Power Calculations

jduncan · 13th November 2001, 07:12 PM

I've started working on the Aleph 4 and I had one particular question... I'm guessing that this is VERY trivial but I couldn't come up with the solution at first glance.

I see that each channel dissipates approx. 288W (48V rails so 96 * 3 = 288W). How is the max power output figure of 100W calculated? I couldn't quite workout how to get this.

Any help would be greatly appreciated!

wuffwaff · 14th November 2001, 11:06 AM

take the supply voltage 48 volts minus the voltage drop caused by the fets and source resistors (approx. 4-5 volts).
After that it´s simple 44 / sqrt(2) = Veff.
Veff^2 / 8 = power into 8 Ohms (115 Watts in this case) For power into 4 Ohms you need to know the max. current available.

william

jduncan · 14th November 2001, 07:37 PM

ok....

Does the maximum voltage at the output point to calculate this take into account the drop over the output transistors and source resistors and the negative rail too?

I'm confused here just looking at the schematic in this case.

Also, from everything I've read, because this is a single-ended design, the power into lower loads only decreases instead of increasing as happens with push-pull designs.

How does that occur here?

wuffwaff · 14th November 2001, 08:06 PM

Yes, the 4-5 volt I mentioned are the volstage drop over the output fets and the source resistors.

Also, from everything I've read, because this is a single-ended design, the power into lower loads only decreases instead of increasing as happens with push-pull designs.

How does that occur here? [/B][/QUOTE]

it doesn´t. Look for example at the Aleph 5. Pass claim a max output of 30volts (i.e 34V supply voltage -4V drop) and 8A. Theoretically this gives about 56 watts into 8 ohms at 2.65A eff. and 112 watts into 4 Ohms at 5,3A eff Max power should be 30 x 8 /2 = 120 watts at 3.75 Ohms. In practice the supply voltage will go down (unless regulated) so the gain in power into lower impedances won´t be that big.(claim is 90 W into 4 Ohms)

hope this helps,

william

jduncan · 14th November 2001, 08:10 PM

But the Aleph 5 has a claimed 100Wpc output into both 8 AND 4 ohms....it doesn't go up.....

So what about the drop across the FETs and source resistors in the current source?

wuffwaff · 14th November 2001, 08:22 PM

mmmm.......

my owners manual says 60 watts @ 8Ohms and 90 watts @ 4 Ohms for 1% distortion and a max. output of 30V/8A

The voltage drop is the 4-5V I mentioned before. The voltage drop depends on the value of Vgs, the source resistor, Rds on and the current thats going through.

william

jduncan · 14th November 2001, 08:57 PM

sorry I meant the Aleph 4 has 100wpc into both 8 and 4 ohms

wuffwaff · 14th November 2001, 09:46 PM

sorry to disagree again but I can´t find a power claim into 4 Ohms for the aleph4. Only 100Watts @ 8 Ohms
With a 950VA transformer for both channels (estimated from the primary fuse) it should be aprox. 165 Watts into 4 ohms.

william

AudioFreak · 14th November 2001, 10:23 PM

The Aleph 4 was designed to output almost the same power into 4ohms as into 8ohms just with quite a bit more distortion.

[Edited by AudioFreak on 11-14-2001 at 05:43 PM]

jduncan · 14th November 2001, 11:25 PM

right.... It definitely doesnt put MORE power out into 4 ohms...a non single-ended design is needed to do that right?

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13th November 2001, 07:12 PM	#1
jduncan diyAudio Member Join Date: Nov 2001 Location: Boston, MA, USA	I've started working on the Aleph 4 and I had one particular question... I'm guessing that this is VERY trivial but I couldn't come up with the solution at first glance. I see that each channel dissipates approx. 288W (48V rails so 96 * 3 = 288W). How is the max power output figure of 100W calculated? I couldn't quite workout how to get this. Any help would be greatly appreciated!

14th November 2001, 11:06 AM	#2
wuffwaff diyAudio Member Join Date: Aug 2001 Location: Ingolstadt Germany	take the supply voltage 48 volts minus the voltage drop caused by the fets and source resistors (approx. 4-5 volts). After that it´s simple 44 / sqrt(2) = Veff. Veff^2 / 8 = power into 8 Ohms (115 Watts in this case) For power into 4 Ohms you need to know the max. current available. william

14th November 2001, 07:37 PM	#3
jduncan diyAudio Member Join Date: Nov 2001 Location: Boston, MA, USA	ok.... Does the maximum voltage at the output point to calculate this take into account the drop over the output transistors and source resistors and the negative rail too? I'm confused here just looking at the schematic in this case. Also, from everything I've read, because this is a single-ended design, the power into lower loads only decreases instead of increasing as happens with push-pull designs. How does that occur here?

14th November 2001, 08:06 PM	#4
wuffwaff diyAudio Member Join Date: Aug 2001 Location: Ingolstadt Germany	Yes, the 4-5 volt I mentioned are the volstage drop over the output fets and the source resistors. Also, from everything I've read, because this is a single-ended design, the power into lower loads only decreases instead of increasing as happens with push-pull designs. How does that occur here? [/B][/QUOTE] it doesn´t. Look for example at the Aleph 5. Pass claim a max output of 30volts (i.e 34V supply voltage -4V drop) and 8A. Theoretically this gives about 56 watts into 8 ohms at 2.65A eff. and 112 watts into 4 Ohms at 5,3A eff Max power should be 30 x 8 /2 = 120 watts at 3.75 Ohms. In practice the supply voltage will go down (unless regulated) so the gain in power into lower impedances won´t be that big.(claim is 90 W into 4 Ohms) hope this helps, william

14th November 2001, 08:10 PM	#5
jduncan diyAudio Member Join Date: Nov 2001 Location: Boston, MA, USA	But the Aleph 5 has a claimed 100Wpc output into both 8 AND 4 ohms....it doesn't go up..... So what about the drop across the FETs and source resistors in the current source?

14th November 2001, 08:22 PM	#6
wuffwaff diyAudio Member Join Date: Aug 2001 Location: Ingolstadt Germany	mmmm....... my owners manual says 60 watts @ 8Ohms and 90 watts @ 4 Ohms for 1% distortion and a max. output of 30V/8A The voltage drop is the 4-5V I mentioned before. The voltage drop depends on the value of Vgs, the source resistor, Rds on and the current thats going through. william

14th November 2001, 08:57 PM	#7
jduncan diyAudio Member Join Date: Nov 2001 Location: Boston, MA, USA	sorry I meant the Aleph 4 has 100wpc into both 8 and 4 ohms

14th November 2001, 09:46 PM	#8
wuffwaff diyAudio Member Join Date: Aug 2001 Location: Ingolstadt Germany	sorry to disagree again but I can´t find a power claim into 4 Ohms for the aleph4. Only 100Watts @ 8 Ohms With a 950VA transformer for both channels (estimated from the primary fuse) it should be aprox. 165 Watts into 4 ohms. william

14th November 2001, 10:23 PM	#9
AudioFreak Warp Engineer On Holiday Join Date: Oct 2001 Location: Queensland, Australia	The Aleph 4 was designed to output almost the same power into 4ohms as into 8ohms just with quite a bit more distortion. [Edited by AudioFreak on 11-14-2001 at 05:43 PM]

14th November 2001, 11:25 PM	#10
jduncan diyAudio Member Join Date: Nov 2001 Location: Boston, MA, USA	right.... It definitely doesnt put MORE power out into 4 ohms...a non single-ended design is needed to do that right?