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Old 1st September 2010, 11:08 PM   #1
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Default Amp gets very hot

While playing music for five minutes in a high volume (3 out of 10 in this amp face plate is pretty loud), i place my hand on the big alluminum cooling unit, which the transistors are screwed to and the unit is
very hot to the touch (while the amp cover is open).

I can't really measure the temprature but it's very hot to the touch.

Is that normal? does it need to be only a bit warm?
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Old 1st September 2010, 11:12 PM   #2
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Your information needs to be more precise for an answer to your question. What amplifier? How much power? What temperature? Does it get hot with volume at zero?

With a typical class B amplifier at, say, 50% efficiency, it would dissipate one Watt for every Watt of power output. A little more than that, actually.
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Old 1st September 2010, 11:44 PM   #3
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Quote:
Originally Posted by rg12 View Post
Is that normal?
Well, if it works for 5 minutes, it's probably normal. It could be somebody has fiddled with the internals though, turned up the bias current. That could result in it getting hot but still working. The only way to be sure is to show it to somebody expert enough to know.

w
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Old 1st September 2010, 11:50 PM   #4
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Originally Posted by bob91343 View Post
Your information needs to be more precise for an answer to your question. What amplifier? How much power? What temperature? Does it get hot with volume at zero?

With a typical class B amplifier at, say, 50% efficiency, it would dissipate one Watt for every Watt of power output. A little more than that, actually.
It's a Pioneer SA-7300 amplifier 37 watts per channel.

What does class B mean?

I didn't try it with the volume at zero.
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Old 2nd September 2010, 05:02 AM   #5
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Google Class B amplifier to find out. At 37 W per channel, both channels at full output, you are cooking the heat sink with over 70W. Not trivial. But you should check the bias, particularly if it gets hot with no signal.
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Old 2nd September 2010, 06:14 AM   #6
Mooly is offline Mooly  United Kingdom
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Is the speaker impedance correct... not too low ?

If turning the volume back down allows the hot amp to cool again then it's just the way it is... or you are pushing it too hard perhaps into an unsuitable load.
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Old 2nd September 2010, 09:18 AM   #7
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I will try the amp at volume zero for 10 minutes and let you guys know.

I didn't say i was listening to music with the volume at max, i said it was
3 out of 10 in the dial.

My speakers say 4-8 ohm
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Old 2nd September 2010, 10:42 AM   #8
AndrewT is offline AndrewT  Scotland
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Hi,
the speakers may be part of the problem.
4 to 8ohms speakers are usually a 2way with a crossover connecting the amp to the two drivers.
The bass/mid driver is usually a 4ohm unit and the treble is usually an 8ohm unit.

Most of the average power going to the 4 to 8ohm speaker actually goes to the 4ohm bass/mid unit.

The amp thinks it is driving a 4ohm load.

Is the amp specified for reactive 4ohm speakers?

I suspect there is another problem inside the amplifier. Get it checked/sorted before you damage it or your speakers.
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Old 2nd September 2010, 10:58 AM   #9
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You don't sound technically minded but just try measuring the DC voltage at the speaker terminals with NO music and ZERO volume. If its not ZERO (or VERY close to ZERO), the amplifier has a problem.

Also, if you've got access to a multimeter, also try disconnecting the speakers and measure their DC resistance. It should lie somewhere in the 2 - 60 Ohm range. This may not be valid with speakers with crap crossovers in them.

Another quick check to see if the speakers are the problem is to run the amplifier with no speakers. DO NOT do this with a valve amplifier.
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Old 2nd September 2010, 11:24 AM   #10
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Quote:
Originally Posted by rg12 View Post
I will try the amp at volume zero for 10 minutes and let you guys know.

I didn't say i was listening to music with the volume at max, i said it was
3 out of 10 in the dial.

My speakers say 4-8 ohm
Just because the volume control is at "3 out of 10" doesn't mean that the amp isn't putting out full power. The position of the volume control isn't an indication of the relative output power.
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