DC-current

jjj84 · 22nd April 2003, 02:54 PM

I checked my amplifier speaker outputs for DC and i found +100mV DC.. is this bad? Can it do any damage to my speakers? Amplifier is made of stk4231II.
Is there any way of removing this DC?

ps. sorry bout my bad english, i hope you get the point..

moamps · 22nd April 2003, 10:09 PM

Hi,

this voltage on output is on the borderline value, IMHO. If amp is old, check input caps and caps in NFB line; C5, C6,C9 and C10 according original manual.

My english is also poor, but ...

Regards

thylantyr · 22nd April 2003, 10:54 PM

I've read archived data from this forum that indicated
that some individuals tolerated as much as 1000mv of
DC offset.

moamps · 23rd April 2003, 05:27 AM

Hi,

I use batery with 1,5V to detect what is + on some bass speaker. With 1V too, you see clearly membrane moving. With this DC bias speaker work for my point of wiev in inproper condition (also is 125mW on 8E).

Regards

EchoWars · 23rd April 2003, 05:39 AM

Quote:

Originally posted by jjj84
I checked my amplifier speaker outputs for DC and i found +100mV DC.. is this bad? Can it do any damage to my speakers? Amplifier is made of stk4231II.
Is there any way of removing this DC?

ps. sorry bout my bad english, i hope you get the point..

Your english is fine...

Caps are a possibility, but more than likely you have a differential amp in the input stage that is unbalanced. Solution: Replace input pair transistors. You may match them for optimum results.

My own experiance is that offset of as little as 25mV degrades sound quality noticeably. Others may argue, but I hear what I hear. 100mV is worth tracking down and fixing.

jjj84 · 23rd April 2003, 09:02 AM

Quote:

Originally posted by EchoWars
Caps are a possibility, but more than likely you have a differential amp in the input stage that is unbalanced. Solution: Replace input pair transistors. You may match them for optimum results.

In the picture u can see that i cant change those transistors..
In my amplifier input caps are changed from 2.2uF to 10uF, can this cause it? I think not. The amplifier is only 2 months old.

datasheet stk4231II

Jan Dupont · 23rd April 2003, 10:06 AM

Hello to you all.
The DC on the output should be below +/-10mV (my amps runs with app. +/-0,1 mV after 15 min. warm up

peranders · 23rd April 2003, 11:55 AM

I think we all can conclude this to:

1 How much DC voltage before we get distortion due to displacement of the woofer (not tweeter)?

2 How much DC voltage before a smell can be detected?

1) < 0.5 V (guess), <0.1 V feels good (or safe), <20 mV very OK

2) Depending on how big the woofer is, < 5-10 W I'll guess

100 mV creates a click when the speaker is switched on and off and this can be irritating but hardly harmful for the speaker.

Together with a DC-servo you can reduce the offset to almost nothing, around 1 µV (mean value).

(My new SMD headphone amp with AD8610/BUF634 has only 0.04-0.08 mV at the output! Amazing!)

jjj84 · 24th April 2003, 07:06 AM

Now i think that i know where the problem is..

Input coupling capacitors are in the original schematics 2,2uF and the input bias resistors are 56k ohms. This way dc current should be zero.

I my schematic these capacitors are changed to 10uF and the bias resistor is 10k ohms. I think that the reason for this 100mV of dc is caused by wrong value of the input bias resistor.

Does anyone now how to calculate right value for this resistor?

Thanks a lot if someone could help me.

jan.didden · 24th April 2003, 08:56 AM

jjj84,

Despite all the expert advice, you're doing fine!

I would like to help also, but can't find the schematic. Is it somewhere on the net?

Jan Didden

22nd April 2003, 02:54 PM	#1
jjj84 diyAudio Member Join Date: Apr 2003 Location: tku	DC-current I checked my amplifier speaker outputs for DC and i found +100mV DC.. is this bad? Can it do any damage to my speakers? Amplifier is made of stk4231II. Is there any way of removing this DC? ps. sorry bout my bad english, i hope you get the point..

23rd April 2003, 10:06 AM	#7
Jan Dupont diyAudio Member Join Date: Apr 2003 Location: Copenhagen, Denmark	Hello to you all. The DC on the output should be below +/-10mV (my amps runs with app. +/-0,1 mV after 15 min. warm up __________________ Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com

23rd April 2003, 11:55 AM	#8
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	I think we all can conclude this to: 1 How much DC voltage before we get distortion due to displacement of the woofer (not tweeter)? 2 How much DC voltage before a smell can be detected? 1) < 0.5 V (guess), <0.1 V feels good (or safe), <20 mV very OK 2) Depending on how big the woofer is, < 5-10 W I'll guess 100 mV creates a click when the speaker is switched on and off and this can be irritating but hardly harmful for the speaker. Together with a DC-servo you can reduce the offset to almost nothing, around 1 µV (mean value). (My new SMD headphone amp with AD8610/BUF634 has only 0.04-0.08 mV at the output! Amazing!) __________________ /Per-Anders (my first name) or P-A as my friends call me Tube Buffered Gainclone in work \|Thread

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22nd April 2003, 10:09 PM	#2
moamps diyAudio Member Join Date: Oct 2002 Location: Croatia	Hi, this voltage on output is on the borderline value, IMHO. If amp is old, check input caps and caps in NFB line; C5, C6,C9 and C10 according original manual. My english is also poor, but ... Regards

22nd April 2003, 10:54 PM	#3
thylantyr diyAudio Member Join Date: Feb 2001 Location: Mars	I've read archived data from this forum that indicated that some individuals tolerated as much as 1000mv of DC offset.

23rd April 2003, 05:27 AM	#4
moamps diyAudio Member Join Date: Oct 2002 Location: Croatia	Hi, I use batery with 1,5V to detect what is + on some bass speaker. With 1V too, you see clearly membrane moving. With this DC bias speaker work for my point of wiev in inproper condition (also is 125mW on 8E). Regards

24th April 2003, 07:06 AM	#9
jjj84 diyAudio Member Join Date: Apr 2003 Location: tku	Now i think that i know where the problem is.. Input coupling capacitors are in the original schematics 2,2uF and the input bias resistors are 56k ohms. This way dc current should be zero. I my schematic these capacitors are changed to 10uF and the bias resistor is 10k ohms. I think that the reason for this 100mV of dc is caused by wrong value of the input bias resistor. Does anyone now how to calculate right value for this resistor? Thanks a lot if someone could help me.

24th April 2003, 08:56 AM	#10
jan.didden diyAudio Member Join Date: May 2002 Location: Great City of Turnhout, Belgium Blog Entries: 6	jjj84, Despite all the expert advice, you're doing fine! I would like to help also, but can't find the schematic. Is it somewhere on the net? Jan Didden

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