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



Location: Germany

Comments

Post a Comment

Popular posts from this blog

Ready to go: firmware v2022 + patch collection

Image
The v2022 firmware is completed and ready for download! There is even a collection of 100 patches compiled from dedicated contributions of Prophet-600 users (and myself) and including some selected Z80 patches. Official download page:  Prophet-600 v2022 firmware + patch collection + documentation Share your opinion on the firmware and the patches here. I will provide some means of structured feedback in the next months to collect your experience out in the field. Then there is also the list of great feature ideas on the backlog which need user prioritization. So if you want to stay informed or even get involved please watch this space or follow my blog.
Read more

It gets better: Prophet 600 v2022 RC1 (first release candidate)

While I intended to basically release the beta 2022 (2) and only do the smallest and most urgent fixes (hoping of course there would not be any) some very important code changes did came up which now lead up to the improved first release candidate v2022 RC1 ( download ). What happened and what is new?  Apart from those aforementioned small corrections (thanks to the contributors!) there are 2 new features and one really exciting major fix.  The 2 selected features that "sneaked in"were 1) vibrato has now the option to modulate only one of the two oscillators (parameter 222) and 2) the LFO can now be re-triggered when a new key is played (parameter 111) Now to the major fix "tuned pitch shift" : the poly-mod envelope pitch shift of OSC A as well as the LFO pitch shift of OSC A and B are now fully tuned and harmonic. Yes, that wasn't true before. In prior firmware versions tuning was not taken into account so that pitch shifts were detuned depending on how far the...
Read more

Revised envelope shapes: inspired by Prophet 5 rev 1/2

Image
The upgraded Prophet 600 offers two envelope shapes: exponential and linear. These are software generated and in versions 2.0 and 2.1 RC3 they are really exactly that: a pure exponential shape and a pure linear shape. Some users argue that a musical choice is somewhere in between. To the ear, the exponential shape drops very quickly at the beginning and then it tails off long. The linear shape on the other hand is thicker in the early decay phase but then it drops hard to zero. The human ear is stunningly sensitive to envelope shapes, even at very low volumes. In a recent nice YouTube video Starsky Carr directly compares the Prophet 5 (rev 4) envelopes to the Prophet 600 addressing exactly this finding:  Prophet 600 vs Prophet 5 // Is the 600 a better value option? - YouTube Now: the 2022 firmware has completely revised linear decay and release shapes, which are linear at the start but then tail off smoothly. To some degree the shape was inspired by the Prophet 5 rev 1/2 envel...
Read more