Single stage preamplifier for turntables with magnetic system
This simple equalizer pre-amp is designed to connect a magnetic turntable pickup to a linear audio input.
The obsolete germanium transistors can be replaced by silicon types when the 68K ohm resistors are increased to about 2.5 times this value. If NPN types (e.g., BC550C) are to be used, the electrolytic capacitors and the diode must be connect the other way around.
The circuit goes back to a device from Philips. Such a preamplifier can be accommodated directly in the turntable housing or in the stereo amplifier. Of course it can also build as a standalone accessory device. With this single-stage arrangement, a gain of about 30 dB is achieved. This is sufficient to drive an amplifier, which has a linear input with about 50 ... 100mV input sensitivity. This preamplifier has an equalization to compensate for the manufacturing-related cutting characteristic in vinyl recordings.