sn76477

16 Step Sequncer & Synth: An Update

This is a follow up to my original post on the 16 step sequencer/synth that I posted several months ago. It’s taken some time to get moving on this but I finally ordered up 32 pots to test my design and make sure everything was working. The overall concept is to have a 16 step sequencer where each step allows you the flexibility to adjust the VCO, LFO, envelope, noise generator, and filter on each step. The sequencer will allow you to switch, for example, the VCO from individual control on each step to a global setting. This would hold true for all parameters. The sequencer will step forwards, backwards, and allow you to select how many steps to make (1-16). Each step will have an optional output that bypasses the main output when used. Finally, the sequencer section will have a speed or rate control. I’m still debating if I want to figure out how to make this sync to a midi clock or display a BPM reading. When it’s all finished it will have over 80 dials, 50 switches, and plenty of flashing LEDs for those late evening explorations. Video to follow soon…

Also, I’m getting to the point now where I need to consider what type of enclosure all this will go into. I’m looking for carpenters, machinists, and artists to talk about unique ideas and options. If you interested shoot me an email.

Synth - Sequencer

Here we have 32 pots temporarily wired up on a piece of cardboard. This was the cheapest and most reasonable way to wire up the amount of pots for just a test circuit. I do this frequently when I need a quick mock up for controls. These are 1M linear taper pots and they’re all wired with a common ground and then each one is individually wired to a multiplexer input. I should be able to just take these out of the cardboard and drop them into the finished control panel when it’s completed.

Synth - Sequencer

This is full shot of the prototype prior to some sequencing enhancements. You can clearly see the leads from the pots coming into the 4067 multiplexer. It’s only necessary to run one set of 16 leads to the multiplexer, each additional row of pots can be wired to the previous with only the addition of one unique lead to the control input of the sn76477. A 555 timer is wired as an astable multivibrator for the clock and is sufficiently stable for my purposes. Although difficult to see in the image the sn76477 has a regulated 5V DC output to drive your logic ICs regardless of what your power supply voltage is. The group of black leads with green shrink wrap brings over the 4 bit binary count to the second multiplexer. In this image the binary counter is a 4520B dual binary counter. The original plan was to utilize both counters and a comparator to set the sequence length from 1 to 16 steps. The three switches at the top of the rightmost breadboard are for selecting the mix channels of the sn76477. through a combination of these switches you can include a VCO, LFO, decay, noise generator, and filter as well as bypass the sound completely. Like the pots these will be added for every step in the sequence for tailored sounds on every step of the sequence.

Synth - Sequencer

In this photo you can see some changes have been made. I swapped out the 4520B dual binary counter for two SN74LS193N pre-settable up/down 4 bit binary counters. The output of one counter is wired to the multiplexers and controls the sequence and then flows into the 4063B 4 bit comparator. The second counter is manually stepped manually with a push button switch and also feeds the comparator. Count A > count B a high signal is sent to the master reset of the sequencer counter and the sequence starts over at the beginning (0). The two switches off the side of the leftmost breadboard are required to allow for running the sequence in reverse. They serve two functions 1) to switch both counters from up to down counting and 2) to send a preset to the sequence counter on reset. Normally the counters reset to 0, but when going in reverse you want it to reset to 15 otherwise your sequence gets stuck on 0 indefinitely (due to the comparator condition always being met). Make sense?

Synth - Sequencer

This is just a close up of the hectic wiring going on. I only have yellow and white wire so it makes for a confusing time tracking down and correcting problems. In the left-middle you can see the 555 timer obscured by a couple yellow wires. Currently the frequency of the clock is variable with a duty cycle of 50%. One of the next steps is to include another timer so I can retain adjustable frequency and adjust the duty cycle to something much higher like 90%. This won’t impact the sound but it will make the LEDs flow from step to step smoothly… a totally superficial enhancement. On the lower right is a 3 input multiplexer to handle sending the reset number to the sequencer clock when running in count down mode. Another next step is to add an analog switch to replace my two toggles to switch from count up to count down mode.

16 Step Analog Sequencer

A while back Gil Duross over at Philly Techno was talking to me and was thinking about coming up with a analog step sequencer which would cost less than $100. It got me thinking that this isn’t that crazy and it’s likely someone out there has already done something like this. As is it turns out that’s exactly the case. The following video is of my test circuit of a 16 step analog sequencer based on Mauno Tuominen’s schematic for an analog CMOS sequencer based around at 4067n multiplexer/demultiplexer. You can see a DIY version of the sequencer here at studiomanus.com. I had an old sn76477 which I had been planning on turning into something so I started with the basics… indicator lights, tempo, and a simple oscillator. The eventual plan is to expand this out into a large 16 step sequencer/synth based around the sn76477 allowing for extensive sound shaping of each step in the sequence. Although the sequencer is well under $100 by the time this is completely finished it will likely cost well over that but the result should be substantial. In the meantime, take a gander at the initial test circuit. The sounds aren’t the most musical at this time, but it’s function and simple design is more the point.

I’ve expanded on the original design using a simple 555 timer for the clock and the ability to control the number of steps in the sequence through use of the 4063N. This has not been tested… that’s on my to do list. If anyone who reads this is well versed in these components and circuit design I’d love to hear feedback.

sequncer step counter