The mechanical project that is described in previous blog posts is underway now, scans of work pages will be found in the following posts. With the long break coming up I will be unable to work on it for several (3…?) weeks, so now is the time to begin work on my second project. This will be a synthesiser that follows on from the work that I did for the prototype hand in, with improved electronics that action on the knowledge gained during the construction of that prototype.

The oscillator design is the first area for consideration, I will be moving away from op-amp centered designs and instead focusing my efforts on constructing a transistor based VCO, in the hopes that it will reduce the strain on the PSU and thus reduce bleed. To be more specific, I’ll be making an astable multivibrator and then using an op-amp comparator to turn the square wave into a triangle wave.

INITIAL OSCILLATOR EXPERIMENTS

My tests are documented in the image above. This oscillator design seems a lot more tweak-able than the ones I have worked with before with a greater tendency towards odd behaviours and quirks. Imbued with more life than the rigidity of op-amps, this simple circuit topology is the latest in a series of transistor experiments that are wooing me with the analogue flippancy of simple circuits. The principle of biasing transistors is a lot more conversational than the prepackaged and finicky nature of op-amps (so far, that is. I presume that soon I will grow to be frustrated with transistors: I have already blown up a few, which is a rare occurrence with op-amps at low voltages).

After more testing, these oscillators (unmodified) will not be suitable as slope generators, op-amps with diodes in the feedback loop seem superior in that regard, although I’m now getting very curious about what happens when oscillating voltages are fed into the biasing network – what happens if low voltage broadband noise is injected into one of the bases of the transistors? First I shall need to build a noise osc… transistors are well suited to that, I have heard.