Memphis MC 1   Discrete Solid State Moving Coil Phono Stage  
Phono Stage Power Supply Figure 1 below shows the schematic of the power supply. It comprises four 12V lead-gel batteries and four monostable relays with two change-over switches each. In the release state the relays completely separate the batteries from their charging circuits and connect them in series to deliver 48V in 12V increments (operating mode). The batteries are connected with 2200 µF buffering capacitors at the power supply outputs that stay charged through 5k resistors. This avoids high current peaks between the batteries and the capacitors when the power supply is switched from charging mode back to operation mode. Furthermore in the unlikely event of an internal shortcut in a capacitor the current is limited to a comfortable safe region and just slowly discharges the battery. For operation mode the resistors are bypassed by switches S2 to S5.           Fig. 1: Schematic of phono stage power supply                                         Fig. 2: Phono stage power supply The 24V voltage source on the left in figure 1 includes a cheap 18V transformer and a bridge rectifier. If S1 is switched on, the relay coils are energized and the relays connect the batteries to four PB137 voltage regulators which are specifically designed to charge lead acid batteries. The diode D1 is essential to prevent batteries voltage from being fed back into the relay coils which then would not allow the relays to switch back into their release state once S1 is switched off. The 10Ohm resistors simply limit the charging currents. The above figure 2 shows the power supply with its cover removed.
super triode, vinyl, audio, analog, single ended, SE, power amplifier, hybrid, tube, KT66, 6SN7, ECC88, Mosfet, Lundahl, MC phono stage, preamplifier, MM, MC, moving coil, moving magnet, LL1693, LL1667, LL9226, LL1933, RIAA, folded cascode, 2CS5200, MAT12, 2N3810, LL1660S, IXFN32N120P, balancing amplifier