MFOS Ten Step Analog Sequencer

Posted on Feb 5, 2014

This is an intermediate to advanced project and I do not recommend it as a first project if you are just getting started in synths or electronics. Only the circuit and some explanation are shown here. A lot of project building, troubleshooting and electronics experience is assumed. Additionally, electronic equipment ownership (scope, meters, etc. )

MFOS Ten Step Analog Sequencer
Click here to download the full size of the above Circuit.

is taken for granted. If you are interested in building this project please read the entire page before ordering PC boards to ensure that the information provided is thorough enough for you to complete the project successfully. If you bought a prototype board these links show the necessary kludge. You need to add a 470K resistor between the -12V point at U3 pin 4 and the gate of Q11. Support docs for the prototype boards are right here: Page 1 shows the heart of the sequencer which is U1 (CD4017B CMOS Decade Counter with 10 Decoded Outputs). This chip has ten outputs (0 thru 9), each of which goes high sequentially (while the others are low) when the clock input is clocked (goes from low to high) while the clock enable input is low. This circuit uses the clock and the reset inputs only. The Clock enable is tied to ground and the Carry out is not used. The CLK circuit point and the RST circuit point both come from page two of the schematic (explained below). The circuitry on page two generates the clock pulses, manual step pulses and reset pulses. A question I know I`ll get is: "Why did you use a 12 position switch " The answer is: "Because I often see 12 position switches for sale on surplus sites and I rarely see 9 position switches (which is all you actually need). " As shown below you just wire the extra terminals to the last position used and you`re good to go. The 0 thru 9 outputs of U1 go to: Points X0 thru X9, which...

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