"technology of the tonebender (mk 2)" article out there somewhere?

[mordechai]

I just read RG's "technology of the fuzz face" article, which was excellent, and I wonder if there is a similar essay available to walk me through the Tonebender mk 2 circuit.  Anybody know of such a resource?

[mac]

Not exactly, but RG article applies to the FF stage of the circuit. The only difference is the 100k, or 47k suggested by some users, instead of the 33k. A 47k is said to sound less gated.
Some people reported that they prefer biasing Q3 at 7v, others at 3.5v. I guess that since there is a previous stage driving the FF section, Q3 voltage is not so critical as in a pure FF.

Q1 is a simple amplifier biased at a high collector voltage, 7v or more. There is no resistor feeding the base because leakage self bias the transistor. Less leakage, higher collector voltage. A silicon needs around 1M from B to C to get about 8v at C.
I guess the 100k is there to drain excesive leakage and to avoid extreme thermal runaways.
AFAIK no one complained about Q1 thermal problems since leakage always exists and goes up with temperature causing collector voltage to decrease which is not so bad except that the FF section is hit harder. I prefer 8.0 to 8.5v. But I'm 44 and I do not like metal stuff
So Q1 voltage can vary from say 8.7v to 6v depending on your tranny's leakage but it will always work.
For example, a germ leaking 100ua=0.1ma will sit at Vc=Vcc-10k*0.1ma=9v-1v=8v
The sound of Q1 at 8v is not inspiring, it sounds... well, misbiased.
The 0.01uf cap at the input, and the low input impedance shunt highs to gnd, but this thing produces a large amount of upper harmonics, so tone sucking might not be a problem with other pedals in front of it.

The fuzz pot is never clean.  There is a mod I suggested which consists of replacing the fuzz pot with a fixed 1k resistor and placing a 100k-A pot between Q1 and Q2 as in a Big Muff Pi,

Q1 -- 0.1uf -- 100kA pot -- 0.1uf -- Q2

mac

[Derringer]

There is a mod I suggested which consists of replacing the fuzz pot with a fixed 1k resistor and placing a 100k-A pot between Q1 and Q2 as in a Big Muff Pi,

Q1 -- 0.1uf -- 100kA pot -- 0.1uf -- Q2

mac

as in a volume control between Q1 and the input of the FF circuit?

I've done just that using a FET stage for Q1 and it's been on my pedal board for quite a while now, I really like it

[mordechai]

So does that mod allow for a different sort of "fuzz" (or, in the TB Mk 2 vernacular, "attack") control that might allow for a relatively clean minimum setting?

[Derringer]

I still wouldn't call it "clean"

but your 'clean' is most likely different from my concept

Do you have a tone in mind (re: recorded clip) that we could hear?

That mod though does affect the character of the distortion/fuzz

[mac]

as in a volume control between Q1 and the input of the FF circuit?

Looking the pot from above and the lugs to the sky, left lug to left 0.1uf cap, center lug to right 0.1uf cap, and right lug to gnd. I added the right cap to isolate Q2 bias from the pot.

This mod allows a cleanish sound. But it is a major surgery, so expect large differences respect to the original as you lower the volume pot.

Mmhh. What about a pot between 0.1uf cap and Q2 as a variable resistor? see the smooth por in the axis face http://fuzzcentral.ssguitar.com/axisface.php.
This pot and the 1kA fuzz pot could work together...

mac

[fuzzo]

I'm gonna make on Ge tonebender in an orginal box (someone knows where I can find a faceplate like the old one; it's missing on mine. ?) and I'll try to put a 500Ka between the first gain stage and the regular fuzz circuit. 

thanks for the explanation of mac  !

[mac]

I'm gonna make on Ge tonebender in an orginal box (someone knows where I can find a faceplate like the old one; it's missing on mine. ?) and I'll try to put a 500Ka between the first gain stage and the regular fuzz circuit. 

thanks for the explanation of mac  !

breadboard it first!

mac

[fuzzo]

actually I did ! but I didn't try the new placement of the gain pot. I'll see .

A thing that works good was puting a selector on the output cap to add basses (I'm not really fan of this realy "nasal tone" ) .

[mordechai]

Fuzzo, would it be too much trouble for you to either take a snapshot of your breadboard or provide a layout of what you came up with.  As some of you may know from my previous posting, I'm a noob and having trouble figuring out how to move from the schematic to the breadboard.  I understand how to "read" (the former), but apparently, I'm not quite ready to "write".

[Derringer]

as in a volume control between Q1 and the input of the FF circuit?

Looking the pot from above and the lugs to the sky, left lug to left 0.1uf cap, center lug to right 0.1uf cap, and right lug to gnd. I added the right cap to isolate Q2 bias from the pot.

AC coupled, yep. That's what needs to be done there. Messing with the cap values there yields nice results as well. On one version I built, I had a 0.033uF cap coming from Q1's Drain (i used a fet) and then 0.068uF from lug 2 of the 100KA pot to the base of Q2 (Q2 was a 2n3903 with about around 80 hfe)

This mod allows a cleanish sound. But it is a major surgery, so expect large differences respect to the original as you lower the volume pot.

for me, this control acted sort of as a "saturation" control as you turned it up and then made things sound more touch sensitive and less saturated as you turned it down. It's a nice control to have when you're using different guitars with different pickups.

Mmhh. What about a pot between 0.1uf cap and Q2 as a variable resistor? see the smooth por in the axis face http://fuzzcentral.ssguitar.com/axisface.php.

I think this would be most affective before Q1 as it would affect the incoming (weaker) signal to a greater degree than the boosted signal post Q2.
Only your ears will know.

mordechai
Please take some time and read through this page here.
http://www.beavisaudio.com/techpages/SchematicToReality/
There are some sections about IC chips and other things that you don't need to concern yourself with yet, but as you scroll down through the page you'll see a breadboard example. I suggest that you practice breadboarding the project on that page (LPB Boost) a few times so that you get the hang of it.

Then, when you go back to the tonebender, I suggest that you build the Q1 section first and test it to make sure it works (plug your guitar in to the input capacitor and connect the output to an amp ... make sure you use an output capacitor). Then, build the Fuzz Face section (Q2 and Q3) on another spot of the breadboard and test it to make sure it works. Then connect the two together and you should have a working tonebender.

The first circuit I tried to build was a fuzz face. It had me screaming and cursing at it because no matter what I tried it would not work. That lasted for a while. But eventually, I figured out that I had the transistors flipped! and got it to work. (The radio shack packaging of the trannies had the WRONG pinout ... it was mind numbingly frustrating)

Don't give up dude, keep at it. Start small, learn, and build your way up. Hang in there. You'll get it.