Muffin Factory Component Changes to Better Align Operation With Stock Big Muff Circuits

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There are several Muffin Factory component values that require changing for the Muffin Factory (MF) to better sound like one of the stock Big Muff Pi pedals.

I took screenshots of the different sections of the circuit and I show in red the MF component values. The first value is with the DIP switch open and the second value is the computed value of the two components in parallel, with the DIP closed. In this format: xxx / yyy.

Then in blue I show the new suggested component values. These new values were selected based on the most commonly used stock values by Electro-Harmonix.

The new values for the tone stack will give you the stock scoop, flat, a bump and a couple of other maybe useless curves.
The stock scooped tone is with the four DIP switches open.
Flat is with DIP 4.2 closed.
Bump is with DIP 4.2 and 4.4 closed

NOTE: In two places I suggest to relocate resistors across toggle switches because these resistors are for biasing the germanium transistors only. Solder the resistor leads to the solder pads of the switches. Relocating them free's up the DIP's allowing for correct component value choices. See post #3 below.

I used this Big Muff Pi component table to determine the new suggested values:
https://vero-p2p.blogspot.com/2021/01/big-muff-electro-harmonix-component.html

The Muffin Factory and schematic is here: https://docs.pedalpcb.com/project/PedalPCB-MuffinFactory.pdf
A tone stack calculator: https://www.guitarscience.net/tsc/b...39k&RM=100k&RL=1M&C1=39n&C2=10n&RM_pot=Linear
A resistor in parallel calculator: https://www.digikey.com/en/resource...rsion-calculator-parallel-and-series-resistor

PLEASE inform me of any errors. @Feral Feline

 

[jcpst]

Thank you for all the work you’ve done here. I was following the other thread because the timing of that discussion and the MF being in my next batch was serendipitous.

(Link for others)

H

Thread 'Muffin Factory Input Resistors and other build information'

Sep 22, 2024

I'm new around here but I have built a few pedals.

I plan to buy the Muffin Factory PCB and was studying all the options it has. Very very interesting!
Question: On the Muffin Factory schematic R3 input resistor is 110k with R2 47k in parallel controlled by a DIP switch. Why is R3 110K?

https://docs.pedalpcb.com/project/PedalPCB-MuffinFactory.pdf

I understand what the 47k in parallel is giving for input resistance.
But that 110K alone is bigger than any I've seen.
Enlighten me please. Thank you.

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• Replies: 23
• Forum: General Questions

 

[halffast]

@jcpst Happy to help!

I mentioned relocating two resistors that are used to bias the germanium transistors. Here is where they'd go:

 

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Here is the website by Kit Rae. Considered the Big Muff bible.

BIG MUFF TRANSISTORS AND OTHER COMPONENTS

Scroll down a little bit to where he indicates what components have the most affect on the sound. Three things:
1) The tone stack, which I talked about in post #1.
2) The feedback filter caps.
3) And the clipping/blocking diodes.
There are posts out there where people have found this to be true.

The Muffin Factory has DIP switches for the clipping/blocking diodes so we are good there.
The MF does not have DIP switches for the feedback filter caps. But it does for the feedback resistors, which affects the gain.
If a person wanted to be able to customize the feedback filter caps instead of the feedback resistors there is a way.....

After moving the germanium bias resistors (R12 and R20) to across the toggle switches (per my post above) you could move R13 to the now empty R12 position and then put a new cap where R13 was. Thats for clipping stage 1. You then do the same thing for the clipping stage 2 by moving R21 to the R20 spot and put a new cap in.
Historically the Muff values for these feedback filter caps were 470p / 500p/ 560p / 680p.
The Rams Head 1974 #3 is the only Muff to use the 680p. I will probably build my MF with a fixed 470p and a switched 150p for 620p total.
Thats my thinking right now.
This is my reference for the historical cap values: https://vero-p2p.blogspot.com/2021/01/big-muff-electro-harmonix-component.html

One thing about this change is that it the faceplate DIP nomenclature is technically altered. I don't think thats a concern, I'm still scratching my head on what they are currently called. I get it, they had to have names. I just want to understand them better.
I will soon post a DIP switch table to help us.

But I do think moving those resistors to the toggle switches needs to be done.

 

[halffast]

Here's a couple of graphics to figure out exactly what each individual DIP switches affects. This will be very helpful I think.

 

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If someone wants the above DIP switch table with the stock Muffin Factory components let me know.
That faceplate screenshot labeled with the individual component ID's works for the stock MF also.