FF/TB MKII test circuit build report & PCB

[yeeshkul]

Hi guys, i built this circuit to test my TB/FF units before i solder them up.
It lets you
- adjust the resistors for particulat Ge transistors
- play with the voltages/currents to find about what depends on what
- play with the additional, seldom used caps and trims
You can do the same thing on breadboard, but this one doesn't have that many parasite values as the breadboard does and i simply find it comfortable.

PCB (about 10.3 x 9.7 cm)

http://www.hoho.cz/osobni/FF-TBtesting-PCB.gif

PART LAYOUT

http://www.hoho.cz/osobni/FF-TBtesting-parts.jpg

Notes:
- the blue dots mean sockets
- i used the round, horizontal Piher Spain trimpots (about 1cm dia.) and soldered thin lugs on their legs so they fit in the sockets
- the trimmers should socketed so you can take them out and measure the values you've set
- there are additional pads on the PCB for other trims (cerment)
- IN/OUT sockets are the type that can be soldered right into the PCB
- POTs are soldered into the PCB
- the DC socket has "+" on the shield
- if you want to play with Si circuit switch the battery lugs / DC polarity

HAVE FUN

   
http://www.hoho.cz/osobni/FF-TBtesting1.jpg
http://www.hoho.cz/osobni/FF-TBtesting2.jpg
http://www.hoho.cz/osobni/FF-TBtesting3.jpg

[petemoore]

  Pretty beefy looking !
  You've taken some time to get this looking the way it does, very good !
  ...Everything you wanted to know about a FF but were afraid to experiment with !

[yeeshkul]

I've been playing with it since the morning today. I found out a few new things about the Tonebender behaviour i haven't realised so far:

1. if i use 10k bias resistor for the Q1 base, the unit gives no more fuzz than Fuzz Face. When i push the trimpot up to 100k (= base voltage up) there is a hell lot of fuzz coming out of it in comparing to FF (easy comparison due to the FF/TB switch). So simple .
2. even a small starve/filter resistor (divider on the battery) helps with the overall volume a lot - because it works like a common collector resistor for all 3 stages.
3. using 47k resistor (instead of 100k) for Q2C helps a lot with easy biasing Q3C(!) wia 25k trimpot. If you use 100k res. you can have troubles to push the bias down to 4.5V.
4. pushing bias of Q3 to 6.5-7V doesn't affect the sound as far as i can judge and helps with the overall volume.

[noelgrassy]

Holy Crap! Yeeshkul, I hope this is linked to a fatter Mk II thread. If one exists.

I appreciate all the attention you've given this circuit. It's a badass fuzz when you
get a good one. Your work seems to have isolated the quirkiness of the originals.

[bluesdevil]

Very cool, thanks for sharing.

[yeeshkul]

Thanks guys. There is a lot of mojo crap and myths around TB and FF circuits. This way you can skip it and adjust the circuit to the transistors you have before you stitch up the real unit .

[any]

Thanks guys. There is a lot of mojo crap and myths around TB and FF circuits. This way you can skip it and adjust the circuit to the transistors you have before you stitch up the real unit .

How do the trannies sound? (recognised the 2SB's in the pics.)

Cheers,

[Gus]

I did something like this years ago I will give you a design hint.  IMO Trim pots should be about in the middle of the rotation at there most likely to be set point this way you have a good adjustment range.  Can't always do exactly 1/2 but try to get close.
   I did not trace you drawing so I don't know if you did this.  I find schematics to be better for understanding.

In my Si FF board with adjustment trims I used a fixed min value resistor for part of the adjustment resistor.
The feedback I used a 33K fixed with a 100K trim (33K to 133K) middle about 83K
Q1 collector a 10K fixed and 50k trim


You need to be aware of max power dissipation of the transistor, say by a mistake you had the trim at 0 ohms in a collector leg and emitter resistor at 0 and the transistor was full on?