I am using the newest store boards but each channel has a different pcb layout.
Of course - that way both the signal transformer can be at the rear and the transistors on the bottom.
That's why I stated you may have a couple of issues on the other board, but not on the one Russell showed in his photos.
What is the input impedance supposed to be for the diyaudio F6? Wouldn't it just be 47K since its 47K||1K+(some high impedance of the JFETs) at the input? I'm curious because the pdf for the production model indicates that it should be 100K but is this simply different for the diy version? Also does this have any effect on the input sensitivity (i.e. would it effect the 2.83V necessary to drive the F6 to max output?) The reason I ask is because I am having some difficulty getting it to full output with my current preamp so I am trying to figure out why.
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practically value of gate-leak resistor , in this case 47K
put there whatever you find practical for your needs
put there whatever you find practical for your needs
The F6 doesn't have that much gain - it needs closer to 4V for max output, IIRC...
So does the value of the gate-leak resistor affect the input sensitivity? It seems like the ratio between the 47K and 1K near the input would have an effect or am I mistaken? edit: actually now that I think about it isn't the 1K kind of irrelevant since the input impedance of the JFETs is so high?
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Not unless you have a really weedy preamp that can't drive an easy load.
The 47K tells the Jfet input where it lives in the world in respect to ground, and sets input impedance - you may halve or double it with no ill effect.
The 1K is a gatestopper to help against high frequency oscillation.
The 47K tells the Jfet input where it lives in the world in respect to ground, and sets input impedance - you may halve or double it with no ill effect.
The 1K is a gatestopper to help against high frequency oscillation.
Thanks, that will save me a lot time trying to mess around with the input impedance. I'm pretty sure the problem is simply that I thought it only took 2.8V to drive it to full output... It does say that in the manual but then again that used different output devices, if that matters.
Anyone tried adjusting R1 & R2? Is there a minimum value for them with the mosfet version? On the SS version I settled to leave R1 to 0.043 & R2 to none...
Just build BA-3 preamp. Not only is it dynamite as a preamp, it has plenty of gain. Solved my F-5 gain "problem" which is almost the same gain as F-6. It will even "drive F-4" LOL
Russellc
Russellc
Hey Russellc thanks for the advice. Have you tried the JFET BOZ? Do you think it might be good or should I go straight for the BA-3?
Yeah I'm wondering what minimum value Nelson thinks is the bleeding edge for fearing nothing amplifier builders ie using IRFP240. None of this baby stuff "Oh I'm scared it might thermally run away".
Hahaha
Its about 2.5V but 6L6 was saying that it needs up around 4V for full output. I am using a pretty simple op amp based pre that I would really like to replace so this would be a good time to decide on some circuits to try out. The BA-3 sounds nice but I'm having trouble finding a single ended version. If there is one can someone please point me in that direction?
You must have inefficient speakers.
I have the other problem. Too much gain. Hahaha.
Most of the time I run unity gain F4
I have the other problem. Too much gain. Hahaha.
Most of the time I run unity gain F4
I've been thinking of using 0.2. That could be too ambitious but doesn't hurt to try.