Triple Wave Shaper

The Triple Wave Shaper is a three-stage analog wave-shaping module designed to transform basic waveforms—such as sawtooth or triangle—into complex, harmonically rich signals.

Overview
This module is a modern adaptation of the classic 1973 Serge Triple Wave Shaper (TWS), originally developed by Serge Tcherepnin. As described in the 1982 Serge catalog:

“The Triple Wave Shaper (TWS) is a non-linear modifier that can transform a sawtooth wave into a sine wave. It comprises three independent wave-shaping circuits designed to process synthesizer waveforms or signals from preamplified instruments. Although initially intended to shape the output of early Serge oscillators, the TWS has proven to be a highly effective tool for modifying both electronic and acoustic signals. It is especially recommended for subtle timbral transformations that go beyond conventional oscillator/filter configurations.”

While originally conceived as a wave shaper, its applications extend much further. When multiple stages are connected in series, each additional stage introduces a further wave fold, offering extensive potential for harmonic enhancement and tonal complexity.

Single Stage: Basic waveform shaping.

Three Stages in Series: Increased harmonic content through successive folding.

Circuit Functionality
The module consists of three identical wave-shaping sections. When used individually, each section acts as an independent wave shaper. When connected in series, they function as a cascading wave folder.

Waveform Coupling Example:
The schematic illustrates all three identical sections of the Triple Wave Shaper, along with an example of how they may be interconnected.

Notable Historical Variations:
1973 Version:

Input pull-down resistors were 22k (compared to 100k in later versions).

AC-coupled outputs were mounted on the back of the jacks.

By 1975, AC coupling was discontinued and both output jacks were directly linked.

25k potentiometers were used for input level control.

Later Designs:

In two-column panel configurations, the second output was removed.

A “Join” switch was introduced to chain all three wave shapers internally.

Input potentiometers were moved to the front panel, although the PCB layout remained mostly unchanged.

LGE085 Version:

Incorporates additional 220k input resistors to support a Join switch without losing individual input functionality.

The Join switches connect the stages in series while preserving access to each stage’s input/output.

When using the Join switch, the second and third stage input pots are bypassed for the internally chained signal, but still allow additional signals to be mixed in.

Modernized input potentiometers (100k) bring input impedance in line with contemporary standards.

Added Feedback switch w/ Amount control routes signal back from the output to either the inputs of the second or third stages. Center position is off.

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