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FREQUENCYBANDWIDTHGAINVOLUME

125B · 4 knobs

Aion FX

ParsecHarmonic Enhancer

Based on the Systech Harmonic Energizer· 4 other boards clone it

Category
EQ / Filter· Filter / EQ
Controls
Frequency · Bandwidth · Gain · Volume
Difficulty
Easy
Price
$12.50in stock
Buy the PCB at Aion FX Build document1.0.1 (2026-07-16) Mouser parts spreadsheet google

From the vendor

A frequency-variable filter and tone shaper notably used by Frank Zappa, Adrian Belew and others.

The Parsec Harmonic Enhancer is a based on the Systech Harmonic Energizer, a filter/EQ pedal from the mid-1970s that was notably used by Frank Zappa, Joe Walsh, Les Claypool, Greg Lake and Adrian Belew among others.

The Harmonic Energizer uses a fairly straightforward state-variable filter to achieve its frequency boost. This type of filter was more often found in synthesizers and related gear, so it was an innovative idea at the time to use the concept in a guitar pedal.

While the circuit has no intentional clipping stage, the extreme frequency boost can overload the final op-amp for a bit of fuzz at certain settings.

The Parsec is a direct clone of the Harmonic Energizer, with the addition of a volume control at the end to let you dial down to unity volume at higher bandwidth & gain settings.

Schematic

The schematic is in the vendor's build document, page 6. Open the build document. No KiCad fragment has been drawn for this circuit yet.

Parts list 46 rows

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RefValueNormalizedTypeNotes
Resistors 17
R11K1kMetal film resistor, 1/4W
R210M10MMetal film resistor, 1/4W
R322k22kMetal film resistor, 1/4W
R422k22kMetal film resistor, 1/4W
R527k27kMetal film resistor, 1/4W
R65k15.1kMetal film resistor, 1/4W
R710k10kMetal film resistor, 1/4W
R820k20kMetal film resistor, 1/4W
R9510R510Metal film resistor, 1/4W
R10100k100kMetal film resistor, 1/4W
R112k22.2kMetal film resistor, 1/4W
R121k1kMetal film resistor, 1/4W
R131k1kMetal film resistor, 1/4W
R1410k10kMetal film resistor, 1/4W
R1510k10kMetal film resistor, 1/4W
R16100R100Metal film resistor, 1/4W
LEDR10k10kMetal film resistor, 1/4WLED current-limiting resistor. Adjust value to change LED brightness.
Capacitors 12
C12n22.2nFilm capacitor, 7.2 x 2.5mm
C21uF1uFilm capacitor, 7.2 x 5mm
C347n47nFilm capacitor, 7.2 x 2.5mm
C410uF10uElectrolytic capacitor, 5mm
C547n47nFilm capacitor, 7.2 x 2.5mm
C610uF10uElectrolytic capacitor, 5mm
C710uF10uElectrolytic capacitor, 5mmNote that this needs to be installed backwards. See build notes.
C810uF10uElectrolytic capacitor, 5mm
C9100n100nFilm capacitor, 7.2 x 2.5mm
C10100uF100uElectrolytic capacitor, 6.3mmPower supply filter capacitor.
C1147uF47uElectrolytic capacitor, 5mmPower supply filter capacitor.
C12100n100nMLCC capacitor, X7RPower supply filter capacitor.
Diodes 1
D11N58171N5817Schottky diode, DO-41
Transistors 1
Q12N54572N5457JFET, N-channel, TO-92Substitute. Original uses 2N5458.
ICs 2
IC1TL022TL022Operational amplifier, DIP8Can substitute TL072 or other higher quality op-amp.
IC2TL022TL022Operational amplifier, DIP8Can substitute TL072 or other higher quality op-amp.
Potentiometers 4
BAND.5kBB5k16mm right-angle PCB mount pot
FREQ.50kAA50k16mm right-angle PCB mount pot
GAIN50kAA50k16mm right-angle PCB mount pot
VOL50kAA50k16mm right-angle PCB mount pot
Switches 1
FSW3PDT3PDTStomp switch, 3PDT
LEDs 1
LED5mm5MMLED, 5mm, red diffused
Jacks & sockets 5
IC1-SDIP-8 socketDIP-8 SOCKETIC socket, DIP-8
IC2-SDIP-8 socketDIP-8 SOCKETIC socket, DIP-8
IN1/4" stereo1/4" STEREO1/4" phone jack, closed frameSwitchcraft 112BX or equivalent.
OUT1/4" mono1/4" MONO1/4" phone jack, closed frameSwitchcraft 111X or equivalent.
DC2.1mm2.1MMDC jack, 2.1mm panel mountMouser 163-4302-E or equivalent.
Hardware 2
BATTBattery snapBATTERY SNAP9V battery snapOptional. Use the soft plastic type—the hard-shell type will not fit.
ENC125B125BEnclosure, die-cast aluminumCan also use a Hammond 1590N1.

Other boards based on the Systech Harmonic Energizer