Mad Bean Pedals RabbitHole2020 User manual

RabbitHole2020
FX TYPE: Distortion
Based on the EHX® Big Muff™
Enclosure Size: 1590A
“Softie” compatibility: none
© 2020 madbeanpedals
Overview
The 2020 version of the RabbitHole is the exact same circuit as the previous version. The PCB has
been re-designed to conform to the more recent style of 1590A layouts on mbp.
I’ve adopted the Ram’s Head as the “default” BOM for this version, as it is very popular and a good
representative of what the BM sounds like. However, there are many varieties you can build. In the
zip le for this project I have included the old spreadsheet that has different BOMs for a few versions.
Also, I highly suggest you check out the Kitrae Big Muff pages: not only for a complete history of the
effect, but for additional possible BOMS.
http://www.kitrae.net/music/big_muff_history.html
Controls
• VOL - Total Output.
• SUS - Total distortion.
• TONE - CCW - HP lter, CW - LP lter with a huge range in-between.
2.27 - Shopping List updated.
Terms of Use: You are free to use purchased RabbitHole2020 circuit boards for both DIY and small commercial operations. You may not
offer RabbitHole2020 PCBs for resale or as part of a “kit” in a commercial fashion. Peer to peer re-sale is ne, though.
Technical assistance for your build(s) is available via the madbeanpedals forum. Please go there rather than emailing me for
assistance on builds. This is because (1) I’m not always available to respond via email in a timely and continuous manner, and (2)
posting technical problems and solutions in the forum creates a record from which other members may benet.

Parts RabbitHole2020
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Values RabbitHole2020
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Traces RabbitHole2020
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B.O.M. RabbitHole2020
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Resistors Caps Diodes
R1 1M C1 100n D1 - D4 1n914
R2 33k C2 470pF D5 1N4001
R3 100K C3 100n Transistors
R4 470K C4 100n Q1 - Q4 Si
R5 100R C5 470pF Pots
R6 12k C6 100n SUS 100kB
R7 560R C7 100n TONE 100kB
R8 8K2 C8 470pF VOL 100kB
R9 100K C9 100n
R10 470K C10 3n9
R11 100R C11 10n
R12 12k C12 100n
R13 8K2 C13 100n
R14 100K C14 47uF
R15 470K C15 100n
R16 100R
R17 12k
R18 33k
R19 33k
R20 470k
R21 100K
R22 12k
R23 2K7
R24 100R
R25 4k7

Shopping List RabbitHole2020
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I’ve listed the transistors just as “Si” because there
are many BJT that will work here. If you want the
true “Rams Head” experience then I have linked two
versions of the period correct transistors used on the
next page. I’m not sure of the pinouts of the smallbear
transistors.
Value QTY Type Rating
100R 1 Carbon / Metal Film 1/4W
100R 3 Carbon / Metal Film 1/8W
560R 1 Carbon / Metal Film 1/8W
2K7 1 Carbon / Metal Film 1/8W
4k7 1 Carbon / Metal Film 1/8W
8K2 2 Carbon / Metal Film 1/8W
12k 4 Carbon / Metal Film 1/8W
33k 3 Carbon / Metal Film 1/8W
100K 4 Carbon / Metal Film 1/8W
470k 4 Carbon / Metal Film 1/8W
1M 1 Carbon / Metal Film 1/8W
470pF 3 Ceramic / MLCC 16v. Min
3n9 1 Film 16v. Min
10n 1 Film 16v. Min
100n 9 Film 16v. Min
47uF 1 Low Prole Electrolytic 16v. Min
1n914 4
1N4001 1
Si 4 NPN - medium hFE
100kB 3 PC Mount 9mm
2.27 - Updated shopping list to show (1)
100R at 1/4W and (3) 100R at 1/8W.

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Parts Guide RabbitHole2020
2N5133:
http://smallbear-electronics.mybigcommerce.com/transistor-2n5133/
SE4010 (Higher gain version of the 2N5133):
http://smallbear-electronics.mybigcommerce.com/transistor-se4010-fairchild/
Low prole Electrolytic caps:
http://smallbear-electronics.mybigcommerce.com/electrolytic-radial-low-prole-16v-1-f-100-f/
9mm PC Mount pots:
http://smallbear-electronics.mybigcommerce.com/alpha-single-gang-9mm-pc-mount/
Thinline DC Jack:
http://smallbear-electronics.mybigcommerce.com/dc-power-jack-all-plastic-unswitched-2-1-mm/
Enclosed Mono:
http://smallbear-electronics.mybigcommerce.com/1-4-in-mono-enclosed-jack/
http://smallbear-electronics.mybigcommerce.com/1-4-in-mono-enclosed-switchcraft-111x/
Lumberg Mono:
http://smallbear-electronics.mybigcommerce.com/lumberg-1-4-compact-shrouded-mono-jack/

Notes RabbitHole2020
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• There are many transistors you can use in the RabbitHole. Alternatives to the 2n5088 include
BC549C, BC550, BC182L, 2n5089, and MPSA18, as well as many more. Using different
transistors can create unique variations in tone. Be careful to use the correct pin-outs, however.
Some transistors, such as the BC549C will need to be rotated 180° from the silk screen drawing
on the PCB due to its reversed pin-out. Always check the appropriate datasheet for your transistor
BEFORE soldering.
• There is a clipping mod list in the Mudbunny doc. You can certainly do any of those clipping mods
here, if you like. There’s just a lot less room if you want to get fancy with clipping switches, etc.
This is a build where I think it’s best to just keep it simple :)

Wiring Diagram RabbitHole2020
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1590A Drill Guide RabbitHole2020
Note: Drill Guides are approximate and may require tweaking depending on the types of jacks, switches and pots you use.
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•This template will work for either mono enclosed jacks or the “Lumberg”
style.
• It uses the “Thinline” style DC Jack.
• It also shows the 3PDT02 bypass PCB but this is not required. If you are
wiring straight to a 3PDT you can use the same LED location on the right
side or choose a different spot.
•03.19: Drill template updated (moved VOL and SUS pots slightly
outward).

Voltages RabbitHole2020
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• 9.42vDC One Spot
• Current Draw: ~ 2mA
Q1 Si Q3 Si
C 4.12 C 4.12
B 0.64 B 0.64
E 42mV E 42mV
Q2 Si Q4 Si
C 4.12 C 4.96
B 0.64 B 1.55
E 42mV E 0.96

Schematic RabbitHole2020
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Bonus Section RabbitHole2020
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If you are up for something different I’ve come up with an alternate build for the RabbitHole. Call this
the BeanMuff. Or, maybe the SproutMufn. Whatever.
This is based partially on the old mbp GreaseGun which later became the Function F(x) Third Rail.
The difference here is the GG had only one clipping section. The input section has been replaced with
a BS170 for a different avor. The tone section has been dialed for a atter response when the knob
is set to the middle position. It is also tweaked for less low end. I pretty much made it up as I was
putting it together and I think it sounds very cool. Not quite a Muff, but not not-a-Muff.
All four transistors are the opposite pinouts from what is shown on the PCB, so you will need to ip
them around. The image below shows how they should be oriented.

Bonus Section RabbitHole2020
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BeanMuff
Resistors Caps Diodes
R1 1M C1 100n D1 - D4 1n914
R2 10k C2 150pF D5 IN4001
R3 1M C3 10n Transistors
R4 1M C4 100n Q1 BS170
R5 220R C5 470pF Q2 - Q4 BC550B
R6 4k7 C6 47n Pots
R7 1k C7 47n SUS 100kB
R8 10k C8 470pF TONE 100kB
R9 100k C9 47n VOL 100kB
R10 470k C10 10n
R11 220R C11 10n
R12 12k C12 100n
R13 10k C13 100n
R14 100k C14 47uF
R15 470k C15 100n
R16 470R
R17 12k
R18 15k
R19 22k
R20 470k
R21 100k
R22 12k
R23 2k7
R24 100R
R25 4k7

Bonus Section RabbitHole2020
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BeanMuff Shopping List
Value QTY Type Rating
100R 1 Carbon / Metal Film 1/4W
220R 2 Carbon / Metal Film 1/8W
470R 1 Carbon / Metal Film 1/8W
1k 1 Carbon / Metal Film 1/8W
2k7 1 Carbon / Metal Film 1/8W
4k7 2 Carbon / Metal Film 1/8W
10k 3 Carbon / Metal Film 1/8W
12k 3 Carbon / Metal Film 1/8W
15k 1 Carbon / Metal Film 1/8W
22k 1 Carbon / Metal Film 1/8W
100k 3 Carbon / Metal Film 1/8W
470k 3 Carbon / Metal Film 1/8W
1M 3 Carbon / Metal Film 1/8W
150pF 1 Ceramic / MLCC 16v min.
470pF 2 Ceramic / MLCC 16v min.
10n 3 Film 16v min.
47n 3 Film 16v min.
100n 5 Film 16v min.
47uF 1 Electrolytic 16v min.
1n914 4
IN4001 1
BS170 1
BC550B 3
100kB 3 PC Mount 9mm

Build Pic RabbitHole2020
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Couple notes on the BeanMuff build here.
You’ll notice D5 is missing. It’s because I put the
damn thing in the wrong way! Took the pic before
replacing it.
I used 100kA pot for the Vol. This is more of a
personal preference for me. All Muffs have plenty
enough output that there’s no reason to use a linear
taper instead of audio.

Bonus Section RabbitHole2020
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