R3 P&T Peak and Trough
The R3 Peak and Trough contains two modules of similar function, a voltage processor that returns a minimum of all voltages present at its inputs, and a voltage processor that returns a maximum of all voltages present at its inputs. Both are limited to the 0V to 6V range. Effectively the Peak is an analog OR gate, returning the highest voltage (the peak) at any of its inputs, while the trough is an analog AND gate, returning the lowest voltage (the trough) at any of its inputs.
The Peak is frequently used as a digital OR gate, to combine gate signals from the R16 sequencer.
They are an under-appreciated module that can be used combine control voltages, such as from multiple envelopes, in interesting ways.
Between the 1973 and 1975 models, the only difference was in the choice of transistor used. This is insignificant, as any general purpose transistors of the correct polarity and voltage rating will work in this circuit. Likewise, the diode type is not critical, the general purpose signal diode 1N4148 being quite suitable. Both transistors and diodes should be silicon, and the voltage drop of the diodes is cancelled by the voltage drop in the output transistor.
Functionally it is remarkably simple. Diodes form the linear equivalent of an OR gate or an AND gate. There is a 0.6V voltage loss across the diodes. This is followed by a complementary emitter follower which loses 0.6 volts in the opposite direction, thus compensating for the loss in the diodes. A constant current source acts as a pull-up or pull-down for the emitter follower. The "no inputs" base state is derived from a resistor pull-up or pull down to an appropriate voltage rail, while using another diode to clamp it to either 6 volts (trough) or 0 volts (peak).
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