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Old 29th December 2012, 05:50 AM   #1
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Default 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
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Old 29th December 2012, 08:37 AM   #2
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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.
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Old 29th December 2012, 08:50 AM   #3
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according to nelsons pow calculations 3.6A Bias
( 3.6 x 2 )^2*8 = 414.72W peak and for continuous 293W in 8 ohms
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Old 29th December 2012, 08:52 AM   #4
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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.
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Old 29th December 2012, 09:01 AM   #5
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a 8pair F5 turbo with dual input fets can meet the demands.
with 2x55V transformer. so +/-65V rails.
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Old 29th December 2012, 09:13 AM   #6
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Quote:
Originally Posted by rhythmsandy View Post
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
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Old 29th December 2012, 09:13 AM   #7
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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.
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Old 29th December 2012, 09:18 AM   #8
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katie. that depends on bias and rail voltage.
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Old 29th December 2012, 09:19 AM   #9
Boscoe is offline Boscoe  United Kingdom
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Quote:
Originally Posted by peranders View Post
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!
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Old 29th December 2012, 09:20 AM   #10
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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.

Last edited by KatieandDad; 29th December 2012 at 09:23 AM.
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