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Old 7th April 2001, 02:55 AM   #11
blmn is offline blmn  Brazil
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Rljones,

Check the gate capacitances of both mosfets (N and P) in the databook and you you see they are different. It explains why did you have to put the capacitor in one side only.

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Old 9th April 2001, 08:18 PM   #12
Koy is offline Koy  Czech Republic
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Thank you for email. I completed my knowledge about current mirror. As far as I am able to understand it could work as local feedback, keeping current ( voltace across input MOSFEts and DC offset) at the same level.
Do your results come only from simulation? Did you notice any differrencies in sound? I made some simulations with Aleph 3. This amp appeared a little slow ( SR round 15V/us). What is experience?
Did you think how the current source (by signal end MOSFEt) affected the sound? best regards koy
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Old 11th April 2001, 08:41 PM   #13
rljones is offline rljones  United States
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Geoff-

I'm afraid I didn't look at the patent pages (I don't understand them anyway). As for the Aleph 4 nomenclature, I wrote my comment from another computer that has a different set of downloads. I looked over the ones on this other computer and you are correct, it doesn't match what I wrote. In any event, the R34-C6-R31 are the resistor-capacitor-resistor that is the feedback from the output to the upper current source. Using a copy (rev 0, 1996) of the Aleph 5 schematic, these are R19-C10-R21 for transitor Q5. The R30 I referred to is R17.

blmn-

I only used N-channel devices (IRFP240) in both sides. There are no P-channels in the output stage of the Alephs.


Koy-

I think the sound is more dynamic and how can I say it otherwise: smoother sounding. If the slew rate came down to 15V/us that still is plenty fast. (NP himself is the one who, if I'm not mistaken, calculated that music only slews at about 1-2V/us.)

As for the current source affecting the sound. Well, all I was saying is that the upper CS _measureably_ affects the sound by effectively turning the amp into a class AB at greater drive levels, especially at greater frequencies (most noticeable above 6kHz with my measurements). As for sonically being noticeable, I can't say. In the past, we did notice a definite modulation of the source upon the output with the Zen amp. This is because the feedback is not isolated from the input and so some preamps will interact with the Zen: driving the input and also modulating the feedback and re-driving, if you will, the amp. By having an input stage (Aleph), the preamp is better isolated from adversely interacting with the output stage. (As an aside, this should not be an issue with SOZ, as there is not feedback loop.)

Robert
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Old 12th April 2001, 02:46 AM   #14
blmn is offline blmn  Brazil
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Rljones,

Sorry, I made a mistake because I read you made a symmetrical "design" (not layout as you really wrote). I don't know this design very well. I remember now it was the same that I made an analysis in another thread. Since you have different functions for the devices (current source and modulator), I think it would be a good starting point to understand why you needed to add capacitance just for one gate.

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