The Doepfer A-151 module (Quad Sequential Switch) is an electronic, 4-stage rotary (sequential) switch.

It has a trigger input, a reset input, 4 input / outputs and a common output / input. 

The voltages are in the range of -12V to +12V. 

The inputs and outputs are interchangeable, meaning the module works bidirectionally. With each pulse at the trigger input, the common output / input is switch to the next input / output. After the connection with the pulse at the reset input switches, the common output / input is switched back to the first input / output with the next trigger pulse. 

In order to protect the electronic switches in the event of a defective patch (e.g. connection of two outputs), there is a 1k protective resistor in the O/I line. When transmitting CV voltages for VCOs, there can be a very small drop in pitch.

Key Features:

• 4-way sequential switch module for Eurorack modular synthesizers
• Allows 1 signal (audio or CV) to be switched between 4 different outputs
• Trigger input switches signal to the next output in the sequence
• Reset input switches the signal back to the first output
• Select from 2-, 3-, or 4-step sequencing
• Size: 4HP wide, 35mm deep
• Power usage: +20mA (+12V)/-10mA (-12V)