The REGA IOS is the British brand’s ultimate phono preamplifier. This means that it has been designed to bring out 200% of the musicality of the APHETA cartridge! It is also part of the company’s flagship ‘Reference’ range, joining the ranks of the Isis and Osiris. It is only compatible with MC cartridges! Rega do without moving magnets entirely, which may appear to be surprising, but we feel it is fully justified given the range of the product. As soon as it is unpacked, its 17 kg weight is already impressive!
It has both symmetrical and asymmetrical inputs and outputs. Its internal architecture has been thoroughly optimised and designed to reduce surface noise to a minimum. The wiring uses conductors with very low capacitance and resistance. The circuit only includes the highest quality components, spread across four symmetrical amplification stages. The first stage uses a top quality step-up transformer: the SOWTER 8055 (report 1/10). The second comprises discrete components only, most notably the low noise Hitachi transistors. The third stage is also fully symmetrical and is a class A differential amplifier. It controls the low frequency part of the RIAA equalisation stage. The fourth stage is an low noise operational amplifier with a very high bandwidth. The signal path uses low tolerance (1%!) polypropylene capacitors only. Particular care has been taken over the IOS’ power supply. It uses fast, low noise diodes and regulators.
On the front panel, there is a two position gain selector (64 or 70 dB), a 5-position resistive load selector (50, 100, 150, 300 and 400 ohms) and a 5-position DC load selector (6.25, 8.75, 11.25, 13.50 ohms, nominal). A button controls the mute function and, another, the mono function. Plus curieux, Rega features a filter that is designed for the Apheta and the under-damped cartridges or giving a treble that is slightly too strong! It is also recommended with some pressings from the early sixties that were sensitive to surface noise. We recommend you try it out and use it sparingly…
We could not resist combining the Rega IOS with our RP10 and its Apheta. From the first beats, we were forced to note that this is a fearsome combination. Quality and musicality were not lacking! The dynamics are amazing and span evenly across the entire spectrum. The bass is deep and very well controlled. We discover the articulation and clean sound of the 'major' phono stages! It cannot be compared on any way with its little brother Aria. The sound stage is wide and very deep, but for all that the precision is just as good. The vocals are perfectly positioned in the centre of the speakers and have outstanding presence. You could say that the equipment completely retires before the music. The sound quality is entirely proportional to the quality of the work and the pressing. This IOS Reference gives amazing results with other cartridges than the ones available from Rega. With our benchmark MC, we found all the qualities mentioned above, with slightly more transparency and neutrality.
This REGA IOS Reference can be considered to be one of the best preamplifiers on the market. If you have a RP10 and an Apheta, no longer seek the absolute preamplifier! We have found it... Franck
Input sensitivity: 200mV
Output: 61uV - 70dB gain setting I 118uV - 64dB gain setting II
Gain: 64dB Minimum 70dB Maximum
Input load: 50, 100, 150, 300 & 400Ω
DC resistance: 5 to 7.5Ω (6.25Ω nominal) 7.5 to 10 Ω (8.75Ω nominal) 10 to 12.5Ω (11.25 Ω nominal) 12.5 to 15 Ω (13.5Ω nominal)
MC transformer: Sowter 8055
Max. input: 8.7mV - 64dB gain setting 4.5mV - 70dB gain setting
Max. output level: 14.7V RMS
Min. output level: 200mV
Output resistance: 100Ω
Min. output resistance: 1KΩ for –3dB to 15Hz
RIAA accuracy: 0.2dB
Frequency response: 14Hz to 54KHz (-0.5dB)
Distortion: under 0.008%
Output level: -85dBV. 64dB gain at 15Ω
Inputs: RCA and XLR
Outputs: RCA and XLR
Power supply: 230V
Power supply: 21 Watts