The contour lines enter from the DMUX board at the upper left hand portion of the schematic where the ATTACK, DECAY and RELEASE are buffered and applied to the 3310 Contour Generator. The usual ADSR contour includes an ATTACK, two holds and a RELEASE, but if a second note is played the contour would start back up from whatever DECAY or RELEASE setting it subsided to and reach its ATTACK setting more rapidly than is normal. This is not a desirable condition for the rearticulation of chords, therefore turning ON the RETURN TO ZERO FRONT PANEL switch causes the Contour Generator to short to zero, thus providing a rearticulation of the entire ATTACK phase of the chord. In the UNCONDITIONAL CONTOUR mode, once a trigger is established, the contour will continue & the entire ATTACK phase automatically will proceed into the RELEASE phase (if a note is not held down). In the KEYBOARD FOLLOW mode, the control voltage from the individual VOICE CARDS is used to reduce the ATTACK, DECAY and RELEASE times as notes are played up the keyboard. It is like a piano in which a note played on the bottom lasts a long time, while a note played at the top lasts only a short time. The keyboard follows or simulates that accoustic property with control voltages and as the keyboard is played with higher pitches, with the KEYBOARD FOLLOW switch ON, the DECAY, ATTACK and RELEASE get progressively shorter. There is also a RELEASE SWITCH which when OFF, the contour drops to zero immediately following the ATTACK, DECAY and SUSTAIN phases. When it is ON, the contour fades away at the rate set by the RELEASE potentiometers.
LOUDNESS ENVELOPE GENERATOR CIRCUITRY All the contours are generated by a series of six 3310 Envelope Generators. There are five control voltage inputs for the ENVELOPE GENERATORS: ATTACK, DECAY, SUSTAIN and RELEASE and attack out. The 3310 has its own current mirrors, comparitor and exponential current sources. Therefore, by changing the voltage on pin 16 of U17, it changes the charge time during the ATTACK phase, thereby creating a voltage controlled Envelope Generator. Considering the 3310 as a straightforward Envelope Generator, every time a key is depressed on the MEMORYMOOG, the keyboard logic decodes which note is on and which VOICE CARD it is on. Thus, pressing a key would result in one of trigger inputs A-F actuating. If TRIGGER A is on, for example, the trigger is coupled through the 74LS32 U16A to the input and is differentiated by C24 and applied to the 3310 trigger input. This starts the ATTACK phase.
Without a trigger, the Envelope Generator will not start but once the gate is on, U17 operates as a standard Envelope Generator. When the ATTACK phase reaches the maximum ATTACK level, the comparitor inside goes into a DECAY phase which proceeds to the SUSTAIN level. The DECAY rate is set by the control voltage on pin 13 and the SUSTAIN level is set by the control voltage on pin 12. The exponential input is just like a typical oscillator input operating at approximately 18 millivolts per octave/time. The longest attack time is when U13B is at rero. The more negative this input becomes, the shorter the ATTACK. That time is cut in half for every 18 millivolt decrease.
The SUSTAIN holds for as long as the gate is on. When the gate goes off, the VCA RELEASE phase starts. If the RELEASE switch is ON it will decay at the rate set by the RELEASE control voltage from the DMUX output. If the RELEASE switch is turned OFF, the computer tells the DMUX output to go to maximum which yields the fastest decay time. U18A is a 353 acting as a buffer for the sample/hold capacitor C27. The output of the 353 is fedback into the 3310 and this feedback loop creates exponential-type responses. The Envelope Generator is set by resistor R113 for the longest desired ATTACK time and all the Envelope Generators are similarly matched. The VCA output then has specific wires fed to individual VOICE CARDS.
Looking back at the CONTOUR INPUTS, the UNCONDITIONAL ATTACK phase input is fed to a 393 U14A through a 74LS08 U15C. Whenever a trigger is received on any Envelope Generator during the ATTACK phase, pin 16 will drop slightly negative to about -1 volt. That/ tl turn the output of the 393 on and coup]^|t through the 74LS08 which is ANDED with the UNCONDITIONAL ATTACK This trigger is basically on and operating and the 74LS08 keeps this 74LS32 OR gate on. In other words, when a key is pressed down, U15 turns on and turns the 74LS32 on which holds the trigger on. As soon as it ends the ATTACK phase, it jumps positive again, turns off and eliminates the trigger. If a note is still held down, a trigger will still exist but if the key is just "tapped", the ATTACK will begin and once completed it will go to the RELEASE phase.
The RETURN TO ZERO is accomplished with 08 and Q9. The trigger input is differentiated by C25 and R116 and applied to the base of these transistors such that every time there is a trigger, it momentarily turns on the transistors and shorts C27 and C31. This means it will momentarily bring the contour down to ground. For the KEYBOARD FOLLOW, a bank of 4016s connects to each one of the CONTOUR GLIDE outputs. They are inverted and applied to the 3310 reference, pin 14, from which all the ATTACK, DECAY and RELEASE times are referenced. Therefore,' changing the KEYBOARD VOLTAGE changes the reference voltage which, in turn, changes the apparent ATTACK, DECAY and RELEASE voltages which affects the time rate. Each one of the DMUX outputs is inverted for the ATTACK, DECAY and RELEASE time and is output to the VOICE CARDS on three-*"' V cables.
Was this article helpful?