Integrated Amplifiers

HiFi Rose's active, op-amp-based phono stage is mounted on its own PCB [pictured below] where a row of 10 relays is also visible [top]. These switchin the optional 300Hz, 400Hz, 500Hz, 700Hz and 'flat' LF turnover frequencies together with the 1.6kHz, 2.1kHz, 3.18kHz, 3.4kHz and 6.36kHz HF roll-offs that accommodate RIAA plus Decca, Teldec/AES, NAB, Columbia and CCIR (plus various 78s) equalisation characteristics. Using the RA180, vinyl lovers must not only select the MM/MC input but also enable the 'phono amp'. Input loading is fixed and, as there are no line/preamp outputs on the RA180, testing was achieved through the main Class D amplifier stage. It is impossible to verify the fixed MM and MC gain of the phono board but its RIAA accuracy is within +0.0/–0.8dB of the main amp response from 20Hz-20kHz.

Again, spurious HF tones in the Class D amp rather take the edge off the A-wtd phono S/N, but discounting this spuriae reveals creditable figures of 74dB (MM re. 5mV) and 71dB (MC re. 500µV). Input overload margins are not especially generous, however, with just 22.5mV for MM and 2.4mV for MC (or +13.1dB and +13.6dB headroom re. 5mV and 500µV, respectively). As a result, the RA180 is arguably best suited to medium/high-output MCs being enjoyed via the MM input. High output MMs from Ortofon, etc, are probably best avoided until or unless HiFi Rose improves its phono input headroom. PM