etxbrfa@kklm01.ericsson.se (Bjoern Fahller) (09/21/88)
Not very long ago, I bought a second hand Oberheim OB-X. I got it quite
cheap, because it sounded quite pourly. I didn't think of that as a problem,
because an electronics engineer should be able to fix such things.
Unfortunately, it was much worse than I expected.
A few days later it was quite tuned though, but the filters were impossible
to tune to my ears satisfaction. The AUTO button, which I think is an auto
tuner, does not have the desired effect. Pressing the AUTO button, is the
absolutely best way of getting the synth detuned (and impossible to tune
again, unless powered down).
This isn't very good, ofcourse, but I could cope with it.
But a few days ago, something really bad happened. The four voices 5 to
8 is cronicly detuned. I don't think the error is on the voice cards, but
in some controller thats common for them. The situation now is the following:
Voices 1 to 4: Not correctly (the AUTO tuner) but sounds fairly good anyway.
Voice 5. OSC 2 to low frequency. Can be tuned one octave down.
Voice 6. OSC 1 - II - - II -- -- II --
Voice 7. same as OSC 5
Voice 8. The real looser.
OSC 1 gives a ticking sound at about 3 to 4 hertz. The frequency
is constant. (I think the OP-amp is killed, at least it gets
very hot)
I have noticed, that the voltages on bus A is very different on the cards
5 to 8 compared with 1 to 4. Especially pin 1 on bus A on card 8. Its voltage
is constantly 15 V (the others are between -2.6 V and 0.5 V). I have tried
to swap the cirquits that is closest to bus A on voices 1 to 4 with the ones
on voices 5 to 8, but there was no change.
I hope someone can help me to save the synth, because analog synth's sounds
best and when it comes to analog synthesizers, Oberheim has the absolutely best
sound.
SNAIL: ERICSSON TELECOM Vox humana: (+46) 8 - 719 62 52
Bjoern Fahller
KK/ETX/TT/MLG
S-126 25 STOCKHOLM
SWEDENrwn@ihlpa.ATT.COM (Bob Neumann) (09/24/88)
In article <1842@erix.ericsson.se>, etxbrfa@kklm01.ericsson.se (Bjoern Fahller) writes: > Not very long ago, I bought a second hand Oberheim OB-X. I got it quite > cheap, because it sounded quite pourly. I didn't think of that as a problem, > because an electronics engineer should be able to fix such things. > Unfortunately, it was much worse than I expected. > A few days later it was quite tuned though, but the filters were impossible > to tune to my ears satisfaction. The AUTO button, which I think is an auto > tuner, does not have the desired effect. Pressing the AUTO button, is the > absolutely best way of getting the synth detuned (and impossible to tune > again, unless powered down). I used to own an OB-Xa, which used the same circuitry as the OB-X except for some software changes that allowed for splitting and doubling of the keyboard. The OB-X and OB-Xa voice cards did go out of tune due to age, and are frequently in need of repair. I got rid of my OB-Xa in favor of an OB-8 which had better, more reliable voice card architecture, but the sound just was not the same as the OB-Xa. I also have an Xpander now, but that's another story... Anyway, I would suggest taking the synth in for some service if you do not want to do the servicing yourself. I believe one of the problems with my OB-Xa was unreliable tuning pots, and they were all replaced under warranty. This vastly improved the tuning problem. On my OB-Xa, there was a dip switch located inside the instrument on the inside of the top panel towards the "rear" of the instrument (where the output jacks are located). Flipping these switches "turned off" the voice cards so they could not be used by the keyboard. Turning off only the switches related to the offending voice cards enables you to use the stable voice cards in a 2, 4, or six voice configuration. Check to see if a dip switch like this exists in your instrument. It may help you until the other voice cards can be fixed. Bob Neumann PO BOX 1582 Bridgeview, Ill 60455 USA