PPG 313 Sequential Switch


PPG 313

Overview The PPG313 was developed in 1976 as a more advanced version of the Moog 962, here is what the PPG 300 user manual has to say about this module (translated from German).

Description PPG313 Sequential Switch is an electronic switch that connects one of four input signals to a common output. These signals can be audio signals, control voltages and trigger impulses. The main application is in conjunction with the 314 Sequencer, which can provide up to 32 pre-selected voltages, one after the other. The PPG313 has four stages which are sequenced in series.

The signal inputs are the lower 4 jack sockets labeled SW1, SW2, SW3, and SW4. One of these four inputs can be switched to the Switch Output either manually using the buttons or by trigger signals via the jack sockets SET 1, SET2, SET3 and SET4. The four positions of the electronic switch can be used one after the other, using the front panel button or via the SHIFT jack socket.

The four rotary switches called COUNTER PROGRAMMING are used to preprogram repeating patterns for each of the four stages. For example; with all 4 switches in position 1, the 4 positions are switched through evenly one after the other, according to the impulse that is given to the SHIFT input.

With the rotary switch set to position 4 the input signal for that stage is switched on four times, before the next stage is active. A repeating sequence can be preselected using these switches with either no repeat (1) or a repeat of 2, 3, 4 or 8 times. In position 0, the stage is completely omitted. The trigger 1-4 jack sockets are trigger output sockets, with a trigger at each active stage.

AMSynths Design There are no schematics for the PPG 300 Modular, so I have reimagined the 313 circuit. I have assumed it is based on CMOS logic chips and kept to components available in 1976. The core is a 2-bit binary counter, for the four channels/stages, with the complexity being to create the programmable stages.

The 2-bit counter drives a 4052 analog switch which directs the incoming clock pulses (or shift key press) to one of four 4017 decimal counters. A rotary switch for each 4017 selects the numerical “pattern” which is the number of steps before the next stage is incremented. The output of the four rotary switches are logically OR’d into the counter clock, so it can move to the next stage.

The secondary outputs of the 4052 drive four analog switches (a DG202), the LED’s (mounted in the front panel switches) and four +5V gate outputs. The analog switch outputs are mixed together by an Op Amp which drives the two Output jacks sockets.

The clock input and manual Shift push button go via a transistor Schmitt Trigger to clean up the pulses, and Maxim SMD chips are used to latch the four stage push buttons. The outputs from the latches are level translated to the 15V CMOS which is used throughout. The counter outputs and channel latches are logically OR’d.

Panel Design The panel is 16HP in width and matches the PPG 313 original, except I don’t have space for the Trigger inputs, and the Gate ouputs are more useful anyway. The switches and grey button caps used by PPG are long since obsolete. I have managed to get close by using Marquardt 6425 momentary switches, and light grey buttons with a hole for the LED and dark grey for the solid Shift button.

Outcomes I designed a prototype in December. I plan to use two AMSynths 313 modules in my Klaus “Big Moog” replica.

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