F5 power amplifier

Jump to Latest
#2,264
rhysh said:



Are you saying cviller's statement is incorrect? I dont understand heatsink ratings.

Thanks
Click to expand...

No, I am talking about a different size of the case.

The mine is 4U - 300 mm long, Criviller's 3U - 400 mm.

I just added my experience because sometimes is better
to have a taller case than a longer one.. like for me... 😉

Peppe
 
#2,265
In the article Nelson specifies a heatsink per output device of .6 Deg C / Watt. Then goes on to recommend a heatsink that's 6" x 8" with 2" inch fins per output device which seems larger than what he specifies.

Each channel would be 6"x 16" which is about 150x405 mm or 60,750 square mm.

Going by his recommendation the 4U 400mm case is about the same.

If Cviller is using a 3U case without problem then I guess Nelson leaves a good safety margin when he choses heatsinks.

I like peppe's suggestion of a little taller but shorter case. It may actually work well with the compactness of the board.
 
#2,267
heatsinks

labjr said:
Geez. The prices are pretty good at hifi2000. 114 euros for the case I'd like with nice 10mm panel. I wonder how much the shipping to the USA would be? Maybe I'll have to find a similar case in USA.
Click to expand...


So my thought is, and I cannot remember much of this entire thread, other than max 10A, if the unit is cranked, or someone sets the bias higher, I think bigger would be better.

Is it unreasonable to set nominal bias @ 2A instead of 1.3A? If so, I would imagine the unit would get hot if listening to Metallica through 82db Magnepans.(no I dont own them anymore).

Mike
 
#2,268
labjr said:
Geez. The prices are pretty good at hifi2000. 114 euros for the case I'd like with nice 10mm panel. I wonder how much the shipping to the USA would be? Maybe I'll have to find a similar case in USA.
Click to expand...


Shipping is quite a lot to the USA i think. There is someone on headfi who knows of a US retailer, i will contact them and then get back to you.
 
#2,271
During idle, all current will flow through the 2 output devices, 2 Amps times 48Vpp is 96 Watts dissipation.
At the peak of class A operation, your 2 Amps times 2 will flow only through 1 power mosfet.
With 20V out, Vds is only 4 volts, 4 volts times 4 amps is only 16 watt dissipation.

Biased at 2A, the die of the MOSFETs will be at 120C if you keep the heatsinks at 50C, chance of popping an output device will be 8 times higher.
 
#2,272
Class A amps are different from Class AB ones. The latter become hotter as you play louder (and you increase the bias), while a Class A amp draw a constant current that can be turned into music or heat. Thus, if you play music, part of the energy goes to the speakers not generating heat.
We can then say: the louder you play, the cooler the amp stays
 
#2,273
jacco vermeulen said:
During idle, all current will flow through the 2 output devices, 2 Amps times 48Vpp is 96 Watts dissipation.
At the peak of class A operation, your 2 Amps times 2 will flow only through 1 power mosfet.
With 20V out, Vds is only 4 volts, 4 volts times 4 amps is only 16 watt dissipation.

Biased at 2A, the die of the MOSFETs will be at 120C if you keep the heatsinks at 50C, chance of popping an output device will be 8 times higher.
Click to expand...


massimo said:
Class A amps are different from Class AB ones. The latter become hotter as you play louder (and you increase the bias), while a Class A amp draw a constant current that can be turned into music or heat. Thus, if you play music, part of the energy goes to the speakers not generating heat.
We can then say: the louder you play, the cooler the amp stays
Click to expand...


I learned something today. Sweet.
:idea:
 
You must log in or register to reply here.
Top Bottom