Oberheim OB-Xa Engineering Changing Order

    

ECO

DATE

AFFECTED

REASON OF CHANGE

100

06.03.1981

Lower control board serial numbers 810602 and below

Cassette Interface (Loading Data)

101

30.01.1981

1517 Sheet 1/3 UpperControlBoard
This update is already installed on devices from serial number 810401

Prevents erroneous operation of the POWER-UP CIRCUIT (pup).

102

19.02.1981

1516 Sheet 4/4 Lower Control Board

to decrease the volume in the Low position of the cassette monitor switch.

103

25.02.1981

Sheet 1520 Voice Card

to center the Osc Mod Trimmer, creating a larger usable range

104

25.02.1981

Sheet 1518  Pot Board

to eliminate false VCF frequency potentiometer decoding

When pulse width and VCFpotentiometer are fully CCW.

105

25.02.1981

Sheet 1520 Voice Card

to eliminate the possibility of mutual phase locking of the oscillators.

106

05.03.1981

Mother Board

to increase the gain of the output circuit.

107

06.03.1981

Mother Board Cable #7

to eliminate high frequency noise in the output VCA circuit.

108

19.03.1981

Mother Board
The last motherboard layout already implemented this update.

to eliminate the possibility of blowing up the P-channel FET in the output circuit

when a wire is plugged into the output jack.

109

18.03.1981

1516 Sheet 2/4

Eliminate incorrect keyboard decoding when playing tight chords.

110

13.04.1981

Mother Board

to reduce noise in the output VCA circuit.

111

09.07.1981

1516 Sheet 4/4 LowerControlBoard, 1517 Sheet 2/3 UpperControlBoard

to adjust the LFO gain between the VCO’s.

112

21.07.1981

1521 Modulation Panel

to improve LFO offset adjustments.

113

07.08.1981

1517 Sheet 1/3

Extension of the user program from 32 to 120 with 8 split and double

114

07.08.1981

1516 Sheet 4/4, 1517 Sheet 2/3

for adjusting the LFO gain between voice trays in manual mode

116

24.09.1981

1521 Modulation Panel

to increase the range of the Center Lever trimmer (1k).

118

02.10.1981

1521 Modulation Panel

to avoid beats when OSC2 Only is on.

119

19.10.1981

1517 Sheet 1/3 Upper Control Board

Improve auto tuning.

120

05.03.1981

1516 Sheet 3/4 Lower Control Board

Improve Portamento-Spread matching between different voices.

122

21.10.1981

1520 Voice Card

to change the initial frequency trimmer range, which simplfies the oscillator calibration.

125

19.11.1981

1520 Voice Card

remove filter oscillation.

127

14.12.1981

1519 Mother Board (Lower Tray Only)

to adjust the volume between upper and lower tray if not Split or Double.

129

19.02.1982

None

Reduce the modulation offset.

130

04.03.1982

1519 Mother Board

to eliminate DAC stepping at the output of the balance control.

131

21.01.1982

1518 Pot Board Assy 720055

an optional Hardware Fix for OB-Xa and OB-SX with old firmware.

132

05.03.1982

Control Board Assy 720054 (Change Eprom XA-F0 to XA-FA0.

eliminates a bug that causes audible noise when:

VCO PULSE WIDTH if fully CCW and VCF-RELEASE turned fully clockwise.

134

05.03.1982

1517 and 1516 Upper Control Board Assy 720053, 720054

to reduce the volume of the noise function.

135

05.03.1982

1517 Sheet 2 Upper Control Board Assy 720054

to match Filter Envelope characteristic between upper and lower tray.

136

05.03.1982

1516 Sheet 4 Rear Panel and 1519 Mother Board Assy 720057 and 7200570,

Lower Assy 720061 and 7200610, Upper Assy 7501291 and Cable #7

to increase Gain of Output.

140

04.03.1982

Upper Control Board Assy 720054

to eliminate the Edit Double bug in the XAG0 firmware.

143

05.03.1982

1515 Power Supply

Allows operation down to 90 volts AC.

144

19.04.1982

1516, Lower Control Board Assy 720053

to eliminate filter envelope mismatch,

caused by the noise sensitivity of the 324 (see Eco 135).

145

06.09.1982

1520 Voice Card

to enable the use of filter chips with a wider resonance range in the two-pole filter.