Muffin Factory Input Resistors......

[halffast]

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.

 

[Robert]

Because that is what was in the original.

This and another pair of values (discussed in another thread) have always bugged me...


I suspect that the intention was for those values to be swapped, 47K in the fixed position and 110K switched.

This would allow the dipswitch to select between 47K and 33K input resistance, instead of the current 110K / 33K.

 

[halffast]

Thank you Robert.
Yes, swapping them around makes more sense to me also.
Every schematic I've seen so far of any early Muff's have 30k-ish input resistor so thats why i was wondering.

 

[Feral Feline]

Sifting through Kit Rae's schematics, and maybe a few others I've found online, the range of Muff input resistors found from smallest to largest:

27k, 33k, 36k, 39k, 43k, 47k.

I think that's got them all.


Then there's outliers such as the:

• 2k7 Earthbound SuperCollider
• 3k3 DiceWorks Muff Diver,
• 8k2 AceTone Fuzz Master FM-3,
• 10k Ibanez OD-850 (& Maxon D&S OD-801),
• 12k Blackout Effectors Musket (LPB Boost before Muff, NO input-resistor),
• 15k Civil War w/ Power Booster (PB comes first and has NO input-resistor),
• 39k & 390k (switchable) BAT Pharaoh (if the 390k were in parallel with the 39k it would give 35k45)

Last one is according to Kit Rae's site, but 47k and 470k seems more likely given the rest of the circuit is almost entirely "47x" numbers.


PS: If for some reason you want to target a specific Muff-input resistance, a different value than parallel 110k & 47k — paralleling Tayda-available resistor-values with the biggest Muff-input value, 47k +...

62k = 26k7
68k = 27k7

110k = 32k9 (STOCK Muffin Factory)
113k = 33k19
118k = 33k6
120k = 33k7

150k = 35k78
160k = 36k3

220k = 38k7
240k = 39k3

470k = 42k7
510k = 43k
560k = 43k3


Not sure why anyone would want/need something close such as 47k and 43k; I'd want a bigger spread such as the 33k and 47k, though the most common Muff input resistor values, hazarding a guess, are 33k & 39k.

Using Rob Robinette's SPDT ON-OFF-ON...




BUT WAIT!

... I don't like that the order of magnitude is all mixed up. I want levels to be logical: SMALL MEDIUM LARGE — in that order!​

That gives me the full spectrum of Muff input resistance, from lowest to highest and the 36k in the middle straddles the line between the most common values 33k and 39k — perfect for me!




You could swap the 47k and 27k if that order makes more sense to you;
you could orient the switch so it operates left-to-right;
you could swap out the TYPE 2 for a TYPE 1 on-on-on, easily...

 

[Big Monk]

None of the Classic values are going to make a difference, i.e. 27k-39k.

You have to remember that a lot of those component variations in those old muffs were inventory driven, i.e. If they changed the tone stack resistor from 33k to 39k they’d probably change the input resistor to use them up.

At least that’s how it always seemed to me.

 

[halffast]

Wow Feral.....thanks for your time with the detailed reply. Very helpful!
Because the Muffin Factory already has input resistor R2 on a DIP switch I will use it and stay with the spec'd values resulting in 47k or 33k.
Makes the most sense I'm thinking.

 

[jcpst]

Glad I saw this. The muffin factory is my next PCB I’m populating, and I am just getting started on the big muff rabbit hole.

Besides swapping r2 and r3, are there any other un-muffy things going on in the muffin factory that could be better muffified?

 

[halffast]

@jcpst, I started this thread......
I have not studied the schematic any further but I will and will post back if I have any more questions.
I have looked into the parts needed and I ordered them morning. I was concerned about which header pins to use to ensure the DIP switches sit nicely, flush or a bit above the face plate. So I ordered two different header pins from Tayda, A-7566 and A-4662.
You can enter these numbers in the search box at Tayda to find them. One has a over-all height of 12mm and the other 16mm. They will have to be cut to the 10 pin length.
I discovered short lever toggle switches at Tayda and ordered them to see if I will like the look. Tayda A-2559 and A-3675
And I really liked this DIP-5 switch, it has tall toggle levers. Mouser # 653-A6E5104N
Thats it for now.

 

[jcpst]

Thank you for all the info @halffast

I liked the dip switches on a more recent Muffin Factory in the build reports. This post has a link to them:

Post in thread 'Muffin Factory'
https://forum.pedalpcb.com/threads/muffin-factory.23055/post-290976

 

[Feral Feline]

None of the Classic values are going to make a difference, i.e. 27k-39k.

You have to remember that a lot of those component variations in those old muffs were inventory driven, i.e. If they changed the tone stack resistor from 33k to 39k they’d probably change the input resistor to use them up.

At least that’s how it always seemed to me.

I know EHX always bought on economies of scale and used whatever was at hand, but even so — was the entire Muff input-section modified in other ways to compensate for differences in the specific input-resistor value? Probably not. If not weren't the differences audible?

While 33k to 39k isn't much of a difference, a 27k vs 47k is a pretty big swing and would also affect the input-impedance. Lower resistance on the input-resistor and you've got a hotter signal hitting the rest of the circuit. If this difference is audible or not I don't know, I haven't toyed physically with the circuit much even though I've got PCBs fully socketed for it for experimentation, I've mainly toyed with theories.

For example, some early Ram's Heads had a 10µ input and output cap, so you'd think they'd be great on bass, but the internal workings of the clipping sections have 1µ clipping caps — compare that with the Bass-players' favoured Russky Muffs with 100n input/output caps and 47n clipping caps...

Input resistors — audible differences? Audible in a band mix?
I should spend less time yammering about this stuff and more time physically trying things...

 

[halffast]

Feral has some great observations!
I was quite surprised to see that 110k input resistor. I think I will use a 39k with a 100k in parallel for a choice of 39k or 28k.
I've only recently played around modifying late version Muff's, the most inexpensive ones.

As I am studying the Muffin Factory options on the schematic to the older original Muff versions, I feel like my head is gonna explode!
My hat is off to the designer. Well done!!

It is written that one area of the Muff circuit that has a large impact of the sound is the cap in series with the clipping diodes.
The Muffin Factory schematic shows both clipping stages with a 47n cap with a switchable 100n in parallel.
So we can choose between 47nf or 147nF as it stands. Some Muff's have 1uF and even larger.
So I was thinking of trying .1uf and .68 switched in parallel. I liked both at .47uF in my experimental Muff.

But one issue is that customizing a build will negate the existing setting spreadsheets........