Author Topic: big muff pi- op amp mods?  (Read 3815 times)

plexi12000

big muff pi- op amp mods?
« on: February 10, 2015, 08:13:56 PM »
hey dudes-  i was wondering if anyone can suggest any articles/websites or whatever, for any cool BMP op amp amps. i know there are a gazillion mods for transistor pi's.  Any for the op amps?

I'm not a pedal guru or anything, so i have to 'cheat' -lol  i recently bought a board from the GGG boys and might get going on it this week.

i guess i'll look around on you-tube, as well.  thank you  :)

acehobojoe

Re: big muff pi- op amp mods?
« Reply #1 on: February 10, 2015, 09:31:27 PM »
anything modifying tone would be pretty easy, both pre and post.

You could also see about adding a mix control.

plexi12000

Re: big muff pi- op amp mods?
« Reply #2 on: February 10, 2015, 09:38:47 PM »
thanks acehobojoe....but i aint that good yet!!!  lol

antonis

Re: big muff pi- op amp mods?
« Reply #3 on: February 11, 2015, 07:35:51 AM »
So, to be good (if you like to..) read this: http://www.electrosmash.com/big-muff-pi-analysis and incorporate (in your mind) the two BJT clipping gain stages in IC2's single one... :icon_wink:

Then, all mods concerning diodes, capacitors, filters e.t.c are almost indentical...
Can't follow your signature changes, Stephen..!!

Moonsun

Re: big muff pi- op amp mods?
« Reply #4 on: February 11, 2015, 07:42:19 AM »
i have red LEDs in the first stage and 4148 in second, sounds doomy...
p.s. i was using not the original opamp big muff schematic, but the one from "another" forum, marked as "real" ic big muff 741. in this schematic bjt was replaced with opamps.
« Last Edit: February 11, 2015, 09:03:11 AM by Moonsun »

plexi12000

Re: big muff pi- op amp mods?
« Reply #5 on: February 11, 2015, 11:11:21 AM »
cool--- thank you!  i'll take a look.   i didnt find much on the web about the op amp version mods.  idk.....maybe people dont like them as much? lol

plexi12000

Re: big muff pi- op amp mods?
« Reply #6 on: February 11, 2015, 11:35:58 AM »
i was thinking about getting one of brian wampler's books about pedals.  not sure if there still n print....maybe have to find a used one.   but it looks like as good a place to start as anywhere else.

DiscoVlad

Re: big muff pi- op amp mods?
« Reply #7 on: February 11, 2015, 08:39:08 PM »
Here's a schematic for the Opamp Big Muff that I drew a few years ago. It was based on tracing the board from the photos on KitRae's site, and was meant to cover as many of the available variants as possible.

Mod ideas:
Change the tone stack (C7, C8, C10, R11, R12, POT2).
Add/remove/change clipping diodes for asymmetrical clipping.
Tonestack bypass (C9,R13,R14, SW1).
Increasing the value of the stabilisation cap C6 moves the overall frequency response downwards -> Darker/more bass/muddier sound.
Lower values move it upwards, the "standard" values were either 150pF or 330pF.

nocentelli

Re: big muff pi- op amp mods?
« Reply #8 on: June 07, 2018, 07:52:34 AM »
i was thinking about getting one of brian wampler's books about pedals.  not sure if there still n print....maybe have to find a used one.   but it looks like as good a place to start as anywhere else.



I'd be interested to read Brian Wampler's take on the IC Big Muff. It looks like the (now discontinued) Leviathan fuzz might have elements in common 
Quote from: kaycee
squeeze on the back and never open it up again

MaxPower

Re: big muff pi- op amp mods?
« Reply #9 on: June 07, 2018, 01:00:51 PM »
Waiting for pinkjimi's recommendation of low gain op amps.... :)
What lies behind us and what lies before us are tiny matters, compared to what lies within us - Emerson

BetterOffShred

Re: big muff pi- op amp mods?
« Reply #10 on: June 07, 2018, 03:08:13 PM »
I put a Pharaoh tone stack in mine, toggle for blue LEDs on the second stage clippers, removed the 100k to ground at output, and then put in a 1m pot between output and input to get that really easy feedback loop that makes bananas noises.  It's not done yet but I like it. 

pinkjimiphoton

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Re: big muff pi- op amp mods?
« Reply #11 on: June 07, 2018, 05:22:49 PM »
Waiting for pinkjimi's recommendation of low gain op amps.... :)

i knew it. ;)

alright, i'd start with lm301/8, lf567, tl042 etc for lower gain opamps. i'd have to see the particular layout you're using to advise better.

but that said, in an icbmp, you may find stacking opamps is the way to go. try, say, an lm358 and an ne5532 on top of each other. trim the top opamp legs a little so it will still fit in the enclosure, but try and leave a little room between the chips for air flow. literally solder one chip's legs to the other chip's legs. its easier than it sounds.

but the thing is, and i think it was barber who first came up with the idea online years ago, by combining different styles of opamps, you can get some surprising results.

me and mictester... well, mostly chris... worked up an icbmp using one quad opamp years ago, that sounds bloody killer. like anything else, you can stack different chips to get subtly different tones and responses.

for diodes, in a bmp in general, to MY ear, the best sounding is a combo of ge and PINK 5mm LED'S. the pink ones have a curious "flash over " point that makes for an extremely creamy distortion with the chip muffs in particular. use the anode of like, an 1n34 or 1n60 or whatever connected to the cathode of the led, and then use this simple network in place of each clipping diode. sockets here can be crucial to finding what floats your boat the best. once ya find what ya like, i just solder the components right to the socket... just one leg is usually sufficient to make sure the stuff doesn't fall out at the worst moment <happened to me last thursday... room packed, go to kick into the opener, and wango, my whole rig went down... ONE damn transistor had wiggled free while being bounced around in the truck on the way to the show>

paralleling d4 with a germanium diode will help eliminate some of the noise. the cleaner muff still sounds like a muff, but a lot of people miss the noise. try it and see what ya like.

i prefer usually 47n for coupling caps in these, too.. i'm old, and remember the original bmp's so tend to voice them radically different from the modern ones. the original ones used low gain q's and really did have a creamy violinish sustain unlike ANY modern variants.

i would look at the tone stack too, and add a pot so you can control the midrange.... being able to sweep below, at, and above standard muff values is SICK. added mids can make a muff a different animal.

i build big muffs now with a three band baxendall and a bit of a boost where the tone stack used to be, and use low gain sili q's <not saying which publically, every time i do, someone buys up the whole damn lot of them ffs> with an hFe between about 160 and 220. the sweetest spot for gain is right around 180 for all 4 stages in a transistor muff.. its literally nite and day for the cream and sustain. my variant is what i call a "stiffler's mom",,,,  the biggest muff pi of 'em all...lol

best bet, always, is breadboard, and experiment. DO BE FEARLESS and let the magick smoke out... its how ya learn. try adding extra components and keep notes... also try removing components to see what it will do <this is a great circuit to learn with, really, cuz when its working there is no question of it> and swap out values with caps in particular. the small snubbers can make a huge difference changing their values.
input/output caps and coupling caps, too.

there's more ya can do to mod a transitor muff, really.... but you can still molest the hell out of the circuit. as suggested too, try a feedback circuit... take a 100k-ish pot and wire it between the output side of the output cap <or the output cap from any stage> and feed it back into the input, or try it in different points in the circuit. the 100k <linear> will likely be overkill, but lets ya blend in some of the output which can be brilliant or horrible depending on settings and your taste.

here's a pic of the variation mictester came up with from my miserably lame attempt years ago.. a vero layout, no schematic but ya should be able to follow it point to point ok

digi2t:
"Fuzz, distortion, and wah, are plenty abound. Mutron Flanger, not so much.  8)"
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pinkjimiphoton

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Re: big muff pi- op amp mods?
« Reply #12 on: June 07, 2018, 05:26:34 PM »
i was thinking about getting one of brian wampler's books about pedals.  not sure if there still n print....maybe have to find a used one.   but it looks like as good a place to start as anywhere else.

i talked to wampcat about this a couple years ago, his books ARE out of print, and he's working on a revised version.
brian is an insanely nice guy, and gave us permission to share the digital copies of his work, they can be found thru links at the "other forum" for free.

i DO have pdf's of them. well written, easy to "grok". but you'd have to contact him and get permission to share them from him, if he says he doesn't mind, i have no issue with uploading a copy for ya. but, it depends on whether he's getting ready to release the new book... if so, i bet its worth the wait.

some of the stuff you can find at the indyguitarist.com archives at the wayback machine, too. thats where i found most of the stuff.
digi2t:
"Fuzz, distortion, and wah, are plenty abound. Mutron Flanger, not so much.  8)"
#FuzzyGoodness