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Pavel Dudek's (Upupa Epops) amplifiers II
Pavel Dudek's (Upupa Epops) amplifiers II
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Old 20th December 2009, 09:23 AM   #221
BV is offline BV  Slovakia
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Pavel, he is not worth of ban. We should let him talk with himself, like at his own forum. It is not good to provocate I...t. Ad him to "ignore list".

Last edited by BV; 20th December 2009 at 09:32 AM.
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Old 20th December 2009, 09:26 AM   #222
Upupa Epops is offline Upupa Epops  Czech Republic
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OK, lost fight...
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Old 20th December 2009, 12:40 PM   #223
Federmann is offline Federmann  Czech Republic
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Send a message via ICQ to Federmann Pavel Dudek's (Upupa Epops) amplifiers II
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Originally Posted by Upupa Epops View Post
OK, lost fight...
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Originally Posted by VivaVee View Post
Could you explain what you mean by 'long term thermal shock'?
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Originally Posted by Upupa Epops View Post
Yes: after one hour of full output power into eight ohm...
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Originally Posted by Federmann View Post
What is full output power ? Undistorted music production, or sine signal?
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Originally Posted by Upupa Epops View Post
Nominal output power, i.e. in this case 120 W into eight, Federmann....
When measured Upupa epops really must know what to measure. Why are not writing?
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Old 20th December 2009, 03:08 PM   #224
Upupa Epops is offline Upupa Epops  Czech Republic
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I don't understand, what you can, Federmann...
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Old 20th December 2009, 07:05 PM   #225
VivaVee is offline VivaVee  New Zealand
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Originally Posted by Upupa Epops View Post
Yes: after one hour of full output power into eight ohm...
Thank you, this makes it clear that your temperature measurement was taken after the heat sinks had time to reach thermal equilibrium. This is the best case scenario.

My concern is that the thermal resistance between the transistors and the heat sink is quite high because the heat must conduct laterally (which it does very poorly) before it can conduct to the heat sink.

A more informative test (and the worst case scenario IMHO) would be to take temp measurements while the amp is running under idle conditions, and then run the amp at full power for five minutes while taking the temperature of the transistor case and the heat sink.

It is the time taken to reach equilibrium that is a measure of the 'quality' of the heat sinking arrangement rather than the temperature differential at equilibrium (which you have already measured).
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Old 20th December 2009, 07:07 PM   #226
forr is offline forr  France
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"RMS power" is known to be an incorrect expression.
As power in a resistor is RMS voltage multiplied by RMS current,
we should have a result in RMSē something, don't we ?
Watt are we accustomed to ?
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Old 20th December 2009, 07:08 PM   #227
PMA is offline PMA  Europe
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VivaVee - that's exactly the reason why I would ask for a temperature record vs. time.
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Old 20th December 2009, 07:10 PM   #228
PMA is offline PMA  Europe
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"RMS power"
(Vrms x Vrms)/Rload,

or

(Irms x Irms) x Rload
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Old 20th December 2009, 07:21 PM   #229
PMA is offline PMA  Europe
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Default Regarding output power definition

Regarding output power (sine rms), in every Stereophile power amplifier test John Atkinson does this:

"Before performing any tests on an amplifier, I run it for 60 minutes at one-third its specified power into 8 ohms"

So, if someone announces 500W amplifier, then this amp must be able to work at 166W for 60 minutes, if assessed seriously.

If someone claims 500W amplifier, which in fact is able to give long time output power hardly 50W, then such a claim is nothing but a hoax.
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Old 20th December 2009, 07:27 PM   #230
john curl is offline john curl  United States
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RMS power is by parsing definition, wrong, BUT who cares? It means something in the audio world, and really, that is what counts. This is one of those, what we call, pseudo-intellectual arguments. The 2 stage power transistor mounting is potentially very good, but it is actually the very best to get a heat-sink with an L in its extruded shape, in order to get the thermal resistance to a minimum. We tried to do it the 2 stage way with the Lineage Power Amp in the 80's and it became difficult to do.
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