constant lack of any guidance from KK's side ;
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Old 7th January 2011, 11:23 PM   #4
generg is offline generg  Germany
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All these five ground possibilities are connected on the board, if you ground one they are all connected to ground.

The English word for what I meant is
Protective earthing
On the amplifier, preamplifier and cd-player made enough connection between the devices
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Old 7th January 2011, 11:41 PM   #5
Zen Mod is offline Zen Mod  Serbia
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safety ground
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Old 8th January 2011, 08:33 AM   #6
generg is offline generg  Germany
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thanks Zen Mod
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Old 8th January 2011, 11:51 AM   #7
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I too had hum problems with the KK boards, but only in balanced output mode. I was using the Dantimax output attenuator which has the channel grounds tied together on its board. That forced me to use the Dantimax board as my star ground point.

I eventually rebuilt it with boards from Veteran with no problems whatsoever. I still use it every day.
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Old 10th January 2011, 09:44 PM   #8
Buhl is offline Buhl  Denmark
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Good idea actually, to ask KK. He have been very fast and polite/helpfull in the past - but there have also been some long delays - however, I can not put a finger on his service, in the view of what kind of business he is running.
I have emailed him regarding grounding advice for his PCBs.

I tried to leave all grounds open, only connecting the ground next to the negative input with a jumper, where I route my wire to star point - together with ground from the input and output RCA, and attenuator ground.

There is a difference though, right channel has more of an aggressive buzz to it, left channel a more "relaxed" hum. When I connect a 1mm copper plate that seperates the PSU section from the rest of the preamp to star ground, the left channel gets considerably more quiet - not much to detect on the right channel. Can I have a ground loop of some sort on just one channel?? If the screening helps on one channel, then that indicates induced hum for that particular channel?

Thanks for your efforts trying to help me out!

Best regards
Hans
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Old 10th January 2011, 09:45 PM   #9
Zen Mod is offline Zen Mod  Serbia
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pictures could help
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Old 10th January 2011, 09:57 PM   #10
Buhl is offline Buhl  Denmark
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Good evening ZM!
Do you really want to see pictures of my birds nest preamp?
Or PCB - or the circuit?

BR
Hans
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