PPG 317 VC Modifier

Edgars PPG 217

Introduction The PPG 317 Voltage Controlled Modifier dates back to 1976 and the beginnings of PPG when they were a modular synthesizer company based in Hamburg. The The first set of modules was named the 100 series which are visually similar to the Moog modular but with different circuits and panel lettering in German. Some early modules were marked W.PALM rather than with the famous PPG logo. The 100 series modules were reworked into a short lived 200 series before Wolfgang settled on creating the 300 series of modules with a new visual identity.

The first PPG filter module was the low pass filter 104 based on the Mini Moog filter, which became the 303 Voltage Controlled Modifier with the addition of a VCA section. The 104 was also developed into the 217 Voltage Controlled Filter, which contains two 104 circuit boards. Edgar Froese bought one as used in his Moog Modular rack with some unknown customization. The 217 was then renumbered into the 317 with the same functionality and sold at DM1,560.

PPG 317 – note the mod

Description The 317 is two low pass filter PCB’s 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. A small daughter board sits between the two filter PCB’s to provide the high pass, and band pass and reject modes.

The 317 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. This could be a switch to put the high pass filter into low pass mode.

PPG 317 Inside

Recreation There are no schematics for the 300 series modules, so the AM317 is based on tracing the 303 PCB layout, pictures of a PPG317, and then adding the electronics needed to create the different modes. The original module used a 5-pole rotary switch which is difficult to source in 2021. I have used analog switches to do the same job, controlled by a 1-pole 3-way switch. The AM317 front panels contains these analog switches and the filter mode Op Amps.

Outcomes & Availability A prototype was developed in July 2021 and tested over the subsequent weeks.


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