Schematics by Charles W. Harrison Jr. (January 1956).
The project includes a preamp, a two-way crossover and two
push-pull amps using 5881 tubes.
This phono preamp does not comply with the RIAA curve, it uses instead a variable network to adjust the response curve.
The turnover frequency is centered at 800Hz. It could be
easily changed by varying the caps values in the network by
multiplying them by 800/Fc, where Fc is the desired turnover
frequency. The resistors remain unchanged.
It uses two cathode followers to isolate the network and allowing
a low output impedance.
Power of 10-12W, sensivity around 380mV. The feedback ratio is low: around 10dB.
The power supply is common to the whole project.
