27-11-2016, 09:27 AM
I designed a valve phono amplifier, see attached diagram. It's a tad short on gain, but (to me) works surprisingly well.
The first stage is configured as a voltage-to-current converter, operating into the virtual earth of the second stage grid. So the signal voltage on the anode is peanuts. It's linearised by the unbypassed cathode resistor (so a DC heater would be nice for ultimate lowness in hum, and a floating heater line is a definite no-no!). The second stage is a transconductance current-to-voltage converter, with frequency-selective feedback around it.
The first stage is configured as a voltage-to-current converter, operating into the virtual earth of the second stage grid. So the signal voltage on the anode is peanuts. It's linearised by the unbypassed cathode resistor (so a DC heater would be nice for ultimate lowness in hum, and a floating heater line is a definite no-no!). The second stage is a transconductance current-to-voltage converter, with frequency-selective feedback around it.
