The Teenage Engineering Pocket Operator Modular 400 is a monophonic analog modular synthesizer in kit form. Module types include: square, saw, and sine-wave VCOs, a low-pass filter, two envelope generators, two VCAs, an LFO, a noise source, a random (S&H) generator, a 16-step sequencer, a built-in amp/speaker, and power distribution. Also included in the kit is the metal chassis, 37 trim knobs, 13 value knobs, 4 rubber feet, 14 sheet metal screws, 128 chassis screws, 64 spacers, and a screwdriver. The included manual guides you through the process of assembly.

All three VCO modules offer a key input for tracking 1 volt per octave CV signals from the keyboard/sequencer, plus a CV control input with a scaling knob. The square wave OSC features PWM, while the saw and sine oscillators offer FM. Each VCO includes three outputs for routing to multiple destinations for flexible sound design. The 3-channel mixer includes level control knobs for each input and a master volume control over the mixed signals. The low-pass filter offers frequency and resonance control. There are two control inputs for CV control over the filter frequency, each with scaling knobs. The filter also has three outputs to route the filtered signal to multiple destinations.

Each VCA or voltage-controlled amplifier can be used to simply control the volume, or when coupled with a control signal, such as from the two Envelope Generators, the VCA can be shaped with a longer attack and release for more legato styles of playing. The VCA can be connected directly to a sound system or you may use the onboard amplifier/speaker module for easy monitoring.

A noise source provides two outputs for white noise and two saw wave outputs, well suited for use with the random module, which creates bubbling S&H CV signals. The step sequencer offers 16 tuning knobs for setting the CV for each of the 16 steps. Clock inputs and outputs allow the sequencer to lock to other devices, while the thee sequence outputs allow you to route the pattern to multiple modules.