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-   -   200W class A psu considerations with IRF240 (http://www.diyaudio.com/forums/solid-state/226609-200w-class-psu-considerations-irf240.html)

rhythmsandy 29th December 2012 05:50 AM

200W class A psu considerations with IRF240
 
how about a 200W class A amplifier with the following config

output simple pushpull : IRFP240 IRF9240 ( Total 12 pairs )
Bias current : 3.6 Amps
Psu voltage +/- 60v
Trafo VA: 4000VA
capacitance .4mF/100V
heatsinks type IGBT heatsinks

Boscoe 29th December 2012 08:37 AM

Max class A power into 4r with 3.6A bias is 50W and 100W into 8r. 120V x 3.6A = 432W idle power which isn't really possible passively within a realistic size. To achieve 200W into 8 you will need 5A bias and 65V rails, so you will be dissipating 650W at idle.

rhythmsandy 29th December 2012 08:50 AM

according to nelsons pow calculations 3.6A Bias
( 3.6 x 2 )^2*8 = 414.72W peak and for continuous 293W in 8 ohms

AudioSan 29th December 2012 08:52 AM

boscoe. it is possible in a push pull class A. and it don't have to be big at all. only with natrual cooling and ONLY 2 sides heatsinked.
look at pass aleph 1.2. natrual cooling and not big at all.

AudioSan 29th December 2012 09:01 AM

a 8pair F5 turbo with dual input fets can meet the demands.
with 2x55V transformer. so +/-65V rails.

peranders 29th December 2012 09:13 AM

Quote:

Originally Posted by rhythmsandy (Post 3302795)
according to nelsons pow calculations 3.6A Bias
( 3.6 x 2 )^2*8 = 414.72W peak and for continuous 293W in 8 ohms

What sort of calculations are these? 3.6 amps will give you 50 Watts into 8 ohms if we talk class A.

It's pretty simple:

Irms = 3.6/1.414 = 2.546 A

P = I^2*R= 2.546*2.546*8 = 51.84 watts

KatieandDad 29th December 2012 09:13 AM

Audiosan. Weren't a few of the Pass amplifiers only Class A to a certain point, about 25W I seem to recall, after that they went into Class A/B.

AudioSan 29th December 2012 09:18 AM

katie. that depends on bias and rail voltage.

Boscoe 29th December 2012 09:19 AM

Quote:

Originally Posted by peranders (Post 3302808)
What sort of calculations are these? 3.6 amps will give you 50 Watts into 8 ohms if we talk class A.

It's pretty simple:

Irms = 3.6/1.414 = 2.546 A

P = I^2*R= 2.546*2.546*8 = 51.84 watts

Sorry yes I forgot about to convert to rms I only got up 30mins ago!

KatieandDad 29th December 2012 09:20 AM

http://www.firstwatt.com/pdf/art_leave_classa.pdf

Most of his commercial amps are hybrids.

I see you've got the F5, I've got the Aleph 4, both of those are true Class A. The F5 about 25W, the Aleph 4 about 100W.

As far as I can recall, the A4 runs at +/- 48V with 2.5A bias.


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