Papa did extensive testing with both and his observation was his listeners liked the mosfet version better but it will be interesting hearing your observation as well. I think he put the connection of the 1000uf capacitor for the mosfet version exactly where he wanted it but I could be wrong, it has happened to me before. If he doesn't comment it is because he sees no need to.
Are you talking about the Diyaudiostore's boards here? did you just reroute, or some different values (different from store schematic) as well? You are not using the 240 devices, right?
Russellc
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It should be with the caps returned to the bottom of the source resistors. Otherwise, the difference
in value between the two source resistors would make no sense, and would not enhance the second
harmonic as NP prefers.
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Yes the DIY boards,I have rerouted,am using IRFP240 and 0.47 and 0.57 ohm source resistors.
The way the pcb is designed the negative of the 1000uF cap.is between the source pin of the Fet's and one end of the source resistors.With this configuration you can't adjust 2nd harmonic by having the 2 different values of source resistors (0.47 and 0.56). The harmonic structure is dominant 3rd, thd is very low btw.The harmonic stays the same as having a 0.47 ohm source resistor on each Mosfet. If you re route the negative of the 1000uF cap. to the bottom (not the Mosfet source end) of those resistors now the differences of the source resistors comes into play and the amp has dominant 2nd harmonic which some people like more. Thd is slightly more but still low. Now you can play with resistor values and adjust to suit your tastes. I converted mine and like it much better , one of my previous posts explains what I hear as a difference.
Thank you. Mine is store boards and 240 devices. I will definitely try this, looks like it could be easily reversed if one wanted to. I tend to like dominate 2nd, so very likely will prefer it. The speakers it will drive have a compression driver/waveguide top so I don't need any additional "in your face" effect! Thanks again,
Russellc
I use the DIY F6 schematic, but not the store boards. I also use a diamond buffer instead of the jfets, but that does not make a significant difference in the relation between 2nd and 3rd harmonics.
Could you post some test charts of the harmonic structure of your F6?
With my boards i have a clear dominant 2nd, whitout any tweaking to the circuit (except the diamond buffer).
I use the DIY F6 schematic, but not the store boards. I also use a diamond buffer instead of the jfets, but that does not make a significant difference in the relation between 2nd and 3rd harmonics.
Could you post some test charts of the harmonic structure of your F6?
With my boards i have a clear dominant 2nd, whitout any tweaking to the circuit (except the diamond buffer).
This is with a 4 ohm load ( stacked advent sim )
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Hasn't this been previously addressed?
Post 6202 shows 2 schematics, with and without degeneration.
If you want to adjust the 2nd harmonic you can tap off a pot (10 to 50 ohms
or so is good) across either or both of the 0.47 ohm resistors shown and
attach the wiper(s) to C1 and/or C2.
To minimize degeneration (if that's what you're after, one of these will have
the wiper set to the Source pin and the other will be adjusted slightly away
from the Source pin.
If you would like some degeneration all around, then both wipers head
away from the Source pin.
Glad you're happy with the result. I haven't had a chance to perform the mod as yet (been a bit sick last few days).
Hasn't this been previously addressed?
Post 6202 shows 2 schematics, with and without degeneration.
If you want to adjust the 2nd harmonic you can tap off a pot (10 to 50 ohms
or so is good) across either or both of the 0.47 ohm resistors shown and
attach the wiper(s) to C1 and/or C2.
To minimize degeneration (if that's what you're after, one of these will have
the wiper set to the Source pin and the other will be adjusted slightly away
from the Source pin.
If you would like some degeneration all around, then both wipers head
away from the Source pin.
What we are addressing is that the DIY store boards are built around the non degeneration schematic but show different value source resistors leading dummies like myself to believe the harmonics could be adjusted when in fact they can't without cutting traces and re wiring. I didn't understand this.We now know this and can modify things to suit our tastes.
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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.
It's easy to build the amp "the correct way" with the current board in doing a new build. My guess however is that a lot of people (newbies like me) will not catch these posts and build it the wrong way (same story as the famous 9.1V Zener which hasn't been updated in the build guide).
With already soldered boards using the existing parts it's a bit more annoying... I guess easiest is to just leave the capacitor in place, cut the PCB trace to the one end of the resistor with an exacto knife and wire a jumper to the other end
Pots would be nice but you need a distortion analyzer of some sort to get the benefit. Quick and dirty (and it works from my mod experience) is to cut traces and jumper and use 0.47 and 0.56 ohm resistors.
all traces to the capacitor are quite thin/narrow and can easily be cutted, unfortunately one trace is on top and hidden by the capacitor itself, so this is the only one to be unsolderd. after cutting the traces, just put wire from -side of cap to the resistors bottom side.
at least for me it turned out to be easiest way and caps don´t "hang around" on one leg
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.
at least for me it turned out to be easiest way and caps don´t "hang around" on one leg
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.