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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.

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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.

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5881 PP

Power of 10-12W, sensivity around 380mV. The feedback ratio is low: around 10dB.

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Power Supply

The power supply is common to the whole project.

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