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In Reply to: RE: Would testing for the DC offset help? posted by airtime on July 01, 2014 at 07:00:42
There shouldn't be any DC offset to speak of. If he measures more than 10-mV DC offset there might be something wrong with his amp. I just measured 6-mV DC on both channels of my Parasound Halo A21 with speakers connected.
After measuring DC offset, the first thing I would do is adhere to the original plan of checking AC voltage at the speaker terminals using a test CD playing a mono 100-Hz test tone. If the AC voltage difference between channels is negligible then the imbalance problem is either in one of the speakers or in the speaker/room interface. Of course, if the measurement shows a significant difference, then the problem is almost certainly in the channel with the lowest voltage. At that point I would begin swapping connections to isolate the component responsible for the problem.
Best regards,
John Elison
Follow Ups:
John,
I'll repeat what I wrote since you may not have seen it.
Yes, to your test as far as it goes.
However, what if a driver is bad or 'weak' and is 5 or 6 octaves above your 100hz tone? You won't see it with a DVM.
I'd suggest using 3 or MORE frequencies. I wouldn't worry about the absolute voltage but rather the relative voltage and perceived output. Using a DB meter may help here, and that too, doesn't have to be accurate but rather repeatable.
Using a DB meter in concert with a DVM may help isolate room effects from a real malfunction.
I sure wish I owned a SCOPE. An old 60mhz or even a 30mhz TekTronix Dual Trace would be IT.
Too much is never enough
not really using it any more since I can't fix or work on stereos with my neck problems
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