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are you talking about an amplifier? there should be nearly no measurable DC offset coming out of it.
 

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Most say under 50mv is ok, lower the better. Under 10mv is typical on new amps, some kenwoods have 0 all the time it depends on the design of the amp. If they are over 30 odds are the amp is getting there, over 50 something should be replaced, is generally how I see it but is a matter of opinion. For more quality you want lower of course, you need more quality on say tweeters while a sub would never know 50mv was there. Amps that are old, run hot, beat on, or cheap components tend to get higher readings after a while. It is sometimes the differential amplifier the small transistors get out of spec I have seen this many times with cheaper brands. This is excluding class D.

This can be a fatal issue for tweeters run without a cap it might heat them up eventually, but I don't know how much it would take.
 

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you take a dmm set on dc millivolt setting and measure the speaker outputs on the amp with it on.you can leave the speakers connected or not but have the rca's unhooked and see how healthy the amp is.it's even better if you can find the spec's for your amp.jot down your numbers and what amp's you have tested and share your result's
 

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I don't feel that DC offset is an indicator of overall amplifier health.
Really? You want to hook your expensive speakers up in an active arrangement with it sending out a couple volts DC?

Amps with excessive DC offset have something wrong with them, there is no argument to the contrary. An amp that has 100mV of offset is probably on the verge of kicking in the protection circuit. If not, it is running more 10x the rated THD on the output.

Yes, there can be amps with no DC offset that can suddenly fail as well, but an amp that is off, needs attention. It is a simple check to do. I do it on every new amp that I bring in (home and car audio) before I ever hook speakers to it.
 

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Discussion Starter #8
this is a very simple test to do so you know what shape your amp is in,anyone with a dmm can do it,YOU CAN DO IT!!!!
 

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Really? You want to hook your expensive speakers up in an active arrangement with it sending out a couple volts DC?

Amps with excessive DC offset have something wrong with them, there is no argument to the contrary. An amp that has 100mV of offset is probably on the verge of kicking in the protection circuit. If not, it is running more 10x the rated THD on the output.

Yes, there can be amps with no DC offset that can suddenly fail as well, but an amp that is off, needs attention. It is a simple check to do. I do it on every new amp that I bring in (home and car audio) before I ever hook speakers to it.
I think his point was, that if ther is any DC offset, that mean it is broken. I know he is not suggesting that a good amount of DC offset is good, lol.

you take a dmm set on dc millivolt setting and measure the speaker outputs on the amp with it on.you can leave the speakers connected or not but have the rca's unhooked and see how healthy the amp is.it's even better if you can find the spec's for your amp.jot down your numbers and what amp's you have tested and share your result's
you can do it while it is playing music too. your meter will not measure the AC component of the music and only show you any DC (which as you mentioned, should be nearly zero)
 

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Really? You want to hook your expensive speakers up in an active arrangement with it sending out a couple volts DC?
I have a couple rather "powerful amps" sitting under my bench right now I'll sell you that have ZERO DC offset......

I've seen amplifiers in WICKED oscillation (rather unhealthy) guess what? ZERO DC offset.

It's not a gauge of amplifier health... at all. It's just ONE facet.

It's rather rare that an amplifier will send out a couple volts DC, even without DC protection. It's either gonna send out full rail voltage (if it roached all the emitter resistors on the "good side of the rails") or flat out not come on because the bad side of the finals will be shorted to the output impedance of the good side and appear as a near dead short to the power supply. IF you are finding DC offset in an amplifier it's normally happening BEFORE the drivers, and usuallly the drivers... and given that pretty much EVERYTHING now uses op-amps (servo balanced) even a ****ty LV DC supply would not cause it before the thing oscillates or simply not turn on. On top of this nearly all amplifiers we use use global negative feedback.

Again, It's VERY rare to see a couple volts, VERY.
 

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you can do it while it is playing music too. your meter will not measure the AC component of the music and only show you any DC (which as you mentioned, should be nearly zero)
music can and will actually have offset and if the meter samples fast enough it will catch it.. You need to use a pure waveform, be it sine, square, sawtooth, etc.

For example speech with a lot of plosives or kick drum will notably offset positive.
 

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music can and will actually have offset and if the meter samples fast enough it will catch it.. You need to use a pure waveform, be it sine, square, sawtooth, etc.

For example speech with a lot of plosives or kick drum will notably offset positive.
Yep, complex waveforms like music are no good for this test. You will likely see a fluctuating DC voltage. Sine waves for the win. Agreed also that this is only one facet of amplifier health but if you are popping tweets at low power it is a good thing to check. Better yet just put a cap on the things in case you do something stupid with your active xover.
 

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I have a couple rather "powerful amps" sitting under my bench right now I'll sell you that have ZERO DC offset......

I've seen amplifiers in WICKED oscillation (rather unhealthy) guess what? ZERO DC offset.

It's not a gauge of amplifier health... at all. It's just ONE facet.

It's rather rare that an amplifier will send out a couple volts DC, even without DC protection. It's either gonna send out full rail voltage (if it roached all the emitter resistors on the "good side of the rails") or flat out not come on because the bad side of the finals will be shorted to the output impedance of the good side and appear as a near dead short to the power supply. IF you are finding DC offset in an amplifier it's normally happening BEFORE the drivers, and usuallly the drivers... and given that pretty much EVERYTHING now uses op-amps (servo balanced) even a ****ty LV DC supply would not cause it before the thing oscillates or simply not turn on. On top of this nearly all amplifiers we use use global negative feedback.

Again, It's VERY rare to see a couple volts, VERY.
Good points, all around. I was exaggerating when I said a couple volts. I think we all understand that DC offset is not the ONLY indication of whether an amp is healthy or not. I think you have to agree that if you find offset beyond 50mV, you should be concerned and probably be checking the amp for bad parts.

I personally don't feel comfortable hooking my speakers to anything that has more than 20-30mV DC offset. I'm talking home audio as well. My 2-ch towers are somewhat rare and replacement drivers are unobtanium, so I treat them with care. I also deal with a lot of vintage pieces and it is rare to find 0 DC offset. 10-30mV is common. Beyond that, I start testing for out of spec pieces.
 

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The older, fully discreet stuff will float around a bit more than the newer. Want zero offset? Use tube amps, or the old Mac SS amps with output transformers, not getting DC through an output transformer :D

Another thing to note is even seeing a bit of offset, attach a load, it will normally settle right down. Even say, a wirewound 10W 10 ohm resistor for testing with no output and verified that it's not shooting out full rail voltage.

Gotta love unobtainium drivers. :thumbsup:
 
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