aion POSITRON User manual

POSITRON PREAMP DRIVE 1
PROJECT NAME
POSITRON
BASED ON
EFFECT TYPE
PROJECT SUMMARY
DOCUMENT VERSION
Gorilla TC-35 Tube Cruncher
The preamp circuit of the Gorilla TC-35 amplifier adapted for use as an overdrive pedal.
Overdrive/preamp 1.0.0 (2020-06-05)
BUILD DIFFICULTY
Intermediate
Actual size is 2.3” x 1.86” (main board) and 1.78” x 0.86” (bypass board).

POSITRON PREAMP DRIVE 2
TABLE OF CONTENTS
1Project Overview 7Enclosure Layout
2Introduction & Usage 8Wiring Diagram
3-4 Parts List 9Licensing
5Schematic 9Document Revisions
6Drill Template
INTRODUCTION
The Positron Preamp Drive is an adaptation of the Gorilla TC-35 Tube Cruncher amplifier that first
appeared in 1986. The Gorilla amps were solid-state combo amps aimed at the budget market. They
were not terribly well-regarded in their day, but they caught the eye of Josh Homme from Queens of the
Stone Age who cranked them for their unique overdrive tone.
Interestingly, there are no clipping diodes present, and so all of the overdrive comes from overloading
the opamp. Typically this is an undesirable characteristic that is avoided, but in this circuit it works.
The Positron is an adaptation of the TC-35’s preamp section. It’s a direct clone of the circuitry based on
factory schematics, running on the same voltage as the original, but meant to be used as a standalone
drive pedal instead of a true preamp.
USAGE
The Positron has the following controls:
• Drive controls the gain of the second op-amp stage. At higher levels, it pushes the op-amp into
clipping.
• Bass, Mid and Treble form a 3-band Fender-style passive tonestack located after the drive stage.
• Volume controls the overall output of the effect.

POSITRON PREAMP DRIVE 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 33k Metal film resistor, 1/4W
R2 330k Metal film resistor, 1/4W
R3 10k Metal film resistor, 1/4W
R4 10k Metal film resistor, 1/4W
R5 2k7 Metal film resistor, 1/4W
R6 47k Metal film resistor, 1/4W
R7 10k Metal film resistor, 1/4W
R8 68R Metal film resistor, 1/4W
R9 100k Metal film resistor, 1/4W
R10 10k Metal film resistor, 1/4W
R11 820R Metal film resistor, 1/4W
R12 47k 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 100n Film capacitor, 7.2 x 2.5mm
C2 22n Film capacitor, 7.2 x 2.5mm
C3 2.2uF Film capacitor, 7.2 x 5mm
C4 10n Film capacitor, 7.2 x 2.5mm
C5 220pF MLCC capacitor, NP0/C0G
C6 2n2 Film capacitor, 7.2 x 2.5mm
C7 220n Film capacitor, 7.2 x 2.5mm
C8 22n Film capacitor, 7.2 x 2.5mm
C9 1uF Film capacitor, 7.2 x 3.5mm
C10 100uF Electrolytic capacitor, 6.3mm Power supply filter capacitor.
C11 100uF Electrolytic capacitor, 6.3mm Power supply filter capacitor.
C12 10uF Electrolytic capacitor, 5mm
C13 100uF Electrolytic capacitor, 6.3mm Negative supply filter capacitor.
C14 470n MLCC capacitor, X7R Negative supply filter capacitor.
C15 10n MLCC capacitor, X7R IC1 positive supply filter capacitor.
C16 10n MLCC capacitor, X7R IC1 negative supply filter capacitor.
C17 100n MLCC capacitor, X7R Power supply filter capacitor.

POSITRON PREAMP DRIVE 4
PARTS LIST, CONT.
PART VALUE TYPE NOTES
D1 1N5817 Schottky diode, DO-41
IC1 JRC4558D JFET, N-channel, TO-92 or SOT-23
IC1-S DIP-8 socket IC socket, DIP-8
IC2 TC1044SCPA JFET, N-channel, TO-92 or SOT-23
IC2-S DIP-8 socket IC socket, DIP-8
DRIVE 25kB 16mm right-angle PCB mount pot
BASS 50kB 16mm right-angle PCB mount pot
MID 5kB 16mm right-angle PCB mount pot
TREBLE 25kB 16mm right-angle PCB mount pot
VOL. 1MB 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.

SCHEMATIC
POSITRON PREAMP DRIVE 5
GND
2M2
1N5817
100uF
25kB
5kB 25kB25kB
1MB
+9V
100n
BYP_GND
100n
33k
330k
GND
JRC4558D
JRC4558D
10k
10k
VA
-VA
2k7
22n
GND
GND
47k
10k
68R
GND
2u2
100k
10n
GND
220pF
10k
2n2
GND
220n
22n
820R
GND
GND
1uF
47k
GND
TC1044SCPA
100uF
PWR_GND
-VA
470n
100uF
PWR_GND
10uF
GND
VA
PWR_GND
10n
10n
GND
GND
RPD
D1
C11
DRIVE
1
2
3
MID
1
2
3
TREBLE
1
2
3
BASS
1
2
3
VOLUME
1
2
3
IN
OUT
C17
C1
R1
R2
2
3
1
IC1A
6
5
7
IC1B
R3
R4
84
R5
C2
R6
R7
R8
C3
R9
C4
C5
R10
C6
C7
C8
R11
C9
R12
1
2
3
4 5
6
7
8
IC2
C13 C14
C10
C12
C15
C16

POSITRON PREAMP DRIVE 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 requires the use of closed-frame jacks like the Switchcraft 111X. Open-frame jacks will
not fit in layouts with 5 or more knobs due to the placement of the DC jack.
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: -0.775, y: +1.71 x: +0.775, y: +1.71
ø9/32” ø9/32”
x: -0.775, y: +0.41
ø9/32”
x: 0, y: +1.71
ø9/32”
x: +0.775, y: +0.41
ø9/32”
x: 0, y: -1.20
ø15/32”
x: -0.775, y: -1.20
ø5/16”
CENTER (0,0)
125B
BASSMIDTREBLE
DRIVEVOLUME
FOOTSWITCHLED
ø3/8” ø1/2”
0.385”
0.625” 0.625”
ø3/8”
OUT DC IN

POSITRON PREAMP DRIVE 7
ENCLOSURE LAYOUT
Enclosure is shown without jacks. See next page for jack layout and wiring.
125B

POSITRON PREAMP DRIVE 8
WIRING DIAGRAM
125B
IN +VGND GND 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.

POSITRON PREAMP DRIVE 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.
Projects may be used for commercial endeavors in any quantity unless specifically noted. No
attribution is necessary, though a link back is always greatly appreciated. The only usage restrictions
are that (1) you cannot resell the PCB as part of a kit without prior arrangement, and (2) you cannot
“goop” the circuit, scratch off the screenprint, or otherwise obfuscate the circuit to disguise its source.
(In other words: you don’t have to go out of your way to advertise the fact that you use these PCBs, but
please don’t go out of your way to hide it. The guitar effects industry needs more transparency, not less!)
DOCUMENT REVISIONS
1.0.0 (2020-06-05)
Initial release.