help troubleshooting my tone bender MKII build

[alange5]

Hello all - first post here

A while ago I built a Tone Bender MKII clone with some mods to make it closer to a Supa Fuzz (a bit bassier).  I'd love some help trying to debug it.

Layout and PCB from generalguitargadgets.com.  Transistors are the 2-knob Tone Bender set from Smallbear.  They came labeled Q1, Q2, and Q3.


Problem:  when the volume knob is anywhere below 12:00, there is a volume cut.  12:00 is approximately the same volume as the dry signal.  As the volume knob increases past 12:00, volume is raised very slightly until it is turned all the way up, when the volume is only slightly boosted.  Same goes for the fuzz knob.  No fuzz up until 12:00, when the fuzz comes in gradually.  It only really sounds like a tone bender when both knobs are dimed.

Circuit source:  http://www.generalguitargadgets.com/diagrams/tonebender_m2p_lo_pn.gif (PNP Negative Ground)

Mods: (copied from Fuzz Central) the input capacitor is 10µF instead of 5µF, the bypass capacitor on the "attack" pot is 10µF instead of 5µF, Q2's collector resistor is 47K instead of 100K, the resistor from the base of Q1 to ground is 10K instead of 100K.  (NOTE: the Supa Fuzz uses OC75 transistors - buit I just used the MKII transistors I got from Smallbear)


NOTE: hopefully I measured these voltages right - never done anything like this before, but I followed the directions on the sticky troubleshooting thread on this page.

Unclipped battery voltage: 6.41

Battery attached, pedal turned on:  6.3V at hot output - 0V at ground output

NOTE:  THESE VOLTAGES ARE ASSUMING I GOT THE PINOUT RIGHT.  THE TRANSISTORS WERE A BIT AMBIGUOUS AS TO WHAT THE PINOUT WAS...

Q1
E = 6.24
B = 6.24
C = .08

Q2
E = 6.24
B = 6.15
C = 6.08

Q3
E = 6.14
B = 6.08
C = .75


PIC:

http://i298.photobucket.com/albums/mm264/alange5/PEDAL.jpg




many thanks in advance

[kurtlives]

First off get a fresh battery. A 6V battery isn't a good way to start up a new build with.

Check the pinout of the transistors. Use a DMM tester or ask Steve at SBE, I am pretty sure you got the pinout wrong.

[alange5]

i've got a transistor tester but i never tried it - i'll see if i can get the pinout right.  looks like that's the culprit though?

[tjmicsak]

Once you get it working I would upgrade the trannies to OC75s.

[alange5]

i've actually got some OC81's lying around that I got since I built this - what's the big difference between the OC75's and the OC81's?

[alange5]

ok - pulled out the tester - looks like i got the E and C reversed on Q1.  I'll correct it, test it out, and post back

[alange5]

corrected Q1 pinout - 1000% better.  the fuzz knob acts as it should - going from slight grit to full on spitty fuzz attack as I turn it clockwise.  the volume knob is still a little weird though...  it matches the dry signal in volume at about 9:00 (boosts nicely past that - but cuts volume below that).  Is this normal?  I've never used a Tone Bender style fuzz, but most fuzzes I've ever used boost the volume immediately.  To get the amount of volume boost I'm used to, I've got to set the volume knob at about noon - which I'm fine with - i just want to make sure it's correct

here's the new voltages:

unclipped battery - 9.55

pedal on - 9.55 at board output - 0 at ground

Q1
E = 9.55
B = 9.49
C = .41

Q2
E = 9.53
B = 9.46
C = 9.24

Q3
E = 9.33
B = 9.25
C = 1.93


Does this look right??

[Electric Warrior]

Q3's collector voltage is very low. it should be somewhere between -7,5 and -9 volts.
btw, you might want to get rid of the cap from input to ground. the supa fuzzes with the 10µF electrolytics usually don't have it.

[alange5]

how can I find out why it's so low?

[alange5]

update:  i messed around with resistor values of R6 (originally 8.2K) to get Q3's collector voltage up....  i got it up to about 7.5V - but when I engage the pedal, there is a huge huge volume drop.   any idea what I can do?   if the value of R6 is changed, does something else need to change as well?

[alange5]

bump - still trying to figure out what to do to raise Q3's collector voltage without the gating / volume drop.

any help would be much appreciated