[sdiy] SSB Banana polysynth

[rsdio at audiobanshee.com]

If there’s firmware, then it might be something as simple as running a calibration step to adjust to the new chips. In other words, the difference between Alfa and CEM might not be as great as between one CEM and another CEM.

I say this because a local musician handed me a Six-Trak with a couple of dead oscillators that he wasn’t able to revive, even with new CEM chips. I started out with my usual deep dive into schematics, visual inspection, and CV measurements, noted that the noise source had been reworked and defeated - which I repaired, but I couldn’t get those voices working. It turns out that the Six-Trak has a calibration step that you engage with a button combo at startup, and these values are actually stored in non-volatile memory. That steps was enough to get all of the voices working again, and it turned out that none of the CEM chips were bad after all.

I didn’t write down the exact voltage measurements, but from observation the CV values were vastly different before and after calibration, such that the CEM chip appeared to be dead at first only to work perfectly afterwards.

I’m hoping that your Alfa chips are close enough to work in this SSB.

Brian


On May 26, 2018, at 12:47 PM, MTG <grant at musictechnologiesgroup.com> wrote:
> Yeah that guy has anything Z80 down as well.  Lots of good work by Bob Grieb.  The simplicity of his site betrays the sheer amount of goodness to be found there.
> 
> On 5/26/2018 12:16 PM, Tom Wiltshire wrote:
>> Wow, that whole site is amazing! There’s some serious synth firmware reverse engineering in there.
>> Thanks.
>> Tom
>> On 26 May 2018, at 10:11, rtarcan <rtarcan at superonline.com> wrote:
>>> More docs
>>> 
>>> http://www.tauntek.com/banana.htm
>>> 
>>> , Tom Wiltshire yazmış:
>>> 
>>>> Yes, it had occurred to me too that it simply might not have been economic to mess about with it, even for a fairly simple fix. I don’t know what these things fetch(ed) but the CEMs were certainly worth plenty. If the outside was beat-up too, it might have looked impossible to make any sort of sense out of spending hours on it.
>>>> 
>>>> We’ll see, I guess.
>>>> 
>>>> Thanks for the documents - that’s a *lot* more than I had before.
>>>> 
>>>> Tom