Exquisite Electric Filth
Silicon Tone Bender Mark III / Buzzaround And How To Fix Notorious Biasing Issues

last update: Feb. 4, 2020

Copyright 2020 by H. Gragger. All Rights Reserved. All information provided herein is destined for educational and D.I.Y. purposes only. Commercial re-sale, distribution or usage of artwork without explicit written permission of the author is strictly prohibited. The original units  with their associated  trade-names are subject to the copyright of the individual copyright owner. The Author is by no means affiliated with any of those companies. References to trade names are made for educational purposes only. By reading the information provided here you agree to the Terms of Use.
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Index

Abstract
Circuit Details, General Thoughts On The Architecture
Using The Fuzz Right
Sound Samples
Reference

īMark-III stompbox
The Mark III  (click to enlarge).

A silicon Tone Bender, or Buzzaround derivative (hereafter: TB)

As different to the early designs that use germanium transistors, it uses silicon. Optimized where possible for a clean and smooth, distortion tone (an oxymoron?) with an attitude, it has a lot to claim over a gated sputtery dying germanium unit that was too long in the sun.

The design is chosen to reflect the colorful spirit of the time. The annunciation LED lights up yellow when engaged.

The transistor devices chosen are NPN devices with gain ranges compatible to the values common at the time, which probably accounts for the good result.

I adorned the circuit with the usual goo-gaws, like input RF filter and anti-pop filtering for the LED and the best from east and west, such as a fake for the leakage, that was needed to bias the original GE units (and was probably the reason why some of those units did not work well...)

The savvy 60ies style decals I print directly to anodized aluminium sheet.


Abstract

One of my long time favorites
is Miles Davisīs Agharta. Pete Cosey does things to a guitar unheared of before and after.
So I was setting out to replicate that choking guitar sound. The upshot is, it is not the sound of a misbiased transistor. Pete used an early guitar synthesizer for this, and it is even difficult to describe what it does to tone, letting alone putting this into technical terms.

During this quest, I built a silicon fuzz face, which I found best sounding when not sputtering or choking, and now the Tonebender, or, as you may want to call it with equal validity, Buzzaround.

Germanium has an alleged sought-after elusive tone, but, to be honest, I do not miss anything with a well made silicon device. And I have been through germanium.

One of the disadvantages of germanium is leakage. Ironically, the device described hereafter needs leakage to work.
It thus cannot be simply transferred to silicon. Moreover, the notorious low gain values and the spread thereof lead to more problems, predominately biasing issues. You thus probably wonīt even get a germanium device working in this circuit.

As a matter of fact, they did not even back when these devices were en vogue, so many pedals out there produce nothing but sputtering and gating, letting alone temperature sensitivity.

So biasing is important. I come to believe, that, although some people explicitly want this sort of device for their crazy avantgarde tones and effects, people initially looked for a distortion unit with great sustain and natural decay. This is how I have set up my device. Chances are, with the values given in all the schematics, or, as the case may be, this schematic, you wonīt get the job working well. I hope the subsequent explanations will help you, germanium or not.

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The circuits and concepts depicted here, particularly the artwork, are the sole intellectual property of persons known as Aquataur (Aquataur Music). They are destined for personal use and for educational purposes. Any commercial exploitation thereof is thus at least immoral. Any re-hosting is prohibited.

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Circuit Details, General Thoughts On The Architecture

The Tone Bender Mk.III and the Buzzaround have much in common. The first thought may be, since the Buzzaround has more controls, it must be the successor of the TB, but it is the other way around. The TB came a year later. Maybe they left away some of the questionable controls.

circuit, click to download
Mark III circuit (click to download PDF file):

you are going to need a PDF viewer to view this file.                                      

The Balance Control

Lets look at the Balance control, this changes the bias of Q3. You can adjust the signal for symmetric clipping, or "more to one side or the other". Of course, you change the collector current and thus operating point where the collector resides. This is assuming, there is proper drive on the base. But what does it "balance"?
Yes, and always in situations like that, this alters the texture of the fuzz. As a side effect, it also changes volume, which is why a volume pot was spared.
Huh, plenty of interaction with little result, isnīt it? They eliminated this one with the advent of the TB by using a trimmer to set the bias and be done. I do not know if this control warrants space on the front panel at all. It may well turn out that this is one of the set-and-forget controls, but I leave it there for experimentation.

I stand speechless with what grimness people (particularly those who manufacture devices like that) adhere to things like the Balance pot in their quest for staying retro at all cost, despite obvious flaws.

The Tone Control

The tone controlīs sweep must have been quite revolutionary, but today there is better. Aftermarket productions have replaced this by a Big Muff Pi style tone control, which is what I borrowed. Note that I have put the control in a way that at 7 oīclock bass will be maximum, at 17h treble is maxxed. This seems most intuitive for me.

Biasing The Darlington Stage First - By Ear!

The darlington stage is fairly straightforward. In fact so straight, that some designers (Mictesterīs Buzzaround Alike) decided to replace it by a op-amp stage entirely. They claim the circuit sounds like the original, but some say no. Weīll come back to this later.

When I got the whole thing going, I naturally looked at the darlington stage first. It kinda worked right away, and with an external resistor pulling up the base I could nicely adjust the collector waveform. Then I proceeded to Q3. Now this has no biasing network and relies, coming from a germanium circuit, on a leaky transistor, which exhibits some parasitic current leaking from base to collector. This pulls the base up - hopefully enough. (Maybe this explains why some of those units worked better than others...).

Now silicon does, for all practical means, not suffer from such defects. We have to pull the base up ourselves. R.G. Keen suggests a reverse biased GE diode from B to C to accomplish this task, but this did not seem to work. Mictester, for his unit uses a pullup at the fuzz pot, which would present a variable working point for Q3 dependent on the fuzz pot setting. Hmm.
GGG and others then use a 1M trim pot between C and B that does the job nicely. Case settled.

But what about the collector? The 27k that was there, was way to big for my silicon device. Sputtering and farting galore. I twiddled the pot and lo and behold - beautiful signal on the output!
Some time later, I hot-pulled Q3 to try a different unit, and - believe it or not - nothing changed!
It turned out that the pot hat been at zero, so full signal from B to C without Q3!

This appears a great method to fine-tune the darlington state first. (The complete bias setting procedure is described on the schematic sheet in great detail.). An oscilloscope is one thing, the ear another.

The darlington stage on its own does not sound bad, strongly reminding of a fuzz face with low fuzz setting. Now we come round full circle, this makes me believe that the first stage does matter tone wise. You can change its character by the procedure described. Great distortion always happens in small chunks here and there.

The initial, intuitive choice of PN 2369A (with gains of ~60) proved right, although with all this gain cascading noise is not necessarily low. However, it will be much lower than GE.

Biasing Q3

Back to Q3. I tried any old GE transistor I found, and it worked, but sounded so-so. There was no big "Ah, germanium sound!".
For biasing of Q3 I removed the 27k resistor and replaced it temporarily with a 10k trim pot. It turned out, that it requires something as small as a kOhm or thereabouts. This finally brings Q3īs collector to a position, where it sounds like a fuzz should sound. Balance still works, about half down, and cuts then out, as expected.
Fine tuning the 1M leak pot changes little beyond 500k. Note that C13 on Q3īs input is not necessary for biasing per se, but using the Buzzaroundīs way of setting the fuzz level (with a pot to ground, which yields better control over the amount of signal hitting Q3...), a low setting of the knob would also upset Q3īs bias point, which results in a choked tone. Using the cap leaves its DC bias alone and allows for very small, precise adjustments.

Since I recently obtained a fair batch of 2N2926 (which are listed as replacement for BC108), I tried those. The gain is around 150 and they sound great there. I bought a handful of 2N2222īs that worked equally great, albeit a bit more gainy (180). There was no subjective difference in noise, the biggest source of noise being the darlingtons.
I used a 220pF B-C-cap, to tone down treble just a hair.

Re-visiting The Darlington Stage

I then went back to stage one and played with the collector resistor. A small change can make the sound just a little hairier, a small correction on the base resistor appeared necessary.

So yes, these units need to be tweaked for good tone, question is, what is good tone? And what, if they were not tweaked at all in the old days? What if bias changed with heat? This will leave you with a unit that is largely not functioning as intended, although this has gained some status of its own for a specialized music genre. It is beyond doubt, these units were not made deliberately to sputter and fart (that came later...), they were made for screaming sustain and natural decay.

So, with silicon, once a unit is tweaked, it will remain the same. And it sounds great. Any alleged shrillness can be concealed with a natural overdrive after or a cranked amp. This unit really has a midrange bark that is matchless.

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Using The Fuzz Right

I used to be not particularly fond of such fuzzy devices, until I heard them used by proīs like Jimmy Page and Tommy Bolin. Those are not gated and sputtery, they have great sustain and decay and a very raw and untamed character to them, which reflects the sixtiesī explosive spirit well.


Many amateurīs videos are sputtery and trebly, which, at best, can be used for a special effect or punk. I do not like Joe Goreīs devices as well, because he trims them towards this niché sound, although he is classy in what he does.
Note that on all pro videos made, this is not the case. They sound smooth.

Those devices need to be used under 60ies conditions: into a pretty dark amp. The amps at this time, particularly Marshalls,  were all pretty dark sounding from a start (which is why guys like Vox came into play...), which worsens if you push the thing.
A pushed tube amp will always tend to swallow treble. Hendrix used Twin Reverbīs in his studio work (just because they were reliable and were there...), which are inherently bright, but he thumped them...
  • Run your fuzz into an overdrive

    But for bedroom levels, you can fake this with a suitable overdrive after the fuzz. In this case the overdrive sets the overall loudness. There will be hardly an increase in loudness, even if you run your fuzz into the overdrive at full throttle. I have good results with setting the fuzz somewhat louder, that it really pushes the overdrive. Just as it would push a tube amp.
  • Use some basic loudness

    However, you need a basic loudness. Set you amp to whisper loudness - it will sound shitty. Turn it up somewhat, it will come alive.

  • Use an overdrive that becomes darker when pushed

    Note that not all overdrives behave like a tube amp when driven into saturation - becoming darker.

    I have many of them stomp boxes that become ringy when pushed - be it diode clippers or discrete. No amount of treble filtering will remove that, since it is a dynamic effect.
  • Use an overdrive that stays transparent

    Although being a matter of taste, a transparent overdrive alters your tone the least. Beware that many overdrives, that claim to be transparent, are not! There seems to be some huge misconception about this term. Many of those are far from transparent in the sense, that they donīt prefer or push some part of the sonic range. Most of the latter are tube screamer variants, and you would be surprised how many highly touted units belong to this category[1].

One unit that I found (and, no, I have no connection to them...) that works brilliantly for this job, is the Wampler Ecstasy (resp. Euphoria). Resist however the temptation to use it for anything else[2]. It is a one trick pony, but this it does well. It is advertised as "dumble tone" - ignore that. Ignore all tags. And get a work-a-like clone.

So all recordings you hear, inclusive the ones following, are not whatīs real. It may and it will sound different with your setup and playing. But you can hear its potential.



"All is an illusion"

- Ramana Maharishi                                                                                                                                     

Itīs what every little bit in the sound chain contributes to your tone. We have to live with that.
In this respect, those promotion videos are cheating, but at the same time, they are true. Just be aware of the fact.


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Sound Samples

The recordings have been done using the following setup and no further processing:

  • Strat with Bill Lawrence (Wilde Pickups) microcoils, neck pickup + bridge pickup, full bass
  • J-FET buffer directly after the guitar
  • Mark III: Vol = 10h, fuzz 15h, texture full, tone 9h (bass slightly cut). (Total volume is louder than unity to get the subsequent stage going...)
  • Wampler Euphoria Overdrive, setting = natural. Gain = 1. Slight crunch appears when guit. vol = full and heavy playing.This mimics a tube amp on the edge of breakup
  • Peavey Bandit 112 silver stripe, clean channel, Resonance on, T-Dynamics fully down, volume=9, all others=12
  • Rode M3 mic @ 20cm distance
  • Recording device: Focusrite PC interface into DAW
(Names may be copyrighted by the associated copyright holder, no association with any of them)

A few quick and nasty takes. No exercise in timing or else, excuse the amateur playing. Crank you speakers. On my stereo speakers the recordings sound a bit less trebly than in reality.

Since this is sticking in the ear, doing a bit of Zeppelin. Volume swells in the beginning. Note how the fuzz gets nasty. Note also the endless sustain and the perfect decay.


 
A bit of chord work, riding the volume. Great definition at all distortion levels, great searing lead tone. Never brittle and ear piercing.



A little wah in front. Teams great with a wah. Actually my formant filterīs auto wah section.



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Reference

[1] Non transparent ODīs: some from this category that are fairly popular, are the Timmy and the Klon. Again, those are
    NOT transparent, they are tube screamer derivatives with a strong mid emphasis.

    Brian Wampler: Transparent Overdrives, are there actually any?;  https://www.wamplerpedals.com/blog/talking-about-gear/2019/02/transparent-overdrives-are-there-actually-any/

[2] Pedal Genius: How to Use Your Wampler Euphoria; https://pedalgenius.com/how-to-use-your-wampler-euphoria/

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Update History
  • Feb. 4, 2020  first release
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