R9 Negative Slew

From a 1970s catalog: The DUAL NEGATIVE SLEW (NEG) is one of the unique multi-functional patch-programmable modules in the Serge system. The module features two independent sections with wide range voltage controllable slew rates. The slew is active in the negative direction only and can be patched to perform a number of synthesizer functions. With the Pulse output applied to the input, the module will regenerate for use as a voltage controlled sawtooth oscillator or pulse generator. An audio signal applied to the input will be envelope detected, and the complex envelope will be available at the output. If a pulse is applied to the input, the unit will function as an envelope generator with a fast rise time and a voltage controlled fall time.

Left to right: 1973 panel with some rub-on transfer customization, 1973 PCB


Left to right: 1975 panel, 1975 PCB


The schematic is for the 1973 version. There were some minor changes made by 1975, such as changing the values of some resistors, particularly the values of the output resistors, and the addition of a 4k7, which if omitted, caused some very strange behavior if hooking the two sections to each other. The 1973 version did not suffer from this problem.

PCB connections:
A = input (1)
B = output (1)
C = VC (1)
D = pulse out (1)
E = input (2)
F = output (2)
G = VC (2)
H = pulse out (2)
U = not used (0v)
W = 0v
X = +12v
Y = +6v
Z = -12v



Board with pots removed, courtesy of Dave Brown.


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