I would also like to say that Nelson fellow is a genius to be able to make something so good from 4 active parts---blows me away. Also a big thankyou to 6L6 and the rest of the folks who selflessly donated their time and effort to providing us with the parts to build this amp.
I would not think the store would want to change the board from the official one NP released.
The schematic is my release. I did not do the boards.
😎
make something so good from 4 active parts
Actually, if you have a preamp with a low source impedance you can dispense
with the JFET inputs and go straight into the transformer primary.
😎
I will looking for what you have to say after doing so. I would not think the store would want to change the board from the official one NP released. As Russell said no big deal jumping across the resistor. I assume you are going to just snip the capacitor lead and move it to the other side of the resistor.
Yes, I would rather do that than cut the trace. I wont be doing it with pots, as I don't have equipment to measure all that anyway.
This thing is fine with me as is, 6L6 did a great job. I do want to try the jumper thing, still waiting for chassis.....😕
Russellc
The schematic is my release. I did not do the boards.
😎
Sorry, I meant the official schematic and I was thinking the store boards follows your official schematic without any changes. I guess it does not hurt to try something different but mine sounds great as is but it could even sound better with the changes mentioned. I will wait to hear what others have to say before diving back in my amp.
Actually, if you have a preamp with a low source impedance you can dispense
with the JFET inputs and go straight into the transformer primary.
😎
Widest frequency response that way.
soundwise, when i started the amp again after mod, the amp cold meanwhile, guitars, strings sounded so crazy good, like exploding fireworks within a broad stage, position so good to trace, a nice micro agressivness. when amp warmed up things settled down a bit to more well behaved. i guess i still have to tweak a little. my distortion liking ears also maybe.
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With a cold amplifier (F6) the 3rd harmonic is at maximum.
The 3rd settles down when amp starts warming up.
After an hour or so, the 3rd begins to be at its lowest...
My measurements was taken after about an hour from start up.
Actually, if you have a preamp with a low source impedance you can dispense
with the JFET inputs and go straight into the transformer primary.
What would be the input impedance that way?
soundwise, when i started the amp again after mod, the amp cold meanwhile, guitars, strings sounded so crazy good, like exploding fireworks within a broad stage, position so good to trace, a nice micro agressivness. when amp warmed up things settled down a bit to more well behaved. i guess i still have to tweak a little. my distortion liking ears also maybe.
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This doesn't surprise me.
What would be the input impedance that way?
From the article:
"With the feedback, the input impedance is about 20 Kohm, at lower frequencies – but it has a fair amount of capacitance between the windings, in particular the one seeing the output voltage of the amplifier, and so it's rather limited unless you have a low source impedance. If your preamp has an output impedance of 100 ohms or less, it's no problem, but if it's 600 or 1 Kohm, then it's going to be real soft on the top end."
If your preamp has an output impedance of 100 ohms or less, it's no problem,
but if it's 600 or 1 Kohm, then it's going to be real soft on the top end."
Thanks, I didn't see that. I think the JFET input buffer has a source impedance around 23 Ohms.
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I just checked. My preamp specs say 750 Ohms 🙁
We almost need a buffer module module which is separate from the output boards so it's easier to conserve JFETs and re-use them.
We almost need a buffer module module which is separate from the output boards so it's easier to conserve JFETs and re-use them.
We almost need a buffer module module which is separate from the output boards so it's easier to conserve JFETs and re-use them.
How about the B1?
I don't know how about a plug-in module with just the JFETs on it? The rest of input circuit may be different on every F series amp?
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Why are idss of 7-8 required for F-6?
BTW, Spencer has Jfet pairs available. They are available in proper idss range (7-8), I requested 7.5. I have read that anything over 8 is likely to "burn out" in F-6, I do not know why this would be, can anyone explain?
I am not doubting this, just wondering if it is a real concern, and why this is?
Thanks,
Russellc
BTW, Spencer has Jfet pairs available. They are available in proper idss range (7-8), I requested 7.5. I have read that anything over 8 is likely to "burn out" in F-6, I do not know why this would be, can anyone explain?
I am not doubting this, just wondering if it is a real concern, and why this is?
Thanks,
Russellc
BTW, Spencer has Jfet pairs available. They are available in proper idss range (7-8), I requested 7.5. I have read that anything over 8 is likely to "burn out" in F-6, I do not know why this would be, can anyone explain?
I am not doubting this, just wondering if it is a real concern, and why this is?
It is because of the power dissipation - voltage times current - they are small devices...
Installing source resistors should take care of the higher current if all you have are the higher idss ones.
No, but I do have some sets in the mid 8 to low 9 region. I have some store sets but have no idea
Of their numbers without measuring, which is no biggie, but it looks like this may be important to know ahead of buying for F-6 builders.
Russellc
Of their numbers without measuring, which is no biggie, but it looks like this may be important to know ahead of buying for F-6 builders.
Russellc
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