It may be a little late to send a comment on Grey's posting of 04/01/01, but I have only just caught up with this thread.
In his posting, Grey states that '... at high power a Class B output section will present a widely varying load to the power supply' then follows with 'Of course, one could always go for a Class A output which doesn't vary at all...'
This is not strictly correct. The only amplifier that presents a constant load to the power supply is a single ended Class A utilising a constant current source (or sink)and having only a single supply rail.
In all other cases, one or both of the supply rails will have a current that varies with the output load current. This includes constant current SE amps on split supply rails, voltage controlled current source SE amps on both single and split supplies, active current source SE amps (eg Aleph) on both single and split supplies and all push-pull Class-A output stages.
Geoff
In his posting, Grey states that '... at high power a Class B output section will present a widely varying load to the power supply' then follows with 'Of course, one could always go for a Class A output which doesn't vary at all...'
This is not strictly correct. The only amplifier that presents a constant load to the power supply is a single ended Class A utilising a constant current source (or sink)and having only a single supply rail.
In all other cases, one or both of the supply rails will have a current that varies with the output load current. This includes constant current SE amps on split supply rails, voltage controlled current source SE amps on both single and split supplies, active current source SE amps (eg Aleph) on both single and split supplies and all push-pull Class-A output stages.
Geoff
Geoff,
I've got Alephs (& Zens) on the brain, what do you expect? Actually, I'm hip deep in the water-cooled heatsink aspect, but that's for the Aleph. Once I come up for air (so to speak), I'll need to put on my writer's hat for a while. There's no telling what I'll say, then...
blmn,
I'll try to scrounge up a copy. That might be interesting.
Grey
I've got Alephs (& Zens) on the brain, what do you expect? Actually, I'm hip deep in the water-cooled heatsink aspect, but that's for the Aleph. Once I come up for air (so to speak), I'll need to put on my writer's hat for a while. There's no telling what I'll say, then...
blmn,
I'll try to scrounge up a copy. That might be interesting.
Grey
Geoff,
About the writer's hat? Yeah. I'm an author in addition to being chief cook and bottle washer. Haven't been spending enough time writing. (And while I'm writing, I get distracted and don't always multitask gracefully. Eat breakfast when I should be eating supper--that sort of thing.) I feel kinda guilty about not writing, but the Aleph (plus taxes, plus this, and that...the usual nuisance stuff that life throws at you) has been eating a lot of time. I've got the circuit working; I just need to dissipate the heat. Nearly there. Gotta keep chugging, get the Aleph cooled, then put words down on paper. If I get the right words in the right order, sometimes an intelligible story emerges.
Hopefully, I can then fiddle with some other circuits...
Grey
[Edited by GRollins on 04-10-2001 at 08:28 PM]
About the writer's hat? Yeah. I'm an author in addition to being chief cook and bottle washer. Haven't been spending enough time writing. (And while I'm writing, I get distracted and don't always multitask gracefully. Eat breakfast when I should be eating supper--that sort of thing.) I feel kinda guilty about not writing, but the Aleph (plus taxes, plus this, and that...the usual nuisance stuff that life throws at you) has been eating a lot of time. I've got the circuit working; I just need to dissipate the heat. Nearly there. Gotta keep chugging, get the Aleph cooled, then put words down on paper. If I get the right words in the right order, sometimes an intelligible story emerges.
Hopefully, I can then fiddle with some other circuits...
Grey
[Edited by GRollins on 04-10-2001 at 08:28 PM]
Geoff,
In a prior posting, you had referred to draw on rails in class A circuits. At the moment, I am immersed in building an Aleph 2 (and heatsinks--a non-trivial issue when building an Aleph), and to a lesser degree thinking about Zens in the background. For Alephs and Zens, the current draw is pretty even, since both rely on current sources. For that matter, the Son of Zen should also present a constant draw. That was the context of what I was thinking back in the post from 4/1 or whenever; sorry I didn't phrase that more clearly at the time.
Does that clarify what I meant?
Grey
P.S.: I have 1"x1/4"x8" copper bars in hand. I will be trying one or two variations on the water-cooled copper heatsink over the next few days. I will report results soon.
In a prior posting, you had referred to draw on rails in class A circuits. At the moment, I am immersed in building an Aleph 2 (and heatsinks--a non-trivial issue when building an Aleph), and to a lesser degree thinking about Zens in the background. For Alephs and Zens, the current draw is pretty even, since both rely on current sources. For that matter, the Son of Zen should also present a constant draw. That was the context of what I was thinking back in the post from 4/1 or whenever; sorry I didn't phrase that more clearly at the time.
Does that clarify what I meant?
Grey
P.S.: I have 1"x1/4"x8" copper bars in hand. I will be trying one or two variations on the water-cooled copper heatsink over the next few days. I will report results soon.
Grey
Agreed, the Zen will provide a constant load to the power supply as it is an SE amp with a constant current source fed from a single supply rail.
The Aleph does not provide a constant load. Assuming the active current source has been set in line with NP's patent, the current in each supply rail varies from near zero to twice the quiescent current, so the curent draw is hardly "pretty even".
In fact, the supply rail current variations are exactly the same as those for a push-pull Class-A amplifier or even a Class-B amplifier operating at the same output power. The only difference is that the Class-A amps have a sine-wave current waveform and the Class-B amps have a half-sine-wave current waveform (assuming, of course, a sine wave input to the amplifier).
If the Aleph were provided with a constant current source the situation would be even worse since the quiescent current would be double that for the active current source. In this case, the positive supply rail would have a constant current equal to the quiescent current and the negative supply rail would have a current that varied under load from near zero to twice the quiescent current since the speaker return goes to the mid-point of the power supply.
This is the point I was making in my original posting when trying to correct a factual inaccuracy.
Geoff
[Edited by Geoff on 04-11-2001 at 02:31 PM]
Agreed, the Zen will provide a constant load to the power supply as it is an SE amp with a constant current source fed from a single supply rail.
The Aleph does not provide a constant load. Assuming the active current source has been set in line with NP's patent, the current in each supply rail varies from near zero to twice the quiescent current, so the curent draw is hardly "pretty even".
In fact, the supply rail current variations are exactly the same as those for a push-pull Class-A amplifier or even a Class-B amplifier operating at the same output power. The only difference is that the Class-A amps have a sine-wave current waveform and the Class-B amps have a half-sine-wave current waveform (assuming, of course, a sine wave input to the amplifier).
If the Aleph were provided with a constant current source the situation would be even worse since the quiescent current would be double that for the active current source. In this case, the positive supply rail would have a constant current equal to the quiescent current and the negative supply rail would have a current that varied under load from near zero to twice the quiescent current since the speaker return goes to the mid-point of the power supply.
This is the point I was making in my original posting when trying to correct a factual inaccuracy.
Geoff
[Edited by Geoff on 04-11-2001 at 02:31 PM]
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