aion PEPPERMILL User manual

RUNOFFGROOVE PEPPERMILL 1
PROJECT NAME
PEPPERMILL
BASED ON
EFFECT TYPE
PROJECT SUMMARY
DOCUMENT VERSION
Runoffgroove Peppermill
A super-simple drive created by boosting the signal into a J201 JFET until it clips in a tube-like manner.
JFET overdrive 1.0.0 (2020-06-05)
BUILD DIFFICULTY
Easy
Actual size is 2.3” x 1.86” (main board) and 1.78” x 0.86” (bypass board).

RUNOFFGROOVE PEPPERMILL 2
TABLE OF CONTENTS
1Project Overview 6Drill Template
2Introduction & Usage 7Enclosure Layout
3Parts List 8Wiring Diagram
4Build Notes 9Licensing
5Schematic 9Document Revisions
INTRODUCTION
The Runoffgroove Peppermill is a simple circuit designed to showcase the tube-like clipping
characteristics of the J201. It’s a very minimalist design which is composed of nothing more than a
MOSFET gain-boost stage into a JFET. The gain can be adjusted between the two stages to control the
amount of clipping, and an output volume is present at the end, and that’s it.
The Aion FX version of the Peppermill is a direct adaptation of the original circuit, with one modification:
the addition of a tone control. The original circuit has a R-C lowpass filter right before the volume,
and by making the resistor value adjustable, you end up with a useful tone control without otherwise
affecting the original circuit.
Since the J201 is very difficult to find in TO-92 through-hole format, and many DIY hobbyists are
intimidated by SMD parts, Aion FX offers J201s in SMD format that have been pre-soldered to adapters
so they can be used as through-hole parts.
USAGE
The Peppermill has the following controls:
• Drive controls the volume going into the JFET clipping stage. At higher drive levels, the JFET will
overload and clip the signal.
• Tone is a simple passive low-pass filter that can be adjusted for more or less treble.
• Volume controls the overall output of the effect.

RUNOFFGROOVE PEPPERMILL 3
PARTS LIST
This parts list is also available in a spreadsheet format which can be imported directly into Mouser for
easy parts ordering. Mouser doesn’t carry all the parts (most notably potentiometers) so the second tab
lists all the non-Mouser parts as well as sources for each.
View parts list spreadsheet →
PART VALUE TYPE NOTES
R1 1M Metal film resistor, 1/4W
R2 1M Metal film resistor, 1/4W
R3 4k7 Metal film resistor, 1/4W
R4 1k Metal film resistor, 1/4W
R5 100k Metal film resistor, 1/4W
R6 1k Metal film resistor, 1/4W
R7 5k1 Metal film resistor, 1/4W
RPD 2M2 Metal film resistor, 1/4W Input pulldown resistor.
LEDR 4k7 Metal film resistor, 1/4W LED current-limiting resistor. Adjust value to change LED brightness.
C1 22n Film capacitor, 7.2 x 2.5mm
C2 68n Film capacitor, 7.2 x 2.5mm
C3 1uF Electrolytic capacitor, 4mm
C4 47n Film capacitor, 7.2 x 2.5mm
C5 2n2 Film capacitor, 7.2 x 2.5mm
C6 100uF Electrolytic capacitor, 6.3mm Power supply filter capacitor.
C7 100n MLCC capacitor, X7R Power supply filter capacitor.
D1 1N5817 Schottky diode, DO-41
D2 3mm LED LED, 3mm, red diffused
Q1 2N7000 MOSFET, N-channel, TO-92
Q2 J201 JFET, N-channel, TO-92 or SOT-23 Can use either J201 (through-hole) or MMBFJ201 (SMD).
BIAS 50k trimmer Trimmer, 10%, 1/4"
TONE 100kC 16mm right-angle PCB mount pot
GAIN 250kB 16mm right-angle PCB mount pot
VOL. 100kA 16mm right-angle PCB mount pot
LED 5mm LED, 5mm, red diffused
IN 1/4" stereo 1/4" phone jack, closed frame Switchcraft 112BX or equivalent.
OUT 1/4" mono 1/4" phone jack, closed frame Switchcraft 111X or equivalent.
DC 2.1mm DC jack, 2.1mm panel mount Mouser 163-4302-E or equivalent.
BATT Battery snap 9V battery snap Optional. Use the soft plastic type—the hard-shell type will not fit.
FSW 3PDT Stomp switch, 3PDT
ENC 125B Enclosure, die-cast aluminum Can also use a Hammond 1590N1.

RUNOFFGROOVE PEPPERMILL 4
BUILD NOTES
Setting bias trimmers
Turn the trimmers so that the drain (“D” pad) of the JFETs measure 4.5V with a multimeter (red probe to
“D” pad and black probe to ground). This is just a guideline, though—you can tweak the trimmers a bit to
fine-tune the circuit to your liking. The bias affects the total gain of the circuit, so you can make it a little
cleaner or a little dirtier than stock.
J201 usage
The J201 transistor is very popular in DIY pedal designs, but was discontinued in TO-92 through-hole
format several years ago and is becoming very scarce. Genuine parts are getting expensive and many
counterfeits have entered the market.
The MMBFJ201 is a SMD version that is still in production. On the PCB, two outlines have been included
for each individual JFET, one for TO-92 and one for SMD (called SOT-23) right next to it. Make sure you
only use one or the other—don’t put both a through-hole and surface mount part in the two Q1 spots.
J201 adapters
Many DIY builders are intimidated by the small size of surface-mount parts. Aion FX offers pre-soldered
J201s on adapters so they can easily be used as through-hole parts.

SCHEMATIC
RUNOFFGROOVE PEPPERMILL 5
1N5817
100uF
250kB
100kC
GND
100kA
+9V
100n
VA
22n
1M
1M
2N7000
4k71k
VA
GND GND
68n
100k
GND
J201
50kB
VA
1k
GND
1uF
GND
47n
5k1
2n2
GND GND
D1
C6
GAIN
1
2
3
TONE
1
2
3
VOLUME
1
2
3
IN
OUT
C7
C1
R1
R2
Q1
R3
D2
R4
C2
R5
Q2
BIAS
1
2
3
R6
C3
C4
R7
C5
GND

RUNOFFGROOVE PEPPERMILL 6
DRILL TEMPLATE
Cut out this drill template, fold the edges and tape it to the enclosure. Before drilling, it’s recommended
to first use a center punch for each of the holes to help guide the drill bit.
Ensure that this template is printed at 100% or “Actual Size”. You can double-check this by measuring
the scale on the printed page.
Top jack layout assumes the use of closed-frame jacks like the Switchcraft 111X. If you’d rather use
open-frame jacks, please refer to the Open-Frame Jack Drill Template for the top side.
LED hole drill size assumes the use of a 5mm LED bezel, available from several parts suppliers. Adjust
size accordingly if using something different, such as a 3mm bezel, a plastic bezel, or just a plain LED.
0 1 2
CM
0 1
INCH
x: -0.65, y: +1.71 x: 0.65, y: +1.71
ø9/32” ø9/32”
x: 0, y: +0.66
ø9/32”
x: 0, y: -1.20
ø15/32”
x: -0.775, y: -1.20
ø5/16”
CENTER (0,0)
ø3/8” ø1/2”
0.385”
0.625” 0.625”
ø3/8”
OUT DC IN
125B
VOLUME
TONE
GAIN
FOOTSWITCHLED

RUNOFFGROOVE PEPPERMILL 7
ENCLOSURE LAYOUT
Enclosure is shown without jacks. See next page for jack layout and wiring.
125B

RUNOFFGROOVE PEPPERMILL 8
WIRING DIAGRAM
125B
IN +VGND N.C. N.C. OUT
PCB
IN
GND +V +V JACK GND JACK
OUTIN
GND GND PCB
OUT
Shown with optional 9V battery. If battery is omitted, both jacks can be mono rather than one being stereo.
Leave the far-right lug of the DC jack unconnected.

RUNOFFGROOVE PEPPERMILL 9
LICENSE & USAGE
No direct support is offered for these projects beyond the provided documentation. It’s assumed
that you have at least some experience building pedals before starting one of these. Replacements and
refunds cannot be offered unless it can be shown that the circuit or documentation are in error.
All of these circuits have been tested in good faith in their base configurations. However, not all the
modifications or variations have necessarily been tested. These are offered only as suggestions based
on the experience and opinions of others.
Runoffgroove circuit licensing
Runoffgroove circuits have special licensing that is different from standard Aion FX projects. These
projects are for personal use only and may not be used for commercial endeavors without approval
from Runoffgroove. Here are the terms of use from their site:
runoffgroove.com projects are provided free-of-charge to builders for personal, non-commercial use. We do offer
licensing for builders who wish to sell pedals based on, in whole or in part, our projects. As part of the licensing
agreement, the builder must clearly state that the circuit was developed by runoffgroove.com, both in promotional
literature and on the circuit board. If you see a pedal for sale that seems to be based on a runoffgroove.com project
and does not credit us, the builder may not be officially licensed by us and therefore, not compensating us as the
developer. Please contact us with the information and we will investigate the situation. Thank you.
DOCUMENT REVISIONS
1.0.0 (2020-06-05)
Initial release.