A sequencer used for music is a device that sequences musical events for predictable playback. For early electronic instruments these sequencers often take the form of a collection of switches that are cued in series and which trigger some other device like an VCA. The switches may also be used to control a variable voltage source which controls t
sequencer - schematic

he pitch of an oscillator. The sequencer most commonly has a number of switches that is a multiple of 2 like 4, 8, 12, 16, and has a looping function so that the series of switching may restart as soon as the last switch in series is triggered. The sequencer is primarily designed around the 4017 ic chip. The 4017 is a decade counter that can be reset to start over counting from one at any step. This is achieved by connecting the next sequential step to the reset pin. For example if you want the sequencer to count to five and start over the step six pin is connected to the reset pin, and if you want the sequencer to count to step 8 and start over then the step nine pin should be connected to reset pin. To get further detail about the 4017 chip simply google image search "4017 data sheet" From the 4017 chip several features are provided in the above schematic including a voltage out that can control any VCO (voltage controlled oscillator) like the ones found on Moog, Dot Com, Paia Doepher, and other analog synths. Each step has a potentiometer that may assign a specific voltage for that step. This allows for 8 note melodies or bass riffs to be easily programmed. Another feature is the S-Trigger/Gate output option. This sequencer may be used as a rhythmator type sequencer by using the s-trigger output. The s-trigger can be used to control the through put of any line level audio signal, and by toggling the switches for each...

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