/diy/ - Do It Yourself

>>1721662
DSP is a PITA too, lol.

I've been seeing a lot of posts about analog synthesizers, both in /ohm/ and in /mcg/. So I looked through the Roland TB-303 schematic, copied the oscillator circuit, and fudged the values to create an oscillator that:
>takes 2-5V input CV, at 1V/Oct
>uses only common, entry level parts: 9V power supply, 5V regulator, E6 series resistors, only one matched transistor pair vs. two
>Could be crammed into an 8x10 square of prototype board
>simple and reliable enough for hobbyists and beginners to make blindly
I won't promise that it's the best oscillator, but if you need a ton of simple 1V/oct oscillators - like, say, for a polysynth - it should do the trick.

To match the transistors, buy a reel of at least 20 of your favorite NPN transistors (2N2222, 2N3904, 2SC945 etc). The simplest way is to use the diode-drop setting on your multimeter; place each transistor on a sheet of paper with tweezers, since body heat will change their values. Test the diode drop between the base and emitter, then write the value below it. In less than 15 minutes, you should have several pairs that show the same drop, to the nearest millivolt (and several triplets, quartets, sextets, etc.). There may be better methods out there, but this is sufficient for the hobbiest.
*The extra TL072 op-amp can be used to buffer the CV input or the saw output. To see how saws can be converted into squares, PWM, triangles, see http://korganalogue.net/korgms/images/service/ms20/circ1.gif near the top right.
*The bias voltage, set by the pot on the left, is usually 6.2-7.0V in my experience. Use multiturn trimmer pots for precision, and to save on space.
*2.75V is standardized to A2, or 110Hz. Likewise, 3.75V is 220Hz, and 4.75V is 440Hz.

Cheers