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Old 12th February 2005, 12:40 AM   #1
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Default Aleph30 very very hot

Hello, today, I tried my aleph30 circuit with a variac.
All seem OK except a thing, the temperature.
For the test, I put the 6 mosfet on a 11*8*3 good quality aluminium heat sink and it come very hot after a couple a minutes.
So hot that after 10 min, it was unconfortable to touch it...

One channel draw about 2.6A at 25 V. I have about 0.4 v on each 0.47Ohm resistor, so about less than 1 A each.

Do you think I have any problem with my circuit ???
The dissipate temperature seem to me a little bit excessif.
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Old 12th February 2005, 01:25 AM   #2
Stocker is offline Stocker  United States
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It is the nature of the Aleph series of amplifiers to get extremely hot compared to, say, classB amplifiers.

If it is more than 55 or 60C you may want to add heatsink for safety. If not, just don't lean on it. If you have very small children, it is a great tool for teaching them what "hot" means.














/edit
ok, I'll be a bit more informative:
50-55C is the region where most people's sensation goes from "quite warm" to "I am cooking my own skin on this here"

50-55C is in the region where most semiconductor devices go from "GAWD it's COLD over here" to "hey, that's more like it!"
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Old 12th February 2005, 02:28 AM   #3
MikeW is offline MikeW  United States
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Default 130 watts

2.6A x 25V for the plus side. 2.6A x -25V for the minus side = 130 watts. Or (.4 Volts/.47) ohms X 6 Mosfets X 25 volts.
Get more heatsinks or turn down the bias.
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Old 12th February 2005, 02:33 AM   #4
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Ok, thank you for your reply.
To turn down the bias, I just have to change R19 for a lower value ???
It's just simple like this ???
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Old 12th February 2005, 03:45 AM   #5
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"So hot that after 10 min, it was unconfortable to touch it..."

Welcome to the class A club!! Hotter(more bias) is much better as long as things are still with in tolerance. This way you won't burn down your house!!

Mark
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Old 12th February 2005, 05:15 AM   #6
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Just as a reference, 50C on a metal surface will allow one to touch it for ~10sec before it is intolerable. 55-60C is unbearable after ~1sec, 65-70C will have one flinching back instantly. It's part of the body's built in protection to have a nonlinear response to high temperatures. A 50C heat sink temperature is only 25C above normal ambient, and nothing to get really excited about. It is unreasonable to expect a cold or lukewarm heat sink in a sizable class A amplifier, unless one is using extensive forced air or water cooling. Inexpensive DVMs with thermocouple attachments and thermometers that plug into DVMs are not too hard to come by, and can be used to figure out precisely what is going on.
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Old 12th February 2005, 01:52 PM   #7
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Thank you for the information.
But i was very surprise, I have a zenV4, and it take about 1 hour to come hot.
The aleph30 take only a couple a minute, maybe because the heat-sink is not the same material and size to.

So It is better to keep the high bias if my heat sink is enough big ???

What I can expect if I turn down the bias ???
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Old 12th February 2005, 01:55 PM   #8
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"So It is better to keep the high bias if my heat sink is enough big ???"

Absolutely! You will get lower dostortion readings.

"What I can expect if I turn down the bias ???"

You would end up with higher distortion readings and less pure sound, smaller soundstage, etc. So searching out large enough sinks is generally a worthwhile thing to do.
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