Schematic Diagram

1. The four diodes in rectifier bridge 1 B1 are bypassed with rattle suppression capacitors to ensure minimum noise on the supply rails to the opamps.
2. This makes it possible to feed the ;l5V regulator from the raw voltage across Ca (+) and C10 (-) of the existing »;l8.5 V supply while the inputs of the volume control of the head- phone amplifier are driven direct from the outputs of IC4 l l (R) and IC4’ (L).
3. At the l input side, few problems are i expected to arise when using gold-plated phono sockets mounted onto a separate ABS or epoxy plate. When a good quality, insulated, 6.3 mm, stereo headphone socket proves , unobtainable, the —nearest r i alternative is a non-insulated ‘ -type, whose common tag is connected direct to the ground point on the PCB, between C1 and C18 to effect central earthing.
4. Opamps IC1 and IC; should be soldered direct onto the PCB, and are preferably fitted with a DIL-type heatsink. Provision has been made to screen the amplifiers and the supply on the Q board by means of two sheets of brass or tin plate, which are l mounted vertically onto the dot- ( ted lines, and secured with i three soldering pins each. Series regulators T1 and T2 ( can do without a heat-sink. l When the board is complete, , its underside should be A thoroughly cleaned with a brush dipped into white spirit or alcohol to remove any residual resin.
5. The headphone amplifier circuit can function optimally only if great care is taken both in the choice of the components and in the construction on PCB Type 87512, details of which are shown in Fig.2. As already stated, the headphone amplifier is suitable for building into the Top-of-the-Range Preamplifier.
6. Next, the track · side is sealed with a suitable plastic spray. When possible, use insulated sockets for the stereo input and output of the amplifier.
7. At power—on. Mains-borne interference and clicks from St are suppressed in varistor R9 and high-voltage capacitor C19. 

 Mains transformer Tri is preferably a toroidal type fitted behind a metal screen to ensure  minimum hum and other interference picked up by the amplifier inputs. Presets Pz and P! are trimmed for minimum offset voltage at the respective  amplifier output—this is likely to require a very sensitive DMM. The headphone amplifier can be terminated in 100 Q to 1 1