The Cyrus One (tested in Issue 144) was a bold new departure for Cyrus. In a redesigned, more cost-effective half-sized case (not the evergreen traditional cast Cyrus case of the company’s more long-standing range), the One was a bold move for the company because it was app controlled, sported an aptX Bluetooth receiver and used Cyrus’ own Class D amplifier circuits in everything except the headphone amp. Because it was designed for a new generation of buyers, the remote control was moved out of the box, typically meaning users would control the amp from their smartphones.
While the Cyrus One stays in the range, the Cyrus One HD has been developed to meet the demands of a more connected audience, in the process giving Cyrus the opportunity to revisit the original One and improve the circuit slightly. The headline differences are the use of Cyrus’ fourth-generation Class D circuits in place of the third-generation found in the original model, which beef up the power to 110W per channel, and a built-in DAC (with S/PDIF and USB connections). The only other big change is the remote; there is one with the One, whereas the One HD recognises that task is now taken up by the app and the remote handset is now a thing of the past. Otherwise, the two are on-paper identical; both have a great Class AB headphone amp stage, and a built-in MM phono stage, both feed the Class D stages via a linear power supply, and both use a Speaker Impedance Detection system to ensure the frequency response remains flat for different loads.
Cyrus Speaker Impedance Detection works by measuring the high frequency impedance of the connected loudspeaker using a microcontroller. By performing some maths, we then apply an appropriate correction curve to remove the frequency response deviations that would otherwise be present from the Class D reconstruction filter. Unlike other Class D amplifier systems (often off-the-peg modules), the custom-made designs in the One HD are perfectly comfy driving some traditionally off-limits loads for a Class D design.