Does a singlerail PP need to be more complicated? - diyAudio
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Old 16th December 2009, 04:12 PM   #1
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Default Does a singlerail PP need to be more complicated?

A Zen/Schade-inspired driver for the two output devices. With PP, current can be set lower than SE for the same Pout. Could this go very wrong?

The choke could be substituted by a voltagecontrolling AC-CCS. And how the floating bias voltage should be arranged I don´t know. Global feedback shouldn´t be needed as the PP SF is 100%feedbacked already.

This was just a fantasy in the car on my way home from work today....
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Last edited by revintage; 16th December 2009 at 04:15 PM.
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Old 16th December 2009, 08:20 PM   #2
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Nice idea!

I would prefer using a DN2540 instead of a sk170 j-fet. The Supertex DN2540 can run a 100 - 200 mA.
Why not a White cathode follower type of output arrengemant? I dont like mixing N and P devices as complimentary pairs. The output should run in class A anyways to lower distortion...
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Old 16th December 2009, 08:34 PM   #3
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Hey Johannes,
The 2SK170 has a Ciss of 30pF and the DN2540 about ten times as much. To get a descent Zin the first one must be the choice. About the output stage one still wonders: Can it be that simple?
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Old 18th December 2009, 05:08 AM   #4
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Did some adjustment to the circuit above. Now the driver is a JFET mini-Zen with an AC-CCS that controls the drain-voltage. This way we can also simplify the PP-follower by getting rid of the floating bias supply.

By using a PP-follower we also get an environment friendly simple amp that theoretically only needs 50% standing current compared to a standard SE SF. Or with (std) 2A we should get an amp with more muscle for lowZ loads.
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Old 19th December 2009, 09:29 PM   #5
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Why not just use another 2sk170 for the current source it sure would be easier.
I notice you are not using any thermal compensation to prevent the output stage
going into thermal run away.
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Old 20th December 2009, 07:51 AM   #6
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Hey Woody,
A current source wouldn´t fix a stable voltage. This one is a gyrator with fixed and stable midpoint voltage for the outputstage. Also the MOSFET in the gyrator helps tempcomp, so that one is undercontrol(I hope). I get indications of -100mA from 25-100 degrees C.

Last edited by revintage; 20th December 2009 at 08:13 AM.
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