Units for generating drum rhythms have been around for many years. They first started to become popular when home electronic organs incorporated them in their accompaniment sections. The early rhythm unit produced typical dance rhythms such as Rock, Bossa Nova, Swing and Waltz, with sounds that could not really be called typical of a drum kit. Over the years the sounds have been improved considerably as knowledge of synthesis has widened and now the rhythms themselves have come into a period of change. The musician is no longer satisfied with a choice of preset rhythms, he wants to plan out his own rhythms to try and break the monotony of the drum machine. Enter the programmable rhythm units; now it is possible to create your own drum rhythms and set up your own drum sounds.

There are many different analogue and digital sequencers now available which are used to set up a pattern of electronic information for controlling one or more parameters on a synthesiser. Because they generally supply and control voltages as well as a trigger output, the sequencer is more obviously applied to synthesiser pitch and EG control to produce repeated note patterns, bass lines and special rhythmic effects. The sequencer can control a synthesiser without the use of a keyboard and thus enables complex patterns to be sounding whilst the performer plays his instruments.

Many well known soloists and groups have based their compositions on the use of sequencers, including Tangerine Dream, Kraftwerk, Klaus Schulze, Jean Michel-Jarre and Logic System. Even though sophisticated micro-memory sequencers, such as the Roland CSQ-600 computer controlled digital sequencer can be regarded as state-of-the-art systems, often the most convenient sequencer is simply one that can count just a few bars of the chosen time signature to provide live performance control of each pulse within the bar.

So using the Synclock as the music proceeds, the player manipulates the switches and makes subtle changes to the rhythmic control of percussive and melodic sounds. No bar need sound the same and because speed can be set over a very wide range, the sequence can be running faster than it's physically possible to play.

Since the Synclock PCB board with its components measures only a few inches and is very cheap to construct, it should enable any electro-musician to experiment with this fascinating and important part of music-making.

The E&MM Synclock is a compact and uniquely expandable control sequencer which can be used to trigger the Syntom and Synwave, as well as most synthesisers and other sound generators, to give new and exciting rhythms and sounds. When used with the Syntom or Synwave, the internal triggers of these devices still operate allowing an even larger scope for filling in further rhythms by hitting the box.

The Synclock has a sequence length variable between 1 and 10 beats and this is of course expandable with further Synclocks. This system allows any number of beats in any time signature to be programmed. There are only a minimum number of controls for ease of use and setting up. The three controls on the top of the unit are: Stop/Start, Sequence Length, and On-Off/Tempo with the programming switches and indicators on the front panel. The sockets for interfacing and control are mounted on the side of the box and finally the clamp is mounted on the bottom if required. All the components except the LEDs and controls are mounted on a PCB and everything fits into the same size box as the Syntom and Synwave.

The Circuitry

The block diagram of the Synclock is shown in Figure 1. As can be seen, there are four blocks: the Clock, Sequencer, Control and Output stage. The Synclock design is based around the popular 4017 (Decade counter divider with ten decoded outputs) and 555 (Timer). The CMOS version of the 555 has been used to keep current consumption as low as possible. The circuit diagram of the Synclock is shown in Figure 2. The timer (IC1) is used in its astable mode to generate the clock signal for driving the 4017 (IC2) the rate being controlled by RV1. The 'clock in' and 'clock out' jack sockets have been included to enable another unit to drive or be driven by the Synclock. The clock signal is also used to gate the output through IC4c. The outputs of IC2 are pulled high by resistors R1-R10 and fed to the ten programming switches (S4-S13) and the sequence length switch (S3), the other side of the programming switches being connected to the anodes of the ten miniature LEDs. The cathodes of the LEDs are all commoned together and taken to ground via R12 to form a ten input diode 'OR' gate. The intensity of the LEDs can be adjusted if required by changing the value of R12, the lower the value the brighter the LEDs, but remember that battery life will be shortened. The output of the 'OR' gate is then fed to IC4c. The other input to IC4c (pin 11) comes from the control circuitry to ensure no output occurs when the sequencer is stopped. IC4c then feeds into the output stage consisting of TR1 and TR2, and then to another diode 'OR' gate to combine the signal with any other trigger information being used.

The most complex part of the Synclock is the control circuitry. The complexity arises due to the need for expansion of the system both serially and in parallel. ICs 3, 4 and 5 are all used in this section and the heart of the circuit is IC3a, a D type flip flop which is connected so that each clock pulse on pin 11 causes the outputs (pins 12 and 13) to change. R23 and C6 are used to provide a power-up reset to ensure the unit is not running when you switch on. The stop/start switch is debounced and fed into IC5f, a Schmitt inverting buffer, and then to IC4b. The control input is differentiated, then inverted by IC5e and fed into IC4b. The other input to IC4b comes from the serial output via the jack socket switch through a differentiator and an inverter (IC5d). The stop/start LED is driven by IC5a from the flip flop Q output. S3, IC5b and IC4a are used to control the sequence length by resetting IC2 at the appropriate point.

Construction

The Synclock is housed in a plastic box (Maplin type MB2) which is the same as that used for the Syntom and Synwave, and a reasonable amount of care is required to fit all the components into the box. If you have only a limited experience in the construction of compact projects you will probably find it easier to use a larger box. Construction can begin with the assembly of the PCB (see Figure 3). The vero-pins should be fitted first and these are pushed in from the component side of the board. The four wire links can then be soldered in place.

Next fit the resistors and capacitors in place, remembering to get the micro resistors in the correct positions and the polarities of C5 and C7 correct. The diodes and transistors can then be soldered in place on the PCB. The PCB assembly can then be completed with the insertion of the ICs. The prototype unit was not fitted with IC sockets as the space on the PCB is very limited, but sockets can be used if there is sufficient room in the case used.

All the ICs are CMOS and require a certain amount of care when being handled - use a low leakage soldering iron and avoid physical contact with the IC pins if possible. The ICs should be left in their protective packing until you are ready to insert them.

The board is now complete and can be put to one side while the box is assembled. Figure 4 shows details of the box and the drilling should be as accurate as possible to ensure all the components will fit into the box. When the drilling has been completed you will need to cut away some of the ribs of the box to ensure that all the components will seat properly - this can be done with a sharp knife.

The ten miniature LEDs can then be pushed into place with the anodes towards the switches (see Photograph) and should not be glued in place until the unit has been tested. Next fit the ten ultra-min. toggle switches in place (due to the closeness of the switches the washers supplied with the switches cannot be used). Now connect the anodes of LEDs 1 to 10 to the nearest contact of switches 1 to 10 respectively and connect the cathodes of the LEDs together. Cut a 4 inch and a 5 inch length of 10 way ribbon cable and then cut and wire one end of each wire to the programming switches (Photo 3). Make use of the wire colour coding, with programming switch 1 connected to the black wire and switch 10 to the white wire. Next take the other end of the 4 inch length of ribbon cable, cut the black wire off an inch from the end and then strip and tin the ends of the remaining 9 wires. Then solder wire 1 (brown) to S3 pin 1, wire 2 (red) to S3 pin 2 etc. Cut a 5 inch length of two way ribbon cable, strip and tin one end of each wire and connect one wire to S3 pin 10 and the other to the wiper of the switch. Next fit and wire up S2, D11, RV1 and S1 with suitable lengths of ribbon cable leaving the end that connects to the PCB floating for the moment.

The jack sockets should now be wired up - this has to be done outside the box. The first thing to do is to change JK6 from a 'break' contact type to a 'make'-contact type. This can quite easily be achieved by bending the outer contact to the other side of the spring contact with a pair of pliers (see Figure 5). Cut one 5 and one 6 inch length of 5 way ribbon cable and use the 6 inch length to wire JK1, 2, 3 and 4 as shown in the wiring diagram and the other piece to wire JK5, 6 and 7 (Photo 4). The two groups of sockets can then be mounted in the box and the positive of the battery connector soldered to S1.

All the components in the box should now be connected up (Photo 5) and the connections to the board can be made. If you wish to fit a clamp to the unit (for a drum rim) this should be fitted prior to connecting the PCB. There are two wire links (A and B) to be made on the back of the PCB first, then the board can be wired as indicated in the wiring diagram (Figure 3). The PCB can then be slotted into the box and the battery connected (Photo 6).

Testing

Set the sequence length to 10 and the ten programming switches down, then switch the unit on. LED number 1 should be on and all the others should be off. If all is correct then press the stop/start button. The start LED should now be lit and the program LEDs should light sequentially. Next, check the sequence length switch operates, the tempo control alters the clocking rate and that the stop/start button will also stop the sequencer and reset the unit so that LED number 1 is on.

If the Synclock has functioned correctly up to now, you can connect the trigger to your Syntom or Synwave trigger input (see Figure 6). Start the Synclock and the Syntom or Synwave should now trigger once on every step. Check all the programming switches are operating by changing the rhythm pattern. The other input and output sockets are best tested with another Synclock unit.

Using your Synclock

It is very easy to learn the best ways of controlling the Synclock and together with the Syntom and/or Synwave the variations on rhythms and sounds give you endless possibilities. There are only a few points to note when using one Synclock: the clock input required is a 9V square wave, the clock output is a 9V square wave the frequency of which is set by the tempo control and the trigger output is an 8V pulse.

The potential of the system really comes to light when two or more Synclocks are available. The wide combination of interconnections and control settings give unlimited scope. Two of the many possibilities are shown in Figures 7 and 8. The parallel connection allows one Synclock to start and stop all the other Synclocks simultaneously and each Synclock can be used to trigger a different sound with its programmed rhythm. The units can all be run from one clock control using the clock in and out jack sockets or they can be controlled with their own tempo pots.

Figure 8 shows how to connect two Synclocks so that a sequence of up to 18 beats can be used. Note the maximum of 18 (and not 20) is due to the fact that the tenth beats have a different reset mechanism. The first Synclock can be used to control the system and the clock signals can again be commoned if required. If a long sequence (more than 10) is being used for one sound generator then the trigger signals need to be combined and this is simply a matter of connecting the output of one to the input of the next. In the serial mode the Stop/Start button will only stop the sequence if it is operated on the unit in which the sequence is running.

Figure 9 shows how a long serial chain may be set up and the legend for the front panel is shown full size in Figure 10 [This image seems to be missing from the printed article.] to enable you to give a professional finish to your project.

Extending the use of the Synclock

The ratio of R22 to R13 determines the amplitude of the output pulse. The amplitude can be increased by reducing the value of R22 and increasing R13 - remember, however, that the effective resistance of R13 is the parallel combination of R13 and the input stage being driven.

The Synclock can be used to drive commercial equipment but a few modifications may be needed. The industry standard for trigger signals is +15V and for this the Synclock really needs an additional output stage. This can consist of a single transistor buffer as shown in Figure 11. The +15V supply is needed as it is impossible to obtain a +15V trigger pulse from a 9V supply.

The length of the trigger pulse in the Synclock is set to approximately 1ms by R18 and C4. The pulse length can be increased by increasing the value of R18 (or C4). Some interesting effects at higher clock rates have been found when using the Synclock with the Syntom, by lengthening the pulse to about 5ms - due to the Syntom trigger circuitry the pitch will vary automatically!