Just thought i'd throw this out there. I had re biased my F6 from 1.3A to 1.5A to see if there was a difference in sound. My speakers are around 87 db sensitivity, 2 ways. I found the sound much darker and compressed sounding,sort of like a veil over it all. I changed back to 1.3A and the sound seemed to open up again. The sound stage wider and a quicker more airy sound overall.The F6 has the IRFP240's and the output degeneration mod. Could this be some sort of sweet spot or am I going nuts?
Do you have the trimpot degeneration mod or fixed resistors?
It may require readjustment of the amount of degeneration.
It may require readjustment of the amount of degeneration.
I've got fixed resistors. Curious how that affects the sound,I have no idea. Probably something Mr. Pass plays with.
I've got a couple of sims at the different biases.I think i'll poke around and see if there is something there. I do know that the distortion drops a bit with the higher bias according to Spice,both 2 and 3 go down by a few db.
Describing sound is difficult
but when I raised the bias on my F6 (vanilla build as schematic.)
I was not as happy with the sound.
At standard bias (0.6v / 1.3A)
It was lighter and more organic
higher and it was going tighter with a stiff sound that I did not like.
I must admit that this was the point that I touched two points with a probe and let the magic smoke out of one board!
So after re-build it now sits happily at 0.6v bias.
but when I raised the bias on my F6 (vanilla build as schematic.)
I was not as happy with the sound.
At standard bias (0.6v / 1.3A)
It was lighter and more organic
higher and it was going tighter with a stiff sound that I did not like.
I must admit that this was the point that I touched two points with a probe and let the magic smoke out of one board!
So after re-build it now sits happily at 0.6v bias.
Colin---I agree with your assessment.I'm curious what people had theirs biased at as some had commented on dull and lifeless etc.
My immediate idea is that with an increase in current you also get an increase in gain and an increase in negative feedback. I seldom like the sound of negative feedback.
It tends to suck the life and soul out of music-reproduction.
Cheers,
Johannes
It tends to suck the life and soul out of music-reproduction.
Cheers,
Johannes
The difference in feedback at higher bias is like a decibel in this case - within
the range of transistor tolerance, so I don't think that's it.
the range of transistor tolerance, so I don't think that's it.
I am interested that someone else could hear a difference with higher bias.
Also that it seems that we are trying to describe the same things.
It would be fascinating to see and compare measurements and different bias.
Spectrum response sweeps and distortion analysis ( including harmonics)
I do not have the equipment, or knowledge to do this
Any volunteers with an F6 and the gear?
Also that it seems that we are trying to describe the same things.
It would be fascinating to see and compare measurements and different bias.
Spectrum response sweeps and distortion analysis ( including harmonics)
I do not have the equipment, or knowledge to do this
Any volunteers with an F6 and the gear?
I currently run my F6 at 550 mv bias at 24.5 v , i have tried up to 700 mv , i did not found any real big change in sound ,only the distortion that goes up a little bit ( made some REW mesurements ) , so I stay at 550 mv ;-)
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All I have is the Ltspice sims and my F6 of course but no analyzers.I found the distortion in the sims drops with increase bias. From .05% @ 1 watt 1.3A to .04% @ 1watt 1.5A.
to my experience the F5 was much more sensitive to bias change. More oomph and solid deph increased with more bias.
With the F6 I went back to "normal" bias. Stage is better "deeper" with F6 from scratch, just missing the incredible "tintinabulation" of the older bro.
Not shure if it has even to do with distortion.
tnx btw for both amps 🙂
With the F6 I went back to "normal" bias. Stage is better "deeper" with F6 from scratch, just missing the incredible "tintinabulation" of the older bro.
Not shure if it has even to do with distortion.
tnx btw for both amps 🙂
Do you have a 50 mOhm resistor and prepared to try something.
I think you might like the result.
Try it like this on one channel and let me know how it sounds. You'll need to rewire it slightly. M1 has no degeneration, and M2 has a small amount of degeneration.
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yup
that proven with ZAP (Generg's Zen Amount Pot , 10-20R pot placed across M2 source resistor)
that proven with ZAP (Generg's Zen Amount Pot , 10-20R pot placed across M2 source resistor)
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