Feedback on 2022 Beta: watch your multiplexers

While the old Z80 based Prophet 600 has a software execution problem, the Teensy++ 2.0 based version has a hardware bottleneck: the multiplexers.

Already during the alpha testing phase it was interesting to explore the software performance on different units. When performance tuned too hard you get effects of glitching, e.g. intermittent wrong voltages especially during fast pitch changes. Through structured testing we managed to pin it down to the multiplexers, which incidentally were different in all testing units. Now with the beta, there has been one case in which one voice never properly updated - and interestingly the same unit works fine with the 2015 GliGli version, but not with the (considerably tuned) 2022 beta. As that problem, too, was solved by replacing the multiplexers, I thought it is time to post something about the importance of the multiplexers in the Prophet 600 so other can benefit from it.

In short: if you have CD4051BE multiplexers (from Texas Instruments), which appear to be factory standard, you should be OK. There are much better alternatives, such as the CD74HCT4051E from Texas Instruments or the MC74HC4051N from Motorola. There are also bad choices and unfortunately these can be found in units, potentially as replacements. For the full story and assessment of different multiplexers look here: Multiplexer: the bottleneck of the Prophet 600


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