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Evolution of the Big Muff Pi Circuit - Part 3 - 1980 to Present

©Kit Rae. Last update January 2013

PART 1 PART 2 PART 3

WHY ARE THE TRANSISTORS LABELED IN THE REVERSE ORDER? - Note that Q1-Q4 and D1-D4 are labeled in reverse order from input to output on these schematics than they are on a typical schematic. This is due to the fact that they are printed in this order on the actial V1, V2, and V3 Big Muff PCB's. To keep it from being confusing for those reading their PCB's, since this is primarily a reference for vintage Big Muff owners, and to keep the EH tradition, we have used this order on all Big Muff schematics, including post 1980's Big Muffs and clones. I have also tried to keep the part numbers consistent from schematic to schematic.

MAXON D&S / IBANEZ OVERDRIVE Second Series, modified Violet Ram's Head Big Muff - An update to Maxon's mid 1970's OD-801 Big Muff clone (shown on page 1), also sold in an Ibanez branded version, the OD-850. This is a trace of my square button version, circa 1979-80, with the FET bypass switching section removed. Looking at just the BMP section of this circuit you will find it is different from the '74 circuit. This one is an exact clone of a 1973 "violet" era Ram's Head Big Muff variant, with the exception of one slight pathway mod in the tone section. Minor changes were made to the circuit for the next several years. Maxon used the same pcbs in a variety of different enclosures, marketed as the Maxon OD-801, Maxon MD-9, Maxon Jet Driver JD-01, Maxon Magnum Distortion MD-9, Ibanez Double Sound (second version), Ibanez Overdrive OD-9. The Ibanez 60's Fuzz Soundtank SF5 and FZ5 were also variations of this circuit.

I have written more about Maxon and the Maxon/Ibanez Big Muff clones here.

Maxon Ibanez OD-859, OD-801 Schematic


VERSION 7 SOVTEK BIG MUFF PI - 3 circuit variants exist, each made in extended manufacturing runs.

The RED ARMY OVERDRIVE and Version 7 "CIVIL WAR" BIG MUFF PI - After several years of being out of production, around 1991 Electro-Harmonix returned to the market with the Russian made Sovtek Big Muffs. The same pedal was branded as both the Big Muff Pi and as the Red Army Overdrive, sold simultaneously. The circuit did not follow the schematic of any previous version, but rather was a reinvented set of component values, giving it a whole new twist on the tone. It was given smaller 390Ω emitter resistors for a lower gain sound, and a slightly less mid scooped tone stack. The small .047µF clipping caps at C6 and C7, usually 1µF, gave these a fat, thunderous bottom end.

Two versions of the circuit were made, shown below, but the only difference was the feedback/filter capacitors at R9, C11, and C12. First editions had 430pF caps, but later changed to 500pF (two 1nF caps in series) for the second edition. Using the caps in series is a strange oddity for the Russian Big Muffs. The reason for this could have been simply due to the factory having a surplus of 1nF caps, but there were several cap types used through the years, indicating that was not the reason. It is more likely that 500pF caps were simply not available, so the factory opted for series caps equating to that value. It makes no difference to the sound if series caps, or a single cap equal to the series value is used.

Notice that an effect on LED has been added to the circuit (a first for a Big Muff) with a limiting resistor at R1 to keep the 9v from burning out the LED.

The Russian transistors were T018 cased, marked KT3102E 9108, or unmarked TO92 packages. NPN 2N5089 or 2N5210 are near equivalents. The original Silicon diodes used were Russian KD521A and KD521V types, no longer made. IN914 (shown on the schematic) or 1N4148 are approximate modern equivalents, but are not identical. The differences are minor, but diode types do affect the sound frequencies that are clipped.

Red Army Overdrive Schematic

Civil War Big Muff Schematic

V7B GREEN CIVIL WAR, and 7C GREEN RUSSIAN "TALL FONT" - Identical to the 2nd Edition schematic shown above, but a polarized 22uF power supply filter cap was added to the 9V rail at C14, and the 1.5k resistor for the LED was moved off board to the foot switch or at the LED base, neither of which matter to the tone. The 500pF (two 1nF caps in series) feedback/filter capacitors remained the standard for the first three stages. I have also seen a few with a 22k low pass resistor in the tone section at R8, like the high pass, but almost all were 20k. The input capacitor was occasionally 43k rather than the standard 39k. Transistors were unmarked TO92, or TO18 cases marked KT3102E 9108. A close equivalent is the modern 2N5089. The Russian transistors were T018 cased, marked KT3102E 9108, or unmarked TO92 packages. NPN 2N5089 or 2N5210 are near equivalents. The original Silicon diodes used were Russian KD521A, KD521V, 2D510A, all no longer made. IN914 (shown on the schematic) or 1N4148 are approximate modern equivalents, but are not identical. The differences are minor, but diode types do affect the sound frequencies that are clipped.

Sovteks were only powered by batteries, which are a clean source of DC power and do not require filtering to remove the stray DC that can leak into the audio signal from unregulated AC power adaptors, so it is odd that E-H added power supply filtering at C14. Perhaps this was added because AC adaptors were becoming available that allowed them to be connected directly to the 9v battery snaps. Since some wall warts (AC to DC power adaptors) do not regulate and filter properly it is necessary to add some filtering to the circuit. Wall warts convert AC to DC using a bridge rectifier, but some of that rippling alternating current can still leak through the power supply rail into the direct current, creating 60 cycle hum noise in the audio signal. big electrolytic cap on the +9v power supply at C14 was added to smoothly filter the AC ripple by draining the ripple peaks to ground, leaving (mostly) straight DC going through the circuit.

I have seen a lot of marketing for green Russian BMP clones that imply there is a difference in the Tall Font and previous Civil War circuits. To make it clear, as stated above, there was a 1st and a 2nd edition V7 circuit, with the only difference being the feedback/filter caps. Sovteks with Civil War graphics used 430pF or 500pF. Green Civil War Sovteks, and Tall Fonts only used 500pF. That is the only difference. Part tolerances come into play where the sound is concerned, but the schematics were the same. I have owned dozens of these and they all sound slightly different from each other. Oddly enough, the parts I have measured are actually not that far out of spec from the printed values. Variances in the different diode spec's may have more to do with it..

Green Russian Big Muff Schematic

V7C GREEN RUSSIAN "BUBBLE FONT", 7D BLACK RUSSIAN, and SMALL BOX BLACK RUSSIAN BIG MUFF PI - Although there were several different pcb layouts used for these versions, they all followed the exact same schematic, with the rare resistor value change for one of a similar value. The only real difference from the previous Tall Font version was changing the two 1nF series (500pF total) feedback/filter capacitors in the first three stages at C10, C11, and C12, to single 470pF caps like the USA made Big Muffs. A slight bit more grit, and less smooth. R8 was sometimes 39k, but rarely. The transistors used were Russian 3102EM, 549C or 547C. The original Silicon diodes used in the green Civil War and Tall Font versions were Russian 2D510A, and a type marked with a black band and black dot, all no longer made. The diodes in the Bubble Font version and Black Russians were KD522B. IN914 (shown on the schematic) or 1N4148 are approximate modern equivalents, but are not identical. The differences are minor, but diode types do affect the sound frequencies that are clipped.

The sound difference between this version and the previous Tall Font version was minimal, but us Big Muff cork sniffers hear it. The parts kept getting cheaper, and the enclosures thinner and smaller as the years went by, so EHX gave it the axe. It was replaced with the excellent Bass Big Muff, which is a similar circuit, although not identical. The Deluxe Bass Big Muff was an upgrade to the Bass Big Muff.

Bubble Font/Black Russian Big Muff Schematic


THE ERA OF BIG MUFF MODS and BOUTIQUE CLONES - In the mid 1990's the Big Muff mods that are common today were only just starting to be discussed worldwide on a few internet forums and chat rooms. Pete Cornish was one of the first people known (though unkown to the public at the time) to have been making modified versions of the Big Muff circuit, going as far back as the late 1970's with the first custom Big Muff pedal made for David Gilmour of Pink Floyd, then with his P-2 and G-2 variations in the 1990's. Jeorge Tripps was one of the first to make a BMP clone with a modified tone section in 1995, the Swollen Pickle, also offering a mids switch option. Ron Neeley of Ronsound started offering mods to Big Muffs in the late 1990's. In 1999 Jack Orman (muzique.com) published his A Close Look at the Big Muff & Proco Rat e-book, featuring an in-depth examination of the circuit and several mods. The first highly successful modified BMP clone hit the market in 1999, the Sustain Punch Creamy Dreamer. In 2001 Jack Orman posted his Muff Boost project online, and in 2002 the Muffmaster, both decent booster stages to place in front of the BMP. Jack also posted his AMZ tone/presence control mod in 2002, one of the best tone section mods for the Big Muff. In 2003 Aron Nelson summarized several mods that apply to the BMP circuit on his Simple, Easy Mods/Tips & Techniques page from DIY Stompboxes, including the idea to change the diodes to LED's, among the many other useful mods.

Ron Neeley of Ronsound started making his own Big Muff clone called the Hairpie in 2003, later adding a mids switch. Marc Ahlfs of Skreddy Pedals began making very popular modified Big Muff clones in 2004, later including a mids switch as a standard feature. Across 2004 and 2005 more and more boutique, hand made BMP's started to appear - Jamie Stillman of Earthquaker Devices created the Hoof pedal, Baja Tech made the Da Moaf, MJM made the Foxey Fuzz, Euthymia made the ICBM, Dice Works made the Muff Diver, and D.A.M. made the Ram Head, among others. In 2005 the Piso-Tones website posted the first collection of Big Muff circuit variant schematics. In 2006 Berarduur (from the old Geekchat website) compiled a great selection of Big Muff specific mods, the Big Muff Pi Mods and Tweaks page, which has become sort of the bible of BMP mods. B.Y.O.C. (Build Your Own Clone) also released the Large Beaver kit in 2006, which was a very versatile, build-it-yourself vintage Big Muff with an adustable tone selector mod. A whole host of new boutique BMP clones continued to appear on the market after this, utilizing these mods or variations of them, many detailed below.

While the reborn Electro-Harmonix company continued to expand and innovate their range of USA Big Muff pedals in the 2000's, dozens and dozens of different BMP clones were being made by dozens of small boutique makers. Many were straight up replicas of vintage BMP circuits, like the superb range offered by Stomp Under Foot, and many were customized variations of the circuit, like those created by Skreddy Pedals. Even the large corporate companies got back into making versions of the BMP, like the Behringer Vintage Distortion and Dunlop Swollen Pickle. Below are schematics of the more popular or interesting takes on the circuit. Apologies to the makers of these modified BMP clones that are in current production (schematics for most of these were already easily available on the web long before I posted these traces of my pedals), and they are all based on pre-existing designs anyway.


PIKLE JUMBO FUZZ modified V6 Big Muff - One of the first popular Big Muff clones, and later a popular mod to the BMP circuit, was the Swollen Pickle Jumbo Fuzz (discontinued). The USA Electro-Harmonix factory was long gone by this time, and the old 1970's American made Big Muffs were increasing in value, so it was natural for some DIY makers to start building clones. The Pickle got it's start in 1995 as a hand made modified BMP clone by Jeorge Tripps (Way Huge Electronics). George made several hundred of these, then Dunlop bought the rights and produced a very different circuit with additional trim pots for a production version in 2009. Note, the schematic below is NOT the current Mark II Swollen Pickle production version made by Dunlop.

Aside from the joke of changing sex of the "Big Muff" name by calling it a "Swollen Pickle", the original Pickle was essentially a V6 era Big Muff clone with a unique tone section mod. The standard .01µF low pass cap at C8 was changed to .047, and the high pass cap at C9, typically .004, is .0033µF here. This provides what some would say are more 'usable' sounds at the extreme ends of the bass and treble, but still retains a deep mids scoop. There is also an additional trace connecting the high pass tone filter at the C9/R5 junction to the path between C3 and the R7/R3 junction. C9 normally meets the junction at R5 and lug 3 of the tone pot, although I don't think it makes any difference either way. This may not seem like much of a mod these days, but back then altering the mid scooped BMP tone stack was something rare.

Another unique construction feature of this clone is that it uses a quad transistor chip instead of individual transistors. This offers some noise reduction benefits and more consistent transistor matching than discreet transistors. It also had the benefit in making the circuit appear to be something other than a Big Muff clone. Another version of the Swollen Pickle included a mids switch mod to reduce the mid range scoop, a mod later utilized by Skreddy Pedals.

Swollen Pickle Schematic


CREAMY DREAMER modified Ram's Head Big Muff - The Creamy Dreamer was a very successful, but short lived modified Big Muff clone made by Jeff Doucette/Sustain Punch in the late 1990's, looseley advertised as a pedal the Smashing Pumpkins used and endorsed (more on that story here.). It seems it was not really endorsed by the band, and its use by the band, if any, is questionable. The hype around it has remained however, and there have been numerous 'creamy dreamer' clones and freely shared mods circulated since this pedal went out of production in 2000. It is generally believed that it was simply a Russian Big Muff clone with emitter lift and limiting resistor mods - but the gooped circuit prevented people from actually tracing it for years, creating some wild speculation about what was actually done. It is finally revealed in all of it's glory here. Well, not so glorious actually, but it is a decent sounding mod.

Looking at the actual circuit I ungooped in my CD, I found it was nothing like Russian Big Muff at all, but very similar to one of the mid '70's Ram's Head variants. I found there was no limiting resistor mod, but the emitter resistors were removed in the first three stages. The tone stage is modified with matching 47k high pass and low pass resistors at R5/R8, flattening the mid scoop out somewhat. Even though there is nothing special about the other component values, pulling those emitter resistors makes for a very high gain Big Muff, and I suppose you could call the EQ from that tone stack 'creamy'. I like it. It is a bit light on the low end for my taste, but that can be remedied by enlarging the clipping caps at C6 and C7 anywhere from .047uF to .1uF, and bringing the feedback filter caps at C11/C12 up to 500pF. (now - you know who you are - you can stop emailing me asking if I have the CD schematic! :)

Creamy Dreamer Schematic


BIG MUFF OVERDRIVE / G2 - Pete Cornish, famed effects rig builder, has built a range of rugged, high quality, custom variants of many classic effects, including the P-1 (Ram's Head based) and P-2 (Russian based) Big Muff variants used by David Gilmour. Pete was creating his customized takes on the Big Muff long before the electronics community had the internet available to pass ideas back and forth. The G-2 was his third take on the BMP circuit, created in the early 1990's for Lou Reed, then sold to the public as a stand alone pedal circa 2002.

This is one of the more unique sounding revisions to the Big Muff circuit, in that it does not sound like a Big Muff at all, but more of a low gain, smooth overdrive. It features some very unusual component values, and trades the Silicon diodes for Germanium. The pedal also included Pete's signature unity gain input/output buffer system for a very clean and balanced signal to your amp. Strip away the buffer components down to the sound circuit and you find the basic Big Muff pathway architecture, with the high pass tone section and part of the low pass removed, and a slightly modified recovery stage (all shown in red). Ge diodes do not compress and distort as much as Si, and they cut the signal level down in the clipping stages, meaning less volume. Pete's blend of component values compensate and take advanatge of that.

Big Muff Overdrive/G2 Schematic


MAYONAISE MUFF WITH MIDS CONTROL Triangle Big Muff clone - An exact clone made in 2004 of a 1972 Big Muff variant, similar to the "standard" V1 variant shown on page 1 (V1 67 #1) but with larger collector resistors at R11, R13. Named after the Smashing Pumpkins song, the Mayonaise (discontinued) was made by Marc Ahlfs of Skreddy Pedals. It was the first in a long line of popular Skreddy boutique BMP's. A common feature in the Skreddy muffs (though not on the original Mayonaise) was a mids switch mod to reduce the mid range scoop, included in the schematic below. Values for C9A and C9B can be tweaked to taste. When C9B is switched on, the values of both caps sum to create a larger cap value, and smaller mid range scoop for brighter mids. Another way to control the mids scoop depth is to add a trim pot to the high pass filter, as shown in the two mods below. George Tripps (Way Huge Electronics, Dunlop) was one of the first to use the mids switch mod in the mid 1990's on the Swollen Pickle, then Ron Neeley of Ronsound, and Jack Orman (muzique.com) was the originator of Big Muff mids pot mods with his AMZ tone/presence control.

There are also many other interesting mods to the BMP circuit that have been produced by Skreddy Pedals throughout the years.

Mayonaise Schematic


DICE WORKS MUFF DIVER modified Triangle Big Muff clone - A discontinued boutique clone made by Eric Holden, circa 2005, of the an original Electro-Harmonix V1 Big Muff circuit shown on page 1 (PNP Triangle 72 #2), with the addition of switchable coupling caps at C4 and C5 to make it sound more like the custom Big Muff known as the P-1 that Pete Cornish made for David Gilmour (of Pink Floyd) in the late 1970's. In reality, it sounds nothing like the P-1, but resembles something in between the Cornish P-2 and G-2 tone. It makes for a very versatile Big Muff. One of my favorites. Another version of the Muff Diver included a switchable input cap setup identical to the Cornish/Original switch in the standard version, switchable Ge diodes in the first clipping stage, and a switch to remove the Si diodes from the second clipping stage.

The original PNP Triangle Big Muff variant this was cloned from was one of the first BMP's to be traced and posted on the world wide web. Even though it was actually not a common V1 circuit at all, most boutique BMP clones used this schematic. Still, it sounds very good and defined what people thought a Triangle Big Muff was supposed to sound like in the early days of boutique BMP cloning through the mid 1990's to the early 2000's. The Dice Works Muff Diver, BYOC Large Beaver Triangle V1, General Guitar Gadgets BMP Triangle, and many other Triangle clones were based on this version.

Muff Diver Schematic


VINTAGE DISTORTION modified Sovtek Big Muff - Behringer came out with a visually blatant, China made knockoff of the BMP in 2005, called the VD-1 Vintage Distortion. Despite the look and name, the circuit was not a clone of a V2 or V3 era BMP, but was based on the Electro-Harmonix small box, black Russian Sovtek Big Muff circuit. The sound is more on the kinder, gentler side than the Russian circuits. Smooth, but with the heavy low end removed by the modified tone section. The component values are very similar to the black Russian BMP, but the tone stage is different. The low pass functions the same, but the high pass pathways have been modified, removing most of the boomy bass, and some of the trademark Big Muff sound. R5 is a 100k resistor, instead of the common 22k high pass resistor, with a huge 2.2M resistor added at R27, creating a boosted mid range. Another interesting effect, I assume caused by the tone section mods, is that when the guitar volume is turned down, the distortion gates and sputters, something like a dying battery in a fuzz pedal.

Even though SMD components get a bad rap in the DIY builder community, it appears the small component size and tight circuit tracks in the Behringer offer noise benefits over larger, old fashioned thru-hole components. This pedal is almost completely silent, even at maximum gain. Something I have never found with any other Sovtek based Big Muff circuit.

Vintage Distortion Schematic


HOOWF modified Violet Ram's Head Big Muff - In 2005 Jamie Stillman of Earthquaker Devices, in between managing tours for The Black Keys, made a superb modified Big Muff clone called the Hoof. Very close to the schematic below, the Hoof is often referenced as a modded green Russian BMP circuit. Indeed, its genesis was with Jamie reverse engineering a Russian BMP owned by Dan Auerbach of the Black Keys, but the current four knob version I own is actually a violet era Ram's Head circuit with mods to the clipping and tone stages. The tones produced by the mods are similar to a Sovtek BMP however, and in that regard, it sounds even better than most of the old Sovtek circuits. The original was a simple, three-knob clone, but the later version added an additional 25k pot in the tone stage.

A popular mod to the BMP circuit was to trade the Silicon transistors out for Germanium transistors, which is basically what we have here in the two clipping stages. Ge transistors in the BMP circuit are said to smooth out the tone because they filter out more high frequncy sound than Si. They also reduce the gain/signal level, which has the affect of smoothing out the tone. Another popular BMP mod popularized around 2002 was to change the standard Silicon clipping diodes for LED's, which are essentially diodes, giving a different voice to the tone. LED's compress the signal less than Silicon, resulting in lower volume and a slightly cleaner and brighter distortion. The Hoof has been made with red, and later, clear LED's. Different colors/types of LED's produce slightly different variations on the clipping tone and gain. In the Hoof these two mods result in a somewhat grittier, sputtery distortion characteristic, similar to the sputter heard in some Germanium fuzz pedals. There is also a slightly less muffled cleanup when the guitar volume is turned down, and the pedal is slightly less noisy than a traditional BMP.

The Shift control is essentially the AMZ tone/presence control mod, and this is probably the best use of the AMZ tone control I have heard in a Big Muff clone, with a wide spectrum of useful tones across the pot sweeps. The volume pot is a huge 1M (1000k) and the sustain pot is 50k, rather than the standard 100k pots typically used in a Muff.

Hoof Schematic


BEAVER modified 1976 Ram's Head Big Muff - In 2006 B.Y.O.C. (Build Your Own Clone) created a built-it-yourself vintage Big Muff kit called the Large Beaver that included all the parts to assemble a Big Muff. It could be built either as a V1 Big Muff (Triangle 72 #2 schematic on page 1), or a Ram's Head (Ram's Head 76 #1 schematic on page 2), two of the best sounding variants. The Beaver also included a tone selector switch, allowing you to choose the stock scooped mid range, flat mid range, boosted mid range, or tone bypass. The BMP mid range scoop is the main reason many people end up not getting along with the BMP. It can sometimes get lost in a band mix, or simply does not sound good with certain amps with a competing mid range. This mod makes the BMP very versatile, overcoming those issues.

Below is the Ram's Head 76 #2 schematic from page 2, similar to the one BYOC used, but better in my opinion, with a similar tone selector mod using my preferred values for the flat and boosted mids.

76 big muff with mids switch mod


POWER BOOSTED BIG MUFF - The Electro-Harmonix LPB-1 (Linear Power Booster) is a simple and effective little booster circuit made by EHX way back in 1968. I have been playing around using it to drive or follow my Big Muffs in the signal chain for years, and it is one of the dream combos I always wished EHX would actually make (a Big Muff - Colorsound Power Boost combo is another). There was a Big Muff/booster combo clone made in 1971 called the Ace Tone Fuzz Master FM-3, but the booster stage was switched separately from the BMP circuit. In the early 2000's I started to see some boutique Big Muffs being made that included the LPB-1 built in, or a similar booster circuit like the AMZ mosfet booster, incorporated as an inline stage of the BMP circuit. The last stage of the Big Muff is basically the same as the LPB-1, so it seemed a natural idea to throw another one in front of the circuit with a gain pot, making a Big Muff with a preamp booster. Below is a trace of a custom modded BMP I found on ebay in 2005. A bit heavy on the saturation and low end for most people.

CW Big Muff with Power Boost Schematic

FUZZ BOOSTED BIG MUFF - Another version of the Civil War Big Muff with a pre-amp booster stage on the front end, slightly better than the one above. The booster here is based on one Jack Orman (muzique.com) came up with, similar to a single BMP gain stage, minus the feedback capacitor. This provides a disortion boost, but the clipping parts shown in red can be removed to give a clean boost to the Big Muff input stage like the LPB-1.

CW Big Muff with Fuzz Boost Schematic

MUSKETT modified Sovtek Big Muff - How do you make the Muff with LPB-1 Power Booster shown above even better? Refine the input saturation and add a bunch of trim pots to make it very tweakable. Blackout Effectors did just that in 2008 and the result is one of the most versatile Sovtek Big Muff clones out there, the Musket, similar to the schematic below. The Focus pot adjusts the LPB-1 saturation into the Big Muff input stage, similar to what the input switch on the Muff Diver (shown above) did. The Mids pot, a variant on the AMZ tone/presence control, lets you adjust the mid-range frequency scoop from flat to boosted. The Big Muff part of the circuit is simply a Black Russian with the .047uF clipping caps changed to .1uF to keep the bottom end in check.

Musket


SUPERCOLYDYR modified Sovtek Big Muff - The Collider was yet another modified Russian Big Muff clone (discontinued), this one a tweakable, bass guitar friendly circuit, built by Earthbound Audio in 2008. Mark at Earthbound added a Depth pot at the input stage, similar to the Focus pot in the Muskett schematic shown above. The tone section has been modified to include a 50k mid range pot at R27, a variant on the AMZ tone/presence control, allowing adjustment to the mid-range frequency. Limiting resistors at R12 and R19 are half the size of the resistors in a Russian Big Muff, and feedback resistors at C12 and R15 are 1M (1000k), around double the size of a Russian Big Muff. This creates a lot more drive, crunch, and gain in each clipping stage than a traditional Russian BMP.

Supercollider Big Muff


PHARO modified 47 Ram's Head Big Muff- The Pharaoh by Black Arts Toneworks followed a few years after the Collider shown above, but was apparently inspired by it. Both use MPSA18 transistors in Q4 and 2N5089 in Q1-3, along with tantalum input and output caps. The basic Big Muff part of the circuit in the Pharoah is very similar to the "47" Ram's Head BMP shown on page 1, with several mods that allow for a wide range of tonal divertsity. The input resistor in the first stage has been converted to a hi (39k) and low (390k) gain switch, affecting the low cut filtering in the input stage, but unfortnately also affecting the input signal level, causing a large volume difference between the two sides. The high side is basically the stock Big Muff input, and the low side allows for lower gain, overdrive-like tones.

A 25k pot was added to the tone stage in place of the R8 low pass resistor, yet another variant on the AMZ tone/presence control, allowing a boost to the highs. The low pass cap at C8 was enlarged to 2.2µF to balance the low pass filtering. The large cap and resistor at C9 and R5 on the high pass sides allow for less mid range scoop than the "47" Ram's Head.

An SPDT (on/off/on) switch was added to the second clipping stage to toggle between bypassing the diodes completely (a popular mod to the BMP circuit originating with the 1973 Supa Tonebender - violet Big Muff clone), or switching to either Germanium or Silicon diodes, another common BMP mod. The Germanium side gives a slightly different voice to the distortion than the traditional Silicon diodes, with a smooth overdrive-like character when the low side of the input switch is selected. The Germaniums also compress the sound slightly less than Silicon diodes, so there is a large volume cut when they are switched on. On average, Ge diodes start to clip at around half the voltage of Si, so the output level is around half. A third Ge diode was added to the Ge clipping loop to help bring the output level back up, but there is still a volume drop when engaged. The volume disparity between the switchable options makes switching between them impractical in a live situation (as does the blindingly bright LED) without having to adjust the volume, but the mods do allow for a much wider, well rounded range of sounds than a stock BMP.

Pharoah Big Muff Schematic


VERSION 9 "NYC REISSUE" BIG MUFF PI - Four versions of the circuit exist

V9 "NYC REISSUE" BIG MUFF - I'll finish off this circuit evolution article going back to the first version of the reborn Big Muff Pi from 2000 (discontinued). Note that this schematic is NOT the circuit from the current current version of the BMP made by Electro-Harmonix, or from any other current version. It also does not include the power filtering, reverse polarity protection, and LED components, just the audio circuit. Also note that the transistors are actually labeled in reverse (Q1-Q4) on the actual circuit board from what is shown on this schematic.

This 2000 reissue version was a new take on the BMP circuit from EHX designer Fran Blanche, from when EHX was just restarting as a company again in the USA. The component values appear to be a mix of the late 70's V2 BMP, with a deeply mid-scooped tone section from one of the early V1 BMP's, and 390Ω emitter resistors in the clipping stages from a Sovtek BMP. The 3003-A revision from 2001 was basically the same. I like the sound of this one a lot. EHX decided to change the circuit in 2007, then again in 2008, so the current model has a different, heavier and doomier sound.

Previous USA Big Muffs used 1N4148 Silicon diodes, but EHX changed to 1N6263 Silicium Schottky diodes for the reissue in 2000. These compress the sound more and make it slightly more trebly, contributing to the different sound of the reissues. EHX changed back to 1N4148 by 2008.

There were, and still are, complainers who say the reissues "do not sound as good as the originals", but as you can see from this article, there never was one "original" to reference as a basis for the sound. The Big Muff Pi is an evolving and ever changing circuit, and this was just the latest evolution. I have no doubt that when this version is 25-30 years old, it will be considered a collectible classic, just as the 1970's Big Muffs are considered today.

NYC Reissue Big Muff 2000 Schematic


STRIP BOARD LAYOUTS - If you are a hobby pedal maker or are handy with a soldering iron and want to build your own, or experiment with these different versions and mods, a compact strip board layout for the BMP can be found at the Turretboard.org website. The layout is well drawn and easy to follow. Part numbers correspond to the part numbers on the Circuit Guide, and all schematics on this website. Through-hole circuits with large capacitors, resistors, diodes, and transistors, are rapidly becoming a thing of the past for mass production pedals. Everything seems to be transitioning to micro sized SMD components, machine populated onto circuit boards. Strip board is a fun way to play around with the old school method of making pedal circuits. Be aware that the startup costs for equipment, parts, and time involved are probably higher than simply buying an Electro-Harmonix BMP or a BMP clone.

I will be adding more schematics of other discontinued production and boutique BMP clones in the future. I will not post the schematics of anything in the current EHX line, like the current Big Muff, Tone Wicker Big Muff, or Bass big Muff, so don't look for them here.

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