Help me identify the pedal I built

[FinkBrau]

Hi, I'm new here and I'm a polite guy so let me introduce myself.

I'm FinkBrau, from France and I'm a mediocre (at best) guitar player, have been for about 12 years. I usually train regularly for a year, get discouraged, and put the guitar away until the itch comes back, about a year later. It's a cyclic thing.
I'm also a bit of a tone nerd, hence my presence here. I've built a few pedals over the year from online guides, sometimes using a purchased PCB, sometimes using a stripboard. I don't understand how electronics work, never have, never will (I'm a mechanical engineer...), but I can put the components at the right place with a layout.

Now for the problem that brought me here :

I got the itch again. So I've been putting my gear back together, even bought a new guitar

10 years ago I built a Tonebender Mk3 replica (I remember specificly it was a Mk3, but maybe I'm wrong?) using a stripboard, from a layout I found online, don't remember where. I know it's a 2 knob, 2 transistor version with positive ground.
Knowing nothing about transistors except that germanium sounds better, I bought a pair of OC76 PNP off ebay, and the other components from pedal parts plus.

The pedal works, but does not sound good. Hard to describe with my english, but it's very messy and when I turn the "Attack" pot too high up it just mutes the higher notes.

I assume it's the transistors and I'd like to replace them, but I just can't find which version of the ToneBender Mk3 I built, so I don't know which transistors to get.

I thought maybe some of you could help me?


If that helps, here's the components I ordered at the time. Pretty sure the list is complete :

8003           Xicon 1/4W 1% Metal Film Resistor 1K                 1
8002           Xicon 1/4W 1% Metal Film Resistor 10K                1
8519           Xicon 1/4W 1% Metal Film Resistor 47K                1
8001           Xicon 1/4W 1% Metal Film Resistor 100K               2
8006           Xicon 1/4W 1% Metal Film Resistor 2.2M               1
7503           Alpha Single-Gang Linear Taper 16mm 1K Potentiometer       1
7501           Alpha Single-Gang Audio Taper 16mm 100K Potentiometer      1
3019           Xicon Radial Electrolytic Capacitors 16V 4.7uF 20%      2
3015           Xicon Radial Electrolytic Capacitor 16v 47uf 20%          1
3050           Xicon .01uf / 630V Capacitor                         1
3031           .1 uf  63v ( Green) Polyester Film Capacitor          1


Cheers,
F.

[antonis]

I'm a polite guy...

germanium sounds better..

No polite guy should state the above without taking the risk of his own statement..!!


P.S.1
A picture of your build should be extremely helpful..

P.S.2
Welcome..!! 

[Mark Hammer]

Premierement, bienvenue.

Such problems, are generally a matter of the biasing of the transistors, and not the transistors themselves.  This appears to be likely in your case since you indicate that the sound quality deteriorates as the Attack (gain) control is turned up.

One of the mods I like to do to fuzzes that use the basic 2-transistor Fuzz Face structure is to increase the value of the resistor that goes from the 2nd transistor back to the base of the first one.  Most fuzz schematics will list the value that provides a nice fuzz with good sustain.  Increasing it a bit beyond that will produce a quality that is variously described as "zippering", "glitchy", "gated", depending on how much further you increase it.  It also interacts with the setting of the Attack/gain control.  So, I am wondering if you either used a value that was too high (maybe misreading a colour code on the resistor), or perhaps simply didn't connect that resistor properly.

[antonis]

To make things more clear..
(BTW, 2 transistor Tonebender should be MKII..)



Mark refers on red circled 100k resistor from Q2 Emitter to Q1 Base..

P.S.
470R on schematic could be your 1k and 8k2 could be your 10k but I can't recall any Tonebender circuit with 2M2 resistor & 10nF capacitor..
In case 10nF cap is placed instead of any of feedback caps, it surely has an unacceptable big value..
(second feedback cap is also missed..)

[Electric Warrior]

edit: never mind, it seems to be a MK1.5.

but that does read a lot like a MKII shopping list... probably for this schematic, which has some inaccuracies that will cause bias issues:
http://fuzzcentral.ssguitar.com/mkII/voxmkIIschematic.gif

[FinkBrau]

Thanks guys, I'll post pics a bit later!

Will try to draw the schematic later too.

[FinkBrau]

Hey guys, here are the pictures. I'll try to find some time this week to work on the schematics.

Oh, and as it turns out, it's a 3 transistors version 

[Electric Warrior]

Good. Bias problems are expected with the schematic you used. If you haven't fried the transistors by soldering them in with short leads, it could be an an easy fix.

Could you measure the voltages between each transistor lead and ground?

[FinkBrau]

Good. Bias problems are expected with the schematic you used. If you haven't fried the transistors by soldering them in with short leads, it could be an an easy fix.

Could you measure the voltages between each transistor lead and ground?

Here ya go:

T1
E 0 V
B 84 mV
C 6,43 V

T2
E 0 V
B 87 mV
C 206 mV

T3
E 118 mV
B 203 mV
C 8,42 V


T1 being the left one on the first picture, T2 middle and T3 right. Took the ground on the jack, is that correct?

[PRR]

[pinkjimiphoton]

Good. Bias problems are expected with the schematic you used. If you haven't fried the transistors by soldering them in with short leads, it could be an an easy fix.

Could you measure the voltages between each transistor lead and ground?

your voltages seem kinda wonky, pnp circuit, right? should be reading negative voltages... you want the meter's red lead to ground in this case, opposite what you'd normally do.

q2 seems kinda wonky to me, but i'm not all that versed on tonebenders.

Here ya go:

T1
E 0 V
B 84 mV
C 6,43 V

T2
E 0 V
B 87 mV
C 206 mV

T3
E 118 mV
B 203 mV
C 8,42 V


T1 being the left one on the first picture, T2 middle and T3 right. Took the ground on the jack, is that correct?

[FinkBrau]

Correct, PNP circuit. Didn't pay much attention to polarity when measuring though!

[FinkBrau]

Hey guys, being locked-down has some advantages as it turns out. Finally took some time to test out those mods.

The 330r solved the problem. I don't know if it sounds as a ToneBender but it definitely sounds good now.


Thanks a lot!