Presented preamplifier is one of my line preamplifier with low gain (up to ~10x) designed to be used with ECC82 and 6N30P tubes. First stage is responsible for voltage amplification (VAS) and is based on SRPP topology. Second stage is cathode follower which isolates VAS from output load and provide less than 100R output impedance. This combination gives us wide frequency response and can easily drive any load even 300R headphones.
Parameters:
- Frequency response: 2Hz – 1.35MHz to 47k load (2.2uF output capacitor)
- Amplification factor: base 10V/V (20dB)
- Anode supply: 300V 60mA
- Heater supply: 6,3V 1500mA
- Output impedance: ~100R
Additional features:
- input resistor divider for gain reduction to desired one
- place for bypass capacitor on cathode resistor of SRPP circuit to increase gain
- muting relay at the output
- possibility to change heater style from ECC88 like tubes to ECC82 like tubes in SRPP circuit
Instead of expensive 6N30P, cheaper 6N6P could be used. This has influence on output impedance and linearity of circuit (more THD). Further price reduction can be achieved by replacing ECC82 with 6N1P (this modification should be preceded by changing cathode resistor) what gives the same side effect.
Board could be used with one of my high voltage power supplies: semiconductor or fully tube.
MuzgDIY 
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