|tube audio .. RH DESIGN||
The reference preamp
solutions made to change your world
by Aleksandar Kitic
The phono section has enough gain to handle MC higher output (more than 0.5mV) cartridges. If lower output MC cartridges are applied, there are changes to be made in the line output section (to provide more gain).
RL should be adjusted for optimum load: if MM -- 47k, if MC --whatever value recommended by the manufacturer of the cartridge. CL should be adjusted as well: for MM 100pF - 330pF depending on the cartridge and the capacity of the other cables involved; if MC, usually a value between 10nF and 68nF is adequate: do not underestimate the importance of this cap for MC !
The phono stage does not invert absolute phase; the line stage inverts absolute phase -- therefore all output is phase inverted: use inverting inputs to the power amp if available or reverse loudspeaker cable polarity at the amplifier !
The extention of the power supply is placed in the second chassis together with the audio section.
A+ powers the line stage, B+ powers the phono stage, (+) and (-) 12.6V powers the heaters of all triodes (pin 4 and 5)
The main power supply includes all power transformers (or one with three secondaries), as well as the High Tension (HT) and 12.6V heaters supply.
The main power supply is connected to the audio section chassis with an umbillical cord made of 4 solid core isolated wires. As connectors, Cannon plugs can be safely used.
The 4 wires carry:
1) HT audio (250-275V DC)
2) GROUND (obviously, central ground)
3) +12,6 V DC for the heaters of the audio section triodes
4) -12,6 V DC for the heaters of the audio section triodes, referenced to approx
1/4 of High Tension to prevent exceeding the cathode/filament max. voltage differential (approx. 100V DC for the tubes used: 12AX7, 12AT7, 12AU7)