Two-stage preamplifier for turntables with magnetic system
This circuit of a two-stage preamplifier for vinyl record magnetic systems goes back to a specified in the book Niederfrequenzverstärker mit Röhren und Transistoren (low-frequency amplifiers with tubes and transistors, author: Fritz Kühne) circuit of an Elac preamplifier. Instead of the PNP transistors specified there, I first used exemplars of the type AC122. Later, I replaced them with NPN transistors, as shown in the diagram, which required reversing the operating voltage and all the electrolytic capacitors.
The gain achieved with this two-stage arrangement is sufficient to raise the small signal from the pickup system so far that a linear input with approximately 250 ... 500mV input sensitivity can be drived. For stereo, of course, the circuit is needed twice. The frequency response is matched approximately opposite to the cutting characteristics of the records. With the 1.5nF capacitor in the input, the levels of high frequencies are lowered accordingly and with the negative feedback via the 4.7nF capacitor the depths are raised.
I had built such a circuit directly into a self-made housing for a turntable chassis (model P157 from BSR). This I equipped with a magnet system of the type M75 from Shure. The whole thing I ran with good success with a stereo amplifier with each one tube ECC83 and two tubes ECL86, which is shown elsewhere.