200W class A psu considerations with IRF240 - Page 2

AudioSan · 09:26 AM

Quote:

Originally Posted by peranders

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

no. the formula will be: (3.6x2)x(3.6x2)x8/2=207W

accordind to your calculation. the First watt F5 will give 6.7W class A at 8ohm.(1.3A bias) acctualy it gives 27W

peranders · 29th December 2012, 09:31 AM

3.6 amps is the bias and is the same thing as the peak current (in class A) and the rms current is 1.414 times lower. Do we talk about the same thing here?

AudioSan · 29th December 2012, 09:35 AM

peak current is TWICE the bias

AudioSan · 29th December 2012, 09:40 AM

from F5 manual:

For this sort of circuit, a 1.3 amp bias means that the amplifier will operate Class A to 2.6
amps of output current. To understand this, imagine a condition where Q3 and Q4 are
idling at 1.3 amps, so that all the current is going from the V+ voltage rail to the V- voltage
rail, and none is going through the loudspeaker.

The power of 2.6 amps into 8 ohms is I^2 * R, or 2.6 * 2.6 * 8 = 54 watts. This is the peak
value, and the nature of an undistorted sine wave is that the peak wattage is twice the
average, so this circuit would operate 27 watts average Class A into 8 ohms. At currents
above 2.6 amps one of the transistors will shut off, leaving the other to continue to increase
beyond the 2.6 amps in what is known as Class AB.

KatieandDad · 10:00 AM

So 1.3A is giving you 27W Class A from the F4.

With the Aleph 4, 2.5A bias gives you a true 100W RMS Class A.

AudioSan · 29th December 2012, 09:57 AM

katie. class A power have nothing to do with your rail voltage.
it is, (2.5*2)*(2.5*2)*8/2=100W class A power at 8ohm.

rhythmsandy · 29th December 2012, 02:22 PM

check this thread how nelson calculates the class A power..
Leaving Class A? Martin Colloms vs Nelson Pass

djk · 29th December 2012, 02:35 PM

I would build it with a tiered power supply.

With a ±20V supply for the low rail the idle would only be 144W, that could be done with only two or three pair of IRFP240/9240.

bobodioulasso · 03:20 PM

Quote:

Originally Posted by rhythmsandy

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

414w peak is 207w average. 60V is about right for 200W/8ohms. Air forced cooling Mandatory.

rhythmsandy · 29th December 2012, 07:03 PM

I would be using the IGBT heatsink and each heatsink will have 4 Hexfets dimensions
heatsink width 5 inch length 6 inch depth is also 6 inches... wouldnt that be sufficient?

how do I calculate how much each hexfet is dessipating the heat?

29th December 2012, 09:31 AM	#12
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	3.6 amps is the bias and is the same thing as the peak current (in class A) and the rms current is 1.414 times lower. Do we talk about the same thing here? __________________ /Per-Anders (my first name) or P-A as my friends call me Tube Buffered Gainclone in work \|Thread

29th December 2012, 09:35 AM	#13
AudioSan diyAudio Member Join Date: Feb 2009 Location: Trondheim	peak current is TWICE the bias __________________ aleph P1.7 pre. F5 power amp. CDpro2(need DAC). Vivaldi8 speakers

29th December 2012, 09:40 AM	#14
AudioSan diyAudio Member Join Date: Feb 2009 Location: Trondheim	from F5 manual: For this sort of circuit, a 1.3 amp bias means that the amplifier will operate Class A to 2.6 amps of output current. To understand this, imagine a condition where Q3 and Q4 are idling at 1.3 amps, so that all the current is going from the V+ voltage rail to the V- voltage rail, and none is going through the loudspeaker. The power of 2.6 amps into 8 ohms is I^2 * R, or 2.6 * 2.6 * 8 = 54 watts. This is the peak value, and the nature of an undistorted sine wave is that the peak wattage is twice the average, so this circuit would operate 27 watts average Class A into 8 ohms. At currents above 2.6 amps one of the transistors will shut off, leaving the other to continue to increase beyond the 2.6 amps in what is known as Class AB. __________________ aleph P1.7 pre. F5 power amp. CDpro2(need DAC). Vivaldi8 speakers

29th December 2012, 09:46 AM	#15
KatieandDad diyAudio Member Join Date: Nov 2011 Location: UK	So 1.3A is giving you 27W Class A from the F4. With the Aleph 4, 2.5A bias gives you a true 100W RMS Class A. Last edited by KatieandDad; 29th December 2012 at 10:00 AM.

29th December 2012, 09:57 AM	#16
AudioSan diyAudio Member Join Date: Feb 2009 Location: Trondheim	katie. class A power have nothing to do with your rail voltage. it is, (2.52)(2.52)8/2=100W class A power at 8ohm. __________________ aleph P1.7 pre. F5 power amp. CDpro2(need DAC). Vivaldi8 speakers


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29th December 2012, 02:22 PM	#17
rhythmsandy diyAudio Member Join Date: Aug 2012	check this thread how nelson calculates the class A power.. Leaving Class A? Martin Colloms vs Nelson Pass

29th December 2012, 02:35 PM	#18
djk diyAudio Member Join Date: Feb 2001 Location: USA	I would build it with a tiered power supply. With a ±20V supply for the low rail the idle would only be 144W, that could be done with only two or three pair of IRFP240/9240. __________________ Candidates for the Darwin Award should not read this author.

29th December 2012, 07:03 PM	#20
rhythmsandy diyAudio Member Join Date: Aug 2012	I would be using the IGBT heatsink and each heatsink will have 4 Hexfets dimensions heatsink width 5 inch length 6 inch depth is also 6 inches... wouldnt that be sufficient? how do I calculate how much each hexfet is dessipating the heat?

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