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Old 15th March 2006, 07:22 AM   #11
JCM is offline JCM  United States
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Where to start ? What's a good amp ? One you can build and not regret, one that isn't blown away by some other version you wish you'd built instead ?

This is the way I look at it :

Look at the evolution of the Zen. Notice, immediately, one thing about it which is - not so good : the low input impedance. This really reduces the signal - wastes a good deal of it. I have looked at it on a scope, it gets really distorted at that point. It asks a lot of the preamp.

So one pretty much HAS to add series resistance - which further attenuates, which I regret in such an amp with low gain to begin with.

There was no way around an input buffer - it can drive that low impedance, and give a much higher one. NP has done that, characteristically, in the simplest way possible. This is the Penultimate Zen, "The Zen Variations, Part 4".

Also look at the low efficiency - but with the Aleph style current source, also in the Penultimate Zen, theoretically 50 % efficiency is possible. This version also use global degeneration.

I plan to create a version of this amp, with switch selectable degeneration, and also current source mode. I figure on a 5W / 10 W amp. I'm keeping the input buffer.


****NP has said of that amp, "I would match it up against an Aleph 3 without hesitation."****

This scheme would retain the sound I like, of the common source mosfet, and gives the option of none, or some overall degeneration, and also the current source mode option. It seems to me about the best of all possible worlds in terms of these types of amps - like you, my power demands are modest. I find 2 watts of honest Class A is pretty good, 5 would be perhaps all I would ever need, yet I would have the option of 10.

With this scheme, if you like feedback, you can have it, if not, you can avoid it, and if you don't like the sound of the Aleph style current source you can also avoid it. Any combination.

Beyond this, one of the Aleph amps, which I know nothing about is the other option. But I have a sneaking suspicion the Penultimate Zen Version 4, as I described, would hold its own very well.

P.S. Note that in some Zen versions, some experimental ones,
NP toyed with the use of resistors instead of a current source (probably not going to be too good), inductors, light bulbs instead of current sources. I think those are interesting, especially the light bulbs are - "neat-o", I have to say - but I am thinking sound-wise none of those would ever best a good current source. What that leaves is really only ONE amp = the Penultimate Zen - all the good has been retained, and simple improvements introduced.

So I think the only real choice is between that amp (Zen), and one of the Alephs. Two choices : Zen or Aleph.
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Old 18th March 2006, 03:23 AM   #12
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Thanks to everybody whom responded. I appreciate your suggestions. I have decided to build a ZV9, as I am intrigued with the FET transfer curve resembling that of a triode.

My preamp is a tube-type with a cathode follower, so I do not have to worry about the low input impedance of Zen. Another nice thing about ZV9 is the capability of configuring it as a current source, which is what my full-range speakers might like driving them.

For now I will again review the Zen white papers, while acquiring the necessary components. Big heat sinks seem to be the most difficult and expensive parts to obtain; I'd appreciate some guidance as to where I can purchase them at reasonable cost (USA). Any other advice regarding passive component selection is also welcome. There are some pretty large electrolytics in the Zen signal path; my experience with electrolytics is that they impart a sonic "veil" when compared to a good film cap. What are people using for coupling caps on the Zens?

One last note: JH, I found your comments regarding Nelson Pass both distasteful and disrespectful. To imply that his hearing is poor, or that his ability to recognize high sonic quality is absurd. I do not want any threads of mine to be associated with such language. We should all be grateful that one of the world's most highly innovative audio engineers is sharing his genius with us...for FREE, mind you. Never bite the hand that feeds you...

Regards all,

Dennis
San Diego, CA
USA
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Old 18th March 2006, 03:33 AM   #13
moe29 is offline moe29  United States
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Hey Dennis,

don't worry about jh.. he's a big fan, and i'm sure has nothing but
respect for Mr. Pass. He's also built a lot of these circuits.

at the best of times sarcasam and joking can be hard to pull off when
posting in a forum. When English is a second language it can be
even harder.

i don't mean to speak for JH, just thought i'd mention my observations.
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Old 18th March 2006, 04:27 AM   #14
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Moe:

I'd prefer that this thread not turn into a flame war. I carefully considered the language issue before I wrote my postscript, and I continue to stand by it.

The best policy, especially in public forums, is to never be critical of individuals or their personal attributes. One can (and should) discuss or criticize the performance of a circuit, but even then it should be done with respect for the person whom is behind the design.

Let's please end this right here.

Dennis
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Old 18th March 2006, 06:35 AM   #15
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Dennis,

You are probably relatively new to the forum and don't know the relationship that JH and Nelson share on the forum. JH certainly meant quite the contrary to your understanding of his statement regarding Nelson.

I am also pretty sure that Mr. Pass is looking at what we are saying to each other and chukling!!
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Old 18th March 2006, 07:43 AM   #16
JCM is offline JCM  United States
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If you're concerned about too many capacitors in the signal path, note that with the Penultimate Zen (Zen Variations Part 4), NP has configured the input buffer so that it needs no capacitor coupling to its input, making the Total capacitor-in-the-signal-chain = two. One on the output of the buffer, and one to the speaker. (I plan not to include the little HF cap to the speaker.)

Two capacitors - hard to beat that, imo.

Of course, the one on the buffer output is specified as a 10uF polyester film type.

That leaves only 1 electrolytic - to the speaker. (And the 200uF bootstrap on the current source - which, of course, with the non-Aleph style, isn't needed.)

I was thinking about this - thinking about a bipolar supply. If I understand correctly, the idle voltage across the power mosfet driving the speaker is, like any amp, one half V+, so that one could get away with it. But I don't know enough about that Aleph current source. I would think bipolar operation would work - both power mosfets are the exact same type. But then, I think in that case the degeneration path would have to be tinkered with.

If one could do this, then there would be only 1 electrolytic in the signal chain.

I am currently studying that current source, and others, very simple ones. I highly recommend building and studying small versions of these amps, to get a good feel for them. I cooked up one with an efficiency of almost 40%, (the reason it isn't higher is because Rds (on) of the mosfets I'm using is 0.55 ohms.) When the current source is switched to normal operation, efficiency is back down to around 20%.
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Old 18th March 2006, 01:33 PM   #17
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For what it's worth, I have noticed a number of posts by jh6you recently that have a bit of an edge to them. I believe Dennis has the right of it in this instance.

Grey
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Old 18th March 2006, 01:37 PM   #18
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I'm not going to point fingers, but can we keep this thread on topic please.
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Old 18th March 2006, 01:52 PM   #19
flg is offline flg  United States
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Bipolar supplies are what is used on the aleph designs, with no big output E-Cap.
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Old 18th March 2006, 02:28 PM   #20
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I held the view that skipping big electrolytic caps in the signal's way was a major improvement when switching from single rail circuits to push-pull designs.
I don't like electroytics but after making the Zen V1 i figured it's not that simple.
Mr. Pass demonstrated with the Zen approach that there's no singular truth but there's allways a compomise to be made.

Guys like Lumanauw and JH6You have the greatest respect for Nelson Pass, are intelligent and think things through.
On top of that they have a nice sense of humor, as Mr. Pass does.
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