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

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

100kA

100kB

2M2

GND

100uF

LT1054CP

100uF -VA

470n

GNDGND

100uF

GND

10uF

GND

1N4742A

GND

47k 47k

200pF

GND

2u2

GND

33pF

-VA

2M2

100k

2u2

1MB

120k

GND

5pF

GND

100k

47n

2n2

47k

CD4069

330k

GND

100R

220uF 220uF

GND GND

22k CD4069

68k

22k 68k

10k

82pF

100k

CD4069

2u2

100k

CD4069

470k

CD4069

GND

120k

10uF

100k

-VA

33pF

2u2

15k

4k7

GND

22n

10k

100n

GND

12k

GND

22k

100k

GND

4k7 91k

10n

-VA

100n

GND 100n

100n

GND

12k 8k2

12k

10n

GND

4n7

GND

3k3

GND

27n

-VA

100n

GND

220k

1N458A1N458A

-VA

150R

2u2

10uF

220uF

GND

220uF

GND

C38

TREBLE

BASS

LEVEL

MID

RPD

C29 1

4 5

IC5

C31 C32

C33

C30

R1 R2

IC1A

IC1B

DRIVE A

DRIVE B

R5 R6

IC2A

1 2

IC2P

7 14

R34

C34 C35

R10 IC2B

3 4

R11

R12 R13

R14

R15

IC2C

5 6

C10

R16

IC2D

9 8

R17

IC2E

11 10

IC2F

13 12

IC3A

R19

C11

R18

IC3B

C12

C13

R20

R21

C14

R22

C15

R23

R24

R25

R26 R27

IC4B

C16

IC4A

C23

C24

C25

C26

R28 R29

R30

C17

C18

R31

C19

IC6A

C27

C28

R32

D2D3

R33

C20

C21

C22

C36 C37

IC6B

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

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”

BETA PREAMP 10

ENCLOSURE LAYOUT

Enclosure is shown without jacks. See next page for jack layout and wiring.

1590BBS

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