Rega Ios Reference - Manual (Page 6)

INTRODUCTON
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. The IOS phono pre-amp incorporates remarkable and innovative design
ideas. For those interested in the technical details, these innovations are
described more fully in the next section of this manual. Alternatively, you can
simply switch on, sit back and let the IOS speak for itself.
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.
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