AM317 Dual Voltage Controlled Filters

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OVERVIEW The AM317 14HP module is two 24dB low pass filters augmented with additional circuitry. One low pass filter is converted to a high pass by mixing in the original signal out of phase at the output using an Op Amp. 

  

These two filters can be used independently, with the mode switch set to SEPARAT. This switch also puts the filters into parallel or series, to create band pass and band reject filters. This switch also converts the frequency controls to band width and band frequency. 

  

The AM317 is a powerful filter providing the classic 24dB ladder filter into four different types and used by Tangerine Dream for many years. Modifications were made to these filters by Tangerine Dream, typically it is a toggle switch on the left hand filter, sometimes with LED’s. 

  

DESCRIPTION The AM317 has been carefully engineered to improve on the sound and format of the original.

    

• Behringer V2044A cascaded "moog" filter chips at the core of each filter
• Q compensation on the low pass filter
• Toggle switch for setting the first filter to LP or HP mode
• WIMA Polypropylene capacitors (THD) in the transistor ladders
• V/OCT trimmer added for precise frequency tracking
• Brightly coloured caps on black plastic knobs

 

This is recreation of the PPG 317 dual voltage controlled filter fom 1976, used by Klaus Schulze, Chris Franke and many others. The design has been reverse enginereed from photographs of the original PCB's. 

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CONNECTIONS There are ten 3.5 mm jack sockets on the anodised aluminium front panel:

  

• IN and OUT - input and output of the high pass filter
• IN and OUT - input and output of the low pass filter
• CV1, CV2, HP-CV - 1V/octave control voltages for high pass cutoff
• CV1,CV2 and CV-LP - 1V/octave control voltage inputs for low pass filter cutoff

  
There are high quality Alpha rotary potentiometers for adjusting frequency cutoff, resonance and the two control signal input levels.
 
The module comes with a set of M3 mounting screws and washers, and a standard 10 to 16-way Doepfer power cable.

The AM317 is a pair of traditional Mini Moog style ladder filters which can be used as seperate low and high pass filters or combined to create band pass and band reject modes. The module is designed to complement the Behringer System 55 Modular System, with a 14HP panel width and the absence of audio signal attenuators.

 

PRODUCT STATUS: IN DEVELOPMENT FOR AUTUMN 2026