These are some material I have collected regarding my OB-8. I have also received material on the Xpander and Matrix-1000 from Johan Boberg.
I've scanned the OB-8 service manual. Actually, I have two of them, slightly different but curiously enougth carrying the same part number and the same revision. After a quick look the only difference you see is that the format differs, one is A4 and one is A3 style sizes. So, if you assume that one is the copied-down version of the other then? Big misstake! The Table of Contents is adapted to give correct page numbers of that format. Also, other layout aspects of the pages will differ to make them equalent except for the format. Below is the scan of the US. Letter (A4 style) version.
These are the tabulated form of the OS releases that I know of.
|OB-8 OS Releases|
|Rel. No||Date||Reason for change||Ref ECO|
|A4||821222||To add the output 3080 (U503) offset calibration procedure to the test software.||410|
|A6||830411||To add separate calibration storage and retreival from tape and clearing calibration.||425|
|A7||830509||Implement two new tests and improve offset cal.||427|
|A8||830712||Add new features.||434|
|B3||840131||Add OB-8 MIDI interface to OB-8.||436|
|B5||840815||Adds MIDI features.||439|
Many thanks goes to BJ for tracking down the B5 EPROMs and doing the sweettalking to a local dealer in order to allow me to copy them. Thanks to these efforts I am now able to bring it onto the web.
These are the tabulated ECOs that I have. I do not know of any other ECOs that relates to the OB-8. Naturally, if you do know of any such thing, I'd love a paper copy.
|OB-8 Engineering Change Orders|
|ECO No.||Date||Reason for change||Drawings affected||Ref ECO|
|402||821209||To eliminate noise when controling the volume with an external low impedance voltage source.||1679A Sheet 2/4|
|403||821207||To match schematic to board layout.||1682A Sheet 2/3|
|404||821210||Increase the active range of the front panel pots.||1681A Sheet 1/1|
|405||821212||Improve temperature stability and tracking of VCO2 filter env. modulation.||1682A Sheet 2/3 & 3/3||See 409|
|406||821212||The offset calibration routine of the service center test can correct the TL084 for positive or negative offset.||1682A Sheet 2/3|
|407||821215||To reduce power-down glitch at outputs.||1679A Sheet 2/4|
|408||821222||On revision A processor boards, when a sequencer is connected, distorsion becomes present in the noise generator.||1679A Sheet 3/4|
|409||821222||To keep Osc 2 from going sharp when the sawtooth wave is selected.||1682A Sheet 3/3||Mod. 405|
|410||821222||To add the output 3080 (U503) offset calibration procedure to the test software.(A4)||1682A Sheet 2/3||Req. 405, 406 & 409|
|411||830106||Removes noise modulation from bender lever.||1680A Sheet 1/3|
|412||830118||When the new power supply transformer (REF.561021) is used, this change decreases the output thump on the power off.||1679A Sheet 4/4|
|413||830118||Remove leak of noise generator when a voice is gated.||1682A Sheet 2/3|
|414||830120||Resistor at UX06 pins 10, 18 marked RX68 should be RX61. Capacitor in 2-pole/4-pole configuration drawing marked C20 should be C14.||1682A Sheet 3/3|
|415||830126||To eliminate noise at output at low master volume levels.||1682A Sheet 1/3|
|416||830203||To filter out digital noise picked up along the filter pedal line (VCFP) when a sequencer (DSX) is connected.||1682B Sheet 3/3|
|417||830211||Rationalize the circuitery.||1682B Sheet 3/3|
|418||830211||Bring the tracking trimmer in the middle.||1682B Sheet 3/3|
|419||830211||Improves synchro sound.||1682A Sheet 3/3||See 431|
|420||830211||Remove cuts and jumpers.||1682B Sheet 3/3||Impl. 413, 417, 418, 419|
|421||830222||To center OSC 2 detune control when LED goes off with knob significantly counter clockwise of center..||1681B Sheet 1/1|
|422||830310||Improves matching of timing between envelopes of upper and lower tray.||1682B Sheet 2/3||See 433|
|423||830328||Improve margin of "PUP" circuit to inadvertent turn-off, especially at 50 Hz.||1679B Sheet 1/4 and 4/4||See 429|
|424||830411||To avoid possible memory drop caused by short power drop.||1679B Sheet 1/4|
|425||830411||To add separate calibration storage and retreival from tape and clearing calibration.(A6)|
|426||830411||To remove AC hum on audio output.|
|427||830509||Implement two new tests and improve offset cal.(A7)||1682A Sheet 3/3||See 433|
|428||830523||Tighten tolerence on envelope speed capacitor.||1682A Sheet 3/3|
|429||830621||Avoid memory drop.||1679B Sheet 1/4||Mod. 423, Ref. 424|
|430||830407||To correct OB-8 voice board schematics.||1682A & 1682B Sheet 2/3|
|431||830627||Allows use of signetics 4016 & identifies components.||Mod. 419|
|432||830627||Avoid missing pulse on arpegiator external clock.||1679B Sheet 2/4|
|433||830705||The new envelope calibration software starting with A7 (see ECO 427) does not require those resistors to be matched.||1682B Sheet 2/3||Mod. 422, Ref 427|
|434||830712||Add new features.(A8)||1682A Sheet 3/3||Req. 405, 406, 409 and 427|
|435||831017||Remove noise on "VCFP" (VCF PEDAL) line. [Contributed by Kevin Lightner]||1682B Sheet 1/3|
|436 12345||840131||Add OB-8 MIDI interface to OB-8.(B3)|
|437||840615||To stop loss of offset in memory on power down. (like DSX)||1679A Sheet 4/4|
|439 12345678||840815||Adds MIDI features. (B5)|
|440||840907||Remove noise modulation from vibrato lever and correct schematic.||1681B Sheet 1/1|
|441||841004||Lower initial frequency of 3340 to accommodate a wider range of characteristic variations on the 3340.||1682B Sheet 3/3|
This is a transcript of a document that came with my Xpander that i haven't previously
seen on the Internet, so here it is:
- Xpander MIDI controller notes
If you need to update the software in the Xpander you'll need these files (and a EPROM burner):
(Main 1.2, Voice 1.4 )
- Xpander ROM images
Here is a PDF describing the 0ddernmart audio in modification on the Xpander.
I havn't tried this myself. If you do, please let me know the results ;-)
- Oddernmart Audio Input Xpansion
The early Oberheim Xpanders were manufactured in the US, the later ones in Japan.
Here is a bunch of photos from the inside of two different Xpanders:
- Xpander inside
These photos can be helpful if you need to service your Xpander.
Even more helpful perhaps:
- Xpander Users manual
- Xpander Service manual
Most of the components used in the Xpander are easy to find and replace. But there are some that isn't. The rotary encoders are pretty rare, i've seen them on eBay but not very often. If they start jumping numbers twist them around for a minute and they will most often behave well again. The displays are very rare but no one seem to have any problems with them either so no need to worry. The VCO chip (CEM3374) is also rare, but it does not seem to fail often. The most common problem is the filter. If the filter fails the voice sometimes die. Replace the chip (CEM3372) and usually it starts to work again. (Hint: try swapping filterchips between voices to see if this was the problem) The filter chip is luckily still easy to find. Another common problem these days is failing power supplies. This is a major problem because it can destroy other parts of the synth. Make sure to replace the large electrolytic capacitors in the PSU every 15 years or so (uh-oh, the xpander was made 1983). The battery should be replaced too because it can start to leak. The acid from the battery can do seriuos harm to your Xpander.
Lots of patches to download here:
- Xpander patches
HI MOM!, I found the little easter-egg "Page 3" on my Xpander:
All the names of the original Matrix-1000 patches in a convenient format:
- Microsoft Excel version
- HTML version to view online
- HTML version in a zip archive for download.