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Power amp clipping problem?

I recently bought a Pyramid PTA150 1500 watt power amp, and its clipping led's always seem to be lit when my mixer is set to half volume or higher, even when the amp is unplugged. Could they be powered from the input voltage when it is high enough? Is it bad to push my amp when they are lit? and it has a high volume cooling fan so I dont think it will overheat when pushed.?

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exabopper5 years ago
What kind of signal are you sending into this amp? I dunno, but maybe the input signal has a large DC component, so that even if there is "no input", then there may still be a large amount of current coming into the amp's input. Try installing an electrolytic capacitor in series with the input signal - I don't know what the polarity of the signal is, so I can't advise you on the polarity of the cap. Also, make sure everything is grounded properly.
Have you got the speakers arranged properly, for the drive capability of the amp. Post a link to a datasheet for it.

If you've put the speakers all in parallel, I could see that being an issue perhaps.

Steve
macwhiz (author)  steveastrouk5 years ago
They're in parallel, but they're both 8 ohms, making it a 4 ohm load if im correct. They're on 2 separate channels, each channel with 1 sub and 1 head.

If it helps, its a Pyramid ZPA150, not PTA150
Check the mains supply to the unit is stiff enough - it could clip if it can't get enough juice, as well as if it hits the rails.

Or it could be bust - reviews are not encouraging.

Steve
macwhiz (author)  steveastrouk5 years ago
It has a firm, twistlock connection to the wall, all my basement connectors are 20 amp twistlock for my equipment. It has toshiba amp chips, but I think the toroid is a little small for the 1500 watt max power with 400 Watts RMS per channel. Might get a new one, Can I just replace it with a larger one?
220 or 110 ? Its got a 220 in - try that.

Steve
macwhiz (author)  steveastrouk5 years ago
I've already voided the warranty, i replaced the fans with higher quality ones that are quieter and I cut out the fan grates, so I'm perfectly fine with opening it up. It does have a 220 in, but I don't have a connector for it now and most gigs I do don't have 220 power.
Just try it, and see if its that that's causing a PSU issue. Measure the off load voltage on the reservoir caps in the supply, and then try again when its loaded hard.

Steve
macwhiz (author)  steveastrouk5 years ago
Time to go find my Fluke multimeter...its somewhere down here...Just tried it on 220, it does the same thing
Well its not your incoming then.

Steve
macwhiz (author)  steveastrouk5 years ago
I'm not sure if I made this clear when I posted the question, but the clipping leds illuminate even when the amp is off and unplugged, but the input is still plugged in, Its input is my Denon DN-X100 mixer, and when I turn up the volume to about halfway the clipping leds illuminate
It probably WILL "clip" then won't it - the PSU is off and something tries to come through.

Out of interest, disconnect the speakers and see what happens with the power off !

Steve
macwhiz (author)  steveastrouk5 years ago
I disconnected them, and it still happens, but only when there is an input from the source, in this case my mixer, which is connected to my laptop. I believe that the LED's are actually powered by input voltage/current, and are illuminated when enough voltage/current is flowing from the input source. Do you think a larger toroid transformer will help any? Is there a way to actually know when its clipping other than the leds?
You'd need access to an oscilloscope, but it would be pretty easy to tell with that.

I'm surprised the input leaks enough to let enough current flow to trigger the LEDs.

So if the amp is ON, but the volume is OFF what happens ? Clearly, it CAN'T clip then ! If it does, something is telling lies.

Steve
macwhiz (author)  steveastrouk5 years ago
If the amp is on, but the amp volume is off the clipping leds still illuminate...I think they're lying. And Pyramid and Pyle must be the same, because all the components inside have model numbers for Pyramid and Pyle amplifiers
They're lying. Crank it up !

They HAVE to be lying !
Dumb design.
Steve
macwhiz (author)  steveastrouk5 years ago
If only i had the time to build that right now. so busy between school and gigs, and now the holidays...hmm....
Here's a clever idea

http://sound.westhost.com/project23.htm
Yes, you can put a bigger transformer in - but lets see where the problem is. Are you happy to open it up and measure stuff ?

Steve
Its not got a damaged output stage has it ? Did you get it new ?

Steve
macwhiz (author)  steveastrouk5 years ago
I bought it new on amazon, and the output stage doesn't seem to be damaged, and I checked with an audio spectrum meter I borrowed and the waves don't seem to be clipped. I think it might just be a design flaw. If it helps any its driving 2 15 inch subwoofers and 2 15 inch heads with 1 horn and 4 tweeters.