EHX - Big Muff Pi 1977 & 1978 version  [schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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greenskull
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Post by greenskull »

Yeah, you can forget about getting a quick answer to a question once the initial excitement of the topic dies out.
Well anyway, I tried the AG "sustain mod" after trying the original. I gotta say I preferred the original, electronically incorrect version and built it back in!!
The sustain mod seemed to neuter it a bit to my ears and lost some growl.... can't explain why.
fuck smooth tone, fuck eric johnson - Seiche

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Post by monkeyxx »

cool thanks...I was expecting that was one of the possible outcomes. I think I'll try to build one as close to original as possible for starters.

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Post by monkeyxx »

well in case anyone's interested, I made a couple "stock" layouts since that seemed like a good thing to do.

I built the tone bypass version, but the '77 layout is the one I drew up first so it should most likely work too. I would recommend using the tone bypass layout because I think the tone bypass mode "doesn't suck" and I jammed on it for a while and formed a positive bias before flipping it and realizing I was bringing in the tone stack and had been playing in bypass. It's a good sound, try it!

too late tonight, but tomorrow I'm going to add a " '77/'78 " clipping cap switch just to listen for subtle tone difference, and I'll go ahead and do some op amp experimentation.

the sound is nice. It's not sweet (unless you tone it all the way down--but then it's too dark) but it's really raw and aggressive in a good way. Passes for distortion better than most transistor muffs is a better way to say it.

here's my layouts and a picture of my board (notice the crazy mojo caps! a few fat polypropylene films and some other higher V caps like the original muffs seemed to use)

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Post by monkeyxx »

the main improvements over Gila Crisis' layout are I eliminated the pot mounted resistor and the need for multiple ground wires or wire jumpers off the side of the board

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Post by monkeyxx »

spent some more time with this today. I will concur with earlier posters that NE5534AP in place of the 741 and NE5532 in place of the JRC4558 made a serious improvement in the sound of this circuit, and I'll be keeping mine set up like that for now. The low end opens up a lot and the sound indeed is a bit "sweeter" but still good for the big sounding high gain stuff as before. More like a transistor muff, but still with the "glassy" character of the op amp circuit. The op amp muff in comparison to the transistor versions seems well suited to single note lead guitar, as someone mentioned earlier, it's bright and "forward" sounding.

I tried a MOSFET op amp (CA3130EZ) in place of the 741 and the gain dropped quite a bit. I didn't try changing the (bias?) resisistor on pin 3 to 1M as Gottfried Divos suggested in his schematic, that might have fixed it, but other than the lower gain the sound quality was pretty nice.

anyhow I think I'm going to get a lot of mileage out of this thing. for one, I can finally play certain smashing pumpkins songs with a smile on my face instead of ending up with a frown. you really do need the right sound for certain things

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Post by monkeyxx »

pardon the dust, I've just cleaned up the look of my layouts a little, making them smaller so hopefully photobucket won't shrink them down so much. same information. mods can delete those two images if desired. here's the layouts:

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Post by D-Day »

greenskull wrote:Well anyway, I tried the AG "sustain mod" after trying the original. I gotta say I preferred the original, electronically incorrect version and built it back in!!
The sustain mod seemed to neuter it a bit to my ears and lost some growl.... can't explain why.
I built one awhile back for a friend using Mike's layout with the AG mods as well. Something just didn't seem quite rowdy enough when when comparing it with another ICBM clone he owns. So after reading this I removed them and *boom* sounds just about right.

To each his own I guess :thumbsup

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Post by monkeyxx »

pumpkins inspired finish... added a " '77 / '78 " switch for the clipping smoothing cap, so you can get both versions in one build, tweak to amp etc

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Post by The Lifetaker »

monkeyxx your pedal looks great. I'm brand new to this and you've have inspired me to try this build as my very first project. I've been doing some reading up and trying to get all of the parts together. I've been searching http://www.smallbearelec.com. But I have two questions, and I'm sorry if these are bothersome. First, do you have another site or a better site than smallbearwhere I could do my shopping?

And second...

I'm having some trouble trying to figure out which capacitors I need, like I said this is my first pedal. On smallbear I was looking at the topmay low voltage capacitors:

http://www.smallbearelec.com/Categories ... +Poly+Film

But I'm having some trouble figuring out which ones I need. I found this conversion chart:

http://www.translatorscafe.com/cafe/uni ... -%5BmF%5D/

But these were my results:

C1:150 nanofarad = 0.00015 millifarad
C2:1 microfarad = 0.001 millifarad
C3: 4.7 nanofarad = 0.0000047 millifarad
C4: 10 nanofarad = 0.00001 millifarad
C5: 10 microfarad = 0.01 millifarad
C6: 10 microfarad = 0.01 millifarad
C7: 4.7 microfarad = 0.0047 millifarad
C8: 220 nanofarad = 0.00022 millifarad
C9: 330 picofarad = 0.00000033 millifarad
C10: 100 nanofarad = 0.0001 millifarad
C11: 1 microfarad = 0.001 millifarad
C12: 120 nanofarad = 0.00012 millifarad
C13: 220 microfarad = 0.22 millifarad
C14: 150 nanofarad = 0.00015 millifarad

... so yeah, I know this is basic stuff, I'm just a bit lost, and I really want to do this pedal right. Could anyone help me find the right capacitors here?

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Post by Seiche »

The Lifetaker wrote:First, do you have another site or a better site than smallbearwhere I could do my shopping?
What is your location? US or EU or something else?
The Lifetaker wrote:And second...

I'm having some trouble trying to figure out which capacitors I need, like I said this is my first pedal. On smallbear I was looking at the topmay low voltage capacitors:

http://www.smallbearelec.com/Categories ... +Poly+Film

But I'm having some trouble figuring out which ones I need. I found this conversion chart:

http://www.translatorscafe.com/cafe/uni ... -%5BmF%5D/

But these were my results:

C1:150 nanofarad = 0.00015 millifarad
C2:1 microfarad = 0.001 millifarad
C3: 4.7 nanofarad = 0.0000047 millifarad
C4: 10 nanofarad = 0.00001 millifarad
C5: 10 microfarad = 0.01 millifarad
C6: 10 microfarad = 0.01 millifarad
C7: 4.7 microfarad = 0.0047 millifarad
C8: 220 nanofarad = 0.00022 millifarad
C9: 330 picofarad = 0.00000033 millifarad
C10: 100 nanofarad = 0.0001 millifarad
C11: 1 microfarad = 0.001 millifarad
C12: 120 nanofarad = 0.00012 millifarad
C13: 220 microfarad = 0.22 millifarad
C14: 150 nanofarad = 0.00015 millifarad

... so yeah, I know this is basic stuff, I'm just a bit lost, and I really want to do this pedal right. Could anyone help me find the right capacitors here?
Millifarad is not used in stompboxes. Most of them are uF or microfarad (the "uF" is actually a mu) or lower values are nF (nanoFarad) or pF (picoFarad). 1000nF are 1uF and 1000pF are 1nF.

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Post by monkeyxx »

The Lifetaker wrote:monkeyxx your pedal looks great. I'm brand new to this and you've have inspired me to try this build as my very first project. I've been doing some reading up and trying to get all of the parts together. I've been searching http://www.smallbearelec.com. But I have two questions, and I'm sorry if these are bothersome. First, do you have another site or a better site than smallbearwhere I could do my shopping?

And second...

I'm having some trouble trying to figure out which capacitors I need, like I said this is my first pedal. On smallbear I was looking at the topmay low voltage capacitors:

http://www.smallbearelec.com/Categories ... +Poly+Film

But I'm having some trouble figuring out which ones I need. I found this conversion chart:

http://www.translatorscafe.com/cafe/uni ... -%5BmF%5D/

But these were my results:

C1:150 nanofarad = 0.00015 millifarad
C2:1 microfarad = 0.001 millifarad
C3: 4.7 nanofarad = 0.0000047 millifarad
C4: 10 nanofarad = 0.00001 millifarad
C5: 10 microfarad = 0.01 millifarad
C6: 10 microfarad = 0.01 millifarad
C7: 4.7 microfarad = 0.0047 millifarad
C8: 220 nanofarad = 0.00022 millifarad
C9: 330 picofarad = 0.00000033 millifarad
C10: 100 nanofarad = 0.0001 millifarad
C11: 1 microfarad = 0.001 millifarad
C12: 120 nanofarad = 0.00012 millifarad
C13: 220 microfarad = 0.22 millifarad
C14: 150 nanofarad = 0.00015 millifarad

... so yeah, I know this is basic stuff, I'm just a bit lost, and I really want to do this pedal right. Could anyone help me find the right capacitors here?
yes you should stock up on the specific parts for your build, or just a nice assortment of caps in the uF (microfarad) nF (nanofarad) and pF (picofarad) common ranges. Small Bear and other places like Futurlec and Tayda Electronics (recommended) have assortments boxes like ones you can find on ebay also for "poly film caps" green ones in common ranges should cover many projects. You can also order multiples of every cap they have in stock per type at a place like Tayda... just some electrolytics (uF values) plastic flim caps in the uF and nf ranges, and some ceramics to cover the pf ranges would be a good start. you'll probably want a stock of resistors too if you're doing more than one project. get the bulk pack from futurlec or just order 10 or 20 of each value of 1/4 resistor they stock, perhaps focusing more on the K Ohm values more than the Mega Ohm and Ohm values that will be less common in these builds. Tayda has them reeeeeal cheap you could get a nice stockpile going. also look at Digikey and Mouser for specialty caps and other parts, or high quality "mojo" caps if desired. effectsconnection.com has a nice selection of polypropylene caps they sell in the common values, tend to run big though so not for tiny builds. (see them in my build above vs the smaller film caps)

you'll have to do some pencil and paper math to get comfortable converting between uF, nF, and pF. you can sort of think of it using the number 1.000,000 ---- 1 is the uF realm, the first three zeros after the decimal .000 those are the nano Farad values. you'd call 100 nF 0.1 uF because you move the decimal up three places. the last three zeros (millionths of a micro farad) would be the pico Farad range. so 470 pF would also be equal to .47 nF, again because you move the decimal forward to get from pF to nF (and again to uF where .47 nF would be .00047 uF). hope that helps. might take a while to sink in

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Post by The Lifetaker »

Very cool. Thanks so much for your recommendation, because Tayda is awesome! It's way cheaper than any of the other sites I've found and they've got a great selection. I'm just planning on doing what you said and stocking up of different supplies. I want to try and build some of the Devi Ever fuzz effects after I finish the IC Muff project. Plus, I imagine that some of the guys in my band will want me to build stuff for them too. Like I said I'm new to all of this, so I just found the freestompboxes' FAQ forum, so I've been reading through a lot of things there too. I feel like I'm getting a bit better at understanding it. I've worked a bit with tube amps, and electric guitar wiring in the past, but this is my first stompbox/circuit board project from scratch. I'm very excited to get it going.

To answer your question, I'm in the US, Utah to be exact. I've been reading and researching quite a bit these last few days and I'm starting to feel more comfortable with the project. If it all works out, I'll post a demo video for sure!

Thanks so much for your responses and help guys!

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Post by SonicDaeath »

So i've finished up my GuitarPCB IC Big Muff build. It works, but it barely reaches unity gain when engaged. Are there any simple tricks to bump up the volume on it? I really like how it sounds, but its just not loud enough.

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Post by sinner »

Try smaller value of input resistor

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Post by monkeyxx »

the guitarpcb.com version has a weird modified tone stack that's highly scooped if I remember correct. you might try adding back in some mids, that might give the impression of much more volume. you might also try lowering or jumpering any resistors on the schematic that are in the input, output, or coupling stages, as signal pads, the ones that run in a line right from the input side to the output side of the schematic right down the middle of it. maybe lower or lose the 100K to ground that comes after the volume pot, might be a good place to start

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Post by SonicDaeath »

Cool, thanks sinner and monkey, I'll try these tomorrow!

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Post by monkeyxx »

I was really curious so I had to look at the Guitarpcb.com schematic. From what I just learned about tube screamers, R13, the one to ground right after the volume control, is called a shunt resistor, I think, and affects the output impedance and therefore how hard it can drive the next thing in line. I think if you lower this or get rid of it you get more available output (by lowering the output impedance of the effect). If you find that the tone stack is too scooped sounding you might use the yellow colored original values indicated in the build .pdf for the parts in the tone section, might make a difference. you can also use the freeware program "Duncan's tone stack calculator" in its big muff mode to experiment with values to get the mid scoop that you think you would like, from deep to flat to boosted. also tone bypass mode gives a jump in volume, because the "insertion loss" of the tone stack is no longer in place. but then you don't get the characteristic big muff tone stack action, so I guess it's a preference thing. The black arts toneworks Pharaoh is, I think, sort of a big muff that's permanently in tone bypass mode, flatter EQ from low to high, and a lot of people seem to get along with that thing. I think some of the devi ever and dwarfcraft devices fuzzes are "sort of" a similar idea, at least, to my ears.

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Post by Barcode »

monkeyxx wrote:I was really curious so I had to look at the Guitarpcb.com schematic. From what I just learned about tube screamers, R13, the one to ground right after the volume control, is called a shunt resistor, I think, and affects the output impedance and therefore how hard it can drive the next thing in line. I think if you lower this or get rid of it you get more available output (by lowering the output impedance of the effect). If you find that the tone stack is too scooped sounding you might use the yellow colored original values indicated in the build .pdf for the parts in the tone section, might make a difference. you can also use the freeware program "Duncan's tone stack calculator" in its big muff mode to experiment with values to get the mid scoop that you think you would like, from deep to flat to boosted. also tone bypass mode gives a jump in volume, because the "insertion loss" of the tone stack is no longer in place. but then you don't get the characteristic big muff tone stack action, so I guess it's a preference thing. The black arts toneworks Pharaoh is, I think, sort of a big muff that's permanently in tone bypass mode, flatter EQ from low to high, and a lot of people seem to get along with that thing. I think some of the devi ever and dwarfcraft devices fuzzes are "sort of" a similar idea, at least, to my ears.
The resistor on the output is a tad confusing. That resistor is what's called a pull-down resistor, and it's purpose is to give any stray discharge from the output cap a path to ground so that you don't get switch pops. However, usually that resistor would want to be in the 1M range or so. Odd. Remove it all together and see how it sounds, that value is really odd.

I could be mistaken though.

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Post by monkeyxx »

pretty sure it's a shunt resistor as described in http://www.geofex.com/article_folders/t ... sxtech.htm

a pulldown resistor yes would be a 1M or higher value. might not be necessary in this circuit. you could even have both next to each other, I've seen that on a few schematics.

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Post by The Lifetaker »

Well I finally sat down and finished this pedal today. you can imagine my excitement when I hit the switch and the LCD actually turned on. Sadly, no sound came out. No buzz, no hum, nothing. I double checked and I'm pretty sure everything is wired correctly. I'm pretty sure there is something wrong with my veroboard job. I think I'll double check to make sure I have all the right parts, and just try again. :?


I'll get it someday. I'm getting close. :)

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