Provides high frequency stability as required for use in sound synthesizers. Can be synchronized to another oscillator. Uses 555 timer in astable mode, with Tr1a supplying constant current to C2. R12 and R13 should be multiturn pots. Synchronizing square-wave signal having 5-10 V peak can be fed in at R19 for differentiation, and resulting spikes used to control threshold voltage of 555. R4 sets minimum frequency. R22 sets average Output level to 0 V R2 and R3 serve as coarse and fine frequency controls Tr1 can also be BFX11 or BFX36. –T. W. Stride, Voltage Controlled Oscillator Wireless World, Oct . 1977, p 66.
Required Field 
