This is a complex and complete power audio station (at the bottom in above image) with one stereo output and 6 stereo channels input (three of them can be mixed) that includes several stages of amplifiers. It took me a couple of years to build this unit and in 1988 was ready for use.

Technical specification includes:

-power supply: mains 230V/50 Hz
-max current load from mains power supply: 1A
-output impedance for loudspeakers: 2-50 ohm
-recommended impedance for loudspeakers: 2-8 ohm
-maximum measured audio output power (before limitation): 64 W SIN / 4 ohm (16 V ef / 4 ohm at 1000Hz)
-input adapters for: microphones, electromagnetic audio transducers, quartz piezoelectric transducers, line-in standard inputs etc
-mixer amplifiers: 6 inputs on each channel switchable in different combinations. On each channel there are potentiometers that allow the mixing of three signals simultaneously.
-audio filters: 3 active filters on each channel: RUMBLE, LOUDNESS, HISS
-tone correction, Baxendall type with BASS and TREBLE
-one level indicator on each channel, with the possibility of measuring output level on loudspeakers or on mixer output.
-monitor connector and switch with the possibility to insert other audio stages in the signal chain ( EQUALIZER, DNL or guitar effects for example).
-several electronic protections for loudspeakers, including DC signal protection, timer on power on, instant disconnect on dangerous events
-metal aluminium case

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