Vermes
Advanced Member level 4
It is a tiny pocket preamplifier. It is perfect for other audio devices, which does not have enough gain, which makes it impossible to connect them directly to a phone/mp3. The main advantage of this preamplifier is its small size and battery power. It is powered from 2x9V batterries connected in series, what provides symmetrical supply. Its gain is 11v/v, it is also equipped with volume adjustment. Mini Jack 3,5mm stereo input with a channel sumator. Input resistance is 50kohom. Jack 6,3mm mono output. Housing was made of PCBs.
It has a hinged lid of the battery compartment, top screwed on brass screws. Construction is a standard WO application.
Cracks while turning on and off the preamplifier were removed by adding 20ohm resistors in series with the power supply and 220uF capacitors in parallel with the power supply (behind the switch).
Pictures:
Link to original thread - Kieszonkowy przedwzmacniacz