19 comments on “OB-Mx 2-voice board

    • Yes, I did read that a long time ago. I actually got in touch with Lynx Crowe some years later regarding the voice boards and he was very helpful. He mentioned that he would be interested in collaborating on a new synthesizer as long as it wasn’t with Don Buchla!! Don’t know what he’s up to these days though. I also got in touch with Richard Bugg who was in the development team for the original OB-Mx (before Buchla was involved). I have one of their prototypes on the shelf…

  1. Hi, I have an OBMx, one thing that I have always wondered about is that the original prototypes supposedly sounded a lot better i.e. the moog filters actually sounded correct and had real moog punch.
    What did they do to mess up the sound so it has no punch?
    I have always wondered if it was an underpowered section in the signal chain such as a tiny capacitor where there was a big one resulting in a shortage of current? Thoughts? If you could work that mod out there would be a stampede. It has as I understand it good chips, where in the signal chain did it go wrong in your opinion. I wonder if there is a simple mod that can transform the OBMx into what it was meant to sound like http://www.soundonsound.com/sos/1994_articles/sep94/oberheimobmx.html

    • I think there are a couple of things that could contribute to the sound. There are tantalum capacitors at several points in the signal path. Using tantalum caps this way is usually a no-no for audio. Also, a digitally-controlled potentiometer is used for gain trim in the signal path, this could also be an issue. SSM2024 VCA’s are used quite a lot in the signal path. I’ve read that they are not the best sounding VCA’s. However replacing them with another VCA would be a major redesign, and I don’t know how many people with OB-MX’s would be willing to throw out their old voice boards for new ones. However something like swapping out capacitors is more feasible. The original prototype OB-Mx is a completely different design. I have one of these units and one day I may try and ‘finish’ the design as it has some major issues.

  2. Quite an undertaking! I understand this project has been mothballed. If it ever comes back to life let me know. I have an empty OB-Mx that needs filling…

    • I did 20 boards a number of years ago. They work fine, the problem is the cost and complexity of building them and the fact that the CEM’s aren’t available at present.

  3. Hey man,
    You wrote that you make 20 boards. Are they all gone? I’m really interested in some of them. I know the built is difficult and high costs but if I see the prices for a 2 voice card is growing up to the sky and the ic’s I found on ebay and other places , OK with bad price!

    If you want to make an new batch I’m interested too.

    Greetings from Germany

    • I still have them. I have interest from other people as well. Currently I have issues with some of them due to faulty components. I plan to substitute some of the hard to get parts with others, but that will take some time. The first batch were all hand built but if I make any more it will be done by a PCB assembly company. Maybe next year sometime.

  4. I would be sincerely interested in a new batch or the ones you have remaining from the previous batch.
    Look forward to more updates.
    Thanks for all efforts and time.

    • The project is suspended for now, until I can evaluate component availability and see what can be swapped out with more modern parts without affecting the sound. Currently I’ve replaced the CEM3382 final VCA stage with a SSI2162 which has required some additional circuitry to scale and adapt the control voltages properly.

  5. Add me to the waiting list too, please! (If there is one!)
    I’ve just bought an Obmx and will need to give it a check up.
    So upgrade certain mono caps with metal film capacitors and check they haven’t put a PA381 in place of the correct PA382.
    Which are the main caps to change?


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