6DJ8 Tube RIAA Phono and Line Preamp Schematic
6DJ8 Tube RIAA Phono and Line Preamplifier Schematic
This circuit uses 6DJ8 tubes in a two stage RIAA phono preamplifier followed by a one stage line preamplifier with a volume control input. Provisions for input switching and recording are shown and can be adapted to meet your needs. The phono stage will provide 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 regtified and tube regulated and that plays a large part in the high performance of the preamp. This preamplifier should be built with good shielding and mechanical isolation between the preamp circuitry and the power supply for optimal performance. There is more information available about tube power supplies, in the Power Supply Design for Vacuum Tube Amplifiers article.