How much DC offset would you consider harmful to HP and after which point would you throw the... - Page 5

You don't need latex (or wikipedia) to tell someone how to measure an amplifier's dc offset with a dmm...

you seem to have 2 rather vital types of voltage switched around. AC measures rms heating value, DC does not, not even a little bit. otherwise for instance, measuring a fullscale AC signal at the output of an amp, or a dac, or a signal generator with a low leakage cap at the output would still read DC, guess what? it doesnt, it measures 0vdc

What I'm saying is audio signal is fed in to the dmm.  you can set the dmm to DC, but it's pointless as the signal is ac, its an audio signal.  it fluctuates.  Put it in AC, you get the RMS of AC, as the dmm gives you a number, not respresentations of the audio signal fluctuations.  My question is, if you set it to DC, how do you measure the offset?  One idea would be to send in a tone signal of known value. measure rms, do some math and you will get the offset.

many analogue Rms responding voltmeters are AC coupled even. my hp3400A is, so how it could possibly read a few mv of dc i dont know. a large amount would screw with it due to leakage, so you cant have it set to amplify the input too much or you'll kill the input stage, but a small amount wont even make it through

DC causes AC heating reading errors sometimes, but i have never encountered AC causing DC errors

Yet for most humans who do not dwell in the vaunted halls of Wikipedia copypasta, measuring DC from signal to ground with a DMM with no music playing is adequate, as once you have <10mV any DC contained in the actual signal is negligible and would probably be hard to get rid of anyway. In fact, measuring DC on an amp with a source attached with music playing is a really stupid idea to beging with, as any DC from the source will be passed on through the amp and give you innacurate measurements.

I understand what you're trying to say with your talk of scopes, but for audio it really isn't necessary to get that accurate. Our ears and transducers are only so good, after all.

So when the music is not playing, offset is measureable?, and it is infact the same offset that the voltage swing will be centered around when playing?  I'm doing this not because I'm anal about offsets, but to get a better understanding of measuring.  Every little bit helps.

Quote:

Originally Posted by JoetheArachnid 

Yet for most humans who do not dwell in the vaunted halls of Wikipedia copypasta, measuring DC from signal to ground with a DMM with no music playing is adequate, as once you have <10mV any DC contained in the actual signal is negligible and would probably be hard to get rid of anyway. In fact, measuring DC on an amp with a source attached with music playing is a really stupid idea to beging with, as any DC from the source will be passed on through the amp and give you innacurate measurements.

 

I understand what you're trying to say with your talk of scopes, but for audio it really isn't necessary to get that accurate. Our ears and transducers are only so good, after all.

Quote:

Originally Posted by High_Q 

So when the music is not playing, offset is measureable?, and it is infact the same offset that the voltage swing will be centered around when playing?  I'm doing this not because I'm anal about offsets, but to get a better understanding of measuring.  Every little bit helps.

 

Yes. Measure the DC with the amp not playing anything at all. Make sure the amp is turned on and warmed up. 

You should either have your source hooked up or ground the input signal line to ground. 

If you show offset with your source connected then you should first check the source to see if it has offset. Again without music or test tone playing, just idle and turned on.