Thurlby Electronics Harmonic Multiplier



Instructions for use.

The Harmonic Multiplier is an effect unit designed specifically for use with a guitar, and although it can produce spectacular results with any electric instrument, these instructions are intended only to cover the guitar.

The purpose of the unit is to increase the harmonic content of the signal from the guitar. This can be used in several ways:

Lift-off (frequency doubling)

With careful use the unit will cause a note to be lifted up an octave, accurately simulating the harmonic feedback that can sometimes be achieved at very high power levels with good acoustics.

This effect is most readily obtained on notes played fairly high up the fret board (10th fret upwards) and with the base pickup selected, although it is still achievable under other conditions.

Try playing an A on the 3rd string, 14th fret, sustain it and press the switch - the note will gently lift up an octave - release the switch and it will come down again. Some practice may be necessary to perfect this technique. If any other effect pedal, such as a fuzz box, is used at the same time as the Harmonic Multiplier it should be placed on the amplifier side - the guitar must go directly into the Multiplier to achieve good frequency doubling. The only exception to this is a sustain unit which is better placed on the instrument side.

Extra Bite

The unit will greatly increase the bite of notes in the lower registers by adding large amounts of second harmonic. This allows the sound to cut through much better during solos and provides for greater tonal variation.


If two or more notes are played at the same time into the Harmonic Multiplier, a quite different effect is obtained. Extra cross modulation notes are added in at a lower pitch than the originals. Try plucking a pair of notes with a 4th or 5th interval and listen to the result. The unit is now acting like a ring modulator and there is plenty of scope for creating new sounds.

Play a full chord and you've got what sounds like fuzz, but it isn't really. It's a heavier, more complex, sound and unlike a fuzz box the sound is unaffected by the setting of the guitar volume controls - only the volume changes. That means you can put more light and shade into your playing than with the constant volume blur of a fuzz box.


There is only one control and that is the footswitch. With the switch released the sound goes straight through from input to output socket unaffected. Depress the switch and the effect gently comes on, release it and it goes off again. This special biased footswitch action is essential to allow the effect to be cut in and out with the precision required for single note frequency doubling - if the effect is required continuously, the foot must be left resting on the switch.


In order to avoid cross modulation tones being added in when single notes are being played care must be taken to avoid plucking unused strings whilst playing. This may appear difficult when playing alone with a quiet background, but in practise the addition of a small amount of cross modulation is not audible under live conditions.

We must stress that is is not possible to fully appreciate the value of the Harmonic Multiplier in a shop or home environment and that it really comes into its own on a gig.


The Harmonic Multiplier is powered by a standard PP3 type radio battery mounted internally. The unit is switched on by inserting the instrument jack, and consequently in order to achieve a long battery life it is essential that the instrument jack is removed whenever it is not in use.

A low battery is detectable by a reduction in quality of the effect, and possibly the onset of some distortion in the direct signal when the effect is switched out. To replace the battery, unscrew the steel base plate and remove. Carefully hinge up the component board and remove the old battery from its foam housing. Clip in the new battery, bed it down firmly inside the foam and carefully hinge down the component board on top of it. Refit the base plate, making sure not to bend the spring strips that make electrical connection to it, and screw the retaining bolts tightly. A flat battery should be removed immediately since it may leak and cause damage.

The battery should be replaced by a PP3 type from a well known manufacturer - cheap imported varieties should be avoided since they may give a shorter life. An Eveready PP3P will give the longest possible life but this may not be obtainable everywhere.


The Harmonic Multiplier is guaranteed for a full 12 months against any faults excluding damage caused by misuse.

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