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Old 2nd February 2010, 10:40 AM   #711
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The chipamp PCB's use IRF610's on the front-end.
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Old 2nd February 2010, 11:12 AM   #712
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I will use this schematic
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Old 2nd February 2010, 01:55 PM   #713
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Q3 sucks some current from the jfet - and it tries to restore always the quiescent current - how should this work???

And Q4 amplifies the voltage on the sensing resistor - what for??? To much dissipation??? We could use higher resistor value there.

I don't like the bootstrapping - what for?

Maybe you could keep q4, set the idling current with it (see pass current source) and couple the signal of the sensing resistor direct. If you use a high resistor value to couple the Q4 signal to the gate, you could "overwrite" it with the signal from the sensing resistor.

(You need a zehner diode, bridged with a cap - because of the DC voltage drop require. You could use another zty for a current source for the zehner...)

But maybe, my understanding of Q3 is wrong, and Q4 improves all stuff... But what the hell bootstrapping is for - you only need it, if your driver normally requires a higher power supply, but you don't want to pay... ;-)

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Old 2nd February 2010, 02:12 PM   #714
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May I put some correction there:

Q3 seems current limiting - no function under normal conditions. Otherwise it should work.

2 questions:

- Why do you need the resistors without values?
- Why do we need bootstraping???
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Old 2nd February 2010, 02:45 PM   #715
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HV. calm down.
This is almost the aleph J schematic except two red points resistors which are wired differently.
The voltage across the sensing resistor modulates the current source from the emittor of
Q4 instead of from its base (Aleph) because, compared to aleph the sensing resistor voltage is phase opposite.
Though, Wensan would speak better than i do about this as beeing his own idea.

Last edited by bobodioulasso; 2nd February 2010 at 02:48 PM.
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Old 2nd February 2010, 05:07 PM   #716
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Sorry, I'm just getting exited if I don't understand things properly...

That you modulate on the emitter is maybe ok. But I still do not understand that you need the two unlabeled resistors... I still feel, we could drop all the ztx stuff and replace them with the J2 like solution. I cannot see any advantage - but maybe that is only because of my bad knowledge. So sorry if you got my comments in a rough way...

Dirk
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Old 2nd February 2010, 06:07 PM   #717
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The upper resistor is 68.2k like aleph J. I just erased the value by mistake.
The three tied are 0.47R
The resistor from base of Q4 to middle point is about 500R
I do not know precisely for the two last which i count to adjust experimentally for a8 ohm load, and /or to ask the help of Wensan.
I suggest you have a look at the Wensan thread: "Excellent SRPP power amp of MOSFET"

Last edited by bobodioulasso; 2nd February 2010 at 06:12 PM.
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Old 4th February 2010, 07:35 AM   #718
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HV,

sorry, i did not mean to be rude.

The boostrap is as the Aleph j one.

Quote:
I cannot see any advantage
The current source modulation is DC coupled.

My intention is to go one step towards J2..
This is SRPP after all...

FirstWatt J2

Last edited by bobodioulasso; 4th February 2010 at 07:39 AM.
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Old 5th February 2010, 08:26 AM   #719
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No answer from Chipamp but a new Aleph J-X group buy is starting.
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Old 5th February 2010, 01:14 PM   #720
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There are pics of the mini-a boards all over the forum. For 9 bucks how could you go wrong.
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