Theriaa Mk II Phono Stage

Description

The Theriaa MkII phono preamplifier was created as a result of RCM’s research and experience in the field of sound reproduction, the source of which is an analogue turntable. It is a completely new project, which only in general terms refers to the SENSOR IC project.

For the construction of the entire system, RCM used components from the “top shelf” of renowned brands Elna, Sanyo, Nichicon, Wima, TDK Epcos, Vishay, Omron, Burr Brown, Analog Device and others. The use of such elements allowed for the maximum use of available technologies. The Theriaa MkII is a fully dual-mono design and is split into three main blocks. The first is the power supply. Located in a separate housing with a rectifier and a first stage of voltage stabilization. The second and third stage of filtration are located in the main casing of the preamplifier together with the circuits responsible for the riaa correction and amplification of the signal from the cartridge. To maintain optimal working conditions, the left and right channel plates are isolated from you with a 10mm screen and two 5mm screens in the power supply.

A characteristic feature of the preamplifier is the high level of the output signal. RCM say their experience shows that in order to obtain optimal sound, the signal level should not be lower than 1 volt, and preferably it should be at the level of 2 V. Such assemblies place very high demands on the entire system. Another characteristic feature of this device is the ability to change the input operating mode (balanced and unbalanced). The signal coming from the cartridge is a symmetrical one and with the appropriate input configuration we can increase the distance from noise and improve the dynamic range.

The matching of the input impedance and the gain level as well as the change of the input operating mode is controlled by high-quality Omron DIP switches located on the rear panel of the housing. Selected circuits deal with amplification of the signal. Equalization according to the RIAA standard is implemented as a passive system based on low noise resistors and polypropylene capacitors. To ensure accurate signal correction, all elements of the “filter” are measured and selected manually so that the deviation does not exceed 0.2dB in the band from 20Hz to 20kHz. The remaining elements are selected in a way that guarantees uniform operation of the preamplifier in both channels.

The key to a good phono preamplifier sound is the optimal frequency response and RIAA equalization, but without the proper power supply, all the effort is wasted, so the Theriaa MkII is equipped with a symmetrical power supply, the design of which is aimed at maximum noise reduction. It is also important to isolate the transformers from the sensitive equalization and amplification circuits.