aion Lab Series User manual

L4 BASS PREAMP 1
PROJECT NAME
L4 BASS PREAMP
BASED ON
EFFECT TYPE
PROJECT SUMMARY
DOCUMENT VERSION
Lab Series®L4 Bass Preamp
A pedal adaptation of the two-channel preamp of the Lab Series® L4 bass amplifier from the late 1970s,
a downtuned relative of the legendary L5.
Bass preamp, overdrive & compressor 1.0.0 (2023-07-04)
BUILD DIFFICULTY
Advanced
Actual size is 5.48” x 2.61” (main board) and 4.90” x 0.71” (bypass board).

L4 BASS PREAMP 2
TABLE OF CONTENTS
1Project Overview 14-15 Schematic
2Introduction 16-17 Drill Template
3Usage & Circuit Design Notes 18 Enclosure Layout
4Circuit Design Notes 19 Wiring Diagram
5-10 Parts List 20 Licensing
11-13 Build Notes 20 Document Revisions
INTRODUCTION
The L4 Bass Preamp is an adaptation of the preamp section of the Lab Series®L4 bass amplifier,
originally released in late 1977, just a few months after the Lab Series L5 guitar amp hit stores. The L4
is a 200-watt head that was originally sold with a matching 2x15 cabinet, although most of them have
since been separated from the original cabs.
While Lab Series was considered its own brand, the parent company Norlin also owned Moog, who was
responsible for the design of the whole Lab Series lineup. The L4 and its single-channel sibling, the L2,
used the L5’s circuit as a starting point for the preamp design.
The overall topology—in particular the tone controls, overdrive and limiter sections—are nearly
identical to the L5, with tweaks to the frequencies to make it better suited for bass. The major departure
was the addition of a low-noise input section for the second channel, designed specifically for passive
bass guitars. The “Bright” switches on each channel have also been replaced with “Deep” switches
to enhance the bass frequencies. The multifilter feature was also removed since it was designed to
enhance upper frequencies that are less important for bass.
The L4 Bass Preamp project is nearly identical to the original L4 amp. The only substantial change we’ve
made is to convert the input stage of channel 1 from inverting to non-inverting. This reduces the noise,
but the way we’ve designed it, the input impedance and frequency response are exactly the same as the
original amp’s “Lo” input (the higher-gain mode).
Channel 2 is unchanged except for one functional difference. The original amp used a complex
arrangement of switching jacks to automatically configure the second channel in either low- or high-
input mode depending on which input was used. We’ve converted this into an internal slide switch. You’ll
almost certainly want to keep it in the higher-gain mode all the time, even if using an active bass, since
this mode has much more gain available and can always be turned down as much as necessary—but this
way the low-gain mode is at least still available if you want to use it.
Lab Series®is a registered trademark of Gibson Brands. Use of the Lab Series name is not endorsed by Gibson
and is used for comparative purposes only.

L4 BASS PREAMP 3
USAGE
The L4 Bass Preamp has the following controls:
Channel 1
• Deep (toggle switch) boosts bass frequencies at 100 Hz when on. When off, the signal remains
roughly flat.
• Treble, Mid and Bass form a standard Fender-style 3-band passive EQ.
• Volume controls the amount of gain in the first stage, before the EQ and drive section.
Channel 2
• Deep (toggle switch) boosts bass frequencies at 100 Hz when on. When off, the signal remains
roughly flat.
• Volume controls the amount of gain in the first stage, before the EQ and drive section.
• Treble and Bass form a standard 2-band Baxandall control. Each band is flat at the 12:00 position,
and can either cut (CCW) or boost (CW).
• Mid boosts (CCW) or cuts (CW) the midrange frequency selected by the Frequency control.
• Frequency selects the frequency that will be boosted or cut by the Mid control, from 50 Hz at full
CCW to 3.2kHz at full CW.
Both channels
• Master sets the output volume after the drive section of the preamp.
• Limit sets the threshold of the compressor at the end of the circuit.
• Comp (toggle) engages or disengages the compressor.

L4 BASS PREAMP 4
CIRCUIT DESIGN NOTES
Power supply design
Like most solid-state preamplifiers of the era, the L4 ran on a bipolar +/-15V supply. This voltage can’t be
supplied by an external adapter, and the current draw of the circuit is too high to use a charge pump.
When developing the original Lab Series L5 Preamp, we adapted a supply scheme from Alesis rack units
in the early 1990s that involved a 9VAC adapter and an AC voltage tripler. This was then rectified to
bipolar +/-19V DC and regulated down to 15V on each rail.
This solution used cheap and readily-available parts, and it has worked very well for several years since
the L5 Preamp was first developed. But the power adapter requirement has always been the major flaw.
A 9VAC adapter will destroy most other pedals if it’s plugged in, and if you own one, there’s an infinitely
higher chance that it’ll be mistaken for a 9VDC adapter and plugged into the wrong pedal at some point.
Because of this, when developing the IVP Preamp project in 2021, we set out to find a reliable way to
supply +/-15V from a standard DC adapter. Fortunately, there are a few more options available today
than there were in 2015 when the L5 Preamp was originally developed, and a high-quality DC-DC
converter module will give us exactly what we need.
They’re not cheap (USD$9-15 each), but once you account for the fact that you no longer need a
specialized power adapter, the total cost is about the same. We have begun using these DC converters in
all of our preamp projects going forward, including this one.
See the build notes on page 11 for more information on the specific DC-DC converters that are
recommended for use in this project.

L4 BASS PREAMP 5
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 10k Metal film resistor, 1/4W
R2 220k Metal film resistor, 1/4W
R3 47k Metal film resistor, 1/4W
R4 2k2 Metal film resistor, 1/4W
R5 1k Metal film resistor, 1/4W
R6 22k Metal film resistor, 1/4W
R7 5k1 Metal film resistor, 1/4W Taper resistor for Mid pot. See build notes.
R8 22k Metal film resistor, 1/4W
R9 22k Metal film resistor, 1/4W
R10 470k Metal film resistor, 1/4W
R11 47k Metal film resistor, 1/4W 18k in the original amp, but 47k provides better channel matching.
R12 10k Metal film resistor, 1/4W
R13 2k7 Metal film resistor, 1/4W Taper resistor for Volume 1 pot. See build notes.
R14 1k Metal film resistor, 1/4W Taper resistor for Volume 1 pot. See build notes.
R15 6k8 Metal film resistor, 1/4W
R16 2k2 Metal film resistor, 1/4W
R17 1M Metal film resistor, 1/4W
R18 4k7 Metal film resistor, 1/4W
R19 4k7 Metal film resistor, 1/4W
R20 2k2 Metal film resistor, 1/4W
R21 220k Metal film resistor, 1/4W
R22 120k Metal film resistor, 1/4W
R23 220k Metal film resistor, 1/4W
R24 3k3 Metal film resistor, 1/4W
R25 120k Metal film resistor, 1/4W
R26 18k Metal film resistor, 1/4W
R27 1k Metal film resistor, 1/4W
R28 4k7 Metal film resistor, 1/4W
R29 10k Metal film resistor, 1/4W
R30 5k6 Metal film resistor, 1/4W
R31 22k Metal film resistor, 1/4W
R32 22k Metal film resistor, 1/4W
Interactive BOM →

L4 BASS PREAMP 6
PARTS LIST, CONT.
PART VALUE TYPE NOTES
R33 470k Metal film resistor, 1/4W
R34 2k2 Metal film resistor, 1/4W
R35 15k Metal film resistor, 1/4W
R36 2k2 Metal film resistor, 1/4W
R37 100k Metal film resistor, 1/4W
R38 2k2 Metal film resistor, 1/4W
R39 24k Metal film resistor, 1/4W
R40 2k7 Metal film resistor, 1/4W
R41 2k7 Metal film resistor, 1/4W
R42 2k7 Metal film resistor, 1/4W
R43 18k Metal film resistor, 1/4W
R44 18k Metal film resistor, 1/4W
R45 18k Metal film resistor, 1/4W
R46 18k Metal film resistor, 1/4W
R47 1k5 Metal film resistor, 1/4W
R48 1k5 Metal film resistor, 1/4W
R49 2k7 Metal film resistor, 1/4W Taper resistor for Volume 2 pot. See build notes.
R50 1k Metal film resistor, 1/4W Taper resistor for Volume 2 pot. See build notes.
R51 2k7 Metal film resistor, 1/4W
R52 10k Metal film resistor, 1/4W
R53 15k Metal film resistor, 1/4W
R54 1k Metal film resistor, 1/4W
R55 33k Metal film resistor, 1/4W
R56 220R Metal film resistor, 1/4W
R57 10k Metal film resistor, 1/4W
R58 470k Metal film resistor, 1/4W
R59 2k Metal film resistor, 1/4W
R60 47k Metal film resistor, 1/4W
R61 3k3 Metal film resistor, 1/4W
R62 330R Metal film resistor, 1/4W
R63 100k Metal film resistor, 1/4W
R64 6k8 Metal film resistor, 1/4W
R65 15k Metal film resistor, 1/4W
R66 220R Metal film resistor, 1/4W
R67 220R Metal film resistor, 1/4W
R68 820R Metal film resistor, 1/4W
R69 22k Metal film resistor, 1/4W

L4 BASS PREAMP 7
PARTS LIST, CONT.
PART VALUE TYPE NOTES
R70 3k3 Metal film resistor, 1/4W
R71 33k Metal film resistor, 1/4W
R72 10k Metal film resistor, 1/4W
R73 10k Metal film resistor, 1/4W
R74 47k Metal film resistor, 1/4W
R75 47k Metal film resistor, 1/4W
R76 100k Metal film resistor, 1/4W
R77 100k Metal film resistor, 1/4W
R78 10k Metal film resistor, 1/4W
R79 22k Metal film resistor, 1/4W
R80 10M Metal film resistor, 1/4W
R81 2k7 Metal film resistor, 1/4W
RPD1 2M2 Metal film resistor, 1/4W Ch. 1 input pulldown resistor. Can be as low as 1M.
RPD2 2M2 Metal film resistor, 1/4W Ch. 2 input pulldown resistor. Can be as low as 1M.
LEDC 10k Metal film resistor, 1/4W Channel 1 LED current-limiting resistor.
LEDD 10k Metal film resistor, 1/4W Channel 2 LED current-limiting resistor.
LEDR 10k Metal film resistor, 1/4W Bypass LED current-limiting resistor.
C1 220n Film capacitor, 7.2 x 2.5mm
C2 22pF MLCC capacitor, NP0/C0G
C3 22uF Electrolytic capacitor, 5mm
C4 10n Film capacitor, 7.2 x 2.5mm
C5 2n7 Film capacitor, 7.2 x 2.5mm
C6 470n Film capacitor, 7.2 x 3mm
C7 15n Film capacitor, 7.2 x 2.5mm
C8 68n Film capacitor, 7.2 x 2.5mm
C9 22pF MLCC capacitor, NP0/C0G
C10 220pF MLCC capacitor, NP0/C0G
C11 100n Film capacitor, 7.2 x 2.5mm
C12 4.7uF Electrolytic capacitor, 4mm
C13 220pF MLCC capacitor, NP0/C0G
C14 100n Film capacitor, 7.2 x 2.5mm
C15 1n Film capacitor, 7.2 x 2.5mm
C16 4.7uF Electrolytic capacitor, 4mm
C17 15n Film capacitor, 7.2 x 2.5mm
C18 68n Film capacitor, 7.2 x 2.5mm
C19 4.7uF Electrolytic capacitor, 4mm
C20 82n Film capacitor, 7.2 x 2.5mm

L4 BASS PREAMP 8
PARTS LIST, CONT.
PART VALUE TYPE NOTES
C21 82n Film capacitor, 7.2 x 2.5mm
C22 3n3 Film capacitor, 7.2 x 2.5mm
C23 10n Film capacitor, 7.2 x 2.5mm
C24 150n Film capacitor, 7.2 x 2.5mm
C25 2.2uF Film capacitor, 7.2 x 5mm Original amp uses 2.7uF tantalum, but 2.2uF film will work the same.
C26 220pF MLCC capacitor, NP0/C0G
C27 330n Film capacitor, 7.2 x 2.5mm
C28 68n Film capacitor, 7.2 x 2.5mm
C29 2.2uF Film capacitor, 7.2 x 5mm
C30 100pF MLCC capacitor, NP0/C0G
C31 10uF Electrolytic capacitor, 5mm
C32 100n MLCC capacitor, X7R
C33 100n MLCC capacitor, X7R
C34 100n MLCC capacitor, X7R
C35 100n MLCC capacitor, X7R
C36 22uF Electrolytic capacitor, 5mm
C37 22uF Electrolytic capacitor, 5mm
C38 22uF Electrolytic capacitor, 5mm
C39 22uF Electrolytic capacitor, 5mm
C40 22uF Electrolytic capacitor, 5mm
C41 22uF Electrolytic capacitor, 5mm
C42 22uF Electrolytic capacitor, 5mm
C43 22uF Electrolytic capacitor, 5mm
C44 100n MLCC capacitor, X7R
C45 100uF Electrolytic capacitor, 6.3mm
C46 47uF Electrolytic capacitor, 5mm
D1 1N5817 Schottky diode, DO-41
D2 1N457A Rectifier diode, DO-35
D3 1N457A Rectifier diode, DO-35
D4 1N457A Rectifier diode, DO-35
D5 1N457A Rectifier diode, DO-35
D6 1N914 Fast-switching diode, DO-35
D7 1N914 Fast-switching diode, DO-35
D8 1N4004 Rectifier diode, DO-41
D9 1N4004 Rectifier diode, DO-41
Z1 1N4742A Zener diode, 12V, DO-41
Q1 2N5088 BJT transistor, NPN, TO-92

L4 BASS PREAMP 9
PARTS LIST, CONT.
PART VALUE TYPE NOTES
Q2 2N5088 BJT transistor, NPN, TO-92
Q3 2N3904 BJT transistor, NPN, TO-92
Q4 2N3904 BJT transistor, NPN, TO-92
Q5 2N5457 JFET, N-channel, TO-92 Original uses PN4303, but 2N5457 will perform the same.
Q6 2N3906 BJT transistor, PNP, TO-92
Q7 MPSA13 Darlington transistor, NPN, TO-92
IC1 LF356N Operational amplifier, DIP8
IC1-S DIP-8 socket IC socket, DIP-8
IC2 RC4558P Operational amplifier, dual, DIP8
IC2-S DIP-8 socket Operational amplifier, dual, DIP8
IC3 RC4558P IC socket, DIP-8
IC3-S DIP-8 socket Operational amplifier, dual, DIP8
IC4 RC4558P IC socket, DIP-8
IC4-S DIP-8 socket Operational amplifier, dual, DIP8
IC5 RC4558P IC socket, DIP-8
IC5-S DIP-8 socket Operational amplifier, dual, DIP8
IC6 RC4558P IC socket, DIP-8
IC6-S DIP-8 socket Transconductance amplifier, dual, DIP16
IC7 RC4558P IC socket, DIP-16
IC7-S DIP-8 socket Operational amplifier, dual, DIP8
IC8 LM13700N IC socket, DIP-8 Can also use NE5517N.
IC8-S DIP-16 socket Inductor, 10uH
IC9 RC4558P Inductor, 10uH
IC9-S DIP-8 socket Inductor, 10uH
L1 10uH Inductor, 10uH
L2 10uH Inductor, 10uH
L3 10uH Inductor, 10uH
DC1 TEC 3-0923 DC-DC converter, +9V to +/-15V See page 11 for more DC converter options.
COMP. TRIM 20k trimmer Trimmer, 10%, 1/4" Bourns 3362P
DIST. TRIM 20k trimmer Trimmer, 10%, 1/4" Bourns 3362P
INPUT 4PDT slide Slide switch, 4PDT E-Switch EG4208
BASS 1 50kA 16mm right-angle PCB mount pot
MID 1 5kA 16mm right-angle PCB mount pot Original uses 2.5kA. See build notes.
TREBLE 1 50kA 16mm right-angle PCB mount pot
VOLUME 1 10kB 16mm right-angle PCB mount pot Original uses 2.5kA. See build notes.
BASS 2 25kB 16mm right-angle PCB mount pot
MID 2 25kB 16mm right-angle PCB mount pot

L4 BASS PREAMP 10
PARTS LIST, CONT.
PART VALUE TYPE NOTES
FREQUENCY 100kC dual 16mm dual pot, right angle
TREBLE 2 25kB 16mm right-angle PCB mount pot
VOLUME 2 10kB 16mm right-angle PCB mount pot Original uses 2.5kA. See build notes.
MASTER 25kA 16mm right-angle PCB mount pot
LIMIT 50kC 16mm right-angle PCB mount pot
DEEP 1 DPDT Toggle switch, DPDT on-on
DEEP 2 DPDT Toggle switch, DPDT on-on
COMP SPDT Toggle switch, SPDT on-on
BYP. LED 5mm red LED, 5mm, red diffused
CH. 1 LED 5mm green LED, 5mm, green diffused
CH. 2 LED 5mm red LED, 5mm, red diffused
LIMIT LED 3mm red LED, 3mm, red diffused
DC JACK 2.1mm DC jack, 2.1mm panel mount Mouser 163-4302-E or equivalent.
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.
BYPASS 3PDT Stomp switch, 3PDT
CHANNEL 3PDT Stomp switch, 3PDT
ENCLOSURE 1590XX Enclosure, die-cast aluminum

L4 BASS PREAMP 11
BUILD NOTES
DC converter selection
There are several brands and models available, all with the same pinout and similar specifications. Here
are the DC converters we’ve found that will work in this circuit.
BRAND PART # MOUSER # SUPPLY NOTES
Traco TEC 3-0923 495-TEC3-0923 4.5-13.2V Preferred option. More sources on Octopart.
CUI PQMC3-D12-D15-S 490-PQMC3-D12-D15-S 9-18V
XP Power IZ1215S 209-IZ1215S 9-18V
Recom RS3-1215D 919-RS3-1215D 9-18V
Mornsun WRA1215S-3WR2 N/A 9-18V NAC Semi: https://aionfx.com/link/mornsun/
The Traco TEC 3-0923 is preferred for this circuit because its supply voltage range (4.5V to 13.2V) is
perfectly suited for any type of pedal power supply. The TEC 2-0923 cannot be used since the current
handling is not high enough for the full two-channel preamp.
The other brands all have a minimum supply voltage of 9V. Most nominally 9VDC adapters put out
around 9.6V, which is more than enough—but one very notable exception is the Voodoo Labs Pedal
Power series (and likely other similar pedalboard supplies) which regulate to exactly 9.00V.
These DC converter modules are usually specced very conservatively, so it’s very unlikely that there
would be any issues even if the supply voltage was slightly lower than 9V. However, operating on the
extreme lower end of a spec is not ideal from an engineering standpoint, so if we’re going to point you to
a specific module, it’s going to be the one that works reliably in all use cases.
If you are using a standard wall-wart supply that puts out more than 9V, then all this is immaterial and
any of the five units listed above will work the same. All significant specifications are the same aside
from this input voltage range. We haven’t tried all of them directly, but their datasheets indicate they
will perform identically and they have the same pinout and physical dimensions.
This is fortunate, because most suppliers don’t stock more than 20 or 30 of each type at a time. So while
we recommend the Traco TEC 3-0923 as the best overall, it will likely not always be in stock, especially
as we release more preamp projects with converters and more people are using them.
If you’re having a hard time finding any that will work, try searching Octopart for the part number
shown in the Part # column. Most of these brands are also carried by DigiKey, Newark, and several other
suppliers, and this engine will search all of the major distributors at once for easier sourcing.
The Mornsun unit is not available from Mouser, but it’s included here because it’s cheaper than the
others (USD$8.22 as of the time of this writing) with the exact same specs. If you need more than one, it
quickly becomes much more cost-effective than the other options.

L4 BASS PREAMP 12
BUILD NOTES, CONT.
Calibration
The L4 Preamp has two different calibration trimmers, located on the far-left side of the PCB. To set
these, all you will need is a multimeter and a signal generator (which can be a computer or smartphone).
Note that all voltages are taken in AC, not DC, since we are dealing with audio signal levels. The voltages
are also all RMS rather than p-p, so confirm that your multimeter measures RMS if you’re not sure.
Before you start, turn both trimmers all the way down.
Distortion trimmer
The distortion trimmer should be set first. This sets the level at which the overdrive kicks in. The
procedure calls for a 1kHz 30mV sine wave to be inserted onto pin 13 of IC8, and for the trimmer to be
adjusted until you measure 4.4V on pin 12 of IC8.
For convenience, there is a pair of pads marked “TEST” right underneath the “Frequency”
potentiometer’s pads where you can insert your signal. The “+” pad connects to pin 13 of IC10 and the
other is connected to ground. It’s recommended to solder short pins to these pads (about 3/4” in length)
to act as ‘posts’ for alligator clips to attach to. (The clipped leads from a 1N4004 diode work well for this
since they are more rigid than normal component leads.)
If you don’t have a signal generator, look for a smartphone or Mac/PC app that allows selection of wave
type, frequency and gain level. These come and go, so we can’t recommend anything specific, but there
are several free ones available at any given time and they all do the same basic thing.
From here, hook up a 3.5mm male-to-male headphone cable and turned up the phone or computer
volume to maximum, then set the frequency to 1kHz and the wave type to sine. Using a multimeter set
to AC millivolt mode, adjust the volume in the app until you read 30mV. (Don’t rely on the app to tell you
the output signal level; they have no way of knowing the actual real-world level.)
Now, use alligator clips to connect the sleeve and the tip of the headphone cable to the two wires
coming from the test pad. Since it’s AC, the polarity does not matter. This will insert the signal to pin 13
of IC8 so you can adjust the trimmer as specified earlier, targeting 4.4V on pin 12.
Once you know the correct factory setting, feel free to adjust the trimmer up or down and see if you
prefer it in any other position (but consider first marking the trimmer with a Sharpie so you can get
back to the calibrated setting). Since this is a pedal adaptation, you may find it worthwhile to adjust the
distortion so it comes on earlier than it did in the original amps.
Compressor/limiter trimmer
With the 30mV sine wave signal still inserted into pin 13 of IC8, turn the master volume up all the way
and turn the compressor on (switch in the “up” position). Then turn the compressor knob up to about
2:00 (2/3 of the way up) and touch your probe to the “PCB OUT” pad on the right side of the footswitch
board. Turn the trimmer until you measure 1.17VAC.
This will get you in the range of the original amps. If you’re using the L4 primarily as a pedal, you may
want to set this lower so it’s more sensitive to lower-level signals.

L4 BASS PREAMP 13
BUILD NOTES, CONT.
Ch. 1 midrange, Ch. 1 volume, and Ch. 2 volume potentiometer values
The original L4 amp used 2.5kA potentiometers for both Midrange & Volume of channel 1 and Volume
of channel 2. This is a non-standard value today and not available from any standard parts suppliers.
Tayda Electronics carries 2kA, which is certainly close enough and will work fine in this circuit. But in this
project, to get as close as possible, we included parallel and tapering resistors on the PCB so standard
pot values could be used.
For the Ch. 1 midrange pot, we recommend using 5kA, with a 5k1 resistor in parallel (R7). Since it’s wired
as a variable resistor, this drops the resistance value to 2.5k and only steepens the curve slightly.
Both volume pots are wired as true potentiometers with all three terminals used, so it’s a little more
complicated. For these, it’s recommended to use a 10kB pot with a 2k7 resistor (R13 and R49) between
pins 2 and 3, and a 1k resistor (R14 and R50) between pins 1 and 2. This will give a good approximation
of a 2.5k pot, and the resulting taper will be very close to logarithmic.
LM13700 vs. CA3080
Our original L5 Preamp project used CA3080s as in the original amp. These have been discontinued for
a long time, and while they have been reissued and are not terribly hard to find, they are expensive.
The LM13700 is essentially a dual version of the CA3080/CA3094 and is still readily available. Since the
L4 circuit uses two CA3080s, it seemed like a good opportunity to replace them with a single LM13700.
The only change that this required was to add a second 100k resistor (R77) to cut the compressor LED’s
voltage in half, since the LM13700’s IABC pin sits at twice the voltage of the CA3080’s pin. This extra
resistor prevents the LED from staying on all the time, which was the only side-effect of substituting the
LM13700 in place of the CA3080.
Bypass PCB component orientation
Due to the height of the DC converter and electrolytic capacitors, the components on the switching PCB
are mounted on the bottom, the same side as the footswitch. This is in contrast with most other Aion FX
projects where the switch is mounted on the bottom of the switching sub-board and the components
face up. Components are always mounted to the side with the silkscreen footprint.

SCHEMATIC (CHANNEL 1, CHANNEL 2)
L4 BASS PREAMP 14
CH.1 IN
CH.2 IN
DISTORTION
TO
& LIMITER
5kA 50kA
10kB
50kA
2k2
47k
1k
LF356N
10n
GND
GND
6k8
-VA
VA
GND
10k
220n
2n7
22k
470n
GND
5k1
GND
2k71k
GND
47k
VA
-VA
10k
GND
RC4558P
2M2
GND
10n
150n
25kB
RC4558P
RC4558P
RC4558P
18k
18k
18k
18k
1k5
1k5
100kC
100kC
GND
2k7
2k7
2k7
GND
GND
25kB
10kB
25kB
RC4558P
GND
2k22k2
24k
3n3
82n
15k 2k2
82n
100k
GND
2k7
RC4558P
VA
-VA
-VA
VA
4.7uF
220k
GND
22uF
22pF
22pF
RC4558P
RC4558P
VA
-VA
GND
GND
2M2
GND
-VA
VA
2k2
100n RC4558P
RC4558P
220pF
GND
220k
2N5088
-VA
VA
GND
220k
-VA
120k
VA
1n
3k3
2N5088
120k
VA
18k1k
4.7uF
GND
4k7 4k7
4k7
4.7uF
2k2
220pF
100n
GND
1M
GND
VA
-VA
GND
GND
10k
5k6
15n
GND
22k470k
68n
22k
GND
2k71k
15n
22k470k
68n
22k
GND
GND
GND
1N457A
1N457A
1N457A
1N457A
A
MID 1
1
2
3
TREBLE 1
1
2
3
VOLUME 1
1
2
3
BASS 1
1
2
3
R4
R3
R5
IC1
5
1
2
3
6
8
74
C4
R15
R1
C1
C5
R6
C6
R7
R13R14
R11
R12
6
5
7
IC2B
84
RPD1
C23
C24
MID 2
1
2
32
3
1
IC6A
6
5
7
IC6B
2
3
1
IC4A
R45
R44
R46
R43
R47
R48
FREQUENCY A
1
2
3
1
2
3
FREQUENCY B
R40
R42
R41
1
2
3
TREBLE 2
VOLUME 2
1
2
3
BASS 2
1
2
3
6
5
7
IC5B
R34R38
R39
C22
C20
R35 R36
C21
R37
84
84
R51
2
3
1
IC5A
C19
R2
C3
C2
C9
6
5
7
IC4B
2
3
1
IC2A
84
RPD2
R20
C14
2
3
1
IC3A
84
6
5
7
IC3B
C13
R21
Q1
R23 R22
C15 R24
Q2
R25
R26R27
C16
R28 R19
R18
C12
INPUT B
5
6 4
INPUT A
2
3
1
INPUT D
11
12
10
R16
C10
C11
R17
R29
R30
C17
R31R33
C18
R32
B2
B3
B1
DEEP 2B
A2
A3
A1
DEEP 2A
R49R50
C7
R8R10
C8
R9
B2
B3
B1
DEEP 1B
A2
A3
A1
DEEP 1A
INPUT C
8
9
7
D3
D4
D2
D5

SCHEMATIC (DISTORTION, COMPRESSOR, SWITCHING, POWER)
L4 BASS PREAMP 15
OUT
25kA
50kC
10k
GND
15k
33k
GND
1k
GND
470k
220R
10k
20k
220pF
GND
2N3904
2N3904
3k3 2k47k
330R
330n
100k
68n
2N5457
6k8
15k
10M
GND
820R
100pF
220R
220R
GND GND
2k7
1N4004 1N4004
22k
100k
MPSA13
20k
GND
22k
GND
GND
3k3
RC4558P
RC4558P
10k
10k
33k
3mm red
2N3906
10k
GND
47k
1N914 1N914
GND
47k
RC4558P
LM13700NLM13700N
VA
-VA
GND
-VA
-VA
-VA
-VA
VA
VA
VA
VA
-VA
2.2uF
2.2uF
GND
10uF
-VA
GND
VA
VA
GND
GND
100k
-VA
GND
GND
RC4558P
LM13700N
LM13700N
VA
-VA
GND
GND
A
MASTER
1
2
3
LIMIT
1
2
3
R52
R53
R55
R54
R58
R56
R57
DIST. TRIM
1
2
3
C26
Q3
Q4
R61 R59R60
R62
C27
R63
C28
Q5
R64
R65
R80
R68
C30
R67 R66
R81
D9 D8
R79
R76
Q7
COMP. TRIM
1
2
3
R69
R70
2
3
1
IC9A
6
5
7
IC9B
R72
R73
R71
LIMIT LED
Q6
R78
R75
D6 D7
R74
84
2
3
1
IC7A
IC8A
3
4
5
1
2
IC8B
14
13
12
16
15
116
C29
COMP
2
3 1
C25
C31
R77
+
TEST
-
84
6
5
7
IC7B
IC8_BUF1
V+
7
8
IC8_BUF2
V+
10
9
CHANNEL 1
FROM
& CHANNEL 2
100uF
+9V
GND
1N5817
100n
1N4742A
VA
22uF
TEC 3-0923
10uH
10uH
47uF
22uF
10uH
-VA
100n
100n 100n
100n 22uF
22uF
22uF
22uF
22uF
22uF
GND GND GNDGNDGND
C45
D1
C44
Z1
C42
DC1
+VIN
2
-VIN
1
+VOUT 6
COM 7
-VOUT 8
L2
L1
C46
C43
L3
C32
C33 C35
C34 C36
C37
C38
C39
C40
C41
DC/DC CONVERTER
Power supply
CHANNEL C
CH1 LED CH2 LED 10k
5mm red
GND
5mm green
10k
+9V
C2
C3 C1
LEDD
LEDC
OUTPUT
TO
JACK
PCB
FROM
OUT
INPUT
FROM
JACK
TO CH.1 IN
TO CH.2 IN
22k
5MM
GND
GND
+9V
LEDR
BYP_LED
A2
A3
A1
BYPASS A
B2
B3 B1
BYPASS B
C2
C3
C1
BYPASSC
B2
B3
B1
CHANNEL B
A2
A3
A1
CHANNEL A
Channel switching & bypass

L4 BASS PREAMP 16
DRILL TEMPLATE INSTRUCTIONS
Cut out the drill template on the following page, 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 the template is printed at 100% or “Actual Size”. You can double-check this by measuring the
scale on the printed page with a ruler or calipers.
The LEDs are sized for plain LEDs with no bezel, mounted directly to the PCB. If you don’t have a 5mm
bit for the bypass and channel LEDs, use 7/32”. If you don’t have a 3mm bit for the limit LED, use 1/8”.
Important: Due to the high number of PCB-mounted parts, it’s crucial that the drilling be accurate. Since
the PCB uses slotted holes for the toggles, there’s not a lot of room for error.
If the toggles don’t align to the PCB, you can always drill one step larger (9/32”) to allow a little more
room correct any errors. The toggle switch washer and nut will still fully cover the hole.

DRILL TEMPLATE
L4 PREAMP 17
0 1 2
CM
0 1
INCH
ø3/8” ø1/2”
0.385”
0.9” 0.9”
ø3/8”
OUT DC IN
x: -2.33, y: +1.58
ø9/32”
x: -2.33, y: +0.43
ø9/32”
x: -1.50, y: +1.58
ø9/32”
x: -1.50, y: +0.43
ø9/32”
x: -0.41, y: +1.58
ø9/32”
x: -0.41, y: +0.43
ø9/32”
x: +0.41, y: +1.58
ø9/32”
x: +0.41, y: +0.43
ø9/32”
x: +1.24, y: +1.58
ø9/32”
x: +2.33, y: +1.58
ø9/32”
x: +2.33, y: +0.43
ø9/32”
x: +2.05, y: -1.90
ø15/32”
x: -2.05, y: -1.90
ø15/32”
x: -1.28, y: -1.75
ø5mm
x: -1.28, y: -2.05
ø5mm
x: +1.28
y: -1.90
ø5mm
CENTER (0,0)
y: -0.57
x: +2.33
ø1/4”
x: +2.33, y: -0.92
ø3mm
x: -0.41, y: -0.57
ø1/4”
x: -2.33, y: -0.57
ø1/4”
LIMIT
MASTERFREQUENCYMIDRANGE 2VOLUME 2MIDRANGE 1VOLUME 1
BASS 2TREBLE 2BASS 1TREBLE 1
CHANNEL BYPASS
DEEP 2 COMP.DEEP 1

ENCLOSURE LAYOUT
Enclosure is shown without jacks. See next page for jack layout and wiring.
L4 PREAMP 18
1590XX
Note: The upper pads for the dual-gang
gain potentiometer appear to be cut
in half. This is intentional! It’s called a
plated half-hole or castellated via, and it’s
used so that the PCB can lay flat across
the pots instead of angling upward for
the dual pot.
Solder it like you would if they were
normal pads, but bend the upper set
of pins forward slightly so they make
contact with the inside of the pads.

WIRING DIAGRAM
L4 PREAMP 19
OUT GND -V
PCB -V
OUT
GND +V JACK GND JACK
OUTIN
+V
1590XX
+V
CH.2 CH.1
CH.2 CH.1

L4 BASS PREAMP 20
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 (2023-07-04)
Initial release.