HELLO RUNOFF [AND ANYBODY ELSE]

[brian wenz]

Hello Hello--
  Has anybody tried a Multi-Face circuit with two BS-170s??
I have been using Jack Orman's Mos-Face circuit for awhile [one BS-170 in Q2] but don't know how two 170's would work.
Thanks-
Brian.

[b_rogers]

i cant seem to get a mosfet to work in q1 of my multiface..earlier i got a 2n7000 working in q2 and it sounded great.

[brian wenz]

Hello Hello-
   Yeah, I can't get it to work with two BS170.. ........maybe some "creative biasing" for Q1.  
 I have two different "Mos Face" circuits that I like for different reasons.  One is the stock circuit and the other has  Vox Tonebender values [takes alot of the "wooliness" out of it .]
Anyway, there must be some way to get Q1 up and running.....
Brian.

[b_rogers]

maybe a bias pot intead of feedback resistor? evidently b tremblay got them to work, maybe he will give some suggestions..

[brian wenz]

Hello Hello--
 Yeah, I'm waiting for the Runoff guys to chime in!
I keep looking at that 10K..............oh well, I', not at home now, so it's gonna hafta wait.
Brian.

[donald stringer]

http://runoffgroove.com/multiface.html  is this the schematic you built, He lists the 2n7000 in q1 as one of the options. You might have the 2n -7000 pin out wrong. Thats not uncommon, people do it all the time. But it will work. It sounds great. Hope you get it running.

[brian wenz]

Hello--
 Yes, that's the schematic.  
I'm trying to use BS170 in the circuit, not 2N7000, and I can't get it to work [see my original post].  I've got BS170 in Q1 and Q2  and the pinouts are correct........must be something about getting Q1 biased properly.
Brian.

[b_rogers]

i can take the 2n7000 that is working in q2 out and try in q1 and nothing...even messing with the trim pot.

[brian wenz]

Hello B--
  Have you tried changing any res. values on Q1 to bias it differently??
Brian.

[b_rogers]

no i havent really messed with it other than popping one in there. i did my multiface on a radioshack ic board and it looks all pretty so i am gonna leave it alone unless it stops working!...

[brian wenz]

Hello Hello--
 Sometime I just wanna stick with my  1-tranny treble boosters  !!
Brian.

[Gary]

Brian,

What are your pin voltages?  It seems the first mosfet isn't getting enough votlage on the gate or maybe the drain is getting too much.  You can try altering the drain resistor on Q1 to help you out.  If you can take voltage readings on the pins, that would help.

Sorry it took so long to see this post.  I've been enjoying the youngster over the holiday break.

[brian wenz]

Hello Gary--
  Yeah, I figured I'd have to mess with the Q1 res. values.   Crap, this means heating up the soldering iron...........!
 Alright, I put a 22K instead of the 10K in there and it fired up great.......except that now it's  VERY noisey with the BS170 's in both positions......if I put a regular si tranny back in Q1 the circuit is pretty quiet.   Maybe some more "discreet" biasing is called for...
Any thoughts??
Thanks-
Brian.

[Gary]

Brian,

That's the inherent noise in the mosfets.  Maybe we could take a lesson from Joe Davisson and use P channel mosfets?  He says they don't have as much inherent noise as the N channel types.  It would be worth experimenting with, if the noise is too high.  You may find a good setup is a mosfet in the first slot and a Si BJT in the second slot would sound similar with less noise.  I would try as many different combos as you can to see where you get the most desirable sound with the least noise.  Several different combos of trannies can sound very similar.  Tim's "Many Faces of Fuzz" article was what the Multi Face article was written about.  Tim shows several combos that would be great to try.  One of those setups will give you the sound you are looking for.

Best of luck!

[brian wenz]

Hello Gary--
 I've built up two different variations of Jack Orman's Mos Face with great results [regular tranny in Q1 and mosfet in Q2].   I was real curious about trying two mosfets but if noise is an inherent problem  I'll just try some jfets instead.  Thanks for the tip on the mosfets......this will save me hours of frustration trying to jam a square peg into a round hole!
Brian.