Second item from a batch of parts I bought fron GDIY member fluxivity. Transistor amplifier cards marked only "Jh004". I traced out the circuit and it is an odd one to me. Mix of Si and Ge transistors, and a weird feedback circuit. See schematic attached.
I powered one up with +24vdc and the best I could get out of it was about 33dB gain from a 50 ohm source into a 100k ohm load. However the input to the board had to be about -55dB to keep the THD below 1%. Also, lowering OR raising the power supply voltage lowered the gain.
Does anyone have any idea what these boards may be from or what they are for?
I powered one up with +24vdc and the best I could get out of it was about 33dB gain from a 50 ohm source into a 100k ohm load. However the input to the board had to be about -55dB to keep the THD below 1%. Also, lowering OR raising the power supply voltage lowered the gain.
Does anyone have any idea what these boards may be from or what they are for?