Advm Method calibration relative to Internal DVM reference

Set the DVM for DC volt, range lOv 2. Attach the negative lead of the DVM to the ground reference of the ADC on the left side of R65 (10 Ohm) on the pot board. 3. With the positive probe of the DVM, test the ADC reference voltage (pin 9 of U20) on the lower lead of R47 on the pot board. Adjust with trimerTI for B) AUDIO METHOD (Calibration relative to the CV generator reference) 1. Select a single patch appropriate for checking voice tuning. 2. Set voice 1 and 2 to be controled by CV I and CV...

Dynamic Fn Implementation

The Xpander voice allows dynamic linear modulation of VC01 frequency by VC02 triangle output. This is done by sending the triangle output of VC02 (pin 5 of UX09) to the reference input of the multiplying DAC UX04 which has its combination inputs controlled by the latch UX03. The op amp UX05 converts the current output of the DAC into a voltage. The three IC's mentioned above act as a digitally controlled variable gain amplifier where pin 15 of UX04 is the amplifier input, pin 1 of UX05 is the...

Gate And Cv Inputs

The six gates, chain advance and trigger signals are buffered through Q1 and the seven transistors contained in U22. The eight resistors R57 through R63 are either pulling up or down the input according to the state of the lines PULL 1 through PULL7. These lines will be set low ii the corresponding gate polarity is set for + and set high if the gate polarity is set for - . This setup automatically forces an unused input into its passive state. The CV and pedal voltages present on the rear panel...

Introduction

The design philosophy behind (he Xpander was to include all the features of a modular synthesizer in a programmable and easy to use instrument. At the same time, reliability, accuracy, and ease of servicing have been a prime concern through every step of the design. The result is the most complete and accurate analog polyphonic synthesizer ever built, despite the inclusion of 6 trimmers. Besides the schematics and the calibration procedure, this manual includes basic explanations of some of the...

J

Because Cfs value is much larger than C2, it acts as a voltage generator for the 10 ms time interval between refresh. It is, however, neccessary for some specific modulations, such as an LFO with a sawtooth wave, to cancel this RC time constant in order to produce the sharp edge of the wave. This is done in practice by short-circuiting the resistor R. The figure below shows one of the eight sample and holds of a voice with a slightly different placement of the components. If a smooth transition...

Mechanical Assembly

To access the inside of the Xpander you must Remove the 4 screws along the front of the unit. Remove the top screw on the right and left wooden end-bells. The whole front panel can now hinge b3Ck. To access the vacuum fluorescent displays (alpha numeric displays), you must remove the three screws along the top of the display board. The display board can now hinge down.

Pulse Width Calibration

The 50 percent duty cycle of the Xpander's 12 pulse width modulators are adjusted by the voice microprocessor whenever the PW function is selected in the tune page. By using the timer U921, the microprocessor measures the duty cycle for each pulse width modulator, 8nd calculates the proper correction voltages to bring them to 50 percent for a control value of 31. These correction values ere stored in the main processor's battery back up memory for instant recall upon power on. FILTER RESONANCE...

Smoothing Sample And Hold

Most of the modulations in the Xpander ere generated by the voice micro processor and are transmitted to the analog pert of the voice through the DAC and sample and hold. Every 10 ms, the processor computes a new value of the modulation and updates the corresponding sample and hold. Without any special attention in the design of the sample and hold, this would produce a step in the control voltege every 10 ms. To avoid this problem, the Xpander S& H use a circuit which allows smoothing of...

Untune

Vou can cancel all the automatic correction (VCO, PW, RES, VCF tuning) All the correction parameters will be set to 0. This may be useful when for example you wish to find out how much apart the resonance control of two VCFs really are, or if you want to check the linearity of a sample and To retrlve the tuning parameters, do a tune all in the TUNE PAGE.

Vacuum Fluorescent Displays

The three 40-digit vacuum fluorescent displays (VFD) and their drivers are located on the display board. The VFD consists of three basic electrodes in an evacuated glass chamber (see fig. below). The electrodes are the cathode, grid and anode. The cathode is a small diameter oxide-coated tungsten filament running across the length of the display and is directly heated by an AC current. The grid is a thin metal screen mesh covering the area over each digit. The anode is coated with phosphor and...

Xpander Circuitry Overview

The key to the outstanding performance and features of the Xpander is the intensive use made of its two built-in microprocessors. The first microprocessor is called the main processor and is located on the processor board. Its main tasks are Collecting and processing information coming from the front panel controllers ( encoders and switches ). Collecting and processing information coming from the outside of the Xpander through MIDI or control input jacks ( CVs and GATES, PEDAL etc.)....

Vco And Vcf Frfoufncy Tuning

The volts per octave (scaling) parameters of the Xpander's 12 VCOs are adjusted by the voice microprocessor whenever the VCO function is selected in the tune page. By using the timer U921, the microprocessor mesures successively the five following frequencies C4, E5, 6*6, C8, E9 for each VCO, and calculates the proper correction voltages to bring each oscillator in tune These correction values are stored in the main processor's battery back up memory for instant recall upon power on. During...

LEDs TEST

Check for all 16 LEDs lit for approximate 2 seconds. Check then for all LEDs lighting one after each other one at a time. 5. Check for all segments ON for all 120 digits. Check for all segments ON for 1 digit at a time. Check for 1 segment ON at a time for all digits of display 1, then display 1 & 2, then display 1,2 & 3. 1. Set the DVM for DC volt, range lOOv. BRTGHTNESS ADJUSTMENT 55v TEST POINT 3. Turn the three brightness trimmers ell the way up (maximum 4. Turn down the trimers of...

Vco Temperature Compensation

Each 3374 dual VCO chip used on the analog voices includes a temperature sensor circuit that provides on pin 10 a voltage proportional to the chip internal temperature. These voltages are filtered and buffered on each voice by CX35 and UX05. The six voltages are then routed to U805 in the DAC area. The circuitry composed of U805, U614, UR15 allows selection, under the control of the m8in processor, of one of the six temperature reference voltages or a fixed reference to be the DAC. reference...

Processor Board

Oberhelm number_Description_Quantltu 311013 IC 74LS139 DUAL 10F4 DECOD DMULXR 1 31101 IC 74LS42 BCD-TO-DEC DECODER 16 PIN 1 311022 IC 74LS04 HEX INVERTER 2 311025 IC. 74LS367 HEX BUFFER 1 31102* IC 74LS03 QUAD3 IN AND GATE 1 311032 IC 74LS245 OCTAL BUSS TRANSCEIVER 1 311033 IC 74LS374 OCTAL D FLIP-FLOP 3-3 3 311034 IC 74LS393 DUAL 4BIT RIPPLE COUNTER 1 311037 IC 74LS32 QUAD2 IN OR GATE 1 311041 IC 74S32 SCHOTTKY QUAD OR GATE 1 313017 IC 301A HI-PERF OP AMP LM301AN 1 313025 IC TL081 SING B1 FET...

Dual Microprocessor Interface

The two microprocessors of the Xpander are running two different programs in parallel the main processor is mainly in charge of collecting and processing the information of the front panel, and the voice processor generates the envelopes, LFOs, LAG etc. for the 6 voices. At some point it is necessary for the main processor to write a new sound parameter into the voice processor memory (for example, a new speed value for an LFO or a new note value for a voice). This is done through the...

Display Board

241012 V FLOURESCENT DISPLAY FG405A2 ITRON 3 476010 TRIMMER 10 K 375E103B CRMT 4 153013 CAP MYLAR FLM .1 .4LS 1 157021 CAP CER DIP . 1 MF 20' . 50V 1 217005 TERM FEED THR0UGH-025 PIN CONCORD 6 219512 CONN RIBBON 26P RIGHT ANGLE HEADER 1 219902 IC SOCKET 14 PIN ICY-143-S3 1 219903 IC SOCKET 16 PIN ICY-163-S3 8 219905 IC SOCKET 13 PIN 9 219909 IC SOCKET 20 PIN AMP 640464-3 6 311019 IC 74LS42 BCD-TO-DEC DECODER 16 PIN 1 311022 IC 74LS04 HEX INVERTER 1 311033 IC 74LS374 OCTAL D FLIP-FLOP 3-S 6...

FlUlti Function Vcf

Although the VCF implemented in the 3372 is a standard 4-pole low pass, the additional circuitry made of UX14, UX13, UXI5, UX17, and the one percent resistor array on the left of UX 17 allows 15 different filter modes including high pass, band pass, notch and all pass. Understanding how this magic trick happens requires a little theory. The figure below shows a simplified representation of the circuitry. The complex representation of the transfer function of a 1 -pole low pass filter is J_...

Oberheim Part Number Cross Reference Processor Board

219029 DIN ISO DEGREES 5 PINS PCMT 3 281066 SCREW 2X1 4 PPSMS BLUNT PHIL PAN 6 239019 CABLE TIE 4 OVERALL LENGTH T13R 1 310007 XP1.0-0 XPANDER 2764 XP 1.0-0 1 310007 XP1.O-1 XPANDER 2764 XP 1.0-1 1 310007 XP1 0 2 XPANDER 2764 XP 1.0-2 1 310007-XP1.0-3 XPANER 2764 XP 1.0-3 1 316003 MICROPROCESSOR 6SB09 3-BIT 1 317014 RAM 6264 8K CMOS RAM 3 318007 AC IA SERIAL INTERFACE IC MC68B50P 1 318008 OPTICAL IC PHQTOCOUPLER HP 6N138 1 401002 BATTERY 2.9V LITH 440-SPC G 32 13 1 510409 SWITCH SLIDE PC MOUNT...

Dac Calibration

Attach the negative lead from the DVM to the ground lug on the voice board at the left of the DAC. 7. With the positive probe of the DVM, check the output voltage of the DAC on pin 6 of U812 TL081 and adjust with OAC trimerT801 for. NOTE The IC U814 4053 in the DAC area is very sensitive to short circuit. Be very careful when testing pin 6 of U812.

Programmable Panning

The programmable panning is implemented by the IC's U102 through U107. The output signal of a voice is routed to one of the eight outputs of its associated IC. The one or two resistors connected to this point distribute the signal to the left and right audio bus. The eighth output is connected to the direct output jack. The enable inputs of those ICs pin 6 allow muting of all the outputs during the tuning. The only equipment required to perform the Xpander test and calibration 8re a well...

Oberheim Xpander Processor Board Images

High Resolution Dac

The Xpander uses a 14 bit DAC which provides the high resolution needed for the generation of smooth and accurate modulations However an even higher resolution is required to achieve the very high standard of tuning accuracy that Oberheim likes to offer. This is accomplished by the circuitry on the right of the DAC U811 see next page . Whenever a control voltage requiring a very high level of resolution VCO or VCF frequency control must be generated, this voltage will be obtained in two phases...

Power Supply Test

Attach the negative lead from the DVM to the ground lug on the voice board at the left of the DAC. 2. Set the DVM for DC volt, range lOv. With the positive probe, test the 6 following voltages at the power supply connector on the voice board. 3. Check the 5M 5 MEMORY on the right lead of D4 located at the middle top of the processor board. With power ON 4.4v - 600 mv 3.80v to 5.00v With power OFF 2.7v 1.3v - 300 mv 2.40v to 4.00v 4. Set the DVM for DC volt, range lOOv. Check the 55v on pin 6...

Switching Power Supply

In order to decrease the heat dissipation without using bulky heat sinks, the Xpander uses a switching power supply which operates as follows The line AC voltage is first stepped down, rectified and filtered by Tl, 01, 02 and C3 to produce a low DC voltage approximately 13 volts . This DC voltage is then chopped switched by Q1 at a frequency of approximately 30 KHz to produce a-variable pulse width wave. This pulse is applied through the primary of the step transformer T2 which provides in...

Pot Board

151024 157002 157021 219021 219027 219335 219521 219525 219903 219909 245106 232003 236006 236523 311017 311019 311021 311025 311031 311033 311035 311038 313047 313049 315025 315051 315053 475410 476010 47 7037 473100 473102 478103 473104 473153 CAP ALUM ELECT 15 25V RADIAL CAP CER DISC .1 MP 20V CAP CER DIP .1 MF 2OX 50V PH JACK 2 COND PCMT SWRF-'T RNU1PC PH JACK 2 C PCMT W SWITCH RN 112APC CONN PCMT 3 CKT F AMP 1-350212-1 CONN RIBBON 40P RIGHT ANGLE HEADER CONN RIBBON 14P VERTICAL HEADER IC...

Dual Vco Cem 5574

The CEM 3374 contains two completely independent precision voltage controlled oscillators. The 3374 includes an on-chip temperature sensor which generates an output voltage, nominally 2.5V, proportional to the chip temperature with a T.C. of 3300 ppm. Reproduced with permission of Curtis Electromusic Specialities

Signal Processor Cem 5572

The CEM 3372 is an audio signal processing device. It includes a two channel voltage controlled mixer, a dedicated 4-pole low pass VCF with voltage controlled resonance and a final VCA. With the exception of the filter cut-off frequency, all control inputs are very low bias current, high impedance which range from 0 to 5 volts. Reproduced with permission of Curtis Electromusic Specialities