ZEN5 ZENv5 ZEN-v5 The Complementary Zen - Zen Variations - Part 5 by Nelson Pass
Mister Pass have not often really cheated
when he has published his amplifiers.
Whether they are single end Class A or like here Complementary Class A
or X or whatever
he publish the recommendations of supply for his Amplifiers.
It is not like we can see some of us others do.
Just publish an interesting amp schematic with little or nothing else.
Some even do not tell the level of V+ positive and V- negative.
Which is one essential information.
have no fear about Zen v5
If you read the rather long and detailed article by Pass
you will know how to build a very good amplifier:
Amplifiers: Zen Variations - Part 5 by Nelson Pass (c) 2003
The Complementary Zen
This is the final verdict from the constructor.
The Conclusion.
And I know Nelson is not a man often to
say what he does not really mean or say too much.
Me, lineup say:
I believe many of us could live with one Zen-v5 amplifier for very many years.
Eva said:ZEN V5 is a really funny circuit, it will amplify power supply ripple nearly as much as the input signal,
and output stage bias current is not regulated and completely dependent on the magnitude of the supply rails instead.
Such a circuit is only to be powered by attaching the PCB directly to the output binding posts of a high quality bench power supply
An externally hosted image should be here but it was not working when we last tested it.
Mister Pass have not often really cheated
when he has published his amplifiers.
Whether they are single end Class A or like here Complementary Class A
or X or whatever
he publish the recommendations of supply for his Amplifiers.
It is not like we can see some of us others do.
Just publish an interesting amp schematic with little or nothing else.
Some even do not tell the level of V+ positive and V- negative.
Which is one essential information.
have no fear about Zen v5 If you read the rather long and detailed article by Pass
you will know how to build a very good amplifier:
Amplifiers: Zen Variations - Part 5 by Nelson Pass (c) 2003
The Complementary Zen
This is the final verdict from the constructor.
The Conclusion.
And I know Nelson is not a man often to
say what he does not really mean or say too much.
Me, lineup say:
I believe many of us could live with one Zen-v5 amplifier for very many years.
A good question. Here very few examples:
1) Moxtone Lab
http://www.diyaudio.com/forums/solid-state/77176-simple-2-stage-pp-fet-amplifier.html (post #1)
2) ABACUS (theoretical background, advantages in opposite to power followers, only in German)
http://www.abacus-electronics.de/files/ampino-prinzip.pdf
and here additional URLs:http://www.abacus-electronics.de/files/spiegeltest.pdf
http://www.abacus-electronics.de/files/info-ampino.pdf
http://www.abacus-electronics.de/files/info-60-120b.pdf
ABACUS electronics | ABACUS
http://www.diyaudio.com/forums/solid-state/41034-abacus-rieder-60-120-amplifier.html#post2560623
3) "A new Class AB design"
from the authors Wim de Jager,
van Tuy & van der Ven (developed at University of Twente)
Electronics World, December 1999, Page 982; only schematic:
http://francis.audio2.pagesperso-orange.fr/C31_Jager.gif
4) LEF (Carlos Candeias, CEC/SANYO) detailled schematic wanted - who can post this ??
http://www.diyaudio.com/forums/soli...3300-amp5300r-lef-class-schematic-wanted.html
http://www.diyaudio.com/forums/solid-state/127182-lef-load-effect-free-amplifier-technology.html
5) Linn power amplifier "Klout" (power stage) schema see attachement:
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Drain/Collector followers are current sources
From my point of view, the main advantage is that such an output stage is a current source as opposed to the traditional source/emitter-follower stages being voltage sources. The reason is as follows:
For a current source, the power supplied to the speaker is P = R x Isquared
For a voltage source, the power supplied to the speaker is P = Usquared/R
Now the resistance of the speaker is never constant. When the resistance changes, the power supplied to it changes as well. In the case of the current source, the power changes propertionally to the resistance. In the case of the voltage source the power changes reziprocally to the resistance. Thus the voltage source incurs a lot more distortion than the current source.
The current source is less susceptible to the phase shift incurred by the speaker as it is located in the voltage build up by the speakers resistance. This voltage, however, has little effect on the output stage. A voltage source, in contrast, has to supply the blind currents as well.
To sum it up: a current source has much better control over the speaker than a voltage source.
Another advantage of the current source is that one does not have to provide so much power. In the case of the voltage source the current increases when the speaker resistance drops, which is why those amplifiers need a lot of current (and thus: power) reserve.
I think the 'warm' sound of the tube amplifiers has to be mostly credited to the fact that they are current sources, and less to the even harmonics distortion.
Regards,
gh
From my point of view, the main advantage is that such an output stage is a current source as opposed to the traditional source/emitter-follower stages being voltage sources. The reason is as follows:
For a current source, the power supplied to the speaker is P = R x Isquared
For a voltage source, the power supplied to the speaker is P = Usquared/R
Now the resistance of the speaker is never constant. When the resistance changes, the power supplied to it changes as well. In the case of the current source, the power changes propertionally to the resistance. In the case of the voltage source the power changes reziprocally to the resistance. Thus the voltage source incurs a lot more distortion than the current source.
The current source is less susceptible to the phase shift incurred by the speaker as it is located in the voltage build up by the speakers resistance. This voltage, however, has little effect on the output stage. A voltage source, in contrast, has to supply the blind currents as well.
To sum it up: a current source has much better control over the speaker than a voltage source.
Another advantage of the current source is that one does not have to provide so much power. In the case of the voltage source the current increases when the speaker resistance drops, which is why those amplifiers need a lot of current (and thus: power) reserve.
I think the 'warm' sound of the tube amplifiers has to be mostly credited to the fact that they are current sources, and less to the even harmonics distortion.
Regards,
gh
Really? So changes in R cause less 'distortion' than changes in 1/R?
Really? It has no control over bass unit damping, whereas a voltage source has some control.
Really? At a speaker impedance peak, a current source has to provide more power and may have headroom problems as it will still be limited by the DC voltage supply.
I suppose it might be possible to design a speaker to run from a current source, but most people design for a voltage source so the amp should approximate this. Most amps do this by sampling the output voltage for negative feedback. For a current source amp you would need a collector/drain output and sample the current, not the voltage. I have never seen this done for audio, although someone somewhere may have tried it.
The old Musical Fidelity A1 was a good example. Almost full Class A operation avoided any cross conduction problems. It had a 700mA quiescent and current limited at about 2A due to limited base drive, without any current limit circuit. The low voltage losses in the output allowed 20V rails and made the efficiency just about OK.
I might be mistaken, but AFAIK speakers are current sinks, at least the dynamic ones. The magnetic field is built by the current running through the coil, not the voltage. Thus, if the current is constant, there is no change in the force to the membrane, no matter what the impedance is, and thus no distortion. With the voltage source, the current changes, and thus the force on the membrane, and thus there is distortion.
Please explain bass unit damping, I'm not familiar with this issue.
Sure, but how far can such an impedance go up? Going from 4Ohm to 6Ohm is much less critical for the current source than a going from 4Ohm to 2Ohm is for the voltage source.
Regards,
gh
Current Source with Current Feedback
Regards,
gh
How sad. I think this is the only correct way to design a power amp.
Regards,
gh
There is more to speaker linearity than voice coil force. The force is not fully linear with current, as it also depends on where in the gap the coil happens to be - the magnetic field is not completely uniform. Then the suspension is not completely uniform. And on top of this, the actual cone movement depends on things like resonances, so a big cone movement can result from a small current at the right frequency.ghaudio said:
As the voice coil moves in the magnetic field it gets a voltage induced in it, sometimes known as back emf. This creates a current which opposes the driving current. This damps down the speaker resonance. The magnitude of this effect depends partly on amplifier output impedance. Most, but not all, speaker designs rely on this damping. It is completely absent in a current drive amplifier, so this will only work with speakers specifically designed for current drive. Otherwise you will get a huge bass peak at the resonance, which may sound fine for reggae but is not hi-fi.
At a resonance the speaker impedance can easily increase by a factor of 3 or 4, maybe more. So you get 3 or 4 times as much power fed in at just the point you don't want it, because the speaker output will be peaking at the resonance too.
Thinking that is your privilege, but I think you will find that almost everyone takes exactly the opposite view for the reasons I have outlined above. I think you need to find out some more about speakers, mechanical and electrical resonance, electromechanical systems etc. Then you might change your mind.
I don't see how that relates to voltage source vs. current source.
OK, I see your point. I agree that a current source, having a high impedance has a low damping factor. However, if negative current feedback is taken into the picture, the damping factor can be increased. Abacus electronics claims that there transconductance amplifiers have a virtually infinite damping factor, and they achieve this by means of such a feedback.
I agree if you sweep a sine across the frequency range. Music however, typically has lower amplitudes at higher frequencies, so the issue seems to be rather academic.
I admit that my first claim about the distortion is wrong. The level of distortion is the same in voltage and current source if the impedance changes, it just goes in different directions.
I still think the current source is less affected by the phase shifts incurred by the complex load of the (dynamic) speaker. With electrostatic speakers the picture is different, of course.
Regards,
gh
I think DF96 is right about that.
Suppose there isn't any driving current. That is the situation when the amp sends no signal to the speaker, but the bass membrane is still swinging from the previous stimulation. The voltage induced sees an infinite inner resistance in the amplifier. That is what 'current source' actually means: infinite inner resistance.
And as the inner resistance of the amplifier is infinite, there is no damping. This can be countered, however, by negative feedback. The voltage induced by the speaker is fed back to the input of the amp which then eliminates the swinging.
The correct feedback for a current source, however, is current feedback. But this still works, as the voltage induced by the speaker drives a current through the resistor in the feedback loop.
Unfortunately, all the drain/collector output amp designs I have seen so far do use voltage feedback. Except Abacus. They seem to be the only ones who do it right. But they use BJTs and OpAmps, so they are still not close enough to the tube amp yet.
Regards,
gh
Do you know more about this LEF amps ?
http://www.diyaudio.com/forums/soli...3300-amp5300r-lef-class-schematic-wanted.html
http://www.diyaudio.com/forums/pass-labs/5808-cec-amp71.html
No, current feedback does not notice the voltage so there is no feedback from the back emf. If this were not true it would not be a current source. A current source amplifier does not provide any speaker damping, so the speaker design has to provide the required damping via mechanical means. This in turn means that such a speaker would be significantly overdamped if used with a conventional voltage source amplifier.ghaudio said:
in this case this paper could be of interest:
http://www.essex.ac.uk/csee/research/audio_lab/malcolmspubdocs/J10 Enhanced cascode.pdf
http://www.diyaudio.com/forums/solid-state/25172-baxandall-super-pair-9.html
concerning the LEF topology there is a german pdf paper about
http://www.hifi-weiler.de/fileadmin/media/LEF-Technik.pdf
and this thread:
http://www.diyaudio.com/forums/solid-state/168185-how-does-lef-load-effect-free-amplifier-work.html
http://www.essex.ac.uk/csee/research/audio_lab/malcolmspubdocs/J10 Enhanced cascode.pdf
http://www.diyaudio.com/forums/solid-state/25172-baxandall-super-pair-9.html
concerning the LEF topology there is a german pdf paper about
http://www.hifi-weiler.de/fileadmin/media/LEF-Technik.pdf
and this thread:
http://www.diyaudio.com/forums/solid-state/168185-how-does-lef-load-effect-free-amplifier-work.html
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Wouldnt a speaker have to be designed specificaly for a current amp?
A normal speakers (designed for flat freq response from a voltage source) non flat impedance implies non flat current response for flat acoustical freq response. Or you use voltage feedback, but doesnt that negate the amp as a current amp?
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