RG- Keen's layout for Mini tubes 2- preamp!

[Jakeb]

I've made the mini tubes 2-preamp from RG-Keens layout and couldn't get it workin right. Signal seems to die in somewhere after the volume pots, before those 470k ohm resistors. I think F5 is upside down, when compared to the Jack's original schem. Lead channel's volume pot is 100k in the original schem, as RG's layout has 1M.

The converter section is not working also, and I think it's because I have only 7660's and 7662's available, as RG recommends LT1044A:s.

Could anyone help me with these?[/b]

[Mike Burgundy]

the 7660/2 should work just the same as a 1044, except that it won't let itself be "over-clocked" and you run the risk of some whine in the audio path. See GEO for details.
Check the pinout of the Fet - signal should come into it from the volume pots via the 470k at the gate, output and supply at the drain, and the source through a resistor to mass.
Looks like F5 should be flipped.

[Jakeb]

Thank you very much for your help. I have flipped the F5 and now the signal goes throught, but the clean mode has a horrible distortion in it and the clean channel volume is on it's full blast, I have no control over it... May there be a problem in the switching network even if the led's are working fine.

I really have some serious whine with my 7662 chip and I may have to use external power for this pedal. (the original converter board doesn't work at all if loaded, and it is very unstable)


I have used 2N5457's for the fet's but I think the problem is not in those?


- J. -

[Jakeb]

Thank you very much for your help. I have flipped the F5 and now the signal goes throught, but the clean mode has a horrible distortion in it and the clean channel volume is on it's full blast, I have no control over it... May there be a problem in the switching network even if the led's are working fine.

I really have some serious whine with my 7662 chip and I may have to use external power for this pedal. (the original converter board doesn't work at all if loaded, and it is very unstable)


I have used 2N5457's for the fet's but I think the problem is not in those?


- J. -

[Mike Burgundy]

first I'd take out the switching transistors and short out the ones that should be shorted for one channel. Get that working correctly, than wire for the other channel and get that going. Then wire the trannies back in and get the switching working.
There's a very good chance there's a wiring problem off-board, although I haven't really checked the PCB thoroughly. If the clean ch. doesn't react to the volume pot there's definitely a wiring problem.
I might etch one and see.

[Jakeb]

Thanks again, I'll check that out.

There was a wiring problem in the volume pot and there might be another, I'll check it when I have more time...

- J. -