DC offset problem

[carlosfm]

Originally posted by maxw
So I retried with 22uF electrolytic as Ci and got a DC offset of 2mV!!

Originally posted by maxw
I did a listening test today with a Sony CDP, 10k pot and my DIY 2 way speakers. I added the Ci cap as in the above attachment to the unit that had 80mV DC and then was 1-3mV.

Originally posted by maxw
So why doesn't everyone use it? does it affect the sound? (I couldn't tell with one channel using it one not)

You can bypass the 22uf cap with a 100~150nf poly cap.
Let it -in for some days.

If you don't want do make an inverting amp (with buffer, preferably), with NI this is the way to go IMHO.
What's debatable is what has more effect to the sound?
- 80mv DC
or
- Ci caps?

Your speakers may not work so well with 80mv DC.
But the effect of the Ci caps, if they are decent quality, is minimal if not undetectable.

[maxw]

Originally posted by carlosfm
But the effect of the Ci caps, if they are decent quality, is minimal if not undetectable.

Well I cant hear the difference and I like things that are technically good so I will use Ci on my GC. Cool.

One last Q though, I have used a cheap generic cap that is 35V, cost 50c. The only place I can get better ones in NZ is RS so do you think Elna Starget (for example) caps would be worth paying $10-$15 for? or shall I just use generic low ESR ones?

[carlmart]

Originally posted by maxw


Well I cant hear the difference and I like things that are technically good so I will use Ci on my GC. Cool.

One last Q though, I have used a cheap generic cap that is 35V, cost 50c. The only place I can get better ones in NZ is RS so do you think Elna Starget (for example) caps would be worth paying $10-$15 for? or shall I just use generic low ESR ones?

Like I said on another thread, according to an article published in Electronics World and Wireless World, try a bipolar capacitor as feedback DC block. Something reasonable good, not any speaker cap you may find around.

If the feedback resistors you are using are large, particularly the small one, you can even get to use film caps. Something like 2 x 4.7uF should not be expensive to arrange.


Carlos

[phugger]

I am having dc offset problems as well (about 60mV on both outputs). I don't have any .22 uF caps on hand but I do have some 0.1uF caps on hand ( http://www.partsexpress.com/pe/showd...number=027-452 )

Can I use these for Ci?
My gainclone is exactly like noninverting "classic" circuit at http://www.geocities.com/rjm003.geo/...io/diy_gc.html excpet I don't have R5 and C5 on the outputs.

Thanks.

[li_gangyi]

I would say 60mv is pretty ok...you might wanna test them out with a junk speaker 1st though

[Vikash]

I have one channel ~70mv and the other ~130mv. No problems with it.

[skyraider]

maxw,

Did you take offset measurements with the input conected? Because if input is connected to a source, your readings might change again. Same goes for heat, aging effect.. etc.
Dont worry too much about offset, especially if its low like in your case. It will change again after sometime.
I (and many others?) personally disgust of having Ci there in the circuit. What I would suggest is to try as many chips as you could to find a low-offset pair.(like what gaincard guys did?)

[maxw]

Originally posted by skyraider
maxw,
Did you take offset measurements with the input conected?

I think I did but it was long ago, cant remember now
Im sure this problem will crop up again with my LM3886 and LM4780 amps but I wont be so concerned this time
Im glad someone else found this thread usefull too.

[-_nando-_]

Why all these worries about dc offset?

I build a gainclone, two channels, without Ci, and it have 110mv in one channel and 90mv in the other... When I power it on, I don't listen anything, and it do not move the driver surface...


Forget it and be happy !