TB MKII problems, low voltage on Q3??? (UPDATE)

[iBANEZAce]

I read through the posts here and at Harmony Central about this pedal and figured I could still use the help, so let me know what you guys can do:

Ok, finished the Tonebender MKII build last night, hooked it up and got a really wierd sound, barely any distortion when plucking strings normally, but at a certain cutoff point the sound would get very loud, with mega distortion/clipping.

Here's the details:

* Used Fuzz Central layout/PCB and parts
* Used GGG schematic for PNP, Positive ground to check my work
* Made the 20k pot modification in place of the 8k2 resistor off of Q3 (set currently at 8.2k)
* Using transistor set from SmallBear - Marked: 57, 65, 131 (Q1 --> Q3)
* Using 9V wall wart for power
* Wired using 3PDT for true bypass

Here are my voltage readings...from reading the other threads I definately know that my Q3 collector is not getting enough voltage (should be about 4.5V/half the supply, right?)

Q1:
C: 8.52V
B: 52mv
E: 0V

Q2:
C: 165mV
B: 53mv
E: 0V

Q3:
C: 70mV
B: 165mv
E: 62mV

Do any of these other readings look wrong???

I took my time building this, but after I heard the horrible tones it was making I went back through checked the wiring about 10 times, which I am sure is correct since the switching works and I am getting the distorted signal, LED lights up correctly,etc.

I then checked for cold solder joints, fixed any that looked problematic. Checked for bad traces, etc. but found nothing.

It seems that from the sound I am getting that the transistors are misbiased?

Hopefully someone with some working knowledge of this pedal can help me out. Thanks in advance!

[petemoore]

Power supply [?]...
 Analog Kid's been going through the same or similar TB biasing issue...read into that recent thread...
 Something I do is...use a known working FF to test Q2 and Q3...then I know I should have transistors that'll probly work ina TB
 Use transistors known to work in a FF for the TB.
 So it's like I test transistors for TB in a FF I know works, and check TB with transistors I know work...one hand 'washes' the other.
 There's a whole slough of things that can be 'wrong' in a Tonebender, I've had them work for a little while, mine needs work again last time I tried it...was working great for about a week. Must be cause it snowed.

[iBANEZAce]

Yeah, but I get a sound that I can sort of "dial in" with the 20k pot while I'm playing it...but I know it still is totally out of whack, it clips and is gated, loud "popping" sounds...almost like its trying to fuzz but it is misbiased?

Another thing I noted is that I made 2 resistor value changes from the SmallBear schematic to do the fuzz central modified version of this pedal.

Resistors that differ:
R1) The 47k leading into the collector of Q2, I used a 100k per Fuzz Central instructions.

R2) The 1k resistor leading into the 20k pot (or 8k2 if you didn't do the pot mod), I have a 470 ohm resistor there.

Would either of these changes matter?

Or is it more likely the transistors???

Or should a go ahead and do these changes to match the SmallBear schematic???

[MartyMart]

Yeah, but I get a sound that I can sort of "dial in" with the 20k pot while I'm playing it...but I know it still is totally out of whack, it clips and is gated, loud "popping" sounds...almost like its trying to fuzz but it is misbiased?

Another thing I noted is that I made 2 resistor value changes from the SmallBear schematic to do the fuzz central modified version of this pedal.

Resistors that differ:
R1) The 47k leading into the collector of Q2, I used a 100k per Fuzz Central instructions.

R2) The 1k resistor leading into the 20k pot (or 8k2 if you didn't do the pot mod), I have a 470 ohm resistor there.

Would either of these changes matter?

Or is it more likely the transistors???

Or should a go ahead and do these changes to match the SmallBear schematic???

I went with the "small bear" version exactly, using a "matched" pair of AC128's for Q2/Q3 and my Q1 was about hfe 58 and not "leaky"
It was a vero-layout which I'll post this week, ( that may help? ) perhaps I got lucky, but it fired right up and sounds fabulous !
PNP Fuzz's can be a bugger though, even if your soldering/layout is perfect they can be tough to "tune in" and can change when "warm".
My straight "Fuzz Face" changed after "burning in" for a few days and now has another set of AC128's in it !!!!
It just went "splatty" and couldn't be used at all.....

Cheers,
Marty.

[R.G.]

Q3:
C: 70mV
B: 165mv
E: 62mV

Q3 collector is below Q3 base - that means that the transistor is saturated, and cannot amplify. That's clearly a problem.  The only real question is - why is it saturated?

It is possible that the resistors feeding it are open. Can you measure the voltages on the pins of the resistors/pots leading from power supply to Q3 collector and report back?

[iBANEZAce]

Thanks R.G. - you were exactly correct...  

Turns out that MOUSER packaged a whole baggy of 470K ohm resistors in a 470 ohm package! AARRRGGHH!

So I had a 470K in place of the 470...wow, a little off huh...why I didn't check the resistors in the first place is beyond me, but those are the simplest parts, right?

Well, here is where I stand...got Q3 getting exactly 4.5V, the effect sounds good, but I get an INTENSE humming sound as I turn up the VOLUME pot, when it is all the way down there is no hum but as soon as it goes up a little the hum starts and gets really loud by the time the pot is at full...almost louder than the guitar and effect.

Eveything else seems to be working correctly.

Please, could someone tell me how to fix this???  :?: