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The Time Machine

Not, as its name might imply, a wondrous device capable of predicting next week's racing results, but a handy build-it-yourself project that divides down sequencer and drum machine clock pulses. Designer Paul White has the full story.


This project won't give you next week's racing results, but it might be the answer to your syncing problems if you're plagued by drum machines and sequencers of varying timebases.


Designed especially for those who still think that mercury comes from HG Wells, the E&MM Time Machine overcomes two of the most common incompatibility problems musicians encounter when trying to persuade drum machines and sequencers of varying origins to run together in sync.

Problem number one is that not all machines use the same timebase (ie. the number of clock pulses per bar), which means you've got every chance of linking up two drum machines or sequencers only to find that one runs twice as quickly as the other. That's precisely what happen if you try connecting a Roland Drumatix or Bassline with a Korg DDM series drum machine, for instance.

Problem number two is the way in which various clocking devices are started and stopped. If your sequencer or drum machine is fitted with a Roland-style DIN sync facility, its pulse will be stopped and started by means of a discreet control signal which is set to logical '1' for Go and logical '0' for Stop: the clock itself runs continuously. On the other hand, something like a Yamaha RX15 requires only a clock to operate correctly. When the clock is present, it runs; when the clock stops, it stops.

What this means is that if the clock output from, say, a Drumatix is plugged into a Yamaha RX15, the latter will start to play immediately, even though the Roland may not be running yet. This is obviously bad news as far as synchronised starts are concerned: one machine will be halfway through the first verse before the second machine has even got its playing underway, and in most modern musical applications, this is clearly not on.

Design Aims



I'd like to be able to tell you that the Time Machine will synchronise absolutely everything to everything else, print money, and stop the Editor stashing his old Kentucky Fried Chicken wrappers in my in-tray. Sadly, not all of these problems are easily solved, and in the event, I've been forced to confine my attentions to the incompatibilities mentioned above.

The first of these can be overcome in one of two ways, viz using the fastest (in terms of clock pulses per bar) machine as the master and then dividing down the clock frequency until it's correct for the slower machine(s), or alternatively, using a master tempo clock to drive a divider chain, plugging your machines into the appropriate parts of the chain so that they run at the same speed.

E&MM's Time Machine offers both options, with four stages of division giving -1, -2, -4, -8 and -16 which should be adequate for most applications. If you need more than this, adding further stages shouldn't be too complicated, though if you're rich enough to buy the kind of specialist gear that runs at these higher speeds, you can probably afford something more sophisticated than this project to drive it.

In addition to Roland-style DIN sync connections, the Time Machine has a corresponding number of standard jack sockets to supply a gated clock output, ie. a clock output that's only present when the unit (or the master rhythm machine) is in Start mode.

The Circuit



IC1 forms the built-in tempo clock, and has a very wide range to accommodate machines being connected at different points in the divider chain (see Figure 1). It's still fine enough to allow you to set the tempo fairly accurately, but you could add a lower-value pot in series with VR1 to act as a Fine control, or a multiturn pot if your requirements are more stringent still.

ICs 5 and 7 are simply 'D-type' flip-flops configured as divide-by-two stages, while the latch formed by part of IC2 eliminates false triggering due to the switch bounce that will inevitably be present in the mechanics of the start-stop pushbutton.

IC3a divides the switch output so that pressing the switch will alternately start and stop the system, while IC3b synchronises the rising edge of the start signal with either the system clock or external rhythm machine clock depending on what's being used.

IC6 generates a power-on reset which initialises all the counters when the unit is switched on, and the remaining gates simply 'AND' together the divider outputs and the start/stop signal to produce the gated clock outputs. T1 drives the start LED, and the entire circuit is powered from a regulated 12V supply which is built on the PCB to minimise wiring.

Figure 1. Time Machine circuit diagram.
(Click image for higher resolution version)


Figure 2. Time Machine PCB component overlay.
(Click image for higher resolution version)


Construction



Referring to Figure 2, fit the components and wire links into the PCB, taking care to get the ICs, capacitors and transistor the right way round - if you're particularly paranoid, put the ICs in sockets. Use resistor leg offcuts to wire the jack sockets directly to the PCB - don't use special PCB-mounting sockets! Take particular care when soldering as some of the PCB tracks run very close together. Work in good light and check the track side of the PCB carefully before switching on - solder shorts are easily missed.

As you should with all mains powered projects, treat the mains voltage with respect and sleeve the transformer and fuseholder tags with rubber sleeving.

Whatever type of case you choose to house your Time Machine, you'll have to drill a few holes to accommodate the sockets and switches. This should present no problem to the intrepid E&MM reader providing he or she has access to a Black and Decker drill and a centre punch. If you possess a craving for a mains-indicating LED, wire it to the +12V supply via a 1K resistor, though note that there is no specific provision for this on the PCB.


Testing



Put at least two coats of whitewash on the windows, build a shelter against an inside wall using furniture and bags of earth, and make sure there is at least one sofa between you and the Time Machine before you switch on. And don't forget to check the date...

Seriously, the first thing to check is that the 12V power supply is running OK: this must be verified before you proceed any further. With the int/ext switch set to internal, check that the start/stop LED goes on and off when the start/stop switch is pressed. The gated clock outputs are best checked with a scope, but as it's perfectly conceivable that some of you don't actually have a scope, one alternative is to try plugging them into an amp with the volume turned well down and listen for a rasping tone. The next step is to connect a DIN-sync compatible unit such as a Drumatix (set to receive external sync) into the DIN outputs. It should run from all sockets but the speed will obviously differ by a factor of two for each sync socket with the -16 output giving the slowest speed. If you have two such machines, switch to external and use one of these as the master to check out this facility.

In Use



Just about any DIN-sync (no, not MIDI) machine may be plugged into the 'ext' socket to act as the master clock, but 'gated clock' machines cannot be master, I'm afraid. However, the Time Machine's internal tempo clock can be used to drive all the sync outputs so that 'DIN sync' and 'gate clock' equipment may run simultaneously.

One word of caution: check that the slave machine isn't midway through a pattern before you sync everything up, as devices such as the Yamaha RX15 will happily continue from where they left off when triggered externally. Just thought I'd mention it.

There's also no reason why the Time Machine shouldn't be used in conjunction with an MPC Sync Track so that rhythm machines and sequencers can be synced to tape, so the system offers a lot of flexibility for very little outlay.

However, one species of machine that won't accept a sync code from the Time Machine is that which needs a Start tone in addition to the clock code: the Roland MC202 falls into precisely this category. You can still use it as the master machine in the system, though, so all is not lost.

All components are readily available from Maplin or other component suppliers and the total cost should not be much over £25 including a suitable case so you'll still be able to afford next month's E&MM.

PCB available from Mail Order Dept, E&MM, (Contact Details), price £4.95 inclusive of postage and VAT. Please make cheques/postal orders payable to Music Maker Publications, and allow up to 28 days for delivery.

Time Machine Parts List

Resistors

R1,R2,R6,R8 1K ¼W
R3,R4 2K2
R5,R7 10K
VR1 220K lin

Capacitors

C1 0.22μF
C2,C6 110μF/25V axial electrolytic
C3 10μF/25V axial electrolytic
C4 2200μF/25 V axial electrolytic
C5,C7 0.1μF
LEDs Red (2 off)
Diodes D1-D4 IN4004

Semiconductors

IC1 555
IC2,4,6 4011
IC3,5,7 4013
IC8 7812
T1 BC107 or similar

Miscellaneous


SW2 SPDT pushbutton or biased toggle switch (min)
SW1 DPDT toggle (min)
3- or 5-pin DIN sockets (6 of)
¼" jack sockets (7 of)
control knob
instrument case
12V/200ma transformer
Fuse holder
Mains switch
6ba nuts, bolts & washers
PCB



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Electronics & Music Maker - Copyright: Music Maker Publications (UK), Future Publishing.

 

Electronics & Music Maker - Apr 1985

Donated & scanned by: Stewart Lawler

Feature by Paul White

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