aion BETA PREAMP User manual

BETA PREAMP 1
PROJECT NAME
BETA PREAMP
BASED ON
EFFECT TYPE
PROJECT SUMMARY
DOCUMENT VERSION
Sunn®Beta Lead / Bass
A single-channel pedal recreation of the Sunn® Beta Lead and Beta Bass amplifiers, unique in using
overdriven CMOS stages for their drive tone.
Preamp & high-gain drive 1.0.1 (2022-06-06)
BUILD DIFFICULTY
Advanced
Actual size is 3.44” x 2.42” (main board) and 1.77” x 0.87” (bypass board).

BETA PREAMP 2
TABLE OF CONTENTS
1Project Overview 9Drill Template
2Introduction & Usage 10 Enclosure Layout
3-6 Parts List 11 Wiring Diagram
5-6 Usage 12 Licensing
7Build Notes 12 Document Revisions
8Schematic
INTRODUCTION
The Beta Preamp is based on the Sunn® Beta Bass and Beta Lead amplifiers, first released in 1979.
The guitar and bass models were identical except for a handful value changes that made the EQ more
suitable for the frequency range of each instrument.
The Beta amps were unique in that they used overdriven CMOS gain stages for their drive tone. This
had been previously pioneered by Craig Anderton for his Tube Sound Fuzz circuit in 1977, and Electro-
Harmonix released their Hot Tubes pedal in 1978 with a similar topology, but the Beta was the first time
this method had been used in an amplifier.
The Beta Preamp is a single-channel adaptation of the original amplifier. It can be built in either Bass or
Lead configurations by swapping out a few components. While it can be used as a drive pedal, it works
best as a true preamp driving a power amp directly.
The original Beta amplifiers ran on +/-15V, but in this adaptation the supply voltage has been reduced to
+/-9V so it can be powered conveniently by a standard 9V supply. In the original amp, the drive tone is
generated by CMOS hex inverters run on a reduced 8V single-supply, so the heart of the distortion tone
remains exactly like in the original amplifier. All of the other active components will perform the same on
the slightly reduced voltage since there is a great deal of of headroom either way.
USAGE
The Beta Preamp has five controls:
• Drive controls the amount of gain going into the overdriven CMOS stages.
• Treble, Mid and Bass form a 3-band active tone stack. The Lead and Bass amplifiers have different
resistor & capacitor values in this section to optimize the tone stack for the frequencies of the
namesake instruments.
• Level sets the overall output of the preamp.

BETA PREAMP 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 47k Metal film resistor, 1/4W
R2 47k Metal film resistor, 1/4W
R3 2M2 Metal film resistor, 1/4W
R4 100k Metal film resistor, 1/4W
R5 120k Metal film resistor, 1/4W
R6 1M Metal film resistor, 1/4W
R7 100k Metal film resistor, 1/4W
R8 47k Metal film resistor, 1/4W
R9 330k Metal film resistor, 1/4W
R10 22k Metal film resistor, 1/4W
R11 68k Metal film resistor, 1/4W
R12 22k Metal film resistor, 1/4W
R13 68k Metal film resistor, 1/4W
R14 10k Metal film resistor, 1/4W
R15 100k Metal film resistor, 1/4W
R16 100k Metal film resistor, 1/4W
R17 470k Metal film resistor, 1/4W
R18 100k Metal film resistor, 1/4W
R19 120k Metal film resistor, 1/4W
R20 15k Metal film resistor, 1/4W
R21 4k7 Metal film resistor, 1/4W
R22 10k Metal film resistor, 1/4W Lead value. Use 15k for Bass version.
R23 12k Metal film resistor, 1/4W Lead value. Use 27k for Bass version.
R24 22k Metal film resistor, 1/4W Lead value. Use 12k for Bass version.
R25 100k Metal film resistor, 1/4W
R26 4k7 Metal film resistor, 1/4W
R27 91k Metal film resistor, 1/4W Lead value. Use 180k for Bass version.
R28 12k Metal film resistor, 1/4W
R29 8k2 Metal film resistor, 1/4W
R30 12k Metal film resistor, 1/4W

BETA PREAMP 4
PARTS LIST, CONT.
PART VALUE TYPE NOTES
R31 3k3 Metal film resistor, 1/4W
R32 220k Metal film resistor, 1/4W
R33 150R Metal film resistor, 1/4W
R34 100R Metal film resistor, 1/4W
RPD 2M2 Metal film resistor, 1/4W Input pulldown resistor. Can be as low as 1M.
LEDR 4k7 Metal film resistor, 1/4W LED current-limiting resistor. Adjust value to change LED brightness.
C1 200pF MLCC capacitor, NP0/C0G Can also use 220pF.
C2 2.2uF Film capacitor, 7.2 x 5mm
C3 33pF MLCC capacitor, NP0/C0G
C4 2.2uF Film capacitor, 7.2 x 5mm
C5 5pF MLCC capacitor, NP0/C0G
C6 47n Film capacitor, 7.2 x 2.5mm
C7 2n2 Film capacitor, 7.2 x 2.5mm
C8 82pF MLCC capacitor, NP0/C0G
C9 2.2uF Film capacitor, 7.2 x 5mm
C10 2.2uF Film capacitor, 7.2 x 5mm
C11 10uF Electrolytic capacitor, 5mm
C12 33pF MLCC capacitor, NP0/C0G
C13 2.2uF Film capacitor, 7.2 x 5mm
C14 22n Film capacitor, 7.2 x 2.5mm Lead value. Use 56n for Bass version.
C15 100n Film capacitor, 7.2 x 2.5mm
C16 10n Film capacitor, 7.2 x 2.5mm
C17 10n Film capacitor, 7.2 x 2.5mm
C18 4n7 Film capacitor, 7.2 x 2.5mm Lead value. Use 10n for Bass version.
C19 27n Film capacitor, 7.2 x 2.5mm Lead value. Use 47n for Bass version.
C20 2.2uF Film capacitor, 7.2 x 5mm
C21 10uF Electrolytic capacitor, 5mm
C22 10uF Electrolytic capacitor, 5mm
C23 100n MLCC capacitor, X7R
C24 100n MLCC capacitor, X7R
C25 100n MLCC capacitor, X7R
C26 100n MLCC capacitor, X7R
C27 100n MLCC capacitor, X7R
C28 100n MLCC capacitor, X7R
C29 100uF Electrolytic capacitor, 6.3mm

BETA PREAMP 5
PARTS LIST, CONT.
PART VALUE TYPE NOTES
C30 10uF Electrolytic capacitor, 5mm
C31 100uF Electrolytic capacitor, 6.3mm
C32 470n MLCC capacitor, X7R
C33 100uF Electrolytic capacitor, 6.3mm
C34 220uF Electrolytic capacitor, 6.3mm
C35 220uF Electrolytic capacitor, 6.3mm
C36 220uF Electrolytic capacitor, 6.3mm
C37 220uF Electrolytic capacitor, 6.3mm
C38 100n MLCC capacitor, X7R
Z1 1N4742A Zener diode, 12V, DO-41
D1 1N5817 Schottky diode, DO-41
D2 1N458A Rectifier diode, DO-35 Can also use 1N4001.
D3 1N458A Rectifier diode, DO-35 Can also use 1N4001.
IC1 RC4558P Operational amplifier, DIP8
IC1-S DIP-8 socket IC socket, DIP-8
IC2 CD4069UBE CMOS hex inverter, 6 circuit, DIP14
IC2-S DIP14 socket IC socket, DIP-14
IC3 RC4558P Operational amplifier, DIP8
IC3-S DIP-8 socket IC socket, DIP-8
IC4 RC4558P Operational amplifier, DIP8
IC4-S DIP-8 socket IC socket, DIP-8
IC5 LT1054CP Operational amplifier, DIP8
IC5-S DIP-8 socket IC socket, DIP-8
IC6 RC4558P Operational amplifier, DIP8
IC6-S DIP-8 socket IC socket, DIP-8
DRIVE 1MB dual 16mm dual pot, right angle
BASS 100kB 16mm right-angle PCB mount pot
MID 100kB 16mm right-angle PCB mount pot
TREBLE 100kB 16mm right-angle PCB mount pot
LEVEL 100kA 16mm right-angle PCB mount pot Original uses linear taper (B), but audio taper works better.

BETA PREAMP 6
PARTS LIST, CONT.
PART VALUE TYPE NOTES
LED 5mm LED, 5mm, red diffused
DC 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
ENCLOSURE 1590BBS Enclosure, die-cast aluminum

BETA PREAMP 7
BUILD NOTES
Series & parallel operation
While the original Beta Lead and Beta Bass amps each had two channels, the channels were identical
with the same internal circuitry and external controls. This would normally only be useful for effectively
switching between two presets, except for the unique feature that the channels could be run in parallel
and blended together.
We are planning to release a full dual-channel Beta at some point, but in the mean time, you can run two
of these single-channel units in parallel using a passive splitter and mixer to get the same sound.
You can also try running two of these units in series, which is a trick mentioned in the owner’s manual of
the original amplifier that is accomplished by patching the preamp output of “A” into the input of “B”.
Enclosure size
This project was designed for the Hammond 1590BBS enclosure, which has the same height as the
125B or 1590N1. If you don’t use the Hammond brand, be careful—not all 1590BBS enclosures are the
same. For example, Love My Switches sells two different types, and the CNC Pro version is correct while
the standard one is too short.
The 1590BB2 seems like a close equivalent, but it’s about 4mm shorter. It may be possible to fit this
circuit in a 1590BB2, but we have not tested it, so you’re on your own!
Another alternative is the 1590C (also available from Tayda and Love My Switches). It’s about 10mm
taller than necessary, but if that’s all you can find then it will definitely work.

SCHEMATIC
BETA PREAMP 8
OUT
IN
BETA BASS VALUES:
SHOWN WITH BETA LEAD VALUES
C14: 22n -> 56n
C19: 27n -> 47n
R22: 10k -> 15k
R23: 12k -> 27k
R24: 22k -> 12k
R27: 91k -> 180k
C18: 4n7 -> 10n
1N5817
+9V
100n
GND
100kB
100kB
100kA
100kB
2M2
GND
100uF
VA
LT1054CP
100uF -VA
470n
GNDGND
100uF
GND
10uF
GND
GND
1N4742A
GND
47k 47k
200pF
GND
2u2
GND
33pF
VA
-VA
2M2
100k
2u2
1MB
1MB
120k
GND
1M
5pF
GND
100k
47n
2n2
47k
CD4069
330k
GND
100R
220uF 220uF
GND GND
VB
VB
22k CD4069
68k
22k 68k
10k
82pF
100k
CD4069
2u2
2u2
100k
CD4069
470k
CD4069
CD4069
GND
120k
10uF
100k
VA
-VA
33pF
2u2
15k
4k7
GND
22n
10k
100n
GND
12k
GND
22k
100k
GND
4k7 91k
10n
VA
-VA
100n
100n
GND 100n
100n
GND
12k 8k2
12k
10n
GND
GND
GND
4n7
GND
3k3
GND
27n
-VA
100n
100n
GND
GND
VA
220k
1N458A1N458A
VA
-VA
150R
2u2
10uF
10uF
220uF
GND
220uF
GND
GND
VA
D1
C38
TREBLE
1
2
3
BASS
1
2
3
LEVEL
1
2
3
MID
1
2
3
RPD
C29 1
2
3
4 5
6
7
8
IC5
C31 C32
C33
C30
Z1
R1 R2
C1
C2
IC1A
2
3
1
C3
84
IC1B
6
5
7
R3
R4
C4
DRIVE A
1
2
3
DRIVE B
1
2
3
R5 R6
C5
R7
C6
C7
R8
IC2A
1 2
R9
IC2P
7 14
R34
C34 C35
R10 IC2B
3 4
R11
R12 R13
R14
C8
R15
IC2C
5 6
C9
C10
R16
IC2D
9 8
R17
IC2E
11 10
IC2F
13 12
IC3A
2
3
1
R19
C11
R18
IC3B
6
5
7
84
C12
C13
R20
R21
C14
R22
C15
R23
R24
R25
R26 R27
IC4B
6
5
7
C16
84
IC4A
2
3
1
C23
C24
C25
C26
R28 R29
R30
C17
C18
R31
C19
IC6A
2
3
1
84
C27
C28
R32
D2D3
R33
C20
C21
C22
C36 C37
IC6B
6
5
7

BETA PREAMP 9
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.
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
1590BBS
ø3/8” ø1/2”
0.385”
0.9” 0.9”
ø3/8”
OUT DC IN
x: -1.05, y: +1.71
ø9/32”
x: +1.05, y: +1.71
ø9/32”
x: 0, y: -1.775
ø15/32”
x: -0.775, y: -1.775
ø5/16”
CENTER (0,0)
FOOTSWITCHLED
DRIVELEVEL
TREBLEMIDBASS
x: +1.05, y: +0.31
ø9/32”
x: 0, y: +0.31
x: -1.05, y: +0.31
ø9/32”
ø9/32”

BETA PREAMP 10
ENCLOSURE LAYOUT
Enclosure is shown without jacks. See next page for jack layout and wiring.
1590BBS

BETA PREAMP 11
WIRING DIAGRAM
IN +VGND PGND NC OUT
PCB
IN
GND +V +V JACK GND JACK
OUTIN
GND GND PCB
OUT

BETA PREAMP 12
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
1.0.1 (2022-06-06)
Added note about enclosure size. Corrected link to Mouser parts spreadsheet.
1.0.0 (2022-06-03)
Initial release.