Plan B Model 28 Programmable Tap Clock Eurorack Module with Tim Stinchcombe sync upgrade and mods

Accurately replays tapped-in tempos as quarter, 8th and 8th note triplet events
True x2 and x3 freq. Multiplier
Full articulation control.
Manual or ext. start/stop (make-before-break)
Serial out allows for programmable polyrythmic gate patterns
Phase lock of external clocks

Plan B M28 Tap Clock Synchronization upgrade and other mods

Since originally producing this page for the M28 synchronization upgrade (detailed immediately below), it has become apparent that a few other issues with this module could be usefully covered here too:
    - the amplitudes of the  are likely to be noticeably different
    - unusable  for the serial output
    - resistor
    - misshapen serial out, due to  in zener mod incorporation at Rev 1.2?
(the links jump to lower down the page).

Synchronization upgrade

A few minutes experimentation with the feature entitled 'phase lock' on an original M28 will tell you that it does not phase lock—it simply wasn't designed to do that job, and so applying the moniker 'phase lock' was a poor choice that was only ever going to lead to customer disappointment. Fortunately Phil Gallo, the original developer of the software for the on-board microcontroller (the 'firmware'), was willing to work together on a collaborative effort to produce a new version which behaves very much closer to what a user would expect from a function called 'phase lock'—it is perhaps not acting as a phase-locked loop in the usual sense, but the output is able to very closely synchronize with the input, and also track it as it changes (within certain limits of course).

In addition a number of users have noted that the M28 phase lock input cannot be driven from some other clock modules, including (at least) the Doepfer A-160: it turns out that this is because the A-160 has a high(ish) output impedance, and this interacts with the input configuration of the M28 in a detrimental way, stopping it from seeing the clock transitions. Other modules it won't work with include the Doepfer A-146 LFO, but doubtless there are others from other manufacturers too. To make best use of the upgrade requires performing a minor modification to the input circuitry of the M28, and this modification also overcomes these compatibility issues (and indeed could be performed independently of installing the new software upgrade).

The upgrade

Phil has released a : in essence it requires replacing chip U1 (the big 20-pin IC on the board) with one programmed with the new software; the upgrade also requires that the incoming clock signal be inverted—it is recommended that a small hardware modification is made to the module to accomplish this, but the inversion can be performed by the use of other modules external to the M28. [Update Nov 2010]: Whilst recently adding the bit about resistor R5 at the bottom of the page, I realised I hadn't posted my method of performing the hardware mods to a Rev 1.2 board—whilst I provided Phil with my instructions for modding a Rev 1.0 board, the instructions for  are his method. For Rev 1.2 boards I followed a similar pattern to the 1.0 boards—I have placed instructions for both board revision levels , which is really just a slightly updated version of what I provided Phil in the first place.

In addition to greatly improving the units capability to synchronize with the incoming clock, the upgrade includes a new feature that the more synth-DIY-oriented user may be able to take advantage of: the internal 24× frequency has been made available externally as a short pulse at an unused jumper location on the main board; with suitable interfacing to other clock-division modules etc, a new range of possibilities is opened up—for details see Phil's site.