Simple analog sequencer and synthesizer

generate neat music with only five basic IC’s

Sample audio is available on Youtube. https://youtu.be/91aFLi7b4vM

Very easy to build and funny to use. Just turn potentiometers and hear how resulting music alters. You can also start to recording your music with computer. It is super easy for example a program called Audacity. Just plug in audio cable and press record.

Building tips

Building is very straightforward. Put components to their places on to the circuit board and solder in place. Potentiometers needs to be assembled with wires. Length is not critical. Watch correct placement and polarity with reference markings from circuit schematics and printed circuit board.

Technical description

Sequencer part of this device is based on classic Baby-10 sequencer. It uses logic 4017 counter and one adjustable low frequency oscillator made from very basic NE555 timer circuit with fixed 50% duty cycle to generate tempo. There is also two other timer used to produce sound frequencies. To save board space one NE556 dual timer is used along with one ordinary NE555.

4017 counter outputs is connected to first of two sound frequency oscillators with 500k adjustable resistor. Outputs is also connected to rotary switch so user can select how many channel is used to produce sound. Common pin of rotary switch is connected to 4017 reset pin. Every output has it’s own adjustable resistor so there is maximum of ten independently controlled frequencies. Them are tied together through diodes. This output is called control voltage. Second sound frequency oscillator is also adjustable with one 500k resistor. It is connected in series with sequencer control voltage so it’s frequency is also based on that.

These two adjustable sound frequencies is mixed together with XOR gate which is made with diode bridge and one BC557 transistor to save board space from yet another logic IC. With this dual tone and mixer combination it is possible to generate classic cowbell sounds. Low frequency oscillator output is called gate and mixed output of two other oscillator is called tone.

Gate pulse is used to generate envelope with adjustable attack and decay times for tone signal. These are controlled by two 500k adjustable resistor. It is buffered with one half of LM358 dual operational amplifier. Other half is unused and it’s inputs are connected to ground. This envelope signal is then used to control tone and these to waveforms are then combined with one BC547 transistor. Finally there is passive low pass filter to filter out unwanted high frequency clicks.

Now our audio signal is ready to be amplified with LM386. At this point there is also signal level output connector for audio. Power amplifier is made with basic circuit with bass boost because we use small speaker. Output level is suitable for 1W, 8ohm speaker. Volume is adjustable with one 10k potentiometer.

Device works with voltages between 5…9 volts. Transformer is not included. Printed circuit board is designed to fit in CP-18-5 enclosure. It is not included. Basically you can use any suitable enclosure.