Rega Reference IOS Moving Coil Phono Stage

Description

Designed as the ultimate MC phono stage and the perfect match for the RegaApheta MC cartridge Ios has made the transition in to the reference style case to match Isis and Osiris. The new Ios has the addition of balanced XLR connections mute and mono functions. The PCB layout has been redesigned to improve the noise floor and the entire unit has been fully rewired with ultra low capacitance cabling.

The function of a phono pre amplifier is to match the output from a pick up cartridge to the input of a line level amplifier. It is required to amplify the very low signals produced by the cartridge and also to equalise the sound in accordance with RIAA record cutting standard. Rega believes that moving coil and moving magnet cartridges require different types of phono pre amplifiers to achieve optimum performance. The IOS is therefore dedicated to moving coil cartridges and avoids compromises. We have avoided including any superfluous functions as they obstruct the signal path and degrade the sound quality.

Design innovation

The Rega Ios is a four stage all symmetrical amplifier. To provide optimum
performance it is dedicated to amplifying the very low level signals that are
generated by moving coil cartridges.

The first stage uses a 1:10 step-up transformer, which can be optimised to the cartridge by the selection of the correct loading and zobel DC resistance correction network connected across the MC transformer secondary.

The second stage is a symmetrical compound pair class A amplifier, using paralleled low noise Hitachi transistors in the input stage.This drives the passive high frequency part of the RIAA equalisation stage.

The third stage is a symmetrical class A differential amplifier with a common base driver stage; this is also used as the active amplifier in the low frequency part of the RIAA equalisation stage. The fourth stage is the active filter, this configuration uses the same circuit as found in the second stage. The filter element uses a very high bandwidth operational amplifier.

The power supply is a symmetrical discrete tracking power supply using fast diodes and a low noise voltage reference. Each stage has its own localised power supply, and LED referenced current generators. Very high quality, polypropylene capacitors have been used in the signal path. 1% tolerance polypropylene capacitors are used in the RIAA EQ stages and audio grade capacitors are used in the rest of the circuit.