StyloSynth70 – miniature synthesizer

[Vermes]

A bit of history
Stylophone is a portable, miniature sound synthesizer, created in 1967, produced in years 1968-1975. It was renewed with a number of modifications in 2006. Its characteristic feature is the mode of action – user has access to a stylus and metal keyboard. The play is based on closing the circuit: power – stylus – a metal pad of keyboard – corresponding resistor in the circuit of the generator.
The synthesizer consists of a basic generator (VCO) and a slow-variable waveform generator (LFO), which modulated the frequency of course produced by the basic generator – vibrato effect is obtained. LFO generates a course similar to triangular with frequency of about 7Hz. The user has the possibility to tune the basic generator frequency – with decreasing the supply voltage, the device untunes.
The block diagram is shown below:



Construction
It is a renewed second version of the Stylophone from the beginning of the 70s (on the unijunction transistor – relaxation generator). All the equivalents of all elements used in the original stylophone are available, except the resistor ladders produced on request. Finding a speaker with impedance of 75 Ω may be problematic – its replacement may be speaker with 50 Ω used in intercoms and headphones. Starting line was not included.
Diagram of the device is shown below:



VCO output waveforms and LFO achieved in the created system:



The original design used resistor ladders manufactured to order, so for accurate reproduction of the resistors used, a serial connection of resistor and assembly potentiometer was used.
On the front of the housing, there are switches of the power and vibrato effect. On the side of the housing, there is a socket for stylus. On the bottom there is a potentiometer used for tuning the generator and the flap from battery cart.
The system is powered by a standard 9V battery. It is easy to use, the sound is acceptably pleasant. Contrary to appearances, the device is loud.
Components:

• resistors, mounting potentiometers
• speaker
• semiconductors
• potentiometer
• switches
• housing, screws, spacers

Schema with values of the components:



Link to original thread (videos + attachment) – StyloSynth70 - miniaturowy syntezator