ASPEED REGULATOR for a d-c motor driving an a-c generator which will maintain the frequency of the alternator output voltage in synchronism with a frequency source of low power output is described in this article. This is accomplished, in general, by obtaining a voltage proportional to the phase angle between these two frequencies and using this voltage to adjust the field current of the d-c motor, and hence the speed, in such a way as to keep the phase angle constant. By controlling the phase displacement or integral of the speed rather than the speed itself, maintenance of synchronism is ensured, since any steady-state variation in the circuit parameters will be compensated for by a change in the steady-state value of the phase angle.