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Testing amps

C Hart

C Hart

AK Subscriber
Subscriber
Hi AKers. I hope you can help me with a question that has nagged me for a while. Among other gear, I have a .08% THD 5x120wpc-rated receiver. It just doesn't seem that clean when it's turned up and I would like to verify whether it is performing to its ratings.

I'm sure there are high end test rigs that are easily bought for a few $K but is there any cheap DIY way to verify the output power and distortion of an amp?
 
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Any audio repair shop will have the equipment to measure output and distortion. Since there's no troubleshooting or repair involved, you might get it done for as little as $50. :dunno:

What is the receiver?
 
It's a Technics SA-EX510 from ~1996. Few features but lots of power, theoretically.
 
RickB said:
...and, what are the speakers?

Could it be that they just wont do it?
Click to expand...

That is a possibility I guess, given the fantasy ratings by manufacturers. Per the spec sheets, the speakers can handle decent power. JBL L166 (75w continuous, "up to" 150w recommended amp power). Have also used a pair of EV Interface:A (25 w continuous, 250w peak, recommended amp power 250w max).
 
If both sets of speakers exhibit the same lack of cleanness, chances are it's the amp. Why? :dunno: Have you tried a different amp with those speakers?

If looking to replace the Technics, check out pre-HDMI Yamaha. I owned a R-V1105 (85w) that could fill the neighborhood with sound. (And actually had the cops stop by once, asking for a lower volume :oops:.)
 
I don't think it's the speakers - they are ok on this and at least 2 other receivers until the volume knob is at 11 o'clock or so. This amp should go clean and loud with that kind of power, so either I'm pushing it too hard or it isn't up to spec.

Many people love their Yamahas. I would probably go with the next level of watts if I had to move on from this receiver. In fact the whole purpose of the exercise is to find out if I need a different amp. I am considering at a Crown XLi800 which will do 200wpc .5%THD for about $300 - clean enough especially at lower volumes, and tons of headroom.
 
More reading: It looks like way to go is to get a pair of big load resistors and check for clipping with a scope. Anyone done this?
 
There are other things that can be used. Someone uses the electric charcoal lighters that plug in. Not exactly 8Ω but anything from 6-20Ω is probably no problem for the amp. But good load resistors are a nice thing to add to the shop.
 
Yes - agreed, they look like fun and useful additions. I assume that is that how Amir does it over at ASR. I would like to understand how to get similar graphs for this receiver whose numbers hopefully are not too good to be true, as well as for potential future acquisitions.
 
Blue Shadow said:
There are other things that can be used. Someone uses the electric charcoal lighters that plug in. Not exactly 8Ω but anything from 6-20Ω is probably no problem for the amp. But good load resistors are a nice thing to add to the shop.
Click to expand...

Air to air, heat pump HVAC aux heating strips, and selected water heater elements have been known to be successfully used, or so I`ve read here on A/K.
 
I think, in the end, you are dealing with clipping. The spec sheet is nice and all, but it's invalid as soon as you hook up speakers.

I wouldn't expect either speaker to be particularly reactive, but it's possible your amp doesn't like them. In such a case, clipping will come on early.
 
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