Imagining the Keeley Fuzz Bender schematic

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Imagining the Keeley Fuzz Bender schematic

Postby Ichabod_Crane » 06 Jun 2019, 15:06

Hello guys, I saw some demo of the Keeley Fuzz Bender, and I'm trying to imagine the schematic.
Do somebody have the original schematic, please? :D

Anyway, I found some information here:

https://robertkeeley.com/product/fuzz-bender/
https://youtu.be/TOh0eNlIW6c?t=157

The name and the three transistors make me think a Tone Bender based fuzz.
It's an hybrid, silicon and germanium transistors, one and only germanium transistor should be in the last stage. So the Tone Bender should be the MkIII.
Bass and treble control, 20db. It could be a Baxandall.
And a new Bias control? I don't know why is new, but I guess there's more than a way to add it.

Tone Bender schematic
Image

A Baxandall version I like (value can be changed):
Image

Suggestion about a Bias control?

So, assuming it's based on a Tone Bender + Baxandall with a Bias control, can someone help me to draw a schematic?

Thanks. :thumbsup
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Re: Imagining the Keeley Fuzz Bender schematic

Postby karul » 06 Jun 2019, 18:30

The Keeley Fuzz Bender is a 5 knob – 3 transistor modern fuzz using a combination of high-gain silicon and silky smooth germanium. What makes fuzz better? Active EQ. Using two gyrators as an active EQ gives you the ability to create massive fuzz tones not possible with typical square-wave boxes. Pummel your amp with over 20dB of boost/cut at 100Hz and 10K Hz. The Fuzz Bender is built around vintage Japanese germanium to create its monumental fuzz tones. With the all new Bias Control, you control the attack and decay of your notes. Anything from Fat Square Waves to Angular Fuzz to glitchy-Velcro attacks are possible with the Bias Control. The Fuzz Bender’s five knobs confirm size matters when creating a new and epic world of fuzz.


According Keeley's description the tone controls are two gyrators.
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Re: Imagining the Keeley Fuzz Bender schematic

Postby karul » 06 Jun 2019, 18:32

Five Knob Hybrid Fuzz with Japanese Germanium Transistor
Gyrator Bass and Treble controls with 20 dB boost each!
Bias Control for glitchy-velcro attack
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Re: Imagining the Keeley Fuzz Bender schematic

Postby Ichabod_Crane » 07 Jun 2019, 08:06

Oh, yeah. Gyrators are not Baxandall! :slap:
Thanks.
This make the thing a bit more complicated, maybe. Anyway those are just two band: 100Hz and 10K Hz.
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Re: Imagining the Keeley Fuzz Bender schematic

Postby Ichabod_Crane » 10 Jun 2019, 08:34

I need some help to add a pair of gyrators in that Tone Bender circuit.
The opamp based one could be good? http://www.muzique.com/lab/gyrator.htm
Thanks! ;)
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Re: Imagining the Keeley Fuzz Bender schematic

Postby vtguedes » 11 Jun 2019, 20:00

This is a link for a parametric 3 band eq using gyrators. Maybe start from this and tweak?

http://sound.whsites.net/project28.htm

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Re: Imagining the Keeley Fuzz Bender schematic

Postby Ichabod_Crane » 16 Jun 2019, 14:42

Thanks, I'm trying to work on these kind of gyrator in that link, but I look the Boss HM-2, now.
The HM-2 has the Low frequency around 100HZ with 20db boost/cut. Pretty good, it's enough change a bit some value and got something more close to 100Hz. I guess is not important if it's 97Hz or 106Hz, right? :D
But the High in the HM-2 are around 1.2k, and I'm trying to calculate the right values of the parts on line with this: http://www.muzique.com/lab/gyrator.htm
I'm not sure I'm doing it well. Is there something I have to know? In particular I'm a bit worry about the Q.

Then, I don't know if it's important, but I have even a little issue in my simulator. Using the gyrator between a non-inverting opamp input stage and another opamp final stage (this one copied from the HM-2) I got a boost around 131kHz while boost one or the other or both the pots. :hmmm:
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Re: Imagining the Keeley Fuzz Bender schematic

Postby karul » 16 Jun 2019, 16:52

Few hertz lower or higher are not problem. That 100Hz are ideal, calculated value. You are working within tolerances. Why don't you made the gyrators with variable freq?

http://www.geofex.com/article_folders/eqs/paramet.htm
http://sound.whsites.net/articles/gyrator-filters.htm
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Re: Imagining the Keeley Fuzz Bender schematic

Postby Ichabod_Crane » 16 Jun 2019, 18:46

I prefer a simple gyrator, just like the Fuzz Bender with a Bass and Treble control
I know the second link. :)

These are the configuration I got:

Image

All really close to the 100Hz, but what really change is the Q. From 2.38 at 7.39. What does it mean? Small value narrow notch?
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Re: Imagining the Keeley Fuzz Bender schematic

Postby karul » 17 Jun 2019, 01:36

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Re: Imagining the Keeley Fuzz Bender schematic

Postby karul » 17 Jun 2019, 01:43

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Re: Imagining the Keeley Fuzz Bender schematic

Postby Ichabod_Crane » 17 Jun 2019, 15:02

Thanks! It's more clear from that picture. I have to watch the video.

Meanwhile, I tried to simulate the 3 band parametric equalizer by Harald Sabro Bolstad. It has Boost/Cut control, Q and Frequency for every single band.
Anyway, even this schematic make that peculiar issue, boosting the bands I got at the same time a boost in the highest frequencies, around 37kHz. I guess it's unavoidable. :roll:

Now, I'm working just with the gyrators between two opamp stages, I'll do later something with the Tonbender Fuzz.
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Re: Imagining the Keeley Fuzz Bender schematic

Postby vtguedes » 17 Jun 2019, 19:11

No problem with a boost that high. You'll won't hear anything beyond 20kHz, and you could allways use a simple low pass filter to cut anything above 10kHz (the harmonic content of a guitar won't go higher than 6kHz).
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Re: Imagining the Keeley Fuzz Bender schematic

Postby Ichabod_Crane » 18 Jun 2019, 07:51

I tried to cut off some highs, but that cuts a bit even when I set the gyrators at flat. Maybe, as you said, that will be not a real problem if there's a boost or a cut in so high frequencies.
The Fuzz Bender has the High gyrator at 10kHz.

Generically speaking, a boost over 10kHz could we call Presence control?
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Re: Imagining the Keeley Fuzz Bender schematic

Postby vtguedes » 19 Jun 2019, 15:13

I'm not sure how presence works in the frequency spectrum, but it is related to the "sizzle" in the output signal, specially when an amplifier is distorting. Also, it is a control implemented in the negative feedback network of the power amplifier, so it is not a filter in the pre or post gain stages of the pre-amp.

The thing is that a gyrator works differently from a baxandall eq because the usual treble control is a high-pass filter, while the gyrator is a bandpass filter.

One consideration (and I might be completely wrong about it): I am guessing that both gyrators have low Q value in order to be more usefull within the whole guitar frequency range, and I would leave at least a trimmer to tweak it. If I had a guess I would have Q between 0,6 (2 octaves) and 2 (0,7 octaves). To me, it seems like higher Q values work better in the context of a multi-band graphic eq but not for a 2 band eq.
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Re: Imagining the Keeley Fuzz Bender schematic

Postby Ichabod_Crane » 20 Jun 2019, 14:11

Thanks for the info.
I'm agree with you about the Q thing. For just two bands a larger Q is better.
I tried to calculate the right value of the gyrators part for a large Q and to get 100Hz and 10kHz frequencies in muzique.com page. But then occured a thing that I thought it was weird in my emulation software. But maybe it's normal. I had a large Q, but a really little boost/cut. I back to old values, helping just to center the frequencies I wanted, and the emulation now seems ok.
Low and high control, enough large Q I guess, considering that 100Hz and 10kHz are rather far.
I got until 20db boost/cut, but I reach high level of boost/cut just in the last part of the pot.

Here's the graphic:

Image

The 10db boost in flat is because the preamp stage I used.
The third bump is the one I told early. More boost I set with the pot more boost I got there.
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