# Tip o' the hat to member nonreverb: Pimping a Big Muff



## mhammer (Nov 30, 2007)

Brought my amp over to him yesterday for some TLC. And after a very pleasant hour spent in gear-talk, I spotted a Big Muff on the way out. "Oh that. Some customer left it off 6 yearsago, and never came back for it. You can have it."

The BMP is a fun circuit to play with, with a zillion modding options, so even though I have distortions and fuzzes coming out my hindquarters, I couldn't resist. It's a NYC reissue in the big box. Quick as a wink, after I got it home, I looked up the schematic, took it apart, and began playing. It's this particular board:








The layout is a smidgen different than the one shown here, in terms of transistor orientation, but it's the identical circuit.
The 470pf feedback caps in the clipping stages are a little lower in value than earlier issues. I like a slightly warmer fuzz tone, so I tacked a 100pf on the copper side in parallel with one of them to make it 570pf for one of the stages. 

The other thing I did was to replace the .01uf cap, seen here just to the left of the Tone pot. The stock Tone control pans between the outputs of a simple lowpass (treble-cut) filter, and a highpass (bass-cut) filter, with the final tone being a product of how much of each filter contributes to the overall output signal. As is, the Tone circuit provide a lowpass rolling off around 720hz, and a highpass rolling off around 1.8khz. The two filters each produce a shallow, rather than steep, rolloff. So, it's not like there is nothing between 720hz and 1.8khz, but there IS a bit of a midrange dip. Not _quite_ the mid-scoop found in things like the Shin-Ei fuzzes, Superfuzz, and some others, but a dip nonetheless.

Following up on some ideas from Jack Orman (http://www.muzique.com/lab/main.htm), I installed a switch to change the rolloff point of the lowpass section. I removed the .01uf cap, and installed a .0047uf cap. I installed it from the copper/trace side of the board, such that the leads from the cap stuck through onto the component side. I wired up a SPDT toggle with a 5600pf cap between the middle and one of the outside terminal on the switch, and a 10M resistor between the middle and other outside lug. I then ran a wire from each of the two outside lugs on the toggle to the two leads from the new cap, sticking up through the board.

What does this do? When only the 4700pf cap is in circuit, the rolloff for the bass section is now around 1.5khz, instead of 720hz, retaining more mids. In the 7:00 position (full bass) the pedal has a throatier, rather than woolly tone. When the tone pot is rotated fully the other way, it still sounds nasal, but there is a little more meat and substance to it. And of course, in the middle position, there is no midscoop.

The 10M resistor makes sure the 5600pf cap always has a way to bleed off, so that there is no audible pop when you switch it in. The toggle is wired so that there is always a connection for the 5600pf cap to ground, but it has to go through the 10M to get there. Flick the toggle and it bridges the 10M resistor, providing a direct path to round. Doing so now adds the 5600pf to the 4700pf for a combined value of .013, which is close enough to our original value. Keep in mind caps aren't usually EXACTLY what it says on them. So, now I have two different tone-control voicings. The higher rolloff for the bass side makes the full-bass setting more usable.

The original Colorsound Supa Tonebender used what was essentially a Big Muff circuit, but omitted the clipping resistors from one of the stages, such that there was only one clipping stages instead of two. I think the next mod I'll do is to install another toggle to lift the clipping diodes on the first stage, to turn it into a Supa Tonebender.

One of the interesting things about this issue is that re-designer Fran Blanche (formerly the brains behind now defunct _Frantone_ pedals) seems to have dropped the gain of the clipping stages, but substituted Schottky diodes for the silicon ones traditionally used. The Schootky type will have a lower clipping threshold, so that less gain is required to produce clipping. The end result, in theory, ought to be that you get the same sound. I would imagine she may have done this to reduce noise. Bear in mind that whatever little hiss comes in on your cable normally gets amplified by the pedal. So if you don't have to amplify quite as much to get the clipping, you end up with a slightly quieter pedal. Not going to do it tonight, but I may decide to use a 3-position toggle so that I have a choice between stock, no diodes, or 1N4148 silicon diodes. I'm normally not one of those guys who goes bonkers over diodes, but I do like my 3-position toggles, since they can easily add more options for pretty much the same amount of work, no more panel-space, and the same switch cost. And of course, the big chassis easily accommodates the added switches.

Finally, the pedal uses a mini phone-jack for external power. I used my stepper drill bit to enlarge the hole and replaced the mini phone jack with the more standard Boss-type 2.1mm barrel jack.

Thanks, Rich! The pedal has a welcoming new home. :smile-new:


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## Guest (Mar 29, 2015)

to be honest, I have no idea about what I read.
can we hear a clip of it? then I'll know what you're talking about.


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## Gizmo (Aug 7, 2008)

>And after a very pleasant hour spent in gear-talk,

Yup, Richard definitely knows his gear!


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## mhammer (Nov 30, 2007)

laristotle said:


> to be honest, I have no idea about what I read.
> can we hear a clip of it? then I'll know what you're talking about.


A few too many household chores to tend to, so a clip will be a little while in coming. In the meantime, point me to a term, topic, or paragraph that was not clear, and I'll do my best to shed more light.


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## Ti-Ron (Mar 21, 2007)

You're really clear, Mark!
I think it's more our lack of knowledge regarding what is in the box! 

Big muff are my fav fuzz, I like to discover new take of them.

P.S. We are still waiting for a mhammer.com store with you're modded pedals avaible for us!


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## Budda (May 29, 2007)

Hold the phone.

Mark took an electronic device used in the guitar world....to someone else?



Congrats on the new acquisition!


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## YellowBrick (Mar 7, 2015)

Believe it or not I actually read the whole post! 

Lots of great ideas so thanks for sharing. I am currently building a RAM's head BMP for a friend who is a David Gilmour total fan. If I need to tweak its sound a bit I'll come back to your thread and steal some ideas


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## mhammer (Nov 30, 2007)

Budda said:


> Hold the phone.
> 
> Mark took an electronic device used in the guitar world....to someone else?
> 
> ...


As you know from firsthand experience, my large workspace is my garage. And as I learned during my youth, cement floors and high voltages are a lousy combination. :sSc_eeksign:


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## Guest (Mar 30, 2015)

mhammer said:


> A few too many household chores to tend to, so a clip will be a little while in coming. In the meantime, point me to a term, topic, or paragraph that was not clear, and I'll do my best to shed more light.


jes' kidding. I'm not technical anyways (DeVry dropout). lol.


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## mhammer (Nov 30, 2007)

Ocean7 said:


> Believe it or not I actually read the whole post!
> 
> Lots of great ideas so thanks for sharing. I am currently building a RAM's head BMP for a friend who is a David Gilmour total fan. If I need to tweak its sound a bit I'll come back to your thread and steal some ideas


The sheer number of mods out there for the basic BMP circuit are bottomless. Heck, if a person went through all the posted mods for the BMP and the Tube Screamer, they'd be occupied for the rest of their life.

I suppose I have a slightly different approach than some folks. Rather than aim for mods that deliver the "ideal" sound, I'm always more curious about simple changes that simply expand the palette without being too invasive or complicated. The way I figure it, music is big enough that I would eventually find a use for whatever new sounds are enabled by the mods, as long as the mod does something audible and useful, and can fit in the available space. And since I can make stuff for myself, going to extreme lengths to transform pedal A into pedal B holds little appeal. If I _wanted_ pedal B, I could make it. I'm happy just to let pedal A blossom in its own way, and realize a bit more potential.

I'm certainly not _above_ mods that shore up shortcomings on a pedal, but the vast majority of commercial pedals are thought out well enough before coming into production that there is nothing to "fix" in them. The designer/manufacturer stuffs in whatever features and ranges they think will work for most people, provide the most usability for the lowest production cost (which includes NOT having any oddball settings that require explanation as to why they won't work or sound nice).

I think we tend to overlook how much the characteristics of some "classic" pedals were the byproduct of rather dumb stuff. For instance, EHX had a standard chassis produced for them with a hole and a slot for a slide-switch knocked out, which gave us the Dr. Q, Small Stone, Small Clone, Bass Balls, Little Big Muff, and a host of others. They got a volume deal on the chassis, which kept production and retail costs down, but restricting themselves to one pot and one switch obliged them to leave much of the potential of many of their classic pedals untapped. There was nothing "wrong" with the pedals - especially when you consider how many were sold - but they could have been more interesting and flexible with the addition of a hole or two to accommodate a few more controls.


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## ed2000 (Feb 16, 2007)

Thanks for the informative write up.


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## Budda (May 29, 2007)

Aaah. Now it makes sense.


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## YellowBrick (Mar 7, 2015)

mhammer said:


> The sheer number of mods out there for the basic BMP circuit are bottomless. Heck, if a person went through all the posted mods for the BMP and the Tube Screamer, they'd be occupied for the rest of their life.
> 
> I suppose I have a slightly different approach than some folks. Rather than aim for mods that deliver the "ideal" sound, I'm always more curious about simple changes that simply expand the palette without being too invasive or complicated. The way I figure it, music is big enough that I would eventually find a use for whatever new sounds are enabled by the mods, as long as the mod does something audible and useful, and can fit in the available space. And since I can make stuff for myself, going to extreme lengths to transform pedal A into pedal B holds little appeal. If I _wanted_ pedal B, I could make it. I'm happy just to let pedal A blossom in its own way, and realize a bit more potential.
> 
> ...


That's very well put and informative. I agree with you if what you meant between the lines is that a lot of folks are chasing the perfect tone by modding and modding and modding again a pedal that they have, with more or less satisfactory results. True they are a lot of awesome production pedals that can be really enjoyed as is!


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## mhammer (Nov 30, 2007)

Well...THAT was a bit of a waste of time. As I said I likely would, I installed a 3-way switch to select between two types of diodes, and none. You can see an empty space where the two blue diodes used to be (see earlier much clearer picture for comparison). I made use of the available pads, soldering each pair of diodes (Schottky for one pair, and silicon for the other) together and connecting one side of each pair to one of the existing pads that connected them with to the collector of the transistor. I ran another wire from the 1uf cap to the center lug of the toggle, and connected the two diode pairs to the outside toggle lugs. Measured the path, and it does exactly what I said it would. But as the Creator is my witness, I could not hear a singel bit of difference between having diodes and none, or between the two diode types. Granted, I'm listening at levels you can talk above, through 8" speakers, but I would have thought there'd be _some_ audible difference.

All of which mystifies me as to why the BMP uses two sets of clipping diodes, instead of sticking with one pair, like the Supa TB, and saving the cost/trouble of additional parts. I can only think that I might have installed something wrong, or that maybe I need different speakers (or ears) to hearthe difference.

The tone control mod (yellow wires) still works great, and I recommend it. If you were pondering following up on my sincere urging to monkey with the first clipping stage. hold off until I get this sorted out.


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## greco (Jul 15, 2007)

Save everyone some up/down scrolling:











mhammer said:


> .....maybe I need different speakers (or *ears*) to hear the difference.


If you find a supplier, could you please order a pair for me also. Let me know the total (shipped) and if you accept EMT.

Thanks

Cheers

Dave


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## fraser (Feb 24, 2007)

one drunken sunday years ago i stumbled into a flea market and bought a big muff for $2.
it was long before the internet, i had no idea what it was, but the name was enough for me.
didnt really work for me, so i gave it to my bass player. 
it sounded great with his bass.
we couldnt keep a straight face because it sounded to us like a seamonster.
(hey, we were eating loads of acid.)

got to get around to building one of these some day.


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## mhammer (Nov 30, 2007)

So at first I couldn't figure out why I couldn't hear anything. Then a member on another forum suggested I skip diode-comparisons and compare diodes and no diodes. I did, and talk about subtle!

When the pedal was configured like a Supa Tonebender (no diodes in first clipping stage), and then I quickly flicked the switch to bring in the diode and return it to BMP format, I could hear a bit of sizzle returning, after the switch-flick. BUt if I slammed a string, and then switched the other way, from diodes to no diodes, there was no difference.

What this told me was that the diodes were having their greatest influence on the initial pick attack during the first 250-300msec or so. B the time I flicked the switch, in going from diodes to no diodes, that initial transient peak had passed. If I went the other way, there was still enough signal level left, that inserting the diodes into the equation could still make a difference. That difference could be expected to disappear within a half-second, but is present when you pick. It was a little more noticeable with HB than SC pickups.


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## High/Deaf (Aug 19, 2009)

I've got a fuzz with dip switches to put green and/or red leds into the circuit. But it mentions it is putting them in the feedback loop - I have no schematic or anything to confirm, but I can hear a subtle difference between the 'no diodes' sound and '4 green' setting and the '2 red' setting. It is a bit subtle but there is definitely a harder edge with the leds in circuit, and moreso with the '2 reds' than '4 greens'.


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