#505 Rakit Baby8 Sequencer

Building the Rakit Baby8, an 8 step sequencer with CV and Gate outputs and a clock input.

Here’s a quick demo..

Notes

The Rakit Baby8 sequencer kit is a simple 8 step sequencer with CV and Gate outputs and a clock input.

Each step has an associated CV potentiometer, LED and switch. The CV potentiometers can be adjusted to emit anywhere between 0-5 Volts from the CV out jack when the step is active.

The Baby8 belongs to a rich tradition of CD4017-based sequencers. The design goes back to the 70’s and most people quote a column called “Captain’s Analog” that introduced a simple 10-step design called the Baby10 (I haven’t been abled to discover where this column was published or the author’s name beyond it being be a guy called Mark).

Parts

Construction

Rakit have a very clear assembly guide online. Recommended build sequence:

• switches
• resistors (except for 4093 bodge)
• diodes
• capacitors
• ICs
• LEDs
• battery clip
• potentiometers
• mono jacks
• power switch
• 4093 bodge resistor
• stand-offs

After an hour or two - the finished kit…

How It Works

The core of the sequencer is the CD4017 decade counter. This is nothing earth-shattering however - it simply uses the CD4017 as a designed as a decade counter. Each output has a potentiometer to set a specific output level, and diodes are used to steer the outputs to a common CV output.

The Baby8 embellishes the idea with:

• a switch on each output that will either cause the sequence to reset at that output, or skip the output (depending on a master reset/skip selector switch)
• optional external clock source
• 5v regulated power from a 9V+ external supply

A CD4093 Quad 2-Input NAND Schmitt Trigger is used for:

• a NAND oscillator to provide built-in clock source (with adjustable frequency and duty cycle)
• buffer the clock for a few different uses: driving a clock LED; triggering the Gate output

An LM324 low-power quad operational amplifieris used for

• clock duty cycle control (as a comparator)
• output buffering and amplification

Test: Sequencing the Rakit Drum Synth

Some tips published on the Rakit blog: Baby You Can Bang My Drum: linking the baby8 & drum synth

• CV Out ⇨ Pitch - the CV out for each step is set with the corresponding pot. Feeding this into the pitch input will change the pitch at each step.
• Gate ⇨ Trigger - the gate triggers the drum synth at each step.

Here’s a quick demo of the Baby8 driving the Rakit Drum Synth..

Credits and References

• Baby8 Assembly Guide
• Baby You Can Bang My Drum: linking the baby8 & drum synth
• CD4017 datasheet
• CD4093 datasheet
• LM324N Datasheet
• CMOS 4017 Based 8 Step Sequencer - good discussion of how 4017 sequencers work
• Baby10 - Build a Classic Analog Music Sequencer