The Simplex is a moving magnet phono preamplifier compatible with both moving magnet and high output moving coil cartridges, delivering outstanding performance. It uses the same Class A discrete transistor circuit topology that has been so successful in the Rialto, but without the Rialto’s additional moving coil gain stage. The result is truly high-end performance in a simple, compact and affordable unit, rivaling phono stages at many times the price.
Circuit Design
An elegant discrete transistor design, rather than the more common op-amp circuits, lies at the heart of the Simplex. It operates in Class A and uses local feedback instead of global feedback, ensuring high linearity, wide bandwidth and low noise. Built on more than twenty years of phonostage design experience—Rothwell’s first outboard phonostage dates back to the early 1990s—this inherently simple circuit delivers a detailed, spacious and musical sound. Even when music becomes complex and demanding, the Simplex maintains clarity, presenting every detail without ever sounding congested or harsh.
Accurate RIAA equalisation within 0.5 dB is achieved by combining multiple high-quality polypropylene capacitors. Using several capacitors instead of a single one, as often found in lesser designs, not only improves accuracy but also reduces dissipation and minimizes parasitic effects such as dielectric absorption.
Noise is minimized and signal integrity preserved through careful PCB layout, including star grounding and the use of components on both sides of the board. This results in a compact design with minimal loop area and low inductance. The exceptionally quiet circuit has noise levels far below the surface noise of even the best vinyl pressings, allowing you to enjoy music without interference from electronic noise, hum or buzz. Multiple stages of power supply filtering eliminate power-related noise, while the external power supply prevents direct interference with the audio circuit.
Cartridge Compatibility
The Simplex can be used with all moving magnet and high output moving coil cartridges with output levels between 2 mV and 10 mV, delivering performance previously only expected from far more expensive units. When combined with a moving coil step-up transformer, the Simplex can also be used with low output moving coil cartridges, achieving an exceptionally high level of performance.
Beginner’s Guide to Vinyl Playback
For those new to turntables and unsure about the electronics required to play vinyl, a concise guide is available explaining the basic requirements and why each component is needed. (Click here for the beginner’s guide)
Specifications
- Gain | 42 dB
- Input impedance | 47kΩ + 150pF
- Output impedance | 75Ω
- Sensitivity for 500 mV output | 4 mV @ 1 kHz
- Headroom | 20 dB
- Signal-to-noise ratio | >87 dB (MM)
- Power supply | 24V DC, centre positive
- Mains voltage | 100V – 250V AC
- Power consumption | <1W
- Dimensions | 60 x 155 x 92 mm
- Weight | 570 g (excluding PSU)