aion SKYWAVE User manual

SKYWAVE GERMANIUM DRIVE 1
PROJECT NAME
SKYWAVE
BASED ON
EFFECT TYPE
PROJECT SUMMARY
DOCUMENT VERSION
Hudson Electronics Broadcast
A hybrid silicon/germanium boost & drive pedal with a transformer-coupled output, with tones spanning
the decades from vintage to modern.
Germanium fuzz/overdrive 1.0.0 (2023-07-04)
BUILD DIFFICULTY
Intermediate
Actual size is 2.3” x 2.43” (main board) and 1.78” x 0.90” (bypass board).

SKYWAVE GERMANIUM DRIVE 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 Skywave Germanium Drive is an adaptation of the Hudson Electronics Broadcast, a germanium
preamp/overdrive pedal based on vintage broadcast consoles from the 1960s. It uses a hybrid of silicon
and germanium transistors in class-A configuration, plus a transformer at the output that saturates on
higher drive levels.
The Broadcast was originally released in 2015, and has since had a few new variants including one that
runs on 24V and another with a second footswitchable gain mode with its own level control. (There was
also a limited-run version that combined both of these features into one.)
The Skywave is primarily based on the original Broadcast, but it adds a voltage-tripler circuit to allow
selectable 18V or 24V power from a standard 9V supply. It also incorporates a 3-way gain switch, adding
an extra position adapted from the 24V version of the Broadcast.
USAGE
The Skywave has three knobs, one toggle, and one internal slide switch:
• Gain sets the amount of feedback from the germanium transistor stage that is fed back into the
initial silicon transistor stage.
• Low Cut cuts the bass frequencies as it’s turned up, going from mushy or flabby to tight, with the
right mix of fullness somewhere in between.
• Level is an output volume control.
• Gain Mode (toggle) selects between three gain ratios for the first transistor stage—low, medium
and high—which affect the range of the Gain knob.
• Voltage (slide switch) selects between 9V, 18V and 24V supply voltages.

SKYWAVE GERMANIUM 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—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 220k Metal film resistor, 1/4W
R2 5k6 Metal film resistor, 1/4W
R3 5k6 Metal film resistor, 1/4W
R4 68R Metal film resistor, 1/4W
R5 470R Metal film resistor, 1/4W
R6 5k6 Metal film resistor, 1/4W
R7 4k7 Metal film resistor, 1/4W
R8 5k6 Metal film resistor, 1/4W
R9 15k Metal film resistor, 1/4W
R10 33k Metal film resistor, 1/4W
R11 1k Metal film resistor, 1/4W
R12 56k Metal film resistor, 1/4W
R13 33k Metal film resistor, 1/4W
RPD 1M Metal film resistor, 1/4W Input pull-down resistor.
LEDR 10k Metal film resistor, 1/4W LED current-limiting resistor. Adjust value to change LED brightness.
C1 10uF Electrolytic capacitor, 5mm
C2 1uF Film capacitor, 7.2 x 3.5mm
C3 330pF MLCC capacitor, NP0/C0G
C4 100uF Electrolytic capacitor, 6.3mm
C5 100uF Electrolytic capacitor, 6.3mm
C6 100uF Electrolytic capacitor, 6.3mm
C7 1n Film capacitor, 7.2 x 2.5mm
C8 330n Film capacitor, 7.2 x 2.5mm
C9 330uF/35V Electrolytic capacitor, 8mm See build notes for sourcing information.
C10 100uF Electrolytic capacitor, 6.3mm
C11 220uF Electrolytic capacitor, 6.3mm 120uF in original. See build notes.
C12 10uF Electrolytic capacitor, 5mm Power supply filter capacitor.
C13 470n MLCC capacitor, X7R Power supply filter capacitor.
C14 10uF Electrolytic capacitor, 5mm Power supply filter capacitor.
C15 10uF Electrolytic capacitor, 5mm Power supply filter capacitor.
C16 10uF Electrolytic capacitor, 5mm Power supply filter capacitor.
C17 10uF Electrolytic capacitor, 5mm Power supply filter capacitor.

SKYWAVE GERMANIUM DRIVE 4
PARTS LIST, CONT.
PART VALUE TYPE NOTES
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 1N4001 Rectifier diode, DO-41
D3 1N4001 Rectifier diode, DO-41
D4 1N4001 Rectifier diode, DO-41
D5 1N4001 Rectifier diode, DO-41
Z1 1N4742A Zener diode, 12V, DO-41
Q1 2N5088 BJT transistor, NPN, TO-92 Original uses BC549C, but 2N5088 is the USA equivalent.
Q2 2N404A Transistor, PNP germanium See build notes. Original uses either Russian MP20 or NTE 2N404A.
IC1 LT1054CP Operational amplifier, single, DIP8 Can also use TC1044SCPA.
IC1-S DIP-8 socket IC socket, DIP-8
TRIM 1k trimmer Trimmer, 10%, 1/4"
XFM TY-141P Transformer, audio, 10KCT/10KCT Triad Magnetics TY-141P.
VOLTAGE DP3T slide Slide switch, DP3T E-Switch EG2308
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.

SKYWAVE GERMANIUM DRIVE 5
BUILD NOTES
Silicon transistor selection
The Broadcast uses a BC549C for Q1, the NPN transistor. The Skywave layout uses the USA E-B-C
convention, so the 2N5088 is specified as an equivalent, but if you want to use the BC549C then just
rotate it 180 degrees from the silkscreen.
Germanium transistor selection
The manufacturer has used different types of germanium transistors for Q2 across the different models.
The most common type is the Russian MП20 (MP20), which are typically in the range of 60 to 80 hFE
with less than 100µA of leakage current. Others including the Dual Broadcast use the NTE 2N404A, a
new-production germanium that is anywhere from 50 to 250 hFE. The 2N404A taken from a Broadcast
in this video measured at 216 hFE with 125µA leakage.
With this said, given the ranges in the originals, the gain of the germanium transistor likely does not
make a big impact on the sound. Just use what you can find, taking care that the leakage isn’t too high
(perhaps 200-300µA maximum).
330µF capacitor
The Broadcast uses a 330µF electrolytic capacitor for C9, the low-cut section. It’s unlikely that there
would be an audible difference between this and a lower value such as 220µF, but we’ll assume they
chose it for a reason.
330µF is a less common value than 220µF or 470µF, and in this application it needs to be 35V or higher
since it connects directly to the positive supply, which may be as high as 24V depending on the Voltage
slide switch.
The Mouser parts list provides a part number that will fit the Skywave layout, but if you source a
different one, it may be physically larger than the one we designed around. If this is the case, there is
plenty of space for it to be folded over and lay flat on the board if needed.
Gain trimmer
The internal gain trimmer sets the gain of the silicon transistor in the first amplifier stage. This gain
setting applies to all three toggle switch modes. As you turn it up, resistance is reduced and the
transistor gain increases.
This is purely a set-to-taste control, not a bias, so there is no calibration procedure or target voltage. In
the original Broadcast, it’s set to the minimum position by default, but is intended to user-adjustable.
Listen to all three modes of the gain switch across the range of the Gain knob, and adjust the trimmer
until each mode is useful.

SCHEMATIC
SKYWAVE GERMANIUM DRIVE 6
GND
1M
1N5817
220uF
250kA
100kA
1k
10kA
+9V
100n
10uF
1uF
330pF
220k
VA
LT1054CP
1N4001 1N4001
10uF
470n
470n
1k
GND
220uF
1N4742A
VC
1N4001 1N4001
10uF 10uF 10uF
GND
GND GND
GND
56k
33k
VD
10uF
GND GND
VD
2N5088
5k6
100uF
GND
5k6
VC
100uF
68R
GND
470R
2N404A
5k6
GND
4k7
VA
100uF
1n
5k6
330n 330uF
VA VA
100uF
15k
33k
TY-141P
GND GND
GND
GND GND GND
EG2308
EG2308
IN
OUT
RPD
D1
C19
GAIN
1
2
3
LEVEL
1
2
3
TRIM
1
2
3
LO CUT
1
2
3
C20
C1
C2
GAIN_SW
2
3 1
C3
R1
1
2
3
4 5
6
7
8
IC1 D2 D3
C14
C13
C18
R11
C11
Z1
D4 D5
C15 C16 C17
R12
R13
C12
Q1
R2
C4
R3
C5
R4
R5
Q2
R6 R7
C6
C7
R8
C8 C9
C10
R9
R10
XFM
1
2
3 4
5
6
SW1A
5
76
8
SW1B
1
3 2
4
P
S
GND

SKYWAVE GERMANIUM DRIVE 7
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, y: -1.775
ø15/32”
x: -0.775, y: -1.775
ø5/16”
ø3/8”
125B
OUT
LEVEL GAIN
LOW
CUT MODE
GAIN
FOOTSWITCHLED
DC IN
x: -0.65, y: +1.71 x: 0.65, y: +1.71
ø9/32” ø9/32”
CENTER (0,0)
x: +0.85, y: +0.66
ø1/4”
x: 0, y: +0.66
ø9/32”
0 1 2
CM
0 1
INCH

SKYWAVE GERMANIUM DRIVE 8
ENCLOSURE LAYOUT
Enclosure is shown without jacks. See next page for jack layout and wiring.
125B

SKYWAVE GERMANIUM DRIVE 9
WIRING DIAGRAM
125B
IN +VGND NC NC OUT
PCB
IN
GND +V +V JACK GND JACK
OUTIN
GND GND PCB
OUT

SKYWAVE GERMANIUM DRIVE 10
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.