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UC-1 Sequencer

Add-on unit for SCI Pro-One

Add-on for Sequential Circuits' Pro-One

The UC-1 Sequencer is the brainchild of one Per Linné, Service Manager for Sequential Circuits in Sweden, and has its roots in a digital sequencer originally designed by Per for the Maplin 5600S synthesizer. This project never surfaced in any commercial form and was duly placed to one side, until, that was, the designer came into contact with the SCI Pro-One synthesizer.

As he recalls, "Being the Sequential Service Manager in Scandinavia, I noticed that the people who bought the Pro-One often did it because of its built-in sequencer. Then after a short period of joy they realised its limitations - it is difficult to programme and you have to reprogramme it every time you use it. One thing was found to be excellent though and that was the fact that the sequencer was actually part of the synthesizer. No extra cables, switches, knobs etc. were needed. From a technical point of view this solution also gives direct access to the synthesizer's keyboard and digital-to-analogue converter (DAC), without the need for scale factor and temperature dependent A/D and D/A conversions involved with an external sequencer."

The UC-1 (Universal Controller One) is available in semi-kit form with templates and constructional details on how to fit the unit into your existing Pro-One. This operation involves some drilling of both front and rear panels but is quite straightforward.

Once fitted the only visible parts of the UC-1 are a black, rectangular panel located above the keyboard. This contains eight flush-fitting pushbuttons, a clock tempo knob which controls the sequence speed and a small, four character digital display that indicates the current mode of operation. There are also four additional jack sockets on the rear panel providing connections for a tape interface and external clock source.


The UC-1 hardware is based upon a 6502 microprocessor giving 1760 memory locations which are dynamically allocated to 10 separate sequences, 10 transpose sequences and 10 chains (sequence groups). Battery-backup ensures no loss of programs when the power is turned off, which was always a weak point of the original Pro-One 40 note sequencer.

Programming can be done in both real and step time from the keyboard ie. exactly as you play it or one note at a time, and there is a useful Autoglide record facility available in both modes, which effectively gives portamento effects between successive notes.

A maximum of 880 notes can be stored, of variable length. For example, at the highest clock-speed notes of less than two seconds duration use only two of the 1760 available memory locations. Notes of longer duration utilise three. However, the Transpose and Chain functions only require one location per step which means that around 30 minutes of varied tempo music can be stored using the complete memory resources.

The previous Pro-One sequencer was clocked (ie. driven) by the internal LFO, so if you wanted modulation as well as sequencing, the modulation speed would have to be the same as the sequence tempo, which usually sounded horrendous.

This is no longer the case as the UC-1 has its own high resolution clock which means that the LFO can now be used independently for modulation purposes.

The addition of tape interface sockets also means that your sequences can be downloaded onto cassette or tape, for more permanent, longterm storage or whenever the memory is full to capacity. This tape dump procedure takes around two minutes to complete regardless of the sequence length.

The other two rear panel sockets allow an external clock (such as a drum machine) to control, or be controlled from, the UC-1. The Pro-One's existing control voltage and trigger outputs also mean that the UC-1 can be used to sequence other synthesizers - a nice idea if you don't always want to rely upon the Pro-One's analogue voice circuitry to generate your sounds. So be in no doubt that this unit is versatile!

UC-1 control panel.

Panel Switches

The front panel switches on the old Pro-One Sequencer section now have two new functions, indicated by the labels provided with the UC-1. The previous 'SEQ 1' now becomes 'LFO/EXT' and selects whether the internal LFO or the sequencer's own clock drives the UC-1. With LFO selected it is still possible to use the 'Gate In' or 'Audio In' sockets to activate the sequencer, so you could feed the output of a miked up hi-hat or bass drum to control the sequence tempo, for instance.

The previous 'SEQ 2' position now selects 'ARPSEQ' which activates a new arpeggiator function that allows you to replay notes in the order in which they were played. This facility is infinitely better than the previous arpeggiator which only gave 'up' or 'up/down' selections of notes.

Another feature is the Arpeggio Record mode. On the original arpeggiator you could 'latch' the notes you were holding down and have them repeat by selecting Record on the sequencer section whilst holding down the keys. This usually prevented you from using both hands to select arpeggios, as you then had no hand free to switch in Record! Now, however, you can select Record in advance, provided that the Arpeggio mode is already selected, and as long as at least two keys are depressed, you can add more notes to the arpeggio later. Also, if you turn off the arpeggiator but continue in record mode, the arpeggio will remain in memory and can be activated by re-selecting the arpeggio function. An excellent feature for live performance that increases your stage versatility.


This is achieved using the 8 front panel sequencer buttons which select from a staggering 30 possible functions, all of which are cryptically labelled in four rows of mnemonics, such as STPD (step down).

To access either row 2 or 3 functions you are required to hold down one of two 'shift' buttons whilst also depressing the necessary function button. This proved slightly awkward to do with only one hand, but you are helped by the fact that the sequence record mode is not activated until a key is pressed. The fourth row of control functions deal with the single step mode of programming.

In real-time mode a sequence is recorded by holding down the 'NORML' button and pressing 'REPT', then playing the keyboard. You end the sequence by pressing 'NORML' at the point where you want the sequence to repeat from. It takes a bit of practice but you soon get the knack of stopping a sequence loop exactly on the right beat.

As already mentioned, there are 10 possible sequences which are selected from 0-9 by the STPUP (step up) and STPD (step down) buttons. If a new sequence is selected during the playback of a current sequence, it will not begin until the old sequence has been completed. It is also possible during playback to transpose a sequence by a maximum of plus or minus one octave, by pressing the relevant note on the keyboard, either side of note C1.


Tape Interface and Processor boards.

The following brief description of each function should serve as an indication of the facilities on the UC-1:

NORML (normal) is used to reset the sequencer. REPT (repeat play) actually starts whatever sequence is currently shown in the display. This control also restarts the sequence from the beginning if selected whilst a sequence is already running.

TPOUP (tempo up) and TPOD (tempo down) double and halve the speed of the sequence instantly during playback, whilst STOP does just that. However, if pressed continually this latter button can be used to step through a sequence note by note. Pressing REPT starts the sequence again at the point where it was interrupted. XPOSE (transpose) switches on and off any transposed sequence once recorded and STPUP and STPD are used to select the sequence number register.

Using SHFT 1 activates the second row function of each button and here we have CHAIN, which selects this mode causing 'CH' to appear on the display. To create a chain of sequences you first need to select a chain number with the step buttons, then enter shift 1 mode and press CHNPR (chain program). The display reads '00-0' indicating the chosen sequence, on the right, and the number of entries ie. times it is to be played, on the left. Having selected your sequence number you press CHNPR as many times as you wish that particular sequence to play and the display increments to tell you how many repeats you've selected.

XPPRG is used to programme a transposition into a sequence using the keyboard again, and only affects the sequence shown on the display once this mode is entered. Finally on this row, TTAPE (to tape) and FTAPE (from tape) cause the sequencer contents to be dumped onto cassette or loaded from it into memory.

The third row functions become operational when SHFT 2 is held down. We then have CLEAR which is used to erase all memory contents. Pressing CLOCK will give you a visual readout of the UC-1 tempo or the Pro-One's own LFO rate if that is being used to drive the sequencer. NOTED button serves no function at this point in time but will be available through future software updates - no prizes for guessing what this function will do!

TPOED on the other hand provides a programmable tempo facility whose speed can be altered using the TPOD/TPOUP functions on the first row.

GSYNC (get synchronised) and SSYNC (send sync pulses) are used to send a train of sync pulses to an external tape recorder, at a frequency set by the UC-1 clock (or any other clock source) via the 'Tape Out' socket on the rear panel. Selecting GSYNC causes the UC-1 to expect a sync pulse train from tape via the 'Tape In'socket - a very handy facility for multitrack music.

The final button, coloured red instead of black, is labelled SGLST. Pressing this causes all buttons to change to their fourth row functions which concern only the single step record mode.

Programming of notes is done by pressing the required key for pitch, which automatically assigns that note a duration of 1 clock pulse. To increase the duration, you need to press either 'ADD 1' or 'DOUBL' buttons while holding a key down, and increase the number of clock pulses, as shown on the display. Pressing the '+/-' button causes the ADD 1 button to subtract clock pulses when pressed, and 'DELET' deletes the last note entry completely. A rest is automatically inserted when ever a key is released, so to avoid this you need to play legato style when programming ie. press the next note before releasing the one already held. Rest durations can likewise be increased using either ADD 1 or DOUBL function buttons, as long as no key is held. Programming is terminated by pressing 'NORML'. Lastly, the two buttons labelled 'BACKS' and 'FORWD' are reserved for future UC-revisions and did not function on the review instrument.


The UC-1 on first impressions, appears awkward to programme. This situation improves rapidly with familiarity and use though, and you soon come to appreciate the versatility and flexibility of so compact a device. With a UC-1 installed in your Pro-One you really do have a powerful music making tool. There are no leads or extra cases to carry around with you - and that is the beauty of the unit. If you're worried about accidentally damaging your Pro-One when fitting the UC-1 then don't be, as most Sequential dealers are capable of installing the unit for you.

I feel sure many Pro-One owners will want to get hold of the UC-1, and for the modest cost of about £210 it seems a very good buy indeed. As already hinted at in the review, future revisions are already planned for the UC-1, but don't worry about buying a redundant device. Since the UC-1 is EPROM based, continuous software upgrades will be made available to owners. In fact with the version presently delivered, one free software upgrade is included in the price, provided the old EPROM is returned to the manufacturer. There is even talk of development of a MIDI interface board for the UC-1, so rest assured, this sequencer is unlikely to become obsolescent.

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UK Electronica - Electronic Music Festival

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


Electronics & Music Maker - Nov 1983

Donated & scanned by: Stewart Lawler

Review by Ian Gilby

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