Thursday, January 7, 2021

Electro-Harmonix Big Muff Pi Schematic and Component Table

I used Kit Rae schematics, but I did not follow the same component numbering, as I don’t find it all that intuitive.  Kit did it that way for a good reason, this way works better for my brain.  There's also this excellent post by Kit Rae on the EHX forum, broadly describing differences between versions.


GENERIC BIG MUFF SCHEMATIC

GENERIC BIG MUFF SCHEMATIC

ELECTRO-HARMONIX BIG MUF PI COMPONENT VALUES TABLE



GENERIC BIG MUFF LAYOUT - WIDE


GENERIC BIG MUFF LAYOUT - WIDE



If you want to add power filtering, just add an extra row at the top - if you're read this far, I'm sure you can work it out.  

GENERIC BIG MUFF LAYOUT



There's room for the tone pot to be wired on the sides of the vero board, I prefer them to be together, which is why they're popping up out of the middle of the board at the top.

There's enough room on this to add power filtering and polarity protection down the centre two rows (where V+ and ground is).  



GENERIC BIG MUFF SCHEMATIC WITH CAPACITOR POLARITY MARKED

BMP schematic with polarity marked


BUILD TIPS

There are no magic parts in a Big Muff.  It's a well designed circuit and the fact that so many value changes occurred over time and it still sounds like a Big Muff is testament to that.

Transistors

Don't stress about getting the "right" transistors.   There's really quite minimal differences between most transistors - certainly don't spend a lot of money on rare / vintage for a Big Muff.   I know there are lengthy online discussions around what the right hfe is, after spending a lot of time testing on a breadboard with guitar in hand, I decided that it doesn't really matter that much.

Diodes

Again, subtle differences for the most part.  Practically any small signal silicon diode does the job.  

Resistors & Capacitors

Values are important, the type is not.

I will say that some of the odd values seen on the filter section are worth trying to attain.  example 4n and 12n.  If you substitute different values, it will obviously still work, but it doesn't sound the same - the filter section is such a big part of the Big Muff sound.



13 comments:

  1. hello,Andy.
    It's very interesting!
    i'll post your info to our fx club.

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    Replies
    1. Thank you - it has a long way to go before it’s finished. I’m on holiday at the beach, and it has been raining, so I have some time on my hands.

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  2. Hey I was interested in trying the wide layout .The boards are different from each other .The one just showing the cuts is not as wide as the one with the components.Also is it verified Thanks

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    Replies
    1. Good spotting Loyd. I'll update over the weekend.

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  3. Tried the bigger layout works great.Most big muff layouts I have seen have (1) 1m resistor just wondering what that was for ?Many thanks for all your hard work here

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  4. Hello - a lot of people like a 1m resistor on the input to help with the input impedance, and potentially a bit of switch pop.

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  5. This is so awesome!! Thanks for compiling all these :)

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  6. Hi! I'm starting to work on a series of Big Muff and I think I spotted an error:
    Ram's Head - 1974 #3 I think that the input (C1) it's a 10uf not a 100nf.
    As usual, your tables are pretty helpful and awesome!

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    Replies
    1. Good spotting - thank you. There were a few mistakes on that line. Updated now.

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  7. To complement the generic layouts (if you have time and you are in the mood) it will be pretty interesting to mark where the + and - side of the capacitors should go when working with one of the version that use electrolytics (or is only electrolytics like the 3uf).
    Cheers!

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    Replies
    1. Hello Mister Hate - that’s a fair point. I’ll update that shortly

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  8. Andrew, just letting you know that others are making use of this wonderful information you have kindly gathered. See https://forum.pedalpcb.com/threads/muffin-factory-settings-reference-chart.19724/. Happy holidays to you, Darwin999.

    ReplyDelete