Zirclotron: Question for the big guy - diyAudio
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Old 29th July 2003, 12:43 AM   #1
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Default Zirclotron: Question for the big guy

Mr. Pass:

I've abandoned my experimental circuit (a 2-stage mosfet circlotron) for the moment. I've been messing with single stage circlotrons or "Zirclotrons", but I can't figure out why I don't get voltage gain from this (attached) circuit. Is it impossible?

Thanks

Mike
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Old 29th July 2003, 02:40 AM   #2
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It looks like it would work, but I am struck by the notion
that it would be sensitive to power supply noise, much
like ZV5. Driving the inputs with a split secondary transformer
and/or regulating the supplies would cure this, I imagine....
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Old 31st July 2003, 03:41 PM   #3
gwolf is offline gwolf  Austria
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A first question (before thinking further about it):

Why are you using two input signals? Connect the earth at another point (won't make a difference, at least with the Spice simulation) and you need only one source.

This does not yet prove that it works. What is the gain you expect with this? And the noise (as Nelson suspects) ?

I built (and am still enhancing) a MOSFET Circlotron amplifier some years ago. It works fine but uses some more devices... Only later I learned from a tube journal, that they call it Circlotron.

Cheers,

Gerhard Wolf
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Old 31st July 2003, 08:50 PM   #4
gwolf is offline gwolf  Austria
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After having a closer look:

This is definitively a buffer, having gain below 1:

The left side of the load follows the right input, reduced by Vgs2 and V3 noise, the right side follows the left input, reduced by Vgs1 and V5 noise.

So you will also hear the power supply ripple.

Two hands clapping is not enough. You need also your feet (driver transistors) for making enough noise :-)

Gerhard
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Old 31st July 2003, 09:29 PM   #5
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Mr. Pass, Gerhard:

Thanks very much for your replies. I was expecting both voltage and current gain from the common source configuration, instead I get unity voltage gain as if it were a common drain stage. I was driving the circuit balanced, but it also works with the negative input grounded.

I'm interested in the circuit because (if I understand correctly) it can operate in class AB beyond its quiescent bias, without more complex biasing circuits, which gives it a sort of Zen appeal. But, without voltage gain, it isn't a very practical project.

I'm not giving up tho. Do I need to offset the gates somehow?

Thanks again.

Mike
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Old 1st August 2003, 12:16 PM   #6
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Quote:
Originally posted by mrothacher
I'm interested in the circuit because (if I understand correctly) it can operate in class AB beyond its quiescent bias, without more complex biasing circuits, which gives it a sort of Zen appeal. But, without voltage gain, it isn't a very practical project.
Whether it's practical depends, I think, on your power requirements and on the voltage output available from your preamp. For example, you can drive a circlotron (or zirclotron, but I'm not sure there's any advantage) output stage from a balanced Zen line stage for up to 100W or so output. Surely this is at least a "Zen compatible" approach. Also, the circuit will work class AB, but I find that it sounds best, using IRF output devices at least, at 1A or more idle current.
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Old 1st August 2003, 03:04 PM   #7
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Hey Joe!

How have you been? I like your idea. I'm going to finish my balanced Zen linestage and try the zirclotron like a power follower. I'd forgotten that the BOSOZ can swing a lot of voltage. In fact, my first attempt at a two-stage design was really just a zen linestage with a circlotron hung on the outside.

The idea of a 100 Watt "Zen-like" power buffer that idles at 1 A or so is rather appealing after all!

Thanks

Mike
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Old 1st August 2003, 04:40 PM   #8
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Here's a version with cross-connected feedback. Would this reduce the noise a little?

I'll try to wire this puppy together over the weekend and see what happens.
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Old 1st August 2003, 05:14 PM   #9
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Which opens the possibility for this gadget...

What sez ye, Mr. Pass? Is she smart as paint?
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Old 1st August 2003, 06:38 PM   #10
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Quote:
Originally posted by mrothacher
Mr. Pass, Gerhard:

Thanks very much for your replies. I was expecting both voltage and current gain from the common source configuration, instead I get unity voltage gain as if it were a common drain stage. I was driving the circuit balanced, but it also works with the negative input grounded.

I'm interested in the circuit because (if I understand correctly) it can operate in class AB beyond its quiescent bias, without more complex biasing circuits, which gives it a sort of Zen appeal. But, without voltage gain, it isn't a very practical project.

I'm not giving up tho. Do I need to offset the gates somehow?

Thanks again.

Mike

Hi Mike,

I looked at your circuit, but I'm missing some kind of ground reference for the amp. I mean, the whole circuit sort of floats between the signal sources, which are referred to gnd, but the amp isn't. That may be the reason there is no volt gain. If this works at all it may be because spice often assumes implicit gnd refs in device models.

Any expert views on this?

Jan Didden
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