aion Lumitron User manual

LUMITRON RESONANT FILTER 1
PROJECT NAME
LUMITRON
BASED ON
EFFECT TYPE
PROJECT SUMMARY
DOCUMENT VERSION
Mu-tron® III
The very first commercial envelope filter effect, first released in 1972. Famously used by Bootsy Collins,
Jerry Garcia and Stevie Wonder among many others.
Envelope filter / auto-wah 1.0.0 (2023-09-08)
BUILD DIFFICULTY
Intermediate
Actual size is 2.3” x 2.42” (main board) and 1.78” x 0.86” (bypass board).

LUMITRON RESONANT FILTER 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 Lumitron Resonant Filter is an adaptation of the Musitronics Mu-tron III, designed by Mike Biegel
and originally released in 1972.
The Mu-tron III was the very first commercial envelope filter pedal, also called an autowah, using
optocouplers to dynamically control a series of frequency filters based on the level of the input signal.
The vocal-like effect was quickly embraced by musicians and soon became a characteristic effect of
entire genres, particularly funk. Notable Mu-tron III users include Bootsy Collins on bass, Jerry Garcia
on guitar, and even Stevie Wonder, who used it on a Clavinet.
Musitronics was sold to ARP in 1979, who produced the pedals until 1980. Mike Biegel later contracted
with Electro-Harmonix to release an updated version of the circuit in 1995, called the Q-Tron, as well as
the Bi-Filter rack unit with expanded features. The original Q-Tron was later adapted as the Mini Q-Tron,
Micro Q-Tron, and Q-Tron+, the latter two of which are still in production.
In 2019, the Mu-tron brand was resurrected with Mike Biegel once again designing new effects. The
Micro-Tron IV is an updated version of the Mu-tron III, with modernized circuitry, CV input and output,
and swappable optical modules for different reaction times and filter characteristics.
The Lovetone Meatball (available as our Spectron project) was based on the Mu-tron III with a greatly
expanded feature set. If you wish the Lumitron had a lot more knobs and switches, it’s worth a look.
USAGE
The Lumitron has three knobs and three switches:
• Gain boosts the signal level at the input, which drives the envelope detector as well as the main
audio signal path.
• Peak is a feedback control that sets the sharpness or intensity of the filter.
• Volume is the output volume of the effect, which compensates for high input gain levels.
• Filter (toggle switch) selects the filter type. LP (lowpass) accentuates lows. BP (bandpass) cuts lows
and highs while accentuating the peak frequency. HP (highpass) accentuates highs.
• Drive (toggle switch) selects the direction of the sweep. “Up” starts with a hi-cut and adds highs
with the intensity of the signal. “Down” starts with a low-cut and adds lows with the intensity.
• Range (toggle switch) sets the input frequency of the envelope detector. “Lo” is more sensitive to
bass signals while “Hi” is more sensitive to treble signals.

LUMITRON RESONANT FILTER 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 3k3 Metal film resistor, 1/4W
R2 120k Metal film resistor, 1/4W
R3 120k Metal film resistor, 1/4W
R4 4k7 Metal film resistor, 1/4W
R5 12k Metal film resistor, 1/4W
R6 390k Metal film resistor, 1/4W
R7 22k Metal film resistor, 1/4W
R8 22k Metal film resistor, 1/4W
R9 220k Metal film resistor, 1/4W
R10 220k Metal film resistor, 1/4W
R11 560R Metal film resistor, 1/4W
R12 22k Metal film resistor, 1/4W
R13 12k Metal film resistor, 1/4W
R14 1M Metal film resistor, 1/4W
R15 1M Metal film resistor, 1/4W
R16 330R Metal film resistor, 1/4W
R17 47k Metal film resistor, 1/4W
R18 120k Metal film resistor, 1/4W
R19 180k Metal film resistor, 1/4W
R20 120k Metal film resistor, 1/4W
R21 120k Metal film resistor, 1/4W
R22 330R Metal film resistor, 1/4W
R23 1k Metal film resistor, 1/4W Used for envelope indicator LED.
R24 1k Metal film resistor, 1/4W Used for envelope indicator LED.
RPD 2M2 Metal film resistor, 1/4W Input pull-down resistor. Can be as low as 1M.
LEDR 10k Metal film resistor, 1/4W LED current-limiting resistor. Adjust value to change LED brightness.
C1 1uF Film capacitor, 7.2 x 3.5mm
C2 10pF MLCC capacitor, NP0/C0G
C3 100n Film capacitor, 7.2 x 2.5mm
C4 2n2 Film capacitor, 7.2 x 2.5mm
C5 1n Film capacitor, 7.2 x 2.5mm
C6 1n8 Film capacitor, 7.2 x 2.5mm

LUMITRON RESONANT FILTER 4
PARTS LIST, CONT.
PART VALUE TYPE NOTES
C7 2n2 Metal film resistor, 1/4W
C8 1n Metal film resistor, 1/4W
C9 1n8 Metal film resistor, 1/4W
C10 1uF Metal film resistor, 1/4W
C11 2.2uF Metal film resistor, 1/4W
C12 4.7uF Metal film resistor, 1/4W
C13 10uF Metal film resistor, 1/4W
C14 10uF Metal film resistor, 1/4W Power supply filter capacitor.
C15 470n Metal film resistor, 1/4W Power supply filter capacitor.
C16 100uF Metal film resistor, 1/4W Power supply filter capacitor.
C17 100uF Metal film resistor, 1/4W Power supply filter capacitor.
C18 100n Metal film resistor, 1/4W Power supply filter capacitor.
Z1 1N4742A Zener diode, 12V, DO-41
D1 1N5817 Schottky diode, DO-41
D2 1N914 Fast-switching diode, DO-35
D3 1N914 Fast-switching diode, DO-35
IC1 RC4558P Operational amplifier, dual, DIP8
IC1-S DIP-8 socket IC socket, DIP-8
IC2 RC4558P Operational amplifier, dual, DIP8
IC2-S DIP-8 socket IC socket, DIP-8
IC3 RC4558P Operational amplifier, dual, DIP8
IC3-S DIP-8 socket IC socket, DIP-8
IC4 LT1054CP Charge pump, DIP8 Can also use TC1044SCPA.
IC4-S DIP-8 socket IC socket, DIP-8
SWEEP 5k trimmer Trimmer, 10%, 1/4" Bourns 3362P
OPTO1 VTL5C3 Vactrol, fast on/fast off Available from Aion FX. See build notes.
OPTO2 VTL5C3 Vactrol, fast on/fast off Available from Aion FX. See build notes.
GAIN 1MC 16mm right-angle PCB mount pot
PEAK 250kA 16mm right-angle PCB mount pot
VOL. 100kA 16mm right-angle PCB mount pot
DRIVE DPDT on-on Toggle switch, DPDT on-on
FILTER DPDT on-on-on Toggle switch, DPDT on-on-on
RANGE DPDT on-off-on Toggle switch, DPDT center off

LUMITRON RESONANT FILTER 5
PARTS LIST, CONT.
PART VALUE TYPE NOTES
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.

LUMITRON RESONANT FILTER 6
BUILD NOTES
Vactrol selection
The original Mu-tron III used a dual-element optocoupler from Hamamatsu, marked with the part
number 805A, which had a single LED and two fully independent LDRs in one package.
There is no record of the 805A part number in Hamamatsu’s catalogs or datasheets. However, the Mu-
tron III service manual from after the ARP acquisition (1979) lists it as the P873-13, which is a standard
Hamamatsu part with the same dual-LDR configuration and the same physical appearance.
It’s not known whether the 805A is just an internal part number or if Hamamatsu may have produced
it specially for Mu-tron, either a custom specification or selected for certain characteristics. It’s known
that they had Hamamatsu manufacture custom optocouplers for the Phasor II, so they did have a direct
relationship with the company that went beyond just ordering from a catalog.
Regardless, there is nothing particularly notable about the specifications of the P873-13 other than the
dual LDR. Most Mu-tron III clones just use two fully separate optocouplers with the LEDs in parallel,
which makes no difference to the operation.
It’s recommended to use the VTL5C3 here, as it’s been used successfully for years in DIY adaptations.
This is also the type used in the EHX Q-Tron, a variant of the Mu-tron III that was designed by Mike
Biegel for EHX in the 1990s. Other types such as the NSL-32 can be made to work, but you may have to
modify some of the surrounding circuitry since the “on” resistance is much lower.
Setting the Sweep trimmer
The Sweep trimmer is designed to be a sort of bias control for the optocouplers. In the original units, the
resistor in this position varied based on the specs of the optocoupler, but Mu-tron’s process for selecting
a resistor value is not known. In the Lumitron, as with many other DIY clones, we’ve made this a trimmer
so that the resistance value can be adjusted to preference. Start with the trimmer in the middle and turn
it to the left and right to see how it changes the sound, then leave it where it sounds best.
Some Mu-tron clones make this an external control, and you’re welcome to wire it offboard if you like,
but there is generally a sweet spot and on-the-fly adjustment isn’t nearly as useful once it’s been set.
Peak potentiometer value
In the original units, the Peak control was a 150kA (log/audio taper) potentiometer. This value is very
difficult to find today, so it’s recommended to use 250kA with a 390k resistor in parallel (R6), which
approximates a 150kA pot. If you do manage to find a 150kA potentiometer, you can omit R6 entirely.
Envelope indicator LED
The footswitch PCB includes a second LED that shows the envelope. This correlates closely to the
optocoupler LEDs that drive the filter, so it’s a good way of seeing the action directly. Note that if the
“Drive” switch is set to DOWN (in other words, it starts high and sweeps low with the envelope), the LED
will be on by default and will turn off when the envelope detector engages.
If you want to omit this LED, you can just omit the LED as well as R23 and R24 on the footswitch board.
No jumpers are necessary.

SCHEMATIC
LUMITRON RESONANT FILTER 7
IN
OUT
HP
FILTER
BP
LP
UP
DOWN
LO
MED
MED
LO
HI (CENTER) HI (CENTER)
1N5817
100uF
100kA
1MC
5kB
250kA
+9V
100n
GND
VA
LT1054CP
10uF
PWR
GND
PWR
GND -VA
470n
PWR
GND
PWR
GND
100uF
10uF
2M2
3k3
1uF
RC4558P RC4558P
VA
-VA
120k
120k
10pF
100n
GND
GND
4k7
12k
390k
22k
22k
220k
RC4558P RC4558P
RC4558P
RC4558P
VA
-VA
VA
-VA
GND
1n 1n8
220k
1n 1n8
GND
1uF
560R
GND
2.2uF
22k
12k
1M
GND
1N914
1M
1N914 330R
47k
-VA
4.7uF
GND
120k
180k120k
GND
VA
120k
330R
GND
1k
5MM
1k
1N4742A
GND
2n2 2n2
D1
C17
VOLUME
1
2
3
GAIN
1
2
3
SWEEP
1
2
3
PEAK
1
2
3
C18 IC4
1
2
3
4 5
6
7
8
C14 C15
C16
C13
RPD
R1
C1
2
3
1
IC1A
6
5
7
IC1B
84
R2
R3
C2
C3
R4
R5
R6
R7
R8
R9
OPTO1A
OPTO1B
OPTO2A
OPTO2B
2
3
1
IC2A
6
5
7
IC2B
2
3
1
IC3A
6
5
7
IC3B
84
84
C5 C6
A2
A3
A1 RANGE A
R10
C8 C9
B2
B3
B1 RANGE B
A2
A3
A1
B2
B3
B1
C10
R11
C11
A2
A3
A1
DRIVE A
DRIVE B
B2
B3
B1
R12
R13
R14
D2
R15
D3 R16
R17
C12
R18
R19R20
R21
R22
R23
SENSE
R24
Z1
C4 C7
GND
GND
GND GND

LUMITRON RESONANT FILTER 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. Open-frame jacks will
not fit in layouts with 3 knobs along the top row 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.
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, y: -1.775
ø15/32”
x: -0.775, y: -1.775
ø5/16”
CENTER (0,0)
ø3/8”
125B
OUT
VOLUME
x: -0.775, y: +1.71
ø9/32”
PEAK GAIN
x: -0.85, y: +0.41
ø1/4”
DRIVE
x: 0, y: +0.41, ø1/4”
FILTER
x: +0.85, y: +0.41
ø1/4”
RANGE
FOOTSWITCHLED
x: +0.775, y: -1.775
ø5/16”
ENV.
DC IN
0 1 2
CM
0 1
INCH

LUMITRON RESONANT FILTER 9
ENCLOSURE LAYOUT
Enclosure is shown without jacks. See next page for jack layout and wiring.
125B

LUMITRON RESONANT FILTER 10
WIRING DIAGRAM
125B
IN +VGND SNS PGND OUT
PCB
IN
GND +V +V JACK GND JACK
OUTIN
SNS GND PCB
OUT

LUMITRON RESONANT FILTER 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 (2023-09-08)
Initial release.