aion POLYPHEMUS User manual

POLYPHEMUS OPTICAL COMPRESSOR 1
PROJECT NAME
POLYPHEMUS
BASED ON
EFFECT TYPE
PROJECT SUMMARY
DOCUMENT VERSION
Pigtronix®Philosopher’s Tone
An inventive optical compressor noted for its long sustain and blendable overdrive, designed by Howard
Davis, best known as the designer of the EHX Memory Man and Electric Mistress.
Compressor / Overdrive 1.0.0 (2023-07-04)
BUILD DIFFICULTY
Intermediate
Actual size is 2.3” x 2.68” (main board) and 1.78” x 0.90” (bypass board).

POLYPHEMUS OPTICAL COMPRESSOR 2
TABLE OF CONTENTS
1Project Overview 8Drill Template
2Introduction & Usage 9Enclosure Layout
3-5 Parts List 10 Wiring Diagram
6Build Notes 11 Licensing
7Schematic 11 Document Revisions
INTRODUCTION
The Polyphemus Optical Compressor is based on the Pigtronix Philosopher’s Tone, a vactrol-based
compressor & overdrive first released in 2009. It’s known for its incredibly long sustain, and has a
unique diode-clipping overdrive that can be blended in with the clean compressed signal.
The Philosopher’s Tone was designed by Howard Davis, the legendary inventor of the Memory Man and
Electric Mistress when he worked for Electro-Harmonix in the late 1970s. Since that time, he’s designed
several effects on a contract basis, and this is one of a few he did for Pigtronix.
After the original release, the Philosopher’s Tone underwent several revisions and new editions. The
first was the “Germanium Gold” edition, which was in a gold enclosure and featured a single germanium
diode in place of one of the silicon diodes in the clipping section (in other words, a marketing gimmick).
Later, the circuit was reworked into two new and slightly simplified pedals: the Philosopher’s Rock,
which emphasized the overdrive component, and the Philosopher’s Bass, which was tuned for bass
frequencies. These replaced the original Philosopher’s Tone.
Most recently, it was redesigned as a miniature pedal, once again using the original Philosopher’s Tone
name. This version included an onboard charge pump voltage doubler, so it no longer needed its own
15V or 18V adapter. This is the only one currently manufactured as of this project’s release.
The Polyphemus is an amalgamation of all of these, primarily based on the original Philosopher’s Tone
(which had more features than any subsequent versions) but incorporating various modifications
and tweaks from some of the later versions, including the charge pump, germanium diode, and
improvements to the sustain control.
USAGE
The Polyphemus has five controls:
• Sustain controls the amount of compression applied to the signal.
• Grit is the amount of overdrive or clipping applied to the compressed signal. Note that this is closer
to a blend than a gain control, and the clipping level is more or less fixed.
• Treble cuts or boosts the highs at around 2kHz by up to 6dB in either direction, with flat response at
12:00. This comes after the blend, so it’s applied to the dry signal as well as the effect signal.
• Blend sets the ratio between dry and effect signals.
• Volume is the overall output level. Be aware that even at maximum volume, it doesn’t go much
higher than unity gain, so it’s not suitable for use as a booster.

POLYPHEMUS OPTICAL COMPRESSOR 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—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 10k Metal film resistor, 1/4W
R2 470k Metal film resistor, 1/4W
R3 8k2 Metal film resistor, 1/4W
R4 2k7 Metal film resistor, 1/4W
R5 10k Metal film resistor, 1/4W
R6 2k7 Metal film resistor, 1/4W
R7 47R Metal film resistor, 1/4W
R8 2M2 Metal film resistor, 1/4W
R9 220k Metal film resistor, 1/4W
R10 100k Metal film resistor, 1/4W
R11 27k Metal film resistor, 1/4W
R12 1M8 Metal film resistor, 1/4W
R13 56k Metal film resistor, 1/4W
R14 2k7 Metal film resistor, 1/4W
R15 100k Metal film resistor, 1/4W
R16 6k8 Metal film resistor, 1/4W
R17 91k Metal film resistor, 1/4W
R18 100k Metal film resistor, 1/4W
R19 150R Metal film resistor, 1/4W
RPD 1M Metal film resistor, 1/4W
LEDR 10k 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 680pF MLCC capacitor, NP0/C0G
C3 6n8 Film capacitor, 7.2 x 2.5mm
C4 2.2uF Film capacitor, 7.2 x 5mm
C5 560n Film capacitor, 7.2 x 4.5mm
C6 33pF MLCC capacitor, NP0/C0G
C7 1000uF/10V Electrolytic capacitor, 8mm See build notes for sizing precautions.
C8 1000uF/10V Electrolytic capacitor, 8mm See build notes for sizing precautions.
C9 1uF Electrolytic capacitor, 4mm
C10 22pF MLCC capacitor, NP0/C0G
C11 1uF Electrolytic capacitor, 4mm

POLYPHEMUS OPTICAL COMPRESSOR 4
PARTS LIST, CONT.
PART VALUE TYPE NOTES
C12 2n2 Film capacitor, 7.2 x 2.5mm
C13 470uF/16V Electrolytic capacitor, 8mm Reference voltage filter capacitor. See build notes for sizing precautions.
C14 100uF Electrolytic capacitor, 6.3mm Reference voltage filter capacitor.
C15 10uF Electrolytic capacitor, 5mm Power supply filter capacitor.
C16 470n MLCC capacitor, X7R Power supply filter capacitor.
C17 10uF Electrolytic capacitor, 5mm Power supply filter capacitor.
C18 470n MLCC capacitor, X7R Power supply filter capacitor.
C19 220uF Electrolytic capacitor, 6.3mm Power supply filter capacitor.
C20 100n MLCC capacitor, X7R Power supply filter capacitor.
D1 1N5817 Schottky diode, DO-41
D2 1N914 Fast-switching diode, DO-35
D3 1N914 Fast-switching diode, DO-35
D4 1N914 Fast-switching diode, DO-35
D5 1N914 Fast-switching diode, DO-35
D6 1N914 Fast-switching diode, DO-35
D7 1N914 Fast-switching diode, DO-35
D8 1N914 Fast-switching diode, DO-35
D9 1N914 Fast-switching diode, DO-35
D10 1N914 Fast-switching diode, DO-35
D11 1N914 Fast-switching diode, DO-35
D12 Ge Germanium diode, DO-7 Original uses 1N60. Can also use BAT46 Schottky. See build notes.
D13 5mm LED LED, 5mm, red diffused
D14 1N914 Fast-switching diode, DO-35
D15 1N914 Fast-switching diode, DO-35
D16 1N914 Fast-switching diode, DO-35
D17 1N5817 Schottky diode, DO-41
D18 1N5817 Schottky diode, DO-41
Z1 1N4742A Zener diode, 12V, DO-41
IC1 NE5532P Operational amplifier, dual, DIP-8
IC1-S DIP-8 socket IC socket, DIP-8
IC2 TL072 Operational amplifier, dual, DIP-8
IC2-S DIP-8 socket IC socket, DIP-8
IC3 RC4558P Operational amplifier, dual, DIP-8
IC3-S DIP-8 socket IC socket, DIP-8
IC4 LM741 Operational amplifier, single, DIP-8
IC4-S DIP-8 socket IC socket, DIP-8
IC5 LT1054CP Charge pump, DIP-8 Can also use TC1044SCPA.

POLYPHEMUS OPTICAL COMPRESSOR 5
PARTS LIST, CONT.
PART VALUE TYPE NOTES
IC5-S DIP-8 socket IC socket, DIP-8
VACT. VTL5C6 Vactrol, fast on/fast off Available from Aion FX. See build notes for optocoupler information.
BLEND 10kB 16mm right-angle PCB mount pot
SUSTAIN 100kB 16mm right-angle PCB mount pot
GRIT 100kB 16mm right-angle PCB mount pot
TREBLE 100kB 16mm right-angle PCB mount pot
VOLUME 10kA 16mm right-angle PCB mount pot
LED 5mm LED, 5mm, red diffused
IN 1/4" mono 1/4" phone jack, closed frame Switchcraft 111X 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.
FSW 3PDT Stomp switch, 3PDT
ENC 125B Enclosure, die-cast aluminum Can also use a Hammond 1590N1.

POLYPHEMUS OPTICAL COMPRESSOR 6
BUILD NOTES
Vactrol selection
The original Philosopher’s Tone was designed around the resistance range and on/off speed of the
VTL5C6 optocouplers. Substitutes such as the VTL5C3 or home-rolled optocouplers do not sound the
same and are not recommended for this particular circuit.
When the Philosopher’s Rock and Philosopher’s Bass were released, they used the VTL5C9, while at the
same time changing the R7 resistor (the current-limiting resistor for the optocoupler’s LED) from 47R to
470R, presumably with the intention of putting the LDR in a similar resistance range as the 5C6.
However, once Xvive began offering a reissue of the VTL5C6, Pigtronix again switched back to the
VTL5C6 for their Philosopher’s Tone Micro, the only current-production version of this circuit.
Aion FX carries the VTL5C6 specifically for use in this circuit, so it’s recommended to use this type. We
have not tried the Polyphemus circuit with the VTL5C9 and 470R resistor, but if that’s all you can find, it
may work.
Electrolytic capacitor selection
The original Philosopher’s Tone used a massive 2,200µF capacitor in the bridge rectifier section. All
subsequent versions instead used two 1,000µF capacitors in parallel, and that’s what we’ve used in our
version. They will perform the same as a single 2,200µF in this application.
For these capacitors (C7 and C8), the PCB layout assumes 8mm diameter, 3.5mm lead spacing, and
15mm maximum height, which is on the low end of the range for capacitors of this value. They only need
to be 10V minimum since they do not see the full 18V supply.
This is also the case for C13, the 470µF filter capacitor that supplies the reference voltage to the
rectifier. The requirements are the same as C7 and C8 except that it needs to be 16V minimum.
If you use the exact parts listed in the Mouser parts spreadsheet for C7, C8 and C14, they’ll fit without
any trouble. But if they’re ever out of stock (or if you need to order from somewhere other than Mouser)
and you need to source a different type, then be very careful of the dimensions.
C5 capacitor
C5, the coupling capacitor for the effect signal, is 560n (0.56µF), which is a very uncommon value.
The most readily available 560n capacitor is an EPCOS / TDK type from Mouser, part number
871-B32529C564J. The width is not specified in the datasheet, so we initially designed the PCB
assuming 3.5mm, which is the width of similar values from WIMA.
However, they’re actually 4.5mm in width, so there’s barely enough space to fit between IC2 and C13.
It’s recommended to install the IC2 socket first, then fit C5 and C13 together before soldering either of
them so that they can adjust to the position.
You can also use 470n with no real change in behavior, in which case no precautions are needed, since
they’re 3.5mm or narrower. The spacing issue will be fixed on subsequent runs, so if it seems like there’s
plenty of space then you can disregard this.

SCHEMATIC
POLYPHEMUS OPTICAL COMPRESSOR 7
IN
OUT
1N5817
10kB
100kB
10kA
100kB
100kB
+9V
100n 220uF
GND
VA
LT1054CP
1N5817 1N5817
10uF
470n
470n 10uF
1N4742A
GND
91k
100k
VB
GND
GND
10k
22n
470k
VB
NE5532
NE5532
VA
GND
8k2
680pF
6n8
2k7
GND
GND
10k
2.2uF
GND
TL072P
RC4558P
VA
GND
560n
2k7
100uF
470uF
16V
GND
VA
GND
47R
VC
VC
TL072P
RC4558P
VB
2M2
33pF
1N914 1N914
1N914 1N914
1000uF
10V 10V
1000uF
220k
100k
1N9141N9141N914
1N914 1N914 1N914
27k
1uF
GND
22pF
1M8
56k
1uF
GND 1N60 1N914
1N9141N914
2k7
2n2
GND
100k
LM741D
VA
GND
VB
6k8
GND
GND
GND GND
D1
BLEND
1
2
3
TREBLE
1
2
3
VOLUME
1
2
3
GRIT
1
2
3
SUSTAIN
1
2
3
C20 C19
1
2
3
4 5
6
7
8
IC5 D17 D18
C17
C18
C16 C15
Z1
R17
R18
R1
C1
R2
IC1A
2
3
1
IC1B
6
5
7
84
R3
C2
C3
R4
R5
C4
IC2A
2
3
1IC3A
2
3
1
84
C5
R6
C14
C13
R7
6
5
7
IC2B
IC3B
6
5
7
84
R8
C6
VACTA
VACTB
D2 D3
D4 D5
C7
R9
R10
D6D7D8
D9 D10 D11
R11
C9
C10
R12
R13
C11
D12 D
LED
13 D14
D15D16
R14
C12
R15
5
1
2
3
6
8
74
IC4
R16
C8
GND
1M
RPD
150R
R19
GND

POLYPHEMUS OPTICAL COMPRESSOR 8
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.
ø3/8” ø1/2”
0.385”
0.625” 0.625”
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: -1.775
ø15/32”
x: -0.775, y: -1.775
ø5/16”
CENTER (0,0)
ø3/8”
125B
OUT
GRIT
x: 0, y: +1.71
ø9/32”
TREBLE SUSTAIN
x: -0.775, y: +0.41
ø9/32”
VOLUME BLEND
FOOTSWITCHLED
DC IN
0 1 2
CM
0 1
INCH

POLYPHEMUS OPTICAL COMPRESSOR 9
ENCLOSURE LAYOUT
Enclosure is shown without jacks. See next page for jack layout and wiring.
125B

POLYPHEMUS OPTICAL COMPRESSOR 10
WIRING DIAGRAM
125B
IN +VGND NC NC OUT
PCB
IN
GND +V +V JACK GND JACK
OUTIN
GND GND PCB
OUT

POLYPHEMUS OPTICAL COMPRESSOR 11
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 cannotbe 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 (2023-07-04)
Initial release.