Интегральные усилители — MasterSound Box

The MasterSound BoX is an Italian valve integrated amplifier working in class A with a parallel single-ended output stage built around EL34 tubes. It delivers 35 W per channel and runs with 0 dB of negative feedback, so the circuit relies on its output transformers rather than a global loop to set its behaviour.

Key specs that matter

Six EL34 power tubes are fitted, three per channel in parallel, with two ECC802 double triodes handling the signal stages, for eight tubes in all. The rear panel carries three line inputs, one MM phono input and one line-level tape output, all on gold-plated RCA sockets, with no balanced connections. Each channel has speaker binding posts for 4 ohm, 8 ohm and common, so each speaker cable goes to the tap that suits its rating. Bandwidth is quoted as 18 Hz to 25 kHz at 0 dB. The chassis weighs 24 kg and measures 436 x 409 x 185 mm.

Engineering and use context

Three transformers sit inside the chassis. The output transformers are MasterSound's own, wound one at a time by hand using construction methods developed by the Sanavio family behind the brand. The power transformer uses low-loss grain-oriented laminations in a resin bath and is mounted on an anti-vibration support. Automatic biasing keeps the EL34 set correctly biased with no manual trimming. The chassis is antimagnetic stainless steel in a black satin finish, with an anodised aluminium front panel, a perforated top plate for ventilation and a polycarbonate window through which the tubes are visible. Internal wiring uses copper-silver cable made in Switzerland, the circuit board is copper-coated glass, and the volume and input selector knobs are machined from billet aluminium. A small remote handset is offered as an option, and a later BoX-R version is listed with remote control as a feature.

Pairing

With its internal phono section, vinyl playback with MM cartridges needs no outboard preamp, while the three line inputs cover a DAC, streamer or tuner. The tape socket passes the selected source on to a recording deck or a separate headphone unit. With its moderate output from a zero-feedback single-ended stage, it suits loudspeakers of moderate to high sensitivity whose impedance does not dip far below nominal, wired to the matching posts.

Alternatives

Within the same maker's integrated range, the Dueundici is a smaller single-ended class A model with two EL34 giving 2 x 11 W in triode mode.