Aleph-x bias adjustment

[wuffwaff]

Hi,

the magic R shouldn´t 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

[bach2800]

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

[wuffwaff]

Hi,

there are ae few magic R´s:

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

[wuffwaff]

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

[Babowana]

Thanks, William, for the kind details.

[bach2800]

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

[wuffwaff]

Hi,

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

William

[bach2800]

I tried with and without capacitor. Not much difference.

[wuffwaff]

Hi,

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

William

[bach2800]

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 you´ll 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?