Tonebender MkII Questions

[Big Monk]

One of the advantages of a little gating is noise reduction in silent phases

I'm excited to tweak into the in between range of 7.43 and 7.98 and see where I end up.

[Big Monk]

It looks like even if lower voltage sounds are not constant across all NOS devices, at the very least higher voltages, varying somewhere from 7.5-8.0 V on Q3c, are almost universally the recipe for the classic MkII sound.

There's no doubt at all that they were set up with Q3C far from 4.5V.

I once calculated average voltages, based on a couple of sets of OC81D and OC75 MKII voltages:

supply: 100%
Q1C 92%
Q2C 1.82%
Q3C 89%

What's interesting is when I was researching and coming across all the posts at various forums where you have commented on this topic, I just started slapping the values in an Excel sheet and taking averages.

I may have to format the sheet I saved and keep it in my files.

[PRR]

...I once calculated average voltages, based on a couple of sets of OC81D and OC75 MKII voltages:
supply: 100%
Q1C 92%
Q2C 1.82%
Q3C 89%

These have different reasons and causes. Q2C is Vbe(3) + Vbe(2) + (Ib(2)*Rb(2))... so mostly junction drops, not supply voltage. And you can't simply change it, nor should you.

Q3C sets gain and clipping action. Yes, a % of supply may make much sense. Not for nothing do you find many "Fender tube preamp" stages biased to 69% of supply.

89% sounds a little high for a 2-transistor distorter, but on a 3-transistor beast you have the gain and may want to shape the clipping pulse-width ratio.

[Electric Warrior]

The 2 transistor variant (Mk1.5) was biased the same. It's notorious for how farty it gets during the summer, but can sound great at room temperature and below

Arbiter set Q1C a little higher (I haven't seen any under 3% yet) when they cloned the circuit and called it the Fuzz Face. Of course this brings down the voltage on Q2 a bit.

The MKII sounds just amazing at voltages at which a MK1.5 would misbehave. I guess that was the entire point of the circuit. They sure got that one right.

[Big Monk]

Quick update:

I confirmed with Small Bear Electronics that the targeted bias point for Q3c is 4.5 V. So, keep that in mind should you decide to use the resistors shipped with your matched transistors.

[Big Monk]

A few quick updates:

I've turned my current build into a test platform. Some observations:

1.) I had been using a 250k Pre-gain at the input of the circuit, just like the Gagan "Easy Face". I had some concerns initially as to whether it should really be after the interstage coupling cap that follows Q1 similar to the placement of this were a fuzz face type circuit. I added sockets to the input of the circuit, pot lugs and to the coupling cap so I could swap the pregain pot from the input to before Q2 and vice versa. I thought there was a noticeable attenuation with the pot places at the very beginning of the circuit as opposed to before Q2 but I'm not sure how confident I feel about that.

2.) I added a temporary 100k pot to Q2c and am able to go from 7.45 to 8.1 Vdc at Q3c. I am playing around with 0.1 Vdc increments but did gonto the extremes right away. 8.1 was a bit ragged and gated. I'm at around 7.7 Vdc on Q3c right now and I feel there may be a touch more upward swing. Very loud, fuzzy and full of sustain at this bias point. The Pre-Gain allows me to get some tamer (but still fuzzy) sounds as well as some mid forward, crunchy overdrive sounds as well.

3.) I really enjoy the switchable output cap. It gives a pronounced gain boost and is very useful.

[Big Monk]

Was able to hammer out a quick video of the full prototype with switching yesterday:

[Mich P]

4.5 V on Q3 collector favorite spot here too.

[Big Monk]

4.5 V on Q3 collector favorite spot here too.

Have you ever gone higher?

I was not a fan of the TB MKII circuit until I researched, spoke with people a bit more experienced with it, and ultimately tweaked Q3c to > 7v. To me it sounded closer to a Fuzz Face at 4.5v. I had simply assumed that what i read on Fuzz Central all those years ago was the value to shoot for. Turns out I was wrong.

Of course, tone is subjective, and I can only speak for myself and what I've come to like.

[Big Monk]

Goofed around some more today. I of course tried my hands at some "Truth" licks because that's what got me started on the MKII/Supafuzz in the first place. There is some faux tape delay and fixed wah on here in addition to the Fuzz in "Supa" mode with the gain and attack rolled back a bit. Q3C is set to about 8.2 volts and I rolled the guitar volume up and down during the video.

Take it easy on me, I'm no technician on the fiddle:

[Big Monk]

Did some transistor swapping last night. I had a few "issues" (quotes because i like the sound but was looking for small improvements):

1.) Volume seemed only a little above unity when cranked. There was still a considerable amount of distortion and texture so i was not bugged all that much by it.
2.) I wanted to see if i had a combo of transistors that would calm the hiss.

I ended up taking an old Q3 value from a previous set and subbing in the low-gain, low-leakage Q1 I had in. Voltages were as follows:

Vs = 9.23

Q1c: 9.02v (97% Vs)
Q1b: 0.02v
Q1e: 0.00v

Q2c: 0.195v (2.1% Vs)
Q2b: 0.065v
Q2e: 0.00v

Q3c: 8.35 v (90% Vs)
Q3b: 0.19v
Q3e: 0.09v

Q1c is a touch higher than i've seen relative to other voltage data sets but it seemed to give me back a touch more volume without a corresponding sacrifice anywhere else.

I took a short video with the following settings:

[Big Monk]

Finally got around to testing the classic circuit with OC75s this weekend.

They kicked my ass. I had real issues getting the generally accepted stock circuit working without excessive gating. Admittedly, I left the original Sola Sound stock circuit (Q1b = 10k, Q2c = 47k) alone and swapped around my transistors.

I have 7 OC75s, 6 of which are suitable for the circuit. I'll play around some more and tweak some resistor values next go round.

Am I missing something?

[Electric Warrior]

Finally got around to testing the classic circuit with OC75s this weekend.

They kicked my ass. I had real issues getting the generally accepted stock circuit working without excessive gating. Admittedly, I left the original Sola Sound stock circuit (Q1b = 10k, Q2c = 47k) alone and swapped around my transistors.

I have 7 OC75s, 6 of which are suitable for the circuit. I'll play around some more and tweak some resistor values next go round.

Am I missing something?

If it's gating too much, you need to pick a transistor with lower leakage for Q2.

[Big Monk]

Finally got around to testing the classic circuit with OC75s this weekend.

They kicked my ass. I had real issues getting the generally accepted stock circuit working without excessive gating. Admittedly, I left the original Sola Sound stock circuit (Q1b = 10k, Q2c = 47k) alone and swapped around my transistors.

I have 7 OC75s, 6 of which are suitable for the circuit. I'll play around some more and tweak some resistor values next go round.

Am I missing something?

If it's gating too much, you need to pick a transistor with lower leakage for Q2.

I will try that. The breadboard is set up as a Tonebender permanently anyway because I can build boosters and fuzz faces off the general layout.

I'll pop the OC75 circuit back in sometime this week and use a lower leakage unit for Q2.

How much of an impact does Q1 base/collector resistance have on the rest of the circuit. I imagine dialing in Q1 is less of a concern but I'm not 100% sure I understand the downstream affects of its biasing and positioning in the circuit to say definitely.

[Electric Warrior]

Not sure. I tend to just swap things around until it sounds good 

[percyhornickel]

My MKII Germanium build:

Q1c: -7.4V
Q2c: -0.2V
Q3c: -7.3V

Just followed many Electric Warrior advices that I read in some posts, just tweeking Q2c trim until Q3c shows the right volt. My transistors are so leaky (no way I can get any others/I am from Venezuela) and I guess that´s the reason I can not go a little higher cause the sound tends to be too gathed, the sound I get it´s very good anyways with -7.3V at Q3c...  ....I used a 10k for Q1b.

P.H.

[bmsiddall]

Just followed many Electric Warrior advices that I read in some posts,

You could do a lot worse!  That's exactly what I did- aimed straight for Q3C >8V after reading much of EW's TB comments (loves me some gating on tonebenders).

[Big Monk]

Full disclosure: I never swapped any components other than transistors around. I wanted to see if i could make it work stock.

I'm going to follow EW's advice on using a lower leakage unit in Q2 then do some resistor swaps if need be to tweak things. I have a Silicon Mark II on the breadboard now and that sounds fantastic!

[percyhornickel]

Silicon tonebender would be a nice project, I already have 6 circuits finished and tested waiting for a "some day enclosure"...   ....last night finished the I.C. Big Muff (78 Versión)..   ...amazing.

For my Ge TB I will try to put an external bias pot so I can make it sound all the gathe I need in some point.

[Big Monk]

Not sure. I tend to just swap things around until it sounds good 

Fair enough!

I wired up a 100kB dual ganged pot last night. Both are wired as variable resistors and one goes to the Q1b resistor while the other goes to the Q2c resistor. I kept the stock 10k/47k combo.

I ended up using the lowest leakage unit I had for Q2. The dual ganged pot lets me dial down the gating to a useable level and also lets me adjust for when things heat up. It's simply an external "offset" for leakage and worked pretty well.