Home > SDIY, Synths > Oberheim SEM Resurrection – The Backstory

Oberheim SEM Resurrection – The Backstory

Oberheim 4 Voice

   So, once upon a time I had an Oberheim 4 Voice synth. A Beautiful monster but still a monster. If you haven’t seen one before, imagine a white smart car and you are about in the ball park of the girth of this instrument. I bought it from a local guy who in his desire to make it patchable had drilled a series of holes in the synth case behind each SEM and installed a series of 1/8” jacks for the various i/o functions of the SEM. On the one hand this seems like a good and reasonable idea. However, there are more i/o points on the SEM than there is room for behind the SEM and so the result was a series of two rows of extremely cramped and unlabeled jacks running the entire length of the synth. I got a good deal on the 4 Voice as the programmer wasn’t working properly. This was not a particularly big deal for me as even working it is fairly useless and secondly I tend to make my patches as I go and so storage and recall just aren’t how I traditionally work. The programmer was not essential as recalling a patch would set the SEMs into an approximate state for the patch you were looking for but you still needed to spend a substantial amount of time retuning and setting each SEM to sound identical if you were to use them as a poly synth. It turned out that while the 4 voice sounds absolutely amazing (and it really does), 4 note polyphony while revolutionary at the time of manufacture, isn’t really anything to brag about when it comes to playing pretty much anything. As a result, I usually ran the 4 Voice as four monophonic voice blocks. In the end, someone offered to trade me a working Korg Wavestation A/D for my dead programmer. I had done a preliminary exploration of the fixing the programmer myself and determined that it was going to be no simple fix – several major blocks appeared to have malfunctions and most of the programmer appeared to run on electronic black arts involving experimental, esoteric, and unobtanum componentry. Around this time, James Husted, a fellow member on Analogue Heaven made a run of metalwork for racking SEMs.  His cases seemed to provide an obvious solution so I promptly bought four of them and they arrived as advertised. I thought this was going to be a quick in and out project. That was roughly 12 years ago.

   The problem with the SEM is that it’s patchability is incredibly seductive.  Major synth guru Kevin Lightner had a good brief overview of the problem in 1998 around the time I was struggling with this same issue.  There are all kinds of patchpoints brought out to the back of the unit on Molex connectors that make the whole process seem simple. In a sense it is. You stick some signals in, hook some outputs up to a panel and you should be good to go. The problem is that the patch points are somewhere in between a dedicated monosynth and a fully modular voice. If you want the monosynth with limited patchability, everything is fine. However, if you want it to function more as a modular voice, there is a good bit of work and planning to be done – but I’m getting ahead of myself. First, you need to power the things. Not really a problem except that the SEM uses a +/-18.5v supply. A quick search of the Mouser/Digikey/Allied/Newark catalogs will show you that there really are not many options out there. I opted for a remote supply ala Serge. I bought a small project box, bought a Power One adjustable supply and wired it up. That went well enough but as soon as I moved on to design the patch panel everything came to a screeching halt. My DIY and electrical circuit skills at that time were paltry at best. I certainly was skilled enough to wire the patchpoints up but extending the functionality by adding or modding the SEM in any significant way was out of the question.

   While I contemplated my design and my next move, I sent James’ metal work off to a local powder coater to transform them from bare metal to a nice industrial finish black. I know what you are saying, the SEM is white. Well, it is a white – an off-white in fact. Further, it is a little bit of an unusual off-white at that. In any event, it wasn’t a particular shade of white that my powder coater had. If you ever wanted to feel really emasculated, try having a discussion with a powder coater about matching particular shades of off-white. I settled on black. The powder coater was doing this as a side job for me and let me know right off the bat he was backed up and so my little project might be a while. The price was right so I decided to wait it out. Two months later, I had wrestled with the panel design problem and come to the conclusion that what I found minimally acceptable for a patch configuration would require a substantial amount of modifications on my part that while not risky, certainly would require a significant amount of time and effort on my part to accomplish. By the time my racks came back in their manly black, I decided to put the project aside while I thought about it some more. Thus, the SEMs sat in my closet for the past decade plus until a month ago.

   A good friend of mine, Brooks Rongstad came over and like he has done many times in the past inquired about the SEMs. Now that Oberheim is making them again he was curious what all the fuss was about and wondering if they were worth considering. He pestered me enough to get me pull one out of the closet over my protesting that I was not sure if they worked any longer, where the power supply I built ended up etc. Turns out that after putting off dealing with these things for 12 years, it took me all of 15 minutes to get one up and running. The power supply still worked perfectly, and I remembered I had actually cobbled together a temporary panel maybe 7 years ago that had most of the rough functions patched out and was still attached to the SEM. My wife was out of town that evening, my son was spending the night at his grandparents, and I didn’t sleep a wink that evening. The sun came up and found me still sitting in the basement studio with the SEM and a sequencer in my modular rig grinning like a complete lunatic – which I am. Now, this project *has* to be completed.

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