Acid Fuzz Acid Fuzzer MkI



Acid Fuzz (in 2011)

I started building the Acid Fuzzer in 125B enclosures about 1 year ago after a friend of mine, Jimmy James, asked for one.  By the time I tracked down the original Mullard OC75's and TI 2G381's a year or so later, I had lost contact with him and decided to keep it for personal use.  Around the same time I noticed JMI had remade the MKI + other people (D*A*M, Black Cat, + others) were giving the MKI circuit a well deserved shot in the arm.  So, I decided to do a limited run of MK1's in 125B enclosures called the "1965 MKI".  There were only 5 made, and they used one OC75,  and two 2G381 transistors, and featured an on/off power switch in order to be left plugged in on a pedal board.

Later on I received a custom order for a no frills MKI clone in an MDC-531 slanted enclosure.  By this time I was aware that one D. Main had become owner of the trademark "Tone Bender", so I called this one the MKI the "Acid Fuzzer".  All my MKI builds since have been under the "Acid Fuzzer" title. I have had several requests for this particular MKI in the mini wedge enclosure. Unfortunately, I don't have many useable TI 2G381's left, so most new orders are now filled with either US made 2G381's or UK supplied 2G382's that have been re-stamped with "2G381".  Please note that these were not re-stamped by me/Acid Fuzz. Currently, the Acid Fuzzer is more of a custom build than a regular production pedal.

Acid Fuzz

For many the MKI Tone Bender is sort of the Holy Grail of fuzz unobtainability, not only in terms their scarcity, but in terms of their sound.  MK"I" as in number one. The first, the earliest, perhaps the rarest, but by no means the most primitive. For a circuit developed in 1965 the MKI has a thick and "distorted" square wave fuzz sound with some artifacts that can be honed and shaped to produce a very musical fuzz that is both devastating and dynamic.

Unfortunately, we have stopped taking custom orders for our Acid Fuzzer MKI (period correct MKI Tone Bender rebuilds) with the original Mullard OC75/Texas Instruments 2G381 transistor combination.  However, we are trickling out a custom run of about 30 of our "Vintage Series" Acid Fuzzer MKI's.  These are still built the same way they were in 1965, 100% hand made, all point-to-point on paxolin board, Hunts film caps, carbon comp. resistors, and all that jazz. Each pedal in this last limited edition will get it's own custom painted JUMBO two-piece slanted steel enclosure and come loaded with a trio of new old stock germanium transistors: one black glass Mullard OC75 and two Texas Texas instruments 2G381, 2G381A, or 2G382.  We’ll do some swirl finishes and some more tame original style finishes as well.  We will still accommodate some basic custom requests such as LED or 9v jack, just let us know before ordering.  Additionally, if you want your MKI tuned more for single coils or humbuckers, for more low/mids, etc... we can do basic requests like that as well, just drop us a line with what you want and we'll build it for you.

MKI Mini

Fortunately, the original 1965 Mullard OC75/Texas Instruments 2G381 transistor set made from unobtainium is not the only set that sounds great in the MKI type circuit. It still takes careful selection and tuning, but we get excellent results with one N.O.S. Mullard black glass OC75 as the first transistor and two AC128’s as the last two. We use sets like these in our "MKI Mini". With our Mini MKI the idea is to offer alternate transistor combinations that are sonically very similar to the original transistors and just sound amazing in the MKI circuit. If you just want the SOUND of a good MKI in a small pedal board friendly enclosure, this is the way to go. We always load our mini MKI’s  with one new old stock black glass Mullard OC75 in the first position, and two AC128 (or similar) germanium transistors in the second and third stages.

The Sound

Proper transistor selection, along with careful tuning, give every one of our Acid Fuzzer MKI’s a very thick, rich, and musical fuzz tone all around. Gated and gritty at low attack settings, smoother and sustained at higher attack settings. The “Attack” control of the MKI functions differently than most other fuzzes and is in fact a bias control for the second transistor in the circuit.  Rather than a typical tone bender "attack" or fuzz face "fuzz" style of dirt control delivery where you simply expect the sound to get progressively more saturated and "fuzzy" as you turn clockwise, these have a raspy gated “Satisfaction” Maestro Fuzz-Tone like sound at low attack settings.  At higher attack levels they open up to have a singing RAT/MUFF-like smoothness to them, but with an unpredictable note bloom and decay entirely their own. The original design "attack" is a bit of a night and day gated/sustain, with not much in between. We tune our MKI builds to have a much more open and gradual smoother transition that really allows you to fine tune the fuzz to your liking.

One player described the MKI sound generally like this: “I like to visually think of the MKI, as a comet that heats up and then burns out with a long trail of fuzzy cosmic dust at the end”. Yeah it's kinda like that.

For a higher gain fuzz the MKI retains a lot of touch sensitivity, individual note definition and clarity, even when playing full chords. Of course everything is clipped pretty hard, but the MKI's response to your playing is such that the lower notes tend to saturate a bit more and have more dirt and grit and the high notes remain a hair cleaner and this frequency based response variation gives this fuzz a contrast a lot of higher gain pedals lack. When you start getting in to three or more transistor fuzz or any other high gain dirt device, it's really typical for things to get mushy.  I build the Acid Fuzzer MKI's to produce a bold and powerful dynamic sound capable of going from gated Fuzz-Tone to almost Muff-like distortion on the low notes and highs that are more overdriven and articulate than saturated and syrupy, without sacrificing their sustain. These don’t ever clean up nice with your guitar’s volume pot like a two transistor fuzz or even a MKII tone bender, but, unlike Fuzz Face type pedals, they do play nice with most out of the box wah pedals without needing modification. And yes, they do at least calm down to a bit more gated overdriven fuzz sound when you roll your guitar’s volume back.  There's no "clean" clean-up. There's no LED. You know when this is on. Old school 9V battery power only.


  1. “I’ve read that only (name omitted) has the real transistors for MKI’s… are your Texas Instruments 2G381’s real?… I’ve heard that the Mullard OC75 and TI2G381 are impossible to get nowadays.”  Yes.  These are real new old stock transistors, the same exact transistors from the same batch and source as (name omitted) uses in many of their builds.

  2. “Do you always use a real Mullard OC75 as first transistor in your MKI “minis”.  Yes, unless you request otherwise, your MKI mini will arrive with one Mullard OC75 in the first position, and usually two AC128’s in second and third positions.

  3. “Can you do a custom swirl that matches the color of my….”  Sorry, do to the time and mess of the oil dipped swirl process, as well as the difficulty of exactly matching colors from photographs, we do not do custom swirl finishes to order.

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