FET Muff question

[gigimarga]

Hello,

A good friend of mine give me these days a schematic of the FET Muff and ask me if i can  to build him one.
The only initial problem for me seems to be the 3uF NP caps!!
I think i can't find something like that here, or, as i saw on a site, they will be huge (the caps was at 1000V!!!).
What can i do:

1. to use a 1uf NP instead (maximum available)?
2. to use a 3.3uF electrolytical (if yes, where to put the +?)?

Thx a lot!

[dschwartz]

for a non polarized electro, you can put two polarized in series, but oppossed in polarity like this:

-----|(--)|------

but the final value is the parallel of both so.. if you use two 6uF (?) you get 3uF.. or maybe one 4.7 and 10uF that gives 3.19uF..near enough

[soggybag]

I built one of these and I could not get it to sound good. The transistors seemed to be biased funny. So I changed the drain resistors and it sounded better, but still nothing to write home about. I used 1uf cap in place the of the 3u3 caps. I doubt this made much of a difference in the sound. It's my suspicion the FET distortion doesn't work well with clipping diode distortion.

If you get your's working well post some notes and I'll get mine out and tinker with it again. I liked the idea.

[gigimarga]

Thx you both for your answers!!

I've built another FET Muff about 1 year ago to this friend of mine using 2N5457 and it sounded like crap (very soft...a very little overdrive).
I've replaced the trannies with 2SK117 and sound much better (more overdrive).
After that i've replaced all the drain resistors with trimpots and i biased all at 4.5-5V...and a wonderful tone arise from it
The sound was something between Boss BD-2 and TS808...but much nice...very creamy and very transparent!
This friend of mine show it to a friend and that man loves it very much to use it on bass...so he give it to him!

[aron]

The FET Muff was one of my first builds. I remember that the biasing was really important as discussed. This was before we kind of standardized on the J201.

[soggybag]

I use J201s in mine. I used the default resistor values on the schematic I have. It sounded bad. So I checked the bias and realized that the bias was way off for each resisters. I removed the original resistors and put a pot in place and adjust it, then replaced it with the nearest value fixed resistor. This got the bias close to 4.5V for each drain.

I find on mine diode switches do not make any noticeable difference. Do you find they make a big difference in your build?

[gigimarga]

For me, the diode switches do not make any noticeable difference, too ...honestly, i didn't hear any difference but, at that time, i thought that it was a mistake because i used 3.3uF electro instead of NP.

[WGTP]

I suspect a 2.2uf of 4.7uf would work fine.   

[gigimarga]

I will try...thx a lot...it's a must for the cap to be NP?

[petemoore]

  I can't see the schematic. Probably if it shows NP in that or the text, there's a reason for it, such as the voltage can swing +/- at that point.