How much DC is to much?

roibm · 30th April 2004, 11:41 PM

So guys, I am somehow worried about my gainclone's DC output(~85mV and ~65mV).
My question is: how much DC is too much? What valued qould probably blow the speakers(tweeter)?

This is somehow a general question, and I believe of much interest for many.
Any comments are welcomed!

li_gangyi · 1st May 2004, 12:51 AM

most of the time under 100mV will work...but some people believe 0mV is good practice...

roadkill · 1st May 2004, 05:17 AM

85mV offset should not matter much, most woofers will take this quite well. Heat dissipation will be just 0.9 mW for an 8 ohm speaker. Tweeters should be connected through a capacitor, even if you are using an electronic crossover, so the DC offset will not cause problems.

Saurav · 1st May 2004, 05:26 AM

Make sure you check this with the inputs shorted. I thought I had 65mV of DC offset, it dropped to < 10mV when I shorted the inputs.

roibm · 1st May 2004, 09:56 AM

Quote:

Originally posted by Saurav
Make sure you check this with the inputs shorted. I thought I had 65mV of DC offset, it dropped to < 10mV when I shorted the inputs.

Well, what I tested was how much DC is going to my speakers under normal operation.
So the system was playing music, it was not without inputs or under no load. I think this is a fair test. Am I wrong?

carlmart · 1st May 2004, 10:50 AM

Quote:

Originally posted by roibm
So guys, I am somehow worried about my gainclone's DC output(~85mV and ~65mV).
My question is: how much DC is too much? What valued qould probably blow the speakers(tweeter)?

The tweeters should be protected, as long as they have a blocking capacitor in the xover.

What gainclone circuit are you using? IGC?

If you do, are you grounding the non-inverting input or using a resistor from it to ground? A resistor will probably cut the offset.

Carlos

pinkmouse · 1st May 2004, 11:38 AM

Quote:

Originally posted by Saurav
Make sure you check this with the inputs shorted. I thought I had 65mV of DC offset, it dropped to < 10mV when I shorted the inputs.

This may be a problem in terminology or translation, but if you short a chip's output to ground then what do you use as a reference to measure offset from?. This doesn't seem quite right to me

OddOne · 1st May 2004, 02:15 PM

Quote:

Originally posted by pinkmouse
This may be a problem in terminology or translation, but if you short a chip's output to ground then what do you use as a reference to measure offset from?. This doesn't seem quite right to me

Short the inputs, not the outputs.

Basically the idea is to feed absolutely nothing into the amp, and then see what the voltages are doing. The ultimate would be to see zero DC and zero AC with input terminals grounded, but there'll usually be some tiny amount of AC/DC from the amp's bias point, diode junction noise, RFI/EMI coupling, etc. etc. etc.

With my luck I'm just happy as I can be when I apply power and the magic smoke doesn't escape.

oO

Saurav · 1st May 2004, 04:08 PM

What he said. Short the inputs

I'm not sure what noise my amp was picking up with the inputs floating, but it showed up as DC on the output. This was measured with a DMM though, I don't remember if I put a scope on the outputs or not.

pinkmouse · 1st May 2004, 04:31 PM

Ok, so I can't read...

30th April 2004, 11:41 PM	#1
roibm Banned Join Date: Dec 2003 Location: Transylvania	How much DC is to much? So guys, I am somehow worried about my gainclone's DC output(~85mV and ~65mV). My question is: how much DC is too much? What valued qould probably blow the speakers(tweeter)? This is somehow a general question, and I believe of much interest for many. Any comments are welcomed!

1st May 2004, 12:51 AM	#2
li_gangyi diyAudio Member Join Date: Jun 2003 Location: Woodlands Circle	most of the time under 100mV will work...but some people believe 0mV is good practice... __________________ Kids in the back seat cause accidents...Accidents in the back seat cause kids...

1st May 2004, 04:31 PM	#10
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Ok, so I can't read... __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

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1st May 2004, 05:17 AM	#3
roadkill diyAudio Member Join Date: Jan 2003 Location: Fort Collins, CO	85mV offset should not matter much, most woofers will take this quite well. Heat dissipation will be just 0.9 mW for an 8 ohm speaker. Tweeters should be connected through a capacitor, even if you are using an electronic crossover, so the DC offset will not cause problems.

1st May 2004, 05:26 AM	#4
Saurav diyAudio Member Join Date: Sep 2002 Location: Oregon, USA	Make sure you check this with the inputs shorted. I thought I had 65mV of DC offset, it dropped to < 10mV when I shorted the inputs.

1st May 2004, 04:08 PM	#9
Saurav diyAudio Member Join Date: Sep 2002 Location: Oregon, USA	What he said. Short the inputs I'm not sure what noise my amp was picking up with the inputs floating, but it showed up as DC on the output. This was measured with a DMM though, I don't remember if I put a scope on the outputs or not.

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