Aion Electronics PRISM User manual

PRISM FET AMPLIFIER 1
PROJECT NAME
PRISM
BASED ON
EFFECT TYPE
PROJECT SUMMARY
DOCUMENT VERSION
BOSS®FA-1 FET Amplifier
An extremely loud and tonally-flexible boost/preamp with a two-band EQ, most notably used by The
Edge of U2.
Boost / Preamplifier 1.0.0 (2020-07-03)
Actual size is 2.3” x 1.86” (main board) and 2.3” x 0.86” (bypass board).
BUILD DIFFICULTY
Easy

PRISM FET AMPLIFIER 2
TABLE OF CONTENTS
1Project Overview 7Enclosure Layout
2Introduction & Usage 8Wiring Diagram
3-4 Parts List 9Licensing
5Schematic 9Document Revisions
6Drill Template
INTRODUCTION
The Prism FET Amplifier is a pedal conversion of the obscure but highly sought-after BOSS®FA-1 FET
Amplifier. The original, which was manufactured from 1980 to 1984, was an always-on effect that
clipped to your belt and ran on a 9-volt battery.
It’s a solid circuit, but the non-standard implementation prevented it from getting much attention—
although it was famously used by The Edge which caused vintage prices to skyrocket.
The Prism is the same circuit in an alternate format, converting it to a standard pedal with a footswitch,
LED and 9V adapter jack.
The original FA-1 used the long-obsolete HA1457W chip, which is a single version of the LM1458 (as
evidenced by the similarity of “1457” and “1458”, and similar datasheet specifications). For the updated
version of the Prism, extensive A/B testing was done to verify that the LM1458 performs exactly the
same as two HA1457Ws and is sonically indistinguishable.
As a result, this new version eliminates the option to use the HA1457W and only supports dual op-
amps. However, the previous version of the Prism is still available if you really do want to use the
HA1457W.
USAGE
The Prism has the following controls:
• Treble and Bass form a Baxandall EQ allowing for adjustment of the respective frequencies.
• Volume controls the overall output of the effect, from zero to approximately 26dB of gain.
• Low Cut toggle engages a filter that cuts bass frequencies below 200 Hz at -6dB/octave.

PRISM FET AMPLIFIER 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 10k Metal film resistor, 1/4W
R2 3M3 Metal film resistor, 1/4W
R3 10k Metal film resistor, 1/4W
R4 470k Metal film resistor, 1/4W
R5 15k Metal film resistor, 1/4W
R6 470k Metal film resistor, 1/4W
R7 8k2 Metal film resistor, 1/4W
R8 8k2 Metal film resistor, 1/4W
R9 33k Metal film resistor, 1/4W
R10 10k Metal film resistor, 1/4W
R11 470R Metal film resistor, 1/4W
R12 100k Metal film resistor, 1/4W
R13 22k Metal film resistor, 1/4W
R14 6k8 Metal film resistor, 1/4W
R15 15k Metal film resistor, 1/4W
R16 100R Metal film resistor, 1/4W
RPD 2M2 Metal film resistor, 1/4W
LEDR 4k7 Metal film resistor, 1/4W
C1 10n Film capacitor, 7.2 x 2.5mm
C2 470n Film capacitor, 7.2 x 3mm
C3 47n Film capacitor, 7.2 x 2.5mm
C4 10uF Electrolytic capacitor, 5mm
C5 10uF Electrolytic capacitor, 5mm
C6 33n Film capacitor, 7.2 x 2.5mm
C7 33n Film capacitor, 7.2 x 2.5mm
C8 5n6 Film capacitor, 7.2 x 2.5mm
C9 5n6 Film capacitor, 7.2 x 2.5mm
C10 10uF Electrolytic capacitor, 5mm
C11 47uF Electrolytic capacitor, 5mm Reference voltage filter capacitor.
C12 100uF Electrolytic capacitor, 6.3mm Power supply filter capacitor.
C13 100n MLCC capacitor, X7R Power supply filter capacitor.

PRISM FET AMPLIFIER 4
PARTS LIST, CONT.
PART VALUE TYPE NOTES
D1 1N5817 Schottky diode, DO-41
Q1 2N5457 JFET, N-channel, TO-92 Original uses 2SK246(GR). Any general purpose JFET will work the same
here (2N5458, MPF102, etc.).
IC1 LM1458 Operational amplifier, DIP-8
IC1-S DIP-8 socket IC socket, DIP-8
TREBLE 50kB 16mm right-angle PCB mount pot
BASS 50kB 16mm right-angle PCB mount pot
VOL. 1MA 16mm right-angle PCB mount pot
FL/CUT SPDT Toggle switch, SPDT on-on
IN 1/4" stereo 1/4" phone jack, closed frame Switchcraft 112BX 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.
BATT Battery snap 9V battery snap Optional. Use the soft plastic type—the hard-shell type will not fit.
FSW 3PDT Stomp switch, 3PDT
ENC 125B Enclosure, die-cast aluminum Can also use a Hammond 1590N1.

SCHEMATIC
PRISM FET AMPLIFIER 5
IN
OUT
GND
2M2
1N5817
100uF
GND
50kB
50kB
1MA
+9V
100n
VA
10k
3M3
10n
22k 6k8
15k
GND
47uF 10uF
100R
GND
GND
VB VC
VC
2N5457
VA
10k
GND
470n
470k
47n 15k
LM1458N
LM1458N
VB
VA
GND
470k
10uF
10uF
8k2 8k2
33n 33n
33k10k
5n6 5n6
VB
470R
10uF
GND
100k
RPD
D1
C13
BASS
1
2
3
TREBLE
1
2
3
VOLUME
1
2
3
C14
R1
R2
C1
R13 R14
R15
C11 C12
R16
Q1
R3
C2
R4
C3
2
3
1
FLAT/CUT
R5
2
3
1
IC1A
6
5
7
IC1B
84
R6 C4
C5
R7 R8
C6 C7
R9R10
C8 C9
R11
C10
R12
GND

PRISM FET AMPLIFIER 6
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.
0 1 2
CM
0 1
INCH
x: -0.65, y: +1.71 x: 0.65, y: +1.71
ø9/32” ø9/32”
x: +0.85, y: +0.66
ø1/4”
x: 0, y: +0.66
ø9/32”
x: 0, y: -1.20
ø15/32”
x: -0.775, y: -1.20
ø5/16”
CENTER (0,0)
ø3/8” ø1/2”
0.385”
0.625” 0.625”
ø3/8”
OUT DC IN
125B
TREBLE
LOW CUTVOLUME
BASS
FOOTSWITCHLED

PRISM FET AMPLIFIER 7
ENCLOSURE LAYOUT
Enclosure is shown without jacks. See next page for jack layout and wiring.
125B

PRISM FET AMPLIFIER 8
WIRING DIAGRAM
125B
IN +VGND N.C. N.C. OUT
PCB
IN
GND +V +V JACK GND JACK
OUTIN
GND GND PCB
OUT
Shown with optional 9V battery. If battery is omitted, both jacks can be mono rather than one being stereo.
Leave the far-right lug of the DC jack unconnected.

PRISM FET AMPLIFIER 9
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 (2020-07-03)
Initial release.