Pavel Dudek's (Upupa Epops) amplifiers II

[BV]

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".

[Upupa Epops]

OK, lost fight...

[Federmann]

Originally Posted by Upupa Epops

OK, lost fight...

Originally Posted by VivaVee

Could you explain what you mean by 'long term thermal shock'?

Originally Posted by Upupa Epops

Yes: after one hour of full output power into eight ohm...

Originally Posted by Federmann

What is full output power ? Undistorted music production, or sine signal?

Originally Posted by Upupa Epops

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?

[Upupa Epops]

I don't understand, what you can, Federmann...

[VivaVee]

Originally Posted by Upupa Epops

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).

[forr]

"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 RMS² something, don't we ?
Watt are we accustomed to ?

[PMA]

VivaVee - that's exactly the reason why I would ask for a temperature record vs. time.

[PMA]

Originally Posted by forr

"RMS power"

(Vrms x Vrms)/Rload,

or

(Irms x Irms) x Rload

[PMA]

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.

[john curl]

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.