So, i’ve been trying to make a simple, cheap and reliable sine wave VCO.
And found this one paper with the following VCO
It’s a pretty simple build, the output level is self regulating with no additional circuitry, the harmonic distortion is very low and the frequency control is done by a grounded resistor. So it’s exactly what i was looking for!
But now i need a method to vary the circled resistance. But the catch here is that this method needs to be highly linear. otherwise, the output won’t be a sine anymore.
so far the methods i’ve considered are:
a single NPN → it works but it introduces distortion
a single jfet → same as above + jfets are more expensive compared with bjts
a lm13700 like OTA → it introduced a lot of distortion but i might have messed up with the topology + it’s pretty expensive
vactrol → might be the best solution for this case but i’d really really like to use a different solution. so if everything else fails this will be it
Is this for an LFO or an audio oscillator? Do you need accurate 1 V/oct exponential control? Or is less accurate exponential control, or even linear control, good enough?
the oscillator is meant for an ondes mardenot like instrument
sure, i could use a fully ressonant filter (and if everything else fails i will) but i’d need to modify the circuit to eliminate the inputs and lock the filter into ressonant mode. also add the wave shaping
Yeah, so presumably you need exponential control even if it’s not necessarily 1.0000 V/oct, and then you probably would want some level of temperature stability even if it’s not necessarily rock steady. A couple discussions:
