Tone Bender vs fuzz face, what's the point?

[m_charles]

Hi there. This post is in reference to the mkII tone bender here, not the other versions: http://fuzzcentral.ssguitar.com/mkII/mkIIschematic.gif
Here is the question.
As far as I can tell, this circuit is basically a fuzzface (with a few minor differences), with a poorly designed weird buffer in front of it.
What is the point of them throwing this in front of the fuzz face circuit. It would seem that all this would do would be to add a bunch of harshness at the input (hence the .01uF to gnd at input), and make the fuzz sound too squishy.
Am I missing something here?
Also, biasing the third transistor to 7v would only seem to further make it sound worse.
Please let me know if I'm totally missing the point here.
Thx!

[Groovenut]

Actually the first stage is an amplifier not a buffer, so the amount of fuzz and sustain you can get from the MKII is substantially more than a stock FF

[Electric Warrior]

They came without the 0.01 to ground at the input as well. But in any case I wouldn't describe a MKII as harsh or squishy sounding.
To be honest I prefer it to the MK1.5/Fuzz Face. The low end is just right, not as muddy as a fuzz face, not as tight as my MK1.5, and the Attack control is useable over its complete range.

[Chugs]

The point is that they both sound cool in different ways.   

[mcknib]

I'm a TB man I'm also an FF man depending on what tone I want the MK2 or any Tone Bender will sustain for days even Silicon one's, I've built both Germanium and Silicon versions of both and the Tone Bender Si can't be described as harsh like some people say a silicon FF is.

So I'd say build it you won't be disappointed and bias it by ear. That's what I do sometimes the voltage is bang on what's recommended other times it's a good bit off but it sounds good to me and that's what counts innit?

[blackieNYC]

They came without the 0.01 to ground at the input as well. But in any case I wouldn't describe a MKII as harsh or squishy sounding.
To be honest I prefer it to the MK1.5/Fuzz Face. The low end is just right, not as muddy as a fuzz face, not as tight as my MK1.5, and the Attack control is useable over its complete range.

I've been wondering about that - being a booster in front of a fuzz face, why is it not squishy?  Seems to break the DIYSB consensus 1st Commandment, which I've certainly observed to be true.

[Electric Warrior]

You can make it squishy, but it doesn't need to be. It does have a more compressed sound, yes, but not overly so unless someone gets the bias wrong (for example by using a 100k on Q1's base instead of 10k with OC75s).

Does the first stage really boost? I haven't heard it on its own yet.
In any case, it was designed to sound good in combination with the MK1.5 stage, and so it does.
Interestingly I find the MKII much harder to get right than the MK1.5/Fuzz Face. It can be really picky about transistor types and hfe/leakage. The right types make everything a lot easier, but with three transistors you still have six variables that interact with each other. It's not as simple as putting a good sounding booster in front of a good sounding Fuzz Face.

[midwayfair]

Does the first stage really boost?

It definitely sounds louder built as shown. But it depends on how it's built how much signal is actually going into Q2. Don't some versions have a much smaller base resistor? You'd lose a lot of signal there even with Q1 amplifying. You also lose some signal to the collector resistor dividing against the NFB resistor, but not a lot.

OP: Something that hasn't been mentioned that Electric Warrior usually mentions: The biasing is far different on real MKIIs than on the Fuzz Face. When properly biased, Q2 in the MKII (~.2V) is much closer to complete saturation than Q1 is in the Fuzz Face (.5V-1V), and the MKII's Q3 is much closer to cutoff (7-8V) than the Fuzz Face's Q2 (4.5V). The wave is much more asymmetrical in the MKII. Also, the Fuzz Central article has the wrong biasing, and that schematic doesn't let you trim Q2, so it will not sound correct and might sound closer to your description as "harsh" because the biasing really makes a big difference in what the pedal sounds like.

Also, biasing the third transistor to 7v would only seem to further make it sound worse.

Have you tried that or are you just guessing? What's your reasoning behind thinking that 7V would make it sound worse?

[Electric Warrior]

The base resistor was 10k in the OC75 version and usually 100k in the OC81D version. Q2C resistors were 47k for OC75s and 100k for OC81Ds. Voltages and sound are in the same ballpark for both versions.

A french collector recently bought a OC81D unit with the 10k/47k bias setup, though. It doesn't sound significantly different from his OC75 unit. Whoever selected the transistors probably knew what he was doing.

I have a vintage MK1.5 board here. The voltages are not that much different from a MKII.

MK1.5:
Battery: -9.99V
Q1 C -0.31V B -0.08V E  0V
Q2 C -7.64V B -0.31V E -0.24V

Q1C is high compared with the MKII voltages I've seen, Q2C a little low, but still within the range I've seen in MKIIs. But I only have voltage records for this one unit. It might be a freak. 

Here are my MKII voltages for comparison:
Battery: -9.67V
Q1 C -9.02V B -0.03V E 0V
Q2 C -0.17V B -0.08V E 0V
Q3 C -8.44V B -0.17V E -0.11V

I once owned a germanium Fuzz Face and it had a higher voltage on Q3C than either of my Tone Benders. It was quite wild sounding, though. Not sure what a great sounding one would measure. In my experience Q2C is quite low with silicons and higher when some leakage is involved.

[LucifersTrip]

As EW mentioned, I think a great benefit of that 1st stage is that you will get excellent, useable fuzz through the entire rotation of the attack knob....while with a Fuzz Face, it's usually just best at 100%, and then many players use the guitar knob for fuzz control.

Since the Fuzz Face attack (fuzz) knob ain't as useful, many builders remove that and put a gain control up front.

[Electric Warrior]

Also, the MKII has a lot more gain on tap. 

[mac]

In my experience Q2C is quite low with silicons and higher when some leakage is involved

Si have higher Vbe, so Q1C goes up, increasing the voltage and current in Q2 emiter resistor, and so Q2C collector goes down. You need around 5k total or less to get 4.5v with Si FF.
Same thing with TB II Q2 and Q3.

mac

[Bret608]

I recently AB'ed a Supa Fuzz clone I built with a hybrid FF circuit (Q1-Ge, Q2-Si, bigger in and out caps). On the Supa Fuzz, I kept a 0.01uf cap at input to ground as I play through a somewhat bright Fender guitar and amp. It's also got the two 10uf caps rather than 4.7uf.

I'm sure I don't have the best transistors for a MkII on hand (so the gain level isn't necessarily ripping), but it just sounds really well balanced next to the Fuzz Face. No muddy bass but also not too tight, compressed but not overly so. It's got a bit more sustain for sure, and I really like the way the notes blossom as you hang onto one for a long time.

FWIW, my Q2 and Q3 collectors on the Supa are similar to what EW has on his Mk I.V's Q1 and Q2.

[Electric Warrior]

In my experience Q2C is quite low with silicons and higher when some leakage is involved

Si have higher Vbe, so Q1C goes up, increasing the voltage and current in Q2 emiter resistor, and so Q2C collector goes down. You need around 5k total or less to get 4.5v with Si FF.
Same thing with TB II Q2 and Q3.

mac

That explains. 

[Electric Warrior]

I was messing around with a fuzz face bias calculator last night. Leakage does bring up the voltage as well. Different amounts of leakage have a lot of influence on the voltage readings. Much more so than hfes.

[Cozybuilder]

EW- What bias numbers do you aim for in an NPN Germanium ToneBender MkII Pro?

[Electric Warrior]

I have never built a NPN MKII. I have no idea where I'd get suitable transistors. But the voltages should be in the same ballpark, only positive.
As voltages are not an issue for me, I just aim to make it sound good.

[Cozybuilder]

I was hoping. This build has MP35's in all 3 spots, it sounds real good with about 7.2V on Q1-C, 1.2 on Q2B, about 2V on Q2C & Q3B, about 1.3V on Q3-E and about 7V on Q3C. Much smaller resistance needed on Q2-C, a 10K trimmer works well there.

[Electric Warrior]

2V on Q2C is very high, 7V on Q3C rather low. You could try a bigger resistance on Q2C and Q1B. I guess you have too little leakage for the bias setup you're using.

[mac]

I have never built a NPN MKII. I have no idea where I'd get suitable transistors.

You could search for 2N1117 or 2N388 from TI, but these are trebly.
On the other hand, Sanyo 2SD72K have a very low transition frequency Ft. And Matsushitas 2SD352 Ft is even lower.

For silicons, 2N2369, 2SC1730, 2SC1215, hfe below 100, but Ft is very high.
You could try BD237 or BD175 that have low hfe, and Ft is close to an ACxxx.
Even TIPxx or 3055 might work.

mac