I use IRFP9140 in my output stage. A single pair in balanced configuration, common source mode with a CCS between source and voltage rail (its just a high power LTP actually). As my speakers are 4 ohms I need lots of current - So I run 4.5 amps thru each device. And I use big heat sinks! And my CCS (also IRFP9140) has 9 amps going thru it. As long as you design it right, a single pair works fine. My amp has been running for over 10 years, still with original mos fets.
Well, the other channel didn't go so well. I can get bias across the source resistors but dc offset stays at 0 regardless of pot setting. In fact, I can get negative (!) voltage across the source resistors when turning p1, dc offset remains at 0. Mosfets not getting warm even with .5V across the source resistors.
Any ideas what's going on? Other channel works fine.
It looks like this...
Attachments
0.5V across a 0.47 ohm resistor means there is ~1A current through it. Whether it is going through the MOSFET or not is a different matter, though I can't see where it would go unless you had a gross wiring error, like swapped MOSFET polarity. Are the feedback resistors getting warm? Does moving the pot affect the bias?
Moving the pot effects bias but not DC offset. Both pots effect bias but DC offset is always zero. I'll double check everything again later tonight. Source resistors not warm. I didn't check the feedback resistors.
Guess I should check my multimeters too....maybe it's the leads or something.
Guess I should check my multimeters too....maybe it's the leads or something.
Is a 600va transformer and six 33,000uf caps sufficient for a 24V rail/2 pair setup biased at 2.5A?
I am only asking because it used to take the power LEDs a minute or two to dim after shut off. Now, with more pairs of mosfets and bias the LEDs go dark immediately after turn off which leads me to believe the circuit is really drawing a lot more power now.
I am only asking because it used to take the power LEDs a minute or two to dim after shut off. Now, with more pairs of mosfets and bias the LEDs go dark immediately after turn off which leads me to believe the circuit is really drawing a lot more power now.
Well, got to have a good listen tonight at 2.3A bias. Speakers are KEF R700 3 ways w/3.2 ohm min. Most of the audioband is 4-6ohms.
The old setup was a pair of IRF per channel, 1.8A bias. The new setup is 2 pairs 2sk1530/2sj201 per channel at 2.3A total bias. Not really a fair comparison due to the different mosfet and higher bias but here is what I hear:
The 2 pair Toshiba setup is much smoother, more "black". Highs are smoother and less gritty. Greater depth. Bass is suprisingly not that different from the single pair setup. It seems tighter and more true (better quality) but I wouldn't say it has more bass. Perhaps less bass bloom.
But mostly it feels like the multiple pair version is more "in control"...perhaps this is what Nelson means by more relaxed. The single pair F5 would sometimes get a bit spicy, which is good and bad. It's perhaps more exciting but less refined sounding than the multiple pair iteration. I have noticed that the multiple pair version sounds more poised at high volume levels. I also like the cleanliness in the highs (this could be due to the toshibas) but overall the multiple pair version just sounds more refined and silkier and put together at the expense of some of the emotion of the F5.
But I may be overstating the differnces. It's not a night/day difference or like a different amplifier. Just a different flavor maybe.
The old setup was a pair of IRF per channel, 1.8A bias. The new setup is 2 pairs 2sk1530/2sj201 per channel at 2.3A total bias. Not really a fair comparison due to the different mosfet and higher bias but here is what I hear:
The 2 pair Toshiba setup is much smoother, more "black". Highs are smoother and less gritty. Greater depth. Bass is suprisingly not that different from the single pair setup. It seems tighter and more true (better quality) but I wouldn't say it has more bass. Perhaps less bass bloom.
But mostly it feels like the multiple pair version is more "in control"...perhaps this is what Nelson means by more relaxed. The single pair F5 would sometimes get a bit spicy, which is good and bad. It's perhaps more exciting but less refined sounding than the multiple pair iteration. I have noticed that the multiple pair version sounds more poised at high volume levels. I also like the cleanliness in the highs (this could be due to the toshibas) but overall the multiple pair version just sounds more refined and silkier and put together at the expense of some of the emotion of the F5.
But I may be overstating the differnces. It's not a night/day difference or like a different amplifier. Just a different flavor maybe.
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