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In Reply to: RE: Is there a way to check amplifier output at the speaker terminals ? posted by dcuhl on June 29, 2014 at 07:01:53
Many multimeters are designed only for low frequency AC voltage measurements. You should check the AC voltage frequency capability of your multimeter and use a frequency from your test CD that is within its measurement range. Then you can simply measure the AC voltage at each speaker terminal while playing the test CD. Be sure not to turn the volume up too loud. Continuous test tones can damage speakers if played too loud for too long a duration. As long as the loudness is comfortable to listen to, it should be okay.
Best regards,
John Elison
Follow Ups:
Thanks for responding John. The multi-meter is an inexpensive $20.00 Sears DMM so, 60 HZ , or below, is probably the frequency to use from the test-tone cd. I'll give it a shot and see what happens.
Keep in mind that any apparent difference in levels may NOT be found at 60hz if the speakers mid or mid/tweet is not 'right' or the same between speakers.
Even though the meter SHOULD be pretty good at 60hz, it'll read at higher frequencies, too, but not accurately. I'd say it SHOULD be fairly repeatable, so you'll at least be able to COMPARE side-to-side.
If you have access to MEASURED impedance data for your speaker, it may also be possible to computer POWER using ohms law. You might be able to get the same data using multiple meters measuring voltage AND current at the same time. But i've never tried that, so am on less stable ground.
Too much is never enough
If you're just not sure, disconnect the speakers from the amp, and measure directly fromt the speaker outputs of the amps.
Eliminates cables, speakers, impedance issues, etc...
charles
IF a tube amp, No Load is a fine way to damage it.
If a SS amp, no load will result in no output, won't it?
Beg or Borrow or perhaps RENT a Scope. Or maybe a True RMS meter.
Too much is never enough
He has SS gear so he can remove the load safely.
If he's using basically RadioShack meters,then removing the load on SS gear really isn't going to be the deal breaker.
With a scope he would need dual tracings capability.
I think he can get a ball park idea if the imbalance is the amp, preamp, cables, etc... with the meter.
Maybe he can see if the DC offset is the same as well????
would that help?
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
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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