Power Amp output testing

beardog03

Gentlemen`s...

I have (4) Rotel RB980BX`s , and I would like to find out how strong the power output is on each one...

With a Rat Shack Multi-Meter , how would one go about doing this ?

Any help on this would be greatly appreciated...

Thanks in advance for helping me shock the hell out of myself..!!



Bear

TroyD

why, just for the sake of wonderment?

beardog03

pretty much...

I just want to know which one(s) are the strongest (best) ones, or are they all the same...


thats awl....!



that and I got a new multi meter to play with...

heiney9

You can test the output of each amp using test tones and, resistors to simulate a load. This will give you a ballpark figure. However, it won’t really tell you how the amp (s) will act in a “real” world situation. Certainly worth trying for kicks. Post your results. As far as how this is done, not sure, but you may need more than a meter. I’m sure there is info on the net somewhere. I don’t think it’s as simple as just hooking it up to the meter.

Try here: http://www.diyaudio.com/

Good luck

H9

jcaut

I say don't worry about it. If they're all the same model and unmodified, there's not going to be enough difference between them to matter at all. Besides, it's not something that's easily (or accurately) done at home with just a multimeter. The possibility of frying a perfectly good amp is also there, if you happen to mess up. There's the disclaimer.

IF you were going to try it -- and I don't recommend it---

You'd need a 4 or 8 Ohm dummy load resistor, capable of handling the full power output, connected across the speaker outputs on one channel, a sine wave recording of whatever frequency you want to test, and a way to determine when the amp begins to clip. Then you measure AC voltage at the speaker outputs and figure power by squaring the voltage and dividing by the impedance (resistance). 28.3 Vrms into an 8 Ohm load would be 100 Watts.

Jason

nadams

AC voltage? I would've though DC...

TroyD

But seriously, again, what's the point?

Let's just say, for the sake of argument that you have two identical 100wpc amps. One will clip at, say, 110 wpc, the other 118 wpc...the difference between 110 and 118 (again, I'm just using this as an example) is so minute as to not even be worth mentioning.

BDT

PolkThug

I think it would be cool to measure the variance (or lack of).

madmax

Another test which might prove more would be a serious musical listening session to find out which one sounds the best. Of course you wouldn't get to use your new multimeter though...
madmax

bknauss

Although you could get a rough idea of power output from measuring voltage across a resistor, there's a lot of room for error based on what THD level you want. You could have something obscenely low and have power not near the rated output, or it could be obscenely high and you'd be getting more than the rated output.

I suggest looking for a magazine who has done a review on the receiver before, or a receiver that is very similar.

bknauss

Originally posted by nadams
AC voltage? I would've though DC...

Music (and sine waves) is not a constant signal, therefore its an AC signal.

jmierzur

When they were reviewed way back in 94 or 95, the total output of the amp was 137 wpc.

beardog03

Originally posted by TroyD
But seriously, again, what's the point?


I just want to see if one is more solid than the other....

I had 3 of these amps running through the yammie for the HT rig, bought new covers from B&K / Rotel for all three, then stumbled across a 4th one for about the same price as I paid for the other three....couldn`t say no because I`m an audio addict.!!

I started wondering if one might be more solid than the next...
Hence my question....

I now have a Dennon 3802 AVR , and the power output is about the same without the amps...the amps can handle 4ohm loads though...the Dennon cannot.

I found a Parasound 5 ch amp I want , and am considering selling a couple of amps and other gear to get it...


Question....do power amps get weaker over time as the components get more use ?

It would seem logical that a newer amp would have more punch....right..?

Mike682

I used to have a Radio Shack power meter that would measure wattage going to the speaker. It measured two channels and would display up to 200watts on each channel..

I can't find this thing in my basement and Radio Shack said they stopped making them..


Mike

heiney9

Originally posted by beardog03

Originally posted by TroyD
But seriously, again, what's the point?


I just want to see if one is more solid than the other....

I had 3 of these amps running through the yammie for the HT rig, bought new covers from B&K / Rotel for all three, then stumbled across a 4th one for about the same price as I paid for the other three....couldn`t say no because I`m an audio addict.!!

I started wondering if one might be more solid than the next...
Hence my question....

I now have a Dennon 3802 AVR , and the power output is about the same without the amps...the amps can handle 4ohm loads though...the Dennon cannot.

I found a Parasound 5 ch amp I want , and am considering selling a couple of amps and other gear to get it...


Question....do power amps get weaker over time as the components get more use ?

It would seem logical that a newer amp would have more punch....right..?

Your question is logical. And, yes parts can wear out. Mostly they fall out of tolerance or in the case of some by-pass caps (electrolytic), they can dry out. My Nak receiver has 1 channel slightly louder than the other and I suspect one of the caps may be out of tolerance. If you suspect this I would strongly recommend a qualified tech/service center to check them out. Just hooking a VM up to them isn’t going to tell you much.

The most telling sign, as in my case with the Nak, is that you can hear an audible difference. It’s always a good idea to have your gear checked out to make sure it’s still in spec. After time things to tend to wear and it isn’t always noticeable.

H9

beardog03

I have`nt noticed any differencein any of the four amps..

I did a switch out type test and they all sound the same..


still have plenty of punch, and now all the covers are new..!!

TnBilly

All well and good you're enthused but like was said before you're more likely to blow the amp(s) than to get any benefit from it. The output is checked with a fixed - read signal generator - input and measured with an oscilloscope on the output as well to see the clipping before it starts the smoke

If you want to play with the new meter you can and should check the dc-offset of each of the amps. In quick read.... no speakers connected to amp or check speaker outs that aren't being used ...... amp warmed up for at least several minutes.... meter set to lowest dc volts range...... check voltage on left and right speaker terminals (on the amp). Voltage should be between 0 and 30 or so mv and if it's over 75-80 mv or if it's not reasonably stable then the amp has problems that are reliability problems.

Ron

ND13

Originally posted by TnBilly
All well and good you're enthused but like was said before you're more likely to blow the amp(s) than to get any benefit from it. The output is checked with a fixed - read signal generator - input and measured with an oscilloscope on the output as well to see the clipping before it starts the smoke

If you want to play with the new meter you can and should check the dc-offset of each of the amps. In quick read.... no speakers connected to amp or check speaker outs that aren't being used ...... amp warmed up for at least several minutes.... meter set to lowest dc volts range...... check voltage on left and right speaker terminals (on the amp). Voltage should be between 0 and 30 or so mv and if it's over 75-80 mv or if it's not reasonably stable then the amp has problems that are reliability problems.

Ron

Yeah, yeah, what he said.:D