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Old 31st May 2002, 08:19 AM   #1
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Default High speed amplifier

Can anybody help with the following:
Balanced Amplifier, J-fet Input, Mos Fet for the rest, 100 Watt/4Ohm Class A with a full power bandwidth of 300 - 400 Khz.
Every information on Spectral and Metaxas amps would be helpful to, but I would feel more comfortable to have a PASS-like design.
Reinhard
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Old 31st May 2002, 09:28 AM   #2
mlloyd1 is offline mlloyd1  United States
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I'll go out on a limb (I think it's fairly well supported though ) and say you're barking up the wrong tree if you looking for a "Pass-like" design with a full power bandwidth at 400KHz.

Circuitry-wise, Spectral does a lot of things to get the speed and bandwidth they advertise. Many of these techniques fly in the face of "simpler is better".

Maybe you may get a little closer to what you want by looking at Borbely's All FET designs?

And pay some attention to recent discussions around here about phase margin. Many really wide bandwidth, very fast designs are not easily made acceptably stable driving a wide range of loading scenarios.

mlloyd1
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Old 3rd June 2002, 08:54 AM   #3
sonnya is offline sonnya  Denmark
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High speed and driving difficult loads is hard to obtain at the same time without stabilityproblems.... You need to have an outputstage with very low zout and phase change to do such a design. It is a hard task!

You need very fast BJT's, JFET's and MOSFET's .. What i mean is > 100MHz so you can control the phase change through each stage ... At the same time the openloop gain has to be low in each stage.

For an amp with good stability:

The single ended ZEN amplifier from www.passdiy.com It is a singlestage design and in theory it should have a phase margin of 90 degrees with perfect mosfet's (fast)!!

Thats a really good example on a stable amplifier and simple too.

Normaly i would say that a phasemargin of 60 degrees would be a good margin.. I would think that the ZEN amplifier would meet this requirement with no problem at all.. But i have not tested or done any sims on a ZEN....

Good stability is more important than wide bandwidth!

Sonny
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Old 3rd June 2002, 03:26 PM   #4
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Actually, if you put a front end on a SOZ, you should be able to get into that range easily.
The power supply, however, will be the size of a kitchen table and it would be best if you lived in a more northerly clime.

Grey
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Old 3rd June 2002, 03:32 PM   #5
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Talking Kitchen table

How many of you that built SOZs have supplies the size of kitchen tables? Please post image please, I want to see that sucker...... Actually 100 watts for 4 ohms is pretty impractical for
the Son of Zen design, but Grey can help you with the water cooling part.

H.H.
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Old 3rd June 2002, 04:54 PM   #6
SteveG is offline SteveG  United States
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Default 100 watt son of zen- water cooled

Quote:
Grey can help you with the water cooling part
It would be really a great design for somebody with say, a heated pool, or maybe a 1000 person tea party
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Old 3rd June 2002, 07:54 PM   #7
paulb is offline paulb  Canada
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Default Re: High speed amplifier

Quote:
Originally posted by reinhard
100 Watt/4Ohm Class A with a full power bandwidth of 300 - 400 Khz.
Why?
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Old 3rd June 2002, 08:10 PM   #8
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Default It would be really a great design for somebody with say, a heated pool

You know..... my wife has always wanted a heated pool.....maybe you have hit on a great WAF feature!

H.H. (Hottub Harry)
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Old 3rd June 2002, 10:18 PM   #9
sonnya is offline sonnya  Denmark
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OOpppsss !

I forgot to say that i was talking about amps with feedback ... Of course you do not deal with phase margin in a no negative feedback design.

Sonny
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Old 4th June 2002, 07:20 AM   #10
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Default To all the guys

Hello,
thanks Sonny and Grey,

at the time I`m on that way, no overall feedback, only local degeneration.

Regards to the guys in the pool, drinking tea,
have fun and come back with some real tips.

Reinhard
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