THERIAA MkII
PHONO PREAMP MC / MM
The THERIAA MkII phono preamplifier is the result of our research and experience in the field of sound reproduction from an analog turntable. It is an entirely new design that draws on the SENSOR IC design only in terms of its general principles.
To build the entire system, we used top-of-the-line components from renowned brands such as Elna, Sanyo, Nichicon, Wima, TDK Epcos, Vishay, Omron, Burr Brown, Analog Devices, and others. The use of these components allowed us to make the most of the available technologies.
The THERIAA MkII is a fully dual-mono design and is divided into three main sections. The first is the power supply, housed in a separate enclosure with a rectifier and the first stage of voltage regulation. The second and third stages of filtering are located in the main preamplifier chassis, along with the circuits responsible for RIAA correction and cartridge signal amplification. To maintain optimal operating conditions for the circuits, the right and left channel boards are isolated from each other by a 10-mm shield, and in the power supply, by two 5-mm shields.
A characteristic feature of the preamplifier is its high output signal level. Our experience shows that, to achieve optimal sound quality, the signal level should not be lower than 1 volt, and ideally should be 2 V. These requirements place very high demands on the entire circuit.
Another distinctive feature of this device is the ability to switch between balanced and unbalanced input modes. The signal output from the cartridge is balanced, and with the proper input configuration, we can increase the signal-to-noise ratio and improve the dynamic range.
The input impedance and gain level, as well as the input operating mode, are adjusted using high-quality Omron DIP switches located on the rear panel of the enclosure. Signal amplification is handled by carefully selected integrated circuits. RIAA equalization is implemented as a passive circuit based on low-noise resistors and polypropylene capacitors.
To ensure precise signal correction, all filter components are measured and selected by hand, ensuring that the deviation does not exceed 0.2 dB in the 20 Hz to 20 kHz frequency range. The remaining components are selected to ensure uniform performance of the preamplifier in both channels.
The key to a phono preamp’s excellent sound quality lies in its optimal frequency response and RIAA equalization, but without a proper power supply, all that effort is wasted. That is why the THERIAA MkII is equipped with a balanced power supply designed to minimize interference as much as possible.
It is important to isolate the transformers from the sensitive correction and amplification circuits. The power supply is connected to the preamplifier via a shielded cable. A gold-plated Amphenol connector set is used.
The housing is an equally important component. It is the first thing that catches the eye, but it is not its appearance that matters, but rather its mechanical construction and the materials from which it is made. The main housing is made of anodized aircraft-grade aluminum sheets 5 mm and 10 mm thick, bolted together using additional structural components. The result is a very rigid and compact structure. We commissioned its production from the renowned company Fischer Elektronik based on our design.
The power supply’s enclosure is made of a closed-section aluminum profile painted black.
The MkII version is an upgraded version of the base Theria model. The printed circuit boards and some electronic components have been modified, and the RCA jacks have been replaced with high-quality Furutech FT-903R terminals.
Technical Specifications
| Input sensitivity: | 0,2 – 5 mV (adjustable) |
| Sensitivity adjustment: | 0,2 – 0,3 – 0,4 – 0,6 – 0,9 – 1,4 – 2,0 – 2,5 – 5 mV |
| Reinforcement: | 52 – 76 dB (2 V rms exit) |
| Input impedance: | 20 ohm – 47 000 ohm |
| Impedance adjustment: | 20 – 30 – 50 – 100 – 200 – 400 – 1000 – 47 000 ohm |
| Input capacity: | 100 pF |
| Input operating mode: | symmetric – asymmetric |
| Entry: | RCA |
| THD: | 0,01% |
| S/N: | 85 dB |
| Linearity RIAA: | +/- 0,1 dB (20 Hz – 20 kHz) |
| Output impedance: | 70 ohm |
| Output: | XLR, RCA |
| Nominal output level: | 2 V rms |
| Maximum output level: | 9 V rms |
| Dimensions: | 440 x 265 x 120 mm – preamplifier 205 x 270 x 105 mm – power supply |
| Weight: | 9 kg – preamplifier 4,5 kg – power supply |
| Enlistment: | max 17 W |