6DJ8 Tube Phono and Line Preamplifier Schematic
Two stage phono preamplifier and a one stage line preamplifier with a volume control input. Provisions for switching and recording can be adapted to your needs. The phono stage provides enough gain for most moving magnet cartridges and incorporates a passive RIAA equalization.
A single gain stage of 6DJ8 drives a passive RC network which accomplished the necessary equalization for records. The output is fed to a second 6DJ8 gain stage for a total gain of 32 dB. 1% tolerance resistors and capacitors should be used for the filter components. The passive balance and volume controls have a loss of 6 dB. The line amp is a paralleled 6DJ8 and provides a gain of about 24dB at an output impedance of 1.3k.
The power supply is tube regulated and that plays a large part in the high performance of the preamp. This should be built with good shielding and mechanical isolation between the preamp and power supply for optimal performance.
6DJ8 Tube Phono and Line Preamplifier Schematic