16 NOTE SEQUENCER
Courtesy/Thanks to: Practical Electronics
Description: From the March 1979 article of Practical Electronics I have taken this:
The sequencer to be described in this article enables up to sixteen different bits to be programmed and repeated at any speed required. The sixteen bits to be programmed and repeated at any speed required. The sixteen bits can refer to pitches, as is most common, or the timbre, loudness or length of the musical note. The notes are programmed into the sequencer by the use of potentiometers, one for each note. This is the method of sequential control most commonly adopted by all the main synthesiser/sequencer manufacturers, Moog, AR P and Roland for example.
While it may appear a rather simple and crude method of achieving a sixteen note memory compared with all the digital memories available, it is the cheapest and most reliable method as the tuning potentiometers used will remember indefinitely the selected voltage level.
Bearing in mind that the previously mentioned commercial sequencers cost several hundred pounds, the sequencer to be described has features as found on these designs and will cost around f35 in components and hardware.
The method used to generate the sequential function is simply an oscillator driving a digital counter with the output voltages going through a potential divider to obtain the þrocessed voltage. This voltage then controls the frequency of a voltage controlled oscillator, or the cut-off frequency of a voltage controlled filter or the attenuation of a voltage controlled amplifier in the syntesiser.
A prototype sequencer has been used very sucessfully with a Mini-Moog synthesiser and the advanced features
available on commercial versions are possible at a much reduced cost.
The basic layout of the sequencer is as shown in the block diagram (Fig. 1)and each block will now be considered in detail, referring to the appropriate circuit diagram.
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