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Old 25th July 2006, 05:54 PM   #21
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Hi,

the magic R shouldnŽt be to low (>4k7). Startup voltage of around 5-10V is normal, going down fairly quick.

You can do a few more things wich are explained in another thread to raise the magic R for better sound quality without changing the startup voltage.

William
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Old 25th July 2006, 07:06 PM   #22
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Hi William, can you explain a little more about the magic R?
Which one is it? Right now I'm still getting a fairly high absolute DC offset. the pot is turn all the way down.

Thierry
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Old 25th July 2006, 07:19 PM   #23
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Hi,

there are ae few magic RŽs:

R46/47 (original HIfizen schematic) 4k7
Output to ground resistors (30-100 Ohms)

Lowering R46/47 and to lesser effect the output to ground resistors will meke the absolute dc offset lower and more closely controlled.

The disadvantage is that going below 4k7 for R46/47 will slowly worsen the sound quality and lowering the output to ground resistors will waste quite some power wich could go to the speakers.

I tried some different configurations (different current sources, zeners thermal coupling etc.) and described them in a thread wich I will try to find and post.

William
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Old 25th July 2006, 07:22 PM   #24
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http://www.diyaudio.com/forums/showt...975#post856975

here it is,

and one more:

Aleph X - rootcause of absolute DC offset drift

hope this helps

William
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Old 26th July 2006, 01:05 AM   #25
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Thanks, William, for the kind details.

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Old 29th October 2006, 03:33 PM   #26
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Hello everyone,
winter is coming soon here but the good news is that now I have more time to
work on my stuff.

I've powered up my aleph-x for the first time since a few months to play around with my DC offset problem.
I notice something wierd, if I short the input to adjust the offset I get a descent level of DC. But when I try it without shorting or with something feeding the input I'm getting around 3V between binding post cold and about 1.5V after an hour.

Is that a normal behaviour to get such a difference short input versus not short?

Thierry
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Old 29th October 2006, 04:56 PM   #27
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Hi,

do you use input capacitors? If not this could be the cause.

William
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Old 29th October 2006, 11:47 PM   #28
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I tried with and without capacitor. Not much difference.
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Old 30th October 2006, 07:37 AM   #29
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Hi,

you will need two capacitors of the same size to connect plus in and minus in.
If using it unbalanced youŽll have to connect minus in via the capacitor to ground.

William
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Old 30th October 2006, 01:46 PM   #30
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Quote:
Originally posted by wuffwaff
Hi,

you will need two capacitors of the same size to connect plus in and minus in.
If using it unbalanced youŽll have to connect minus in via the capacitor to ground.

William
That might be the problem, I was only using capacitor on the + side, - going directly to the ground. Can't wait to try it tonight.

What would be the right capacitor value to use? And what type?
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