# Need help with Big Muff schematic / Mojo Hand Colossus



## Tremster (Mar 13, 2021)

Dear forum,

I don't feel confident enough with my diagram reading skills, any help would be appreciated.
A friend asked me to build a Mojo Hand Colossus (=a variant of a Russian Muff with mids control and an input cap switch), he had an original years ago.
I can't find a PCB for it, but I have a Fuzzdog BMP board that should do fine: https://shop.pedalparts.co.uk/Big_Muff_Pi/p847124_20010593.aspx
The schematic is in the BOM on page 3: http://pedalparts.co.uk/docs/BMP2018.pdf

The Colossus schematic is on the Kit Rae Muff page: http://www.bigmuffpage.com/Big_Muff_Pi_versions_schematics_part4.html:







The question is (parts numbers are different):
How do I match this bit from the Kit Rae schematic



with this bit from the Fuzzdog schematic




Where does Kit Rae's C14 go on the PCB??
Kit Rae's C9 is parallel to the Mids pot, Fuzzdog's C10 is before the pot??
The Colossus uses much larger values around the Mids pot than other Muffs with a Mids pot (Musket, Hoof; see Fuzzdog doc for those). Is there something wrong?
This is beyond me, I'm sorry.

Thank you!!!!

Here's what I came up with matching the Kit Rae diagram with the Fuzzdog diagram for use on the PCB (The parts numbers are for the PCB, Kit Rae has different numbers). I think I have it all except for the parts around the Mids knob parts mentioned above:

R1 33k
R2 100k
R3 470k
R4 140R
R5 12k
R7 1k
R8 10k
R9 100k
R10 470k
R11 12k
R12 390R
R13 10k
R14 390R
R15 470k
R16 100k
R17 12k
R18 47k ??
R19 10k ??
R21 100k
R22 470k
R23 2k
R24 10k
R25 1M

(no R6 and R20 on PCB)

C1 10nF + 100nF/2u2 on switch
C2 470pF
C3 100nF
C4 100nF
C5 560pF
C6 47nF
C7 100nF
C8 560pF
C9 47nF
C10 22nF ??
C11 47nF ??
C12 100nF
C13 100nF
C14 100uF

D1-2/4-5 1N4148
D3&6 by choice
D7 1N4001
Q1-4 2N5088

Tone / Mids / Sustain 100kB
Volume 100kA


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## Dan M (Mar 13, 2021)

I am doing something similar, building an ultra stoner using a pharaoh board and the tone circuit is different.

I would look at it like this:  
Build the fuzzdog board but omit the shift pot and run a wire from pin 1 to pin 3 on the board.  The result is the Kit Rae circuit minus c14 and the mids pot.  (Stop here and double check that I’m correct)

Then you just need to add the mids pot and c14.  The left side of C10 and R19 are the same node in the circuit.  So I would pick the easiest one to access on the board.  Piggyback a wire on that component and run it to the pin of the mids pot.  Then connect c14 to the other leg.  Then connect c14 into pin 3 of the board for the shift pot (that you jumpered above).

So the pot won’t be mounted tight to the board, it will be floating on wires.

The only trouble I see is making sure you tap into the input side of c10 or r19. Since they are the same node, you could use you multimeter to see which holes in the board are connected. And then make sure the daisy chained pot and cap leads won’t flop around and create a short.


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## Tremster (Mar 14, 2021)

Holy Wow! Thank you very much!!!

Some last questions:



Dan M said:


> The left side of C10 and R19 are the same node in the circuit.  So I would pick the easiest one to access on the board.  Piggyback a wire on that component and run it to the pin of the mids pot.


Pin 3 on the mids pot?



Dan M said:


> Then connect c14 to the other leg.


... of either C10 or R19, whichever I chose on the node?

What's conected to pin 1 (R10?) and 2 of the mids pot?


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## Dan M (Mar 14, 2021)

If this is the board, it looks like R19 is easier to access than C10:  http://pedalparts.co.uk/docs/BMP2018.pdf

Once you figure out which R19 hole is connected to one of the C10 holes:  
-Run a wire from that R19 hole to the middle (pin 2) of your mid pot.  
-Then connect one leg of C14 to pin 3 of the mid pot and the other leg of c14 to one of the shift holes in the board.  
-Pin 1 on the mid pot is not used.  The kit Rae diagram shows pin 1 and 2 connected together.  You can do that if you want,  or leave pin 1 empty.  It will work the same either way.  (I don’t know why some schematics connect then and some don’t. For example look at the mid pot on the supercollider and pharaoh on that same kit Rae page.  They leave the unused pin hanging.  Either way, you get the same signal as you turn the knob.)
-Connect all 3 shift holes together, so that part of the board acts like a single wire.  So you can connect the c14 leg whichever of the 3 is easiest.

I did not draw this out on paper, it might be a good idea to make sure I’m not missing something.


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## Tremster (Mar 15, 2021)

Amazing, thank you so much!


Dan M said:


> I did not draw this out on paper, it might be a good idea to make sure I’m not missing something.


That's not necessary, I think I can take it from here.


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## jrhevron (Jun 28, 2021)

Dan, do you know the Ultrastoner mids tonestack values? I have heard that it is a very good mids knob and would like to replicate it in a build.


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## tcpoint (Jun 28, 2021)

Here's a couple of links that might help,
*Ultrastoner build doc.*
*Muffage spreadsheet*


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## jrhevron (Jun 28, 2021)

Thank you! 

Has anyone used the ultrastoner mids? What did you think? Any comparison to the hoof mids? 

In my build, I have found that I really like just working with the C13 cap (on the mudbunny layout) for either flat or boosted mids. Not sure if I need to do a whole mids pot, but I've been exploring that option.


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## tcpoint (Jun 28, 2021)

Here's one more link.
*Juansolo's muffage page*


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## jrhevron (Jun 28, 2021)

Just messaged with Juan on madbean and he said the following. Seems okay to share and possibly useful to anyone who needs the info: 

Just had a quick look at what you're doing (adding a variable mids pot to a muff stack). The C500 pot is very important, if you deviate from that the frequency of the scoop will shift as you change it rather than just the depth of it. Took a lot of maths, experimentation and plotting stuff to find that out! That simple mod though, works very, very well. You essentially end up setting the max and min frequencies with the caps and it moves smoothly between them.


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## tcpoint (Jun 28, 2021)

Juan is one of the authoritative sources for Big Muffs.  The ultrastoner mids are nice.  So are the hoof mids.  I think I like the ultrastoner ones better.


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## Feral Feline (Jun 28, 2021)

Dan M said:


> ...-Pin 1 on the mid pot is not used.  The kit Rae diagram shows pin 1 and 2 connected together.  You can do that if you want,  or leave pin 1 empty.  It will work the same either way.  (I don’t know why some schematics connect then and some don’t. For example look at the mid pot on the supercollider and pharaoh on that same kit Rae page.  They leave the unused pin hanging.  Either way, you get the same signal as you turn the knob.)



I don't know either, why some circuit designers don't connect hanging pins on pots wired as variable resistors — especially on a tone control. It makes sense to me to not leave pins hanging, if/when a problem occurs with the pot the signal won't be entirely dumped. Connecting the hanging pin, at least the circuit still works.

On something like a power rheostat, I can see it might be better to have an interuption full-stop if the pot fails rather than sending full juice downstream. I guess it all depends on the applications.


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