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Old 23rd June 2003, 12:27 PM   #1
ergo is offline ergo  Estonia
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Default ZEN V4 cascoding ???

I have been running ideas in my head for a next amp project and rereading the various materials about amp design. Reading the article my Mr. Pass about cascoding put me thinking about possible improvements that could be achieved by cascoding the power transistor in ZEN circuit. May be also cascoding the current source.....

Most of the distortion and problems remaining in this design seem to be caused by parasitic capacitances in power transistors - so cascoding should help? I know the downside is that we lose some output voltage swing capability and generato more heat.... + some more components overall.

Ergo
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Old 24th June 2003, 02:46 AM   #2
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I have built some cascoded Zen output stages, and have
planned some of these for later Zen Variations projects.

Ir's easy enough to do; you will find that you simply hook up
a power transistor for the cascode and feed its Gate enough
voltage to leave a minimum of 2 volts across the Gain transistor.

(You might refer to my cascoding article in Audio magazine, which
you can navigate to from www.passlabs.com )

The results are quite good, the primary effect being that it lowers
the distortion at high frequencies with the higher input and
loop impedances that are so desirable.

It does change the sound, and I would be interested in your
reaction after you have tried it.

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Old 24th June 2003, 08:55 AM   #3
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Quote:
Originally posted by Nelson Pass

... and have planned some of these for later Zen Variations projects.

The philosophical simplicity is fading out...?



JH
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Old 24th June 2003, 09:16 AM   #4
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Quote:
Originally posted by jh6you


The philosophical simplicity is fading out...?



JH

Why? The cascode operation let the buffer out and allows less feedback ...

Also remainds me the year that I lived with the SOZ cascoded , and then the discover of the essential X ...
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Old 24th June 2003, 06:16 PM   #5
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Good idea, Ergo! Let us know how it sounds.
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Old 24th June 2003, 09:50 PM   #6
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Quote:
Originally posted by jh6you
The philosophical simplicity is fading out...?
Of course it does. Slowly.

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Old 25th June 2003, 09:22 AM   #7
ergo is offline ergo  Estonia
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Indeed the cascoding would not be the step to make it more simple. I think Nelson himself has already been there and done it as simple as at all possible and also he has shown it to us.

What I think is that this step, even so more complicated, could provide us with better subjective and objective performance. At this point I think the saying "keep it as simple as possible but no simpler" applies

**

Anyway, would you guys keep the power transistors the same type and use the same for cascoding or would it make sense to use a smaller and at the same time faster mosfet as gain device and the high power one for cascoding. With much less voltage on the gain device it would broaden the possible choises I think.

Ergo
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Old 25th June 2003, 04:24 PM   #8
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Quote:
Originally posted by ergo
would you guys keep the power transistors the same type and use the same for cascoding or would it make sense to use a smaller and at the same time faster mosfet as gain device and the high power one for cascoding.

Ergo

It works beautifully with the IRF610 as gain device .

I find that the small transistor produces a *meaningful* better sound than the IRFP 044


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Old 25th June 2003, 10:54 PM   #9
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Quote:
Originally posted by stefanobilliani
I find that the small transistor produces a *meaningful* better sound than the IRFP 044
This would be very subjective thing. Having tried a few variations, I can say that some will find a smaller gain chip like the 610 more accurate on the top and certainly faster, but may lack other characteristics at the lower frequencies. If you are looking at multi-amplification in particular, there is a lot of room for exploration.
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Old 25th June 2003, 10:55 PM   #10
Bricolo is offline Bricolo  France
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Quote:
Originally posted by Nelson Pass

Of course it does. Slowly.

are you slowly telling us that "less is more" is false?
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