Tonebender MKII trouble... only hiss noise.

[ChuckZilla]

Hey guys,

I'm working on a tonebender MKII clone. I have been working on it slowly for about 6 weeks.
I'm using russian germanium PNP transistors. They are GT308v transistors. Tested them with my DMM. The hfe's are Q1-71, Q2-71, Q3-102.
At first, the biases were all messed up. I added a trimmer to Q1's collector.

My transistors voltages/biases:

Battery= 9.41v

Q1c = -8.10v
Q1b = 0.00v
Q1e = 0.00v

Q2c = -0.79v
Q2b = -0.19v
Q2e = 0.00v

Q3c = -4.72v
Q3b = -0.79v
Q3e = -0.59v

I also used:
1) a 1k ohm resistor in place of the 470 ohm between the resistors of Q2c and Q3c.
2) a 2k ohm attack pot
3) a 47k ohm resistor on Q2c
4) trimmer on Q1c set at 33.4k ohms
5) trimmer on Q3c set at 13.5k ohms

The schematic I followed is that on fuzz central's tonebender schematic. http://fuzzcentral.ssguitar.com/mkII.php

I wired it as positive ground since I'm using PNP's.

When I turn on the pedal, all I can hear is hiss. It sounds like the audio out of a television when it's not picking up any signal. Just real hissy sound. I can almost hear my guitar in the background of the hiss, but its hardly audible. Basically it sounds like garbage.

Please let me know if you need any additional information.

Does anyone have any advise to solve this problem? Have you encountered something like this?

Thanks,

Chuck

[LucifersTrip]

My transistors voltages/biases:

Q1c = -8.10v
Q1b = 0.00v
Q1e = 0.00v

before you go any further, sort this out. the base is shorted to ground...so Q1 iis doing nothing.
check everything in that area....and concentrate on getting just that 1st stage (up to the .1 from Q1C) working first, then take it from there

a couple notes

the Fuzz Central voltages are wrong, especially for Q3C, which should be ~ 7 - 8.5V

the MKII sounds best with some leakage and you are using Russians which are extremely low leak. this doesn't mean you won't get any sound, just that it will not sound the same as vintage units

[Pyr0]

Just to echo what LT said about Q3 voltages, I've started adjusting them now to approx 8v on the collector, and it is a great improvement in the overall sound.

[Mustachio]

I used the same transistors in Q1 and Q2 with my TBMKII But I used an AC128 for Q3 . Just wanna say make sure you have the pins right on the Russian transistors. I had to bend one of the leads in and the center out to swap em and put a lil shielding left over from stripped wire on the leads, helps if their socketed.

I'll look for the pinouts later, I think I found an old russian datasheet for those transistors before and figured out I had my transistors leads wrong.

[ChuckZilla]

Thanks for the advise guys. I'm at work right now, but I will check things out when I get home tonight!

I don't have a picture, but the emitter is indicated by a dot on the top of the transistor. The collector is the middle lead, and the base is the last lead. (The leads are ECB with a dot on the top above the emitter.)

Mustachio: Do you get the "vintage" TB sound when you replace Q3 with an AC128?

[ChuckZilla]

Hey guys, got it working... Just thought I'd let  ya know.

I had put a reverse polarity diode into my circuit as the guy at fuzz central is quite fond of em...

As soon as I took that diode out... BAM, it sounded pretty damn good.

Just to let  you guys know what the final product consists of...

Transistors = GT308V
Q1 Hfe =69
Q2 Hfe = 71
Q3 Hfe = 102

Battery voltage: 9.65V
Q1C = -8.45V
Q2C = -0.79V
Q3C = -8.50V

Q1C resistance = 11.5k ohms
Q2C resistance = 47k ohms
Q3C resistance = 2.6k ohms

I think it sounds pretty good. Nice and rich. Plays well to my attack. Is loud as s*** when turned up all the way. Gives my sound some texture. When I pull a string it has this nice clipped sound. Its pretty sweet.
Overall I like it, I don't know how it sounds compared to traditional trannies like the OC44 or OC75. I have never heard one of these tonebenders live, and through my amp.

-Chuck

[Mustachio]

Hey thats great you got it going! I'm not sure if the ac128 gave it a classic tbmk2 sound but it does sound amazing! I tried a few diff germs in Q3 till I was happy with the sound.

I loved how over the top it was with the gain up passed noon. But then I fell in love with it at low gain and higher vol settings! It helps if the transistors are warm , some times ill hold the pedal in my hands for a bit and the sound just opens up. Very nice for blues thru a tweed tube amp.