Muffin Factory: How does it match the original BM20?

[bengarland]

I have 2 questions about the Muffin Factory:

1) How do the DIPs on the Muffin Factory map to the DIPs on the original BM20? It's a bit confusing because there's different terminology used, and the original has 3 toggles + 20 DIPs but the Muffin is 5 toggles + 20 DIPs. I've got it mostly figured out but if anyone has a better understanding, please share.

2) What does the middle (OFF) position of the two SPDT switches do? (these are the ones that change diodes)

I looked at the schematic and it's not clear to me why these are ON-OFF-ON and not ON-ON.

I read the manual for the BM20 but now I'm even more confused

 

[Barry]

The middle "off" allows to remove the clipping diodes

 

[Robert]

SW5 and SW6 are the only two that should be ON/OFF/ON. This is so you can remove the clipping diodes from the circuit entirely in the middle position. This is unique to the Muffin Factory, the other one you mentioned doesn't allow you to change clipping diodes.

The arrangement of the dipswitches is a little different, but all of the functionality (plus more) is there. Rather than just randomly throw them down, in the Muffin Factory they are arranged in order, and by the stage that they affect.

For example, there is no "Add Germanium" dipswitch. This is accomplished by switching the second stage clipping toggle switch to "GE" mode.

To make things more confusing, in the original some of the switch functions aren't "uniform" between the stages. The "Gain" dipswitch in one stage does something completely different from the "Gain" dipswitch in the second stage, etc. Also some of the names of the functions don't really relate to what they actually do. For example the switches named "Clean Gain 1 & 2" actually increase the gain of the clipping stages.

Initially these design changes were a way of making someone happy, but in the end I am much happier with how it turned out.

Input Gain	[Input] Input	Input stage input resistor
Input Coupling	[Input] Depth	Input stage input capacitor
Stage 2 Lows	[Input] Range	Input stage output capacitor
Stage 2 Clip	(Implemented by Toggle Switch)
(Not available in original)	[Input] Comp	Input stage collector resistor
(Not available in original)	[Input] Gain	Input stage emitter resistor
Coupling 2	[Clip 1] Depth	Clip stage 1 input capacitor
Input 2	[Clip 1] Input	Clip stage 1 input resistor
Clip Range 1	[Clip 1] Range	Clip stage 1 output capacitor
Headroom 1	[Clip 1] Comp	Clip stage 1 collector resistor
Clean Gain 1	[Clip 1] Gain	Clip stage 1 emitter resistor
Coupling 3	[Clip 2] Depth	Clip stage 2 input capacitor
Input 3	[Clip 2] Input	Clip stage 2 input resistor
Add Germanium	(Implemented by Toggle Switch)
Clip Range 2	[Clip 2] Range	Clip stage 2 output capacitor
Headroom 2	[Clip 2] Comp	Clip stage 2 collector resistor
Clean Gain 2	[Clip 2] Gain	Clip stage 2 emitter resistor
Tone Control	[Tone] High R	Tone stage High Pass resistor
Tone Control	[Tone] High C	Tone stage High Pass capacitor
Tone Control	[Tone] Depth	Tone stage output coupling capacitor
Tone Control	[Tone] Low R	Tone stage Low Pass resistor
Tone Control	[Tone] Low C	Tone stage Low Pass capacitor

 

[bengarland]

Are there any recommended DIP settings that help highlight the differences in flipping the toggles? I'm barely hearing a difference when flipping the toggles and the DIPs. Some minor differences here and there, but nothing really notable except for when the clipping diodes are completely bypassed. Even flipping the Tone DIPs I can't hear any difference at all, even though flipping the Tone toggle to Bypass is a totally different sound.

I thought maybe I did something wrong in the build, but I did a continuity check on the main PCB points that the DIP switches connect to for each switch, and they are all no continuity when the DIPs are all OFF, and beeps when they're all ON. And when I flip the switches while playing something on my guitar, I can hear a brief pop (microsecond dropout) on the signal which tells me that they're being activated.

But yeah... maybe my expectations are all wrong on this pedal or I just don't have the switches set correctly? I was kinda expecting it to be like flipping all the various switches would give distinctly different variations in tone but it's really not acting that way.

Thanks!

 

[Chuck D. Bones]

A lot of the changes are very subtle. Many (most?) of them interact. Some will only be apparent at certain control settings. Sounds like the board is working as it should. Knowing how the circuit works will help when playing with switch settings. Take a look here:
https://www.electrosmash.com/big-muff-pi-analysis
It's a lot to slog thru, but will provide some insight on what does what. You know how you don't need to be a mechanical engineer to drive a car? Same principle applies to guitar pedals. Except this one. If there was ever a pedal that required special training to operate, it's the Muffin Factory.
If there is a particular sound you're seeking, ask here and maybe we can provide guidance on settings.

 

[bengarland]

So what I need to do is look at the circuits for all of the different Muff variations and flip the DIPs and Toggles to emulate those circuits as closely as possible? And is there anything I should be looking for as far as the GE transistors go, besides something in the HFE range specified in the build guide?

Thanks for the link to Electrosmash... never heard of it but it looks like a great resource.

I still have so much to learn...

 

[Chuck D. Bones]

So what I need to do is look at the circuits for all of the different Muff variations and flip the DIPs and Toggles to emulate those circuits as closely as possible?

That's one way. You'll find out how similar they all are.
I'll give you a tip: the DIP switches that control capacitors in the 1st 3 stages will have the most influence on the sound. If you want sludge or play bass, you want large value caps. I prefer the small caps. The effect of the caps is most pronounced with your guitar volume maxed and the SUSTAIN control maxed.

Honestly, Ge vs. Si for the transistors is cork-sniffing. Don't be surprised if you don't hear a difference. I built the Ungula (EQD Hoof) and the difference in sound is due to the LEDs, not the Ge transistors.

I hope you have sockets for your Ge transistors. You want the lowest leakage ones you can find, otherwise they won't bias right. Measure the collector voltage on the Ge transistors. If it's below 2V they're too leaky. If it's above 6V their HFE is too low. The ones in my Ungula sit between 3.0V and 3.5V.

Most of what is on Electrosmash is accurate. I have found some mistakes there.

Check out Kitrae's Muff pages. Every type of Muff is represented there. A few of the schematics contain typos.

 

[bengarland]

Glad to hear that the GE transistor stuff is mostly cork sniffing. I was starting to wonder why I wasn't hearing any big difference since there seems to be so much hype about it. I've learned to trust my ears more than anything -- there's similar hype in the synth community of analog vs digital. I found in the end it doesn't matter what's under the hood if I like what the end product sounds like.

 

[Chuck D. Bones]

In the Muff the Ge stuff is 90% hype. In some other pedals, the difference is audible.

 

[Robert]

The dipswitches in the Muffin Factory can be very subtle, and some are highly interactive. You may find that four or five dipswitches don't seem to make any difference at all, then flip another one and those five now make relatively drastic changes.

In all reality though, with the exception of a few combinations, these are small circuit tweaks. You can flip them all and it's still a "muff", it doesn't instantly transform the pedal in to a completely different animal. If a Rams Head, Triangle, and Civil War are all basically the same thing to you then the Muffin Factory probably won't blow you away.

This was my personal favorite setting:

Transistors set to Hi, Diodes both set to Si

The following dipswitches ON (all others off):
[Clip 1] Gain
[Clip 2] Depth
[Clip 2] Input

[Clip 2] Range
[Clip 2] Comp
[Clip 2] Gain

[Tone] High R
[Tone] High C
[Tone] Depth

 

[Jbanks]

Once I found a good tone I liked, I haven’t touched the DIP since. Maybe some minor tweaking of pots when playing live, but that’s it. And I thought it was broken at first because all the DIP switches were off. Nice to hear it fire up as you turn them on!

[upon taking a picture of my settings I have most of the mods turned off for each gain channel and the tone channel DIP’s all disabled-pretty basic Muff after all!]