CHECK THIS OUT ...Coool ..why biasing problems??? a must build!!!

[Stephen]

This is a very good sounding pedal but there is a prolblem with the two first trans biasing ...they have trouble keeping stable and need something?
Actually germs that leak are the best believe it or not! I use AC 128 or NTE 102A or 103A

Should there be a 470 ohm resistor between the 33k and the 10k or should there be a biasing feedback like a 22k between the first base and the second emitter trans??

The trans collectors seem to work towards .800-.900mv and than the pedal sounds real bad...that is the first two!!!
As long as the second trans collector stays higher than the first, voltage that is, it is okay!! usually if it is working it will be 7.0 volts and the third collector will be 5-6 volts....The first collector should stay around 150-200mv...

This is a very cool pedal I would like to improve it!!

[birt]

this might be a nice circuit for all those "bad" germaniums :p
(i know i've got plenty)

[Stephen]

Sorry for the funky picture!

This is a pedal worth trying .....I have some low gain 60hfe with 500u leakage Ac188 THEY SOUND REAL COOL BUT THE UNIT WILL DRIFT TO THE 800-900mv.......On the first two trans ..WHY???  They need to be 150-200mv on the first collector to 7.0volts on the second collectors!!

[MartyMart]

I would remove the "Fuzz Intensity" pot at input, gtr volume pot can do that !
Feedback r may help, as you say between 22k and 100k ? ( 47k )
And the 1k from Q2 could be a 1k - 5k pot with the cap from wiper to ground ( FF style )
as fuzz control, set the 1m trim to taste and use a fixed r value ?
I would use trimpots for the collector values, pair of 20k's would do.

MM

[Herr Masel]

Sorry to interject Marty Mart, but that fuzz intensity pot - just trying to understand something - would be more "intense" at full resistance (resistor overloading the next stage or something?) or at minumum resistance (not interfering with the signal).

Thanks.

[MartyMart]

Sorry to interject Marty Mart, but that fuzz intensity pot - just trying to understand something - would be more "intense" at full resistance (resistor overloading the next stage or something?) or at minumum resistance (not interfering with the signal).

Thanks.

Good question , classic "fuzz face" has no input resistor before Q1, just a 2u2 cap, so nothing between pickup/gtr vol
and circuit ( they sound great that way but there is some input impedance issue !)
This would be the same as that 100k pot "full up" - which is min resistance.
fully down, introduces the 100k, between gtr and Q1, then reducing the "drive" into Q1
Does that make sense in a totally "non technical" way ! 

Hope so .... ( I could be wrong but that makes sense to me, a "lowly muso" )

So for me, the gtr vol pot does that job just fine ..
MM.

[Stephen]

I think the biasing problem is it needs 470 ohm between the 33k and 10k and a like 47k feedback resistor like in a fuzz face....I have played a little with this now and the two first trans are holding voltage OK!!!
this is sweet sounding hence SWEET FEETS

[Stephen]

Has anyone else tried this pedal?

[jmusser]

Somehow, I would have guessed Marty would suggest trim pots. Really, with all the inconsistancies, I'm sure how the designs ever got by with fixed resistors. For another thing, you can tweek different tones out germaniums by being able to adjust the collector resistor.

[JHS]

The BIAS for the base of TR2 is set by the collector voltage of TR1 and I think the 33k cause the problem.

First I would set the base of Tr1 to a difined BIAS (470k/47k divider conected to base, aka Rangemaster).

Then I would add a AA114, OA90 or similar on every transistor beiween base and emitter for temp. stabilization and a 1k trimpot as emitter R to Tr1 (colector voltage adj.).

Maybe a neg. FB-loop from TR2 to Tr1 can stabilize TR1 too.

I would drop the 9,3V Zener, supply voltage is only 9V or arr. 8-8,5V at the Zener diode , a 4003 will work fine as as protection diode.

JHS

[markm]

This does look like an interesting circuit.
Anyone have a finalized working layout for it yet?

[Stephen]

This is a very interesting SOUNDING circuit!!   
Very easy to breadboard in an hour
Watch out for the second transistor problem as it will need to stabilize and be.. I find to stay at 7 volts....

OF COURSE USE SOCKETS and watch the voltages.

Useing low gain germaniums is GOOD!!!!

When you get it to work it is SWEET

Go either PNP or NPN just change the cap orientation.

A Stellan schematic.........

[Stephen]

OKAY NOW AFTER ALL DAY........


DO yourself a favor and put a feedback resistor between the base of the first tran and the emitter of the second ....22K is what I find......this will keep the voltages steady   .Everything else is OK!

BUILD this with your germs either type!!!

This is a real nice fuzz .