+48V Supply, +8V Supply | SoundCraft CPS2000 guide

The +48V Supply.

Max current rating is 0.3 Amps. The +48V phantom supply is based on the high-voltage regulator TL783C. (REG1) The AC input is fused by F4 and fullwave rectified by BR4; C1,24 are the reservoir capacitors. The unregulated DC may rise as high as +85V on high mains.

The TL783C maintains a fixed 1.27 V between its ADJ and OUT pins, so the adjustable voltage-divider R1-PR2-R2 gives an output of approx 48V. This can be finely adjusted by PR2. The divider current is also used to power the rail indicator LED3, minimising the current wasted inside the regulator circuit.

An output current of 0.5A and a wide (+10/-20%) mains range means that a TL783C alone is only marginally capable of handling the power dissipation. Therefore preregulator TR16,17, working as an emitter-follower biased from the +48V output by zener DZ5, absorbs some of the voltage drop, so that only approx 62V appears on the TL783C input. C28 ensures HF stability of REG1.

Two protection diodes are included. D1 protects the regulator from reverse voltage if there is a charged capacitor across the output but the voltage on C1,24 has collapsed. D2 prevents the ADJ pin from rising above the OUT pin (due to the charge on C2) if the output is shorted.

Conventional diode D6 on the output allows supplies to be paralleled for redundancy.

The +8V Supply.

Max current rating 1.25 Amps. This supply is primarily intended for powering console internal computers; it will be regulated down to +5V inside the console.

The AC input is fused by F4 and fullwave rectified by BR4. The unregulated DC is about +15V on nominal mains. The LM317T regulator maintains a fixed 1.25V between its ADJ and OUT pins, so fixed voltage-divider R68,69 gives an output of approx 8.4 V. C23 reduces output ripple from 1 mV to approx 180 uV at full load.

Two protection diodes are included. D9 protects the regulator from reverse voltage if there is a charged capacitor across the output but the voltage on C20,21 has collapsed. D10 prevents the ADJ pin from rising above the OUT pin (due to the charge on C23) if the output is shorted.

Conventional diode D11 on the output allows supplies to be paralleled for redundancy.

Mains Voltage Select PCB. SC3817

This PCB (SC3817) carries the inrush suppressor and two DPCO switches that select the transformer primary connections to suit the incoming mains voltage.

The first switch A selects between EUROPE and USA/JAPAN settings. The second switch B selects high and low variations on this:

Mains	Mains	Nominal	Dropout	Dropout
Switch A	Switch B	Mains	Voltage	Voltage

20	Circuit Description