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Old 28th August 2009, 12:16 PM   #1
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Default New Hybrid Driver/Amplifier

Hello all,

I'm simulating a new hybrid amplifier, a pure class A hybrid driver (6N6P differential pair + mosfet) and a AB mosfet output stage.
My ideaa is to build an "universal" hybrid class A driver and try different output configurations, from AB PP to pure SE (both solid state and vacuum based).
The driver should be mounted on a separate PCB, while the power output stage could be mounted on the heatsink or on the amp chassis.
Below the circuit I simulated for the driver and the complete amplifier (the first one) I indtend to try.
Any comment?
What do you think, is it a good idea?
It simulate amazingly well, and it seems stable.
The driver, supplied with a +155V and a -120V can output a 200Vpp signal with 0.017% THD.

You also need the TL431 model to simulate my circuits, please find it HERE.

Driver schematic:
Click the image to open in full size.

Complete amplifier schematic:
Click the image to open in full size.

Driver sim:
Driver

Amplifier sim:
Amplifier

let me know what you think.

Ciao,
Giovanni
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Old 28th August 2009, 08:24 PM   #2
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One problem with tubes is the heat up time.
During this time the output will go to one rail and apply DC to your speaker.

With my hybrid I simply bolt on an SRPP stage to the front of a standard class AB MOSFET amplifier.
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Old 28th August 2009, 09:07 PM   #3
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One more opamp...
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Old 28th August 2009, 11:28 PM   #4
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Quote:
Originally Posted by nigelwright7557 View Post
One problem with tubes is the heat up time.
During this time the output will go to one rail and apply DC to your speaker.

With my hybrid I simply bolt on an SRPP stage to the front of a standard class AB MOSFET amplifier.
Whoops ! not quite true.
As the SRPP tube stage has a gain of 13 I reduce the gain of the MOSFET amp by a factor of 13.
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Old 29th August 2009, 12:52 PM   #5
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Quote:
Originally Posted by nigelwright7557 View Post
One problem with tubes is the heat up time.
During this time the output will go to one rail and apply DC to your speaker.

With my hybrid I simply bolt on an SRPP stage to the front of a standard class AB MOSFET amplifier.
I know, this is why I will add a delay relay at the output, to just avoid DC on the speakers.

Quote:
One more opamp...
Yes, actually. But will this particular opamp sound fine?

At the end I think the only way to really know is to build one of this amp; I'm designing the driver PCB (the output stage will be wired point to point, for the first prototype), so we will see (or, better, listen).

This post was just to see if there is any major issue with the idea, but it seems no one blamed the schematic.

I'll let you know.

Ciao,
Giovanni
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Old 29th August 2009, 03:01 PM   #6
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You may want to check out the hybrid amplifier that appeared in the September 1997 issue of Elektuur. It used an ECC88 capacitor-coupled to a mosfet class AB push-pull stage, no global feedback.

If you PM me, I can get you a PDF version of that article.
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Old 29th August 2009, 05:42 PM   #7
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Quote:
Originally Posted by croccodillo View Post
Yes, actually. But will this particular opamp sound fine?

At the end I think the only way to really know is to build one of this amp; I'm designing the driver PCB (the output stage will be wired point to point, for the first prototype), so we will see (or, better, listen).

This post was just to see if there is any major issue with the idea, but it seems no one blamed the schematic.

I'll let you know.
Giovanni;

after you've done I would suggest you to try to replace R21/M7 by a BJT current mirror and compare results.
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