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Old 23rd June 2002, 11:06 PM   #31
Dave is offline Dave  New Zealand
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From what I remeber Mr. Self refered to the effect as gm doubling which occurs if you bias a Class AB output stage at too high a current. The result is increased cross-over distortion. He was refering to BJT devices though. Would it effect MOSFETs?
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Old 24th June 2002, 09:50 AM   #32
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Originally posted by P.Lacombe

High voltage Hexfets exhibit poor linearity and high Rdson, and are inusable for high end audio.

Is there anything documented regarding this? I would like to read about other peoples experiences. They sound alright to me though. Maybe I'm just easy to please

High Rds on? What about IRFPS60N50C TO-247 max with 500v 60A 390W **0.038** ohms? Doesn't sound too high to me. Have you actually tried them yourself or is this just hearsay? I don't have a pair of them to try out myself, but as always a bird in the hand is worth two in the bush. I do have six IRFPS43N50K's in my grubby paws. From memory they are TO-247 max 500v 43A 0.078 ohms **540w** @ 25 deg C. Wouldn't that make a great class A amp?

I hope this isn't getting too off topic but has anyone ever experimented with using *switching* IGBT's for linear audio power amps rather than complementary pairs that seem to be audio specific? I have a pair of 600v 63 amp 500-and-something watt igbt's but they have a threshold voltage of about 9 volts! The transfer graph looks pretty bent too but we'll see what a little feedback can do.

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Old 24th June 2002, 02:34 PM   #33
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Rdson is a totally irrelevant parameter if we don't talk about the Hitachi types (1.7 ohms is high!). Rdson below 100-200 mohms are of no importance as long as you don't need low saturation voltage.
/Per-Anders (my first name) or P-A as my friends call me
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