Plate amp repair?

[Brendan_L]

I have an Adire Rava which is a Shiva, a box, and a plate amp.
It's this amp, plus or minus the boost:

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=300-796

When it's really going, say from demo disks, it overheats and shuts off.
It does it with bass filled music. It didn't used to do this.
Is there a component in the amp that is prone to failure? caps? circuit breaker?

It works fine until it heats up, and by heating up, the heat sink gets hot to the touch. Then it has to cool before playing again.

Repair? Replace?

[engr_dave]

The short answer to your question is: no there aren't any components that are "prone to failure". In my experience, the most common failure mode of amps is a shorted output transistor which results in immediate and unrecoverable silence.

Does it actually get hotter than it used to... or does it just shut down now when it would keep going before?

If it is actually getting hotter... and you're sure you're not just driving it harder... then it's probably internal osciallations or something in the bias circuit (too much bias current). These are not easy repairs - requiring a competent technician and perhaps not worth it.

If it shuts down with the heatsinks moderately hot, then the thermal switch may be faulty. It should be set to trip when the sinks get to something like 85C. This is very hot, too hot to hold your hand on for any length of time.

This is all assuming that you don't have some sort of partial short that is causing the amp to "see" lower load impedance: frayed wires to the driver, shorted voice coil, etc.

Have you changed anything else in the signal stream to the sub? On rare occasions, DC offset or high-frequency oscillations from an upstream component can cause the sub amp distress.

Hope this helps.

Dave

[Brendan_L]

Dave,

Thanks for the speedy reply. Without actually putting a thermometer on it, it's pretty close to what you describe - too hot to hold your hand on it for more than a few seconds.

It was overheating on my standard setup, and now it's actually loaned out to my neighbor and doing the same thing. I'll pull the amp off and inspect the internal wiring.

If I had another shiva I would test your partial short theory. I will try it with another 12" to see what the result is.

[chasw98]

If you can isolate it to one component or a group in the same area, pick up some freeze spray and cool them down to see if the amp turns back on and starts working. That will give you an idea where to start looking for mischevious behavior by transistors and such.

Chuck

[engr_dave]

I thought the amp was performing a deliberate, protective thermal shutdown. In that case, most amps shut down everything... so the LED would go off until the amp cooled. Is that what's happening?

[digital desire]

As someone who has repaired quite a few amps, I would say it is very possible that you are simply asking too much out of a $128 amp.
If you can play most stuff at a moderate, non ear splitting level, and it does not go into thermal, it is probably maxed out at THAT point. Start pushing a little harder, and it is working harder than it was intended.

[Brendan_L]

I opened it up and detected no wiring shorts. The caps were a little bulged on the end but not as bad as some I've seen.

Also of interest is that the amp is not turning on every time. The LED is on but no sound is created. Sometimes I can remove the power cord and reinsert it a few times and it will go active eventually.

I don't know that this amp has a protection mode, as the LED stays on, but it goes quiet.

And yes, Peter, I may have outgrown this. My current lineup includes more cowbell.

[digital desire]

LOL.
This survey participent voted for the buttkicker from amazon for $252 delivered.
Over a kilowatt has a certain ring to it!

[warnerwh]

I'm also inclined to think you're driving it too hard. A cheap amp like that is easily over driven. It doesn't take much too overdrive a small amp with bass frequencies.

[Brendan_L]

Oh, I have the buttkicker. It's great ;-) It works well on my TC-2000.

Just trying to breathe some life into the Rava so I can give it a new owner.
Shouldn't it be able to play an entire NIN album straight through? :rofl:

[cjd]

Shouldn't it be able to play an entire NIN album straight through? :rofl:

I don't know, it might have some taste and decide it just doesn't want to deal with that, uh, "music" any more.

C