351 Voltage Controlled Filter

(Refer to Synthesizer Board Schematic.) The two pitch ranges. 4' and 8' Polyphonic are summed and voiced on the audio input of the VCF (pin 1, M1). M1 is a 4075 Low Pass Voltage Controlled Filter. It has a cutoff of 24 dB Octave and has a manually variable Q (resonance). The filter accepts negative control voltages (-1 volts octave) on pin 4 to control the filter cutoff point. Z1B sums and inverts external voltages which control the VCF. R22, the CVR (Control Voltage Reset) trimmer, prevents...

352 Adsr Gating

(Refer to Synthesizer Control Board Schematic.) The Master Volume Control (25A) is used to set the output level of Strings, Synthesizer and Main Output. Z5A-1 provides a 0 to -10V control voltage, depending on the position of R22, Master Volume Control Slider. The source of the negative control voltage is from a (+10V) voltage divider found on the Bass Board (at J15-4) which supplies Z5A via R37, 100K resistor. The voltage divider can be interrupted if the volume pedal (commonly called Filter...

353 Adsr

The ADSR Envelope Generator circuit provides a negative going DC voltage to control the VCF cutoff and the VCA. ATTACK When the output of Z3A changes from high to low. -15 volts is applied through CR2 and R46 to the noninverting input of follower Z2. During the attack mode, Q4 is off and R45 is disconnected from ground. Z2 directly follows the voltage on pin 3 and applies -15 volts through CR6, R52 to charge integrating capacitor C13 down. DECAY AND SUSTAIN Z1A is a buffer amplifier following...

36 Phaser Board

GENERAL The Phaser Board contains three identical parallel Phase Shifters each modulated by Low Frequency Oscillators. The Phasers are chiefly responsible for the orchestral string effects of the OMNI-2. 2101 A, 2104B. 2101B and 2102 form a low fre quency oscillator (LFO). This circuit differs from our standard LFO because 2102 (integrator) is driven direct from 21018 and 2104B, instead of 2101A. A 10VPP triangle waveform at 2102 is rounded to a 1.2PP sinewave by diodes. CR101 and CR102 and fed...

375 Main Output

Bass, Synthesizer, and String outputs are coupled to Z68 and sent to the Main output jacks-which are switchable from low level (about 200MVPP at jack) to high level (about 1VPP at jack). Z1 contains a voltage reference which supplies approximately +7 volts to pin 6 of Z1. This voltage is connected through pin 5 to the noninverting input of an op amp. The output of the op amp is connected to an emitter follower, also located in Z1, which controls the pass transistor (01). Should the output of...

Bass Low Note Priority Circuit

The output of the three-input NOR (B) will be a square wave only when the Enable (A) input is a logic 0 (-15 volts). Also note that when this occurs, all audio signals to the right will be prevented from being processed hence, low note priority. NOTE All logic gates in the Bass Low Note Priority Section are COSMOS (Complimentary Symmetry Metal Oxide Semiconductor) devices. For this particular application, they are operated between ground and -15 volts. Therefore, a logic 1 is any voltage...

Suppression Trigger

The Upper Voicing Board contains three 4' gate arrays and three 8' arrays the remaining arrays are on the Lower Voicing Board. All of the arrays have the base pin (7) grounded. Each of the sawtooth waveforms are supplied to an emitter through a 100Kohm resistor (e.g. Tone G 4 is supplied through resistor pack Z30 pins 5 and 6 to pin 12 of Z31.). Keying voltages (denoted by KV) are supplied to the emitters also through l50Kohm resistors (e.g. KV21). As long as the keying voltage is at or near 0...

Typical Wa Veshape Circuit

The square wave from inverters Z9-Z13 and from Z2 are differentiated by capacitors C17-C49 (values are selected for each frequency). CR1 through CR41 clip the negative portion of the differentiated square wave resulting in sawtooth shaped waveforms. By altering the DC bias (P6-7, Waveform Control Bus) some of the negative portion of the differentiated waveform is permitted to pass through diodes CR1-41 when the Waveform Enhancement is selected resulting in a hollow type sound. (Refer to Upper...

U3tcss

OMNI 2 MODEL 2470 ASSEMBLY BASS BOARD OMNI-2 MODEL 2470 SCHEMATIC STRING SWITCH BOARD RESISTOR VALUES AREIH OHrtS,l *H, ALL CAPACITOR VALUES ARE.OC JJ SOV, 20 ALL DIODES ARE FLV3M ALL. TRESIS TORS ARE SAJ3904. OMNI-2 MODEL 2470 ASSEMBLY STRING SWITCH BOARD OMNI-2 MODEL 2470 ASSEMBLY POWER SUPPLY BOARD

Vcf

Monitor pin 10 of filter module M1 with an oscilloscope. 2. Put the VCF FREQ slider and VCF RESONANCE slider fully DOWN. 3. Put the VCF ADSR slider fully UP. 4. Set the ADSR sliders as follows ATTACK. DOWN DECAY. 3 4 UP SUSTAIN, DOWN RELEASE, DOWN. 5. Adjust R22 for minimum amplitude when keys are depressed. 1. Monitor pin 10 of filter module Ml with an oscilloscope. 2. Clip a 33Kohm resistor from pin 10 of M1 to pin 2. 3. Put the VCF FREQ slider fully DOWN and the VCR RESONANCE slider fully UP...

323 Bass Keying Voltage

(Refer to Lower Voicing Schematic, sheet 3 of 3.) The T point of the Bass Keying Reference Generator supplies a voltage to the bass of Ql-20 of the Bass Low Note Priority Circuit which is at least three diode drops higher than the keying voltage supplied to the Lower keyboard bus rod (P1-14). The diode drops are created using CR114, Q30 and CR113. This insures that Q1-20 will be biased ON regardless of the bus voltage which decreases as more keys are depressed. (Refer to Lower Voicing...

326 Waveform Control

(Refer to Lower Voicing Schematic sheet 3 of 3.) The Waveform Control sets the bias point of the clipping diodes in the Wave Shaping circuits for each key. When the output of Z53 is 0 volts, sawtooth waveforms are produced. When the output of Z53 is +15 volts, the hollow sound is produced. J11 -6 is ground when the Waveform Enhancement switch is off, +15 volts when the switch is on. CR107 provides a little extra voltage to the output when the input is + 15 volts since the op amp cannot supply...

37 Bass Voice Circuit

This circuit contains a preset Bass Voltage Controlled Filter, Envelope Generator, String and Synthesizer VCA, and the Main Output Mix Amplifier. The Bass Voltage Controlled Filter, comprised of 24A, C6, Z4B, and C7, form a two pole low pass filter. The Bass Waveforms (8' and 16') are summed in on J15-2 and J15-3. 24A and B act as voltage controlled resistors, whose transconductance is controlled by the voltage at the gates. The initial conduction (or the initial cutoff frequency) is regulated...

311 Master Oscillator And Top Octave Divider

Refer to Upper Voicing Schematic, sheet 1 of 2. LI and Q1 produce a 0 to -15 volt sine wave at approximately 500kHz. The frequency of the oscillator can be varied by adjusting the core of the coil externally accessible . Z1 buffers and squares the waveform from the Master Oscillator and supplies it to the Top Octave Divider. Z2. 22 is a LSI Large Scale Integrated Circuit divider which produces the

Section 6 Parts List32

The ARP OMNI-2 offers the unique combination of polyphonic tone sources and the versatility of synthesizer sound modification. Separate string and synthesizer sections allow orchestral and symphonic sounds simultaneously. The total variability of the synthesizer section permits such sounds as brass, piano, and clavinet without single note limitations. The string, bass and synthesizer sections have separate outputs located on the rear panel. ARP's now-famous systems interface applies to this...