Measuring DC Offset on a HiFi Amplifier

This short video shows how to use your multimeter to check the DC offset of your stereo amplifier. A high DC offset measurement on the amplifier output can cause serious damage to your speakers. This simple technique is really useful if you are connecting a secondhand amplifier for the first time.

Please note, not all faults in amplifiers can be detected using this method, but many different faults do contribute to higher than desirable DC offset levels and so this is a test I would do on any amplifier when I first acquire them.

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Acknowledgements:
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[mjeben]

Straight and simple info. No rambling. Thanks!

[spottedtauren]

This was very useful, thanks! (I have several used amplifiers I have picked up over the years and haven’t had time to hook up speakers to them to try out and now I know when I do finally have time to check the DC offset before I hook up the speakers so I don’t damage them (I have several pairs of vintage speakers and would hate to have any of them ruined when a simple check with a voltmeter would tell me if the amp was ok or not).

[belabertalan]

Great video. Do you turn down the volume knob all the way when measuring dc offset or it doesn't matter?

[juntong]

Thank you very much for the detailed explanation.

[stanionman]

Sorry about this, but what setting do I put my multimeter on ? I received mine today, so a bit confused which setting I'm supposed to use !

[jjohnsonsg]

if it needs adjustment how do you do that?

[hughescoston]

When checking DC offset do you set the volume to its lowest level?

[jimpetersMontreal]

Thanks. I didn’t hear anything about adjusting the volume control before testing. Can you please clarify? Sorry if I missed that

[davidnguyen]

What would be a typical repair if the DC voltage level is high?

[keef]

Nice. I imagined that you had to put a signal in the input, to test the DC output.

[bobnevala]

The Volume Knob should be turned all the way down, all the way up, centered, the position of the Volume Knob doesn't matter? If the DC Offset is incorrect? How does one adjust it? If the E Capacitators have not been replace as of yet, will this affect the DC Offset? Thank-you.

[I.am.KubKab]

thank you for the video. What should be a realistic value for the DC offset? Ideally it should be +/- 0mV, but that's theory.

[taineasy]

What setting do you have you multimeter set at.

[pietpaaltjes]

This is an interesting and simple test. Would the test be more reliable if you would short out the imput?

[mumbles]

Thanks for posting this but can the offset be measured with 8 ohm load resistors across the speaker terminals or should they be removed first?

[pranorre]

Hi, thank you for the nice and clear explanation, just few questions: how do you set the volume pot for this test? does it have any meaning to this? if not, what can mean if dc reading continously increase taking volume pot from min to max? Thank you again.

[Vedantsharma]

Thanks i got a little knowledge. I more think i want to ask is if we preset bias in power board and left channel and right channel has little different dc voltage like 0.02 millivoltv on left channel and 0.09 millivolt on right channel. Will it effect the sound quality?
My next quotation is in service manual of sony ta 1150 it says 25 millivolt on both the channel. Is it safe for speakers?

[jimmychua]

If there's no offset DC output in no source how about if there a source of sound is there a DC out but in my technics class A there's no DC offset even there a sound out in speaker.

[thevault]

I'm hooking up speakers to my receiver right this moment and I noticed the channels in the back have been going out on me to where they're not producing any power at all but been going out one at a time. Right now I am down to only one red and black left out of the four pair I have

[yannickgrams]

Hi, I note that you need to set volume to minimum for this test. I'm wanting to test a poweramp with no volume control (i.e. a fixed volume ouput): is it safe to test it in this manner all the same?