Oberheim OB-X resurrection

[MC]

Last week I brought an OB-X back from the dead and got it to make music. It endured a trip to the annual AHMW gathering quite well, holding its tuning better than the Memorymoog. Still have more work to do. I love my Moogs but this beast is an entirely different animal altogether, that filter makes sounds I haven't heard out of anything else! Some samples of its sound palette below:

http://www.analoguediehard.com/studio/k ... atches.mp3

BTW there is ZERO processing on those samples - completely dry! Some of those thick sounds are unison, the OB-X VCOs combined with unison (and polyphonic portameno) makes some serious phat! And the hard sync is one of the meanest sounding around.

I firmly believe the two essential filters for any polyphonic analog synth is the Moog ladder filter or the Oberheim SEM multimode as in the OB-X. Even better is having both - I have loved having both in my Andromeda. The 12dB mode in the Voyager is nowhere near the timbre of the Oberheim 12dB filter - worlds apart! Am I selling my Moogs? No, they all make sounds the others do not.

I wrote up a page of my ongoing restoration efforts.

http://www.analoguediehard.com/studio/k ... index.html

edit: updated URLs

[Portamental]

Very nice sounding. I have never heard anything Oberheim sounding that good. But then, I never owned one. The new SEM did not convince me to buy one. I guess I'll have to look into vintage once more.

[thealien666]

Very nice! I liked the "man on the corner" and "camera eye" rendition. You've made me realize why, to this day, I've always wanted an Oberheim synth.

These original Oberheim OTA filters sound much better than the Curtis ones used later on... Less harsh, creamier.

Good job on the restauration !

[EMwhite]

My dream as well. Thanks for compiling all of those riffs and even more for documenting as you have. I am unlikely to ever get a 4 voice or a PPG either.

But I had a question: you say in one section that its much like the SEM but then of course mention that it a 12db low pass only. My question is, is band pass hi pass circuitry on the board but not implemented or did Oberheim make design decisions to save space/cost?

[MC]

The OB-X filter *IS* the multimode filter of the SEM, I traced the circuit for both and they are nearly identical. One big difference is the OB-X has VC'd resonance, the SEM did not. But the taps for band pass and high pass are still there on the OB-X filter, just not wired into the audio path. It was a design decision to save space/cost - the voicecard was already pretty large and stuffed full of components, no room for the CMOS switchers and opamp buffers for band/highpass audio, and the feature creep was already making the OB-X really expensive for 1979 dollars!

There's a circuit mod on the net to wire them in, but you would need additional circuitry to switch them in from the embedded system. I do not know if anyone has actually tried this.

To me it's a fair tradeoff, as the OB-X gained full ADSRs while SEM is ADS with shared D/R like the minimoog model D.

[MC]

Yeah I've seen websites that talked about recap, new trimpots. None talked about troubleshooting the embedded system or the design errors I found with the 5.6VDC rail. Collected tidbits of info over the years Kevin and others on AH and GS, and I had studied embedded systems in college so I know my way around them. Just thought it was high time all that stuff got compiled in one place. I also generalized it enough that it would be useful when troubleshooting Prophet-5s, Memorymoogs, and other hybrid polysynths.

[Vince Ascoli]

This page is a really great resource - thank you! Bookmarked! And thank you kindly for not bashing my beloved OB-8;) I've never played an OB-X but owned and sold the OB-Xa (simply not for me), (re)bought a really nice OB-8 and added an Xpander last year...great stuff!

[space_nerd]

Only love for the OBX - it's my favorite analog polyphonic - that 'Tom Sawyer' sweep, rips my soul every time and this sound is also everywhere in 1981 album and live work by Tangerine Dream, as they used the OBX heavily - it was in their live rig for three tours between 1980 and '82.
Many manufacturers tried to copy this sweep sound in their machines, but without these special filters in unison mode and their slight differences in tuning i'ts impossible....
If I had the money, the OBX would be my top call - and yes MC, somehow it's the sound of the 80's - I know, Prophet 5 was there, Memorymoog and Jupiter 8 were there, and even though the OBX has basic specs somehow compared to those others, it's has a very musical, silky and creamy sound

[MC]

The filters are a big part of its charm... very colorful musical resonance and and creamy and silky. Plus they will never track between voices. Indeed, these little "faults" are direct contributors to the "Tom Sawyer" sweep. It was quite a revelation when I hit the UNISON switch while building the patch "ah THAT'S how they did it". THAT'S why no one ever could duplicate the sound. Tried the same trick on Andromeda... nope. Memorymoog... nope.

Oh, BTW... don't forget hard sync. That's another key to the "Tom Sawyer" sweep.

Being a Memorymoog owner for years, I passed up the OB-X because of its basic feature set. It wasn't until I played one in person and heard that filter when I realized that features aren't everything.

[space_nerd]

now, speaking of the memorymoog, I always admire the thing for this particular reason: either it sounds monstrous and dominates the place, and then with a few twists it sounds ethereal and delicate - now, there's another one filter that doing it's own thing....I got to say that...... otherwise, what am I doing here?