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Old 7th October 2012, 05:16 PM   #1261
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L.C., i would like to have you sentiment about this idea (May-be it was yet in your head ?) to have two different output stages technology (BJT, FETs) with the same previous stages ?
To make the things more clear, i believe between all SSA combinations, this had not be tested yet:
I presume it would need some little changes of the temp compensation in the previous stage.
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Old 7th October 2012, 05:51 PM   #1262
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L.C., i would like to have you sentiment about this idea (May-be it was yet in your head ?) to have two different output stages technology (BJT, FETs) with the same previous stages ?
I thought about it too but never tried all mosfet triple like BIGBT. This configuration would be nice to settle with exactly 50% of current splitting between the output mosfets. First Rgs could be trimmers and after finding the value to exactly split the current, can be replace by fixed resistors. The only problem would be loosing quite a portion of output amplitude in regarding to double Vgs value from the rails. Clipping can be around 5 V below the rail potential, lower efficiency in compare to regular emitter follower.

Also as you already mentioned BJT and mosfet outputs could be easily swapped to check sound signature of certain configuration or just because experimenting to find best sounding solution.
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Old 7th October 2012, 06:06 PM   #1263
Jay is offline Jay  Indonesia
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Is it possible??? The hexfet needs to be biased with sufficient current while the latfet needs sufficient Vgs to conduct. Seems impossible to achieve at the same time
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Old 7th October 2012, 06:36 PM   #1264
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Many things possible, especially if you try it in practice. I think YES it is.

Mosfet driver would practically operate at constant Id, its Rds will change just to sustain constant voltage drop on Rgs resistors.
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Old 7th October 2012, 07:19 PM   #1265
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Today i complet at 98% the soft-start/speaker protection board, so i can go foward with CSS testing in TSSA BIGBT HP. The speaker protection wil drive the TLP627 on amp board
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Old 7th October 2012, 07:49 PM   #1266
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The only problem would be loosing quite a portion of output amplitude in regarding to double Vgs value from the rails. Clipping can be around 5 V below the rail potential, lower efficiency in compare to regular emitter follower.
Right, but no problem to provide separate power rails, isn't it ?
Anyway, for experimenting, it will not be a great difference in listening level, with rails >50V. Just power numbers.

An opportunity for Nico Ras to share with us with minimal work more experiences about the sound signature of power devices, BJT, Hex FETs, MOSFETs and try different combinations of them. ;-)

I will try to find some times and courage in next months to explore that too, it really tease-me... I use to prefer the sound of power Hexfets, but this is far to be "scientific" as so many things differed in my comparison's amps.

Can be simulated too, to see if any obvious difference in virtual measurements and save time to eliminate some combinations...
Quote:
Originally Posted by Lazy Cat
Mosfet driver would practically operate at constant Id, its Rds will change just to sustain constant voltage drop on Rgs resistors.
Agree. Not to forget we can play too with gate stoppers and, as you mention, Gate/Source resistances values of the driver.
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Old 9th October 2012, 04:02 AM   #1267
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Tried quickly to sym the idea, both with BJT and FET drivers.
It makes a very efficient modulated oscillator. Driver not fast enough wuth the part i used: The collector/drain of the driver, goes the wrong way (pushed by the hp V) during the transient of square waves.
Bad good idea ?
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Old 9th October 2012, 06:27 AM   #1268
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Dear ersa191

In a glorious spirit of enthusiasm you have made a great leap forward but maybe just a little too fast, so now I only can please you to wait for Idefixes to test the prototype for functionality and than you will both cross the finish line simultaneously.

P.S. ... to ersa's post which vanished ehhehehe

Last edited by Lazy Cat; 9th October 2012 at 06:31 AM.
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Old 9th October 2012, 06:30 AM   #1269
sonnya is offline sonnya  Denmark
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Quote:
Originally Posted by Esperado View Post
Tried quickly to sym the idea, both with BJT and FET drivers.
It makes a very efficient modulated oscillator. Driver not fast enough wuth the part i used: The collector/drain of the driver, goes the wrong way (pushed by the hp V) during the transient of square waves.
Bad good idea ?
Which part of the circuit?
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Old 9th October 2012, 06:33 AM   #1270
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Quote:
Originally Posted by Esperado View Post
Tried quickly to sym the idea, both with BJT and FET drivers.
It makes a very efficient modulated oscillator. Driver not fast enough wuth the part i used: The collector/drain of the driver, goes the wrong way (pushed by the hp V) during the transient of square waves.
Bad good idea ?
At which frequency?
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