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Old 13th February 2012, 07:47 PM   #11
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Unless Cgd goes up so high that one mouth isn't shut when the other starts to sing.
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Old 13th February 2012, 08:43 PM   #12
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Hi

Vtt = Vpp.
No it's not clipping thats at 30 Vpp.
I go back to 2 fets and see if I still have this problem.
And Jacco I raise Vds and see if it helps.
Can somebody else check out if he has this problem?

Rob

Last edited by Rob Dingen; 13th February 2012 at 08:46 PM.
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Old 13th February 2012, 10:52 PM   #13
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I would try higher Source resistor values, and I would also try RC networks
in parallel with R7 and R8. The RC should be 470 ohms or so in series with
1 uF, and see what you get.

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Old 14th February 2012, 07:19 PM   #14
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Hi Nelson

Try the RC network with 470 ohm and 220 ohm but no help.
You told in the turbo paper that you can run it without source resistors so why go higher.
Want to drive 0,4 ohm.
Is it possible that the IRFP9240 from international rectifier is the problem?

Rob
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Old 14th February 2012, 11:00 PM   #15
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I have tried these various and sundry, but I know I didn't run your
circuit up too 100 KHz at power.

You want to try higher Source resistance because it might give us a clue.

If it's not related to that, then in might simply be inadequate drive,
requiring parallel input devices as outlined.

It is possible that the IR parts are at fault, the N channel IR part has
about 50% more Ciss and the P channel 50% more than that. In
addition, the P channel device has what is referred to as the "IR P
distortion" in which the transconductance shelves.

Even so, are you planning on operating this as an audio amplifier?

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Old 15th February 2012, 07:15 AM   #16
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Hi Nelson

Ok I try the source resistors.
Yes it's for driving a true ribbon speaker
At the moment I use it as a driver with the 610 and 9610 to drive 4 sanken 2SA1295 and 2SC3264 and it looks promising.

Rob
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Old 15th February 2012, 04:33 PM   #17
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I am struck by the possibility that the cross-current conduction you are
experiencing is the result of the Jfets operating beyond their bias to charge
the capacitance of the output devices so that there is a net increase in their
average current.

There is something you can try for this.

Connect the Source pins of the two Jfets together and increase the values
of the feedback resistors 100 ohms and 1Kohms. This will increase the
bias current and it will also put more local degeneration on the Jfets. From
there you can parallel Jfets for more current.

I think you still need to try raising the values of the Source resistors of
the output devices.

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Old 11th January 2013, 08:38 PM   #18
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Gosh maybe I am off base here if so Please forgive my Ignorance,If 20khz is the limit for some humans hearing,mine is 16.5khz,Why are you at 100khz anyway ,anything over 20khz is out of audible hearing,try cutting the freq bandwith down to 20khz or If you think you can hear it 22khz and see what it does,I agree with the posts,you can't have them both on at once,And it will burn up,
It's just my 2 cents,goodluck to you.
Regards,
NS
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