Integrated Amplifiers

Unlike other Jadis amplifiers that are configured internally for either 8 or 4ohm operation [HFN Apr '21], the Diapason offers a pair of transformer taps to 'match' with so-called 8ohm and 4ohm loudspeakers. These transformer taps step-down the high voltage/high impedance output of the 6L6GC beam tetrode tubes to better match the lower impedance and higher current demand of the attached loudspeaker. However, in practice few speakers offer a flat 4 or 8ohm impedance, so as the load swings up and down in value across the audio range so too does the system response of the amp/speaker combination.

Typically, solid-state amplifiers offer a sufficiently low source impedance to minimise this effect, but tube amps like the Diapason with its 2-4ohm output impedance incur a lift in response with rising speaker impedance and vice-versa. Into a non-reactive 8ohm load the Diapason shows a gentle bass (–1.6dB/20Hz) and treble (–1.0dB/20kHz) roll-off [dashed trace, inset Graph]. This really does not tell us how the Diapason will 'sound' into a real loudspeaker – as illustrated by it driving likely partners in the form of the little JBL 4309 [black trace, via 8ohm tap; grey trace, via 4ohm tap] and very little Monitor Audio Silver 50 7G [red trace, 8ohm tap; orange trace, 4ohm tap]. In both cases we see how the swings in impedance through the reflex-loaded bass of both speakers moderates the system response, while the inductive upswing in impedance via JBL's 2410H-2's mid/treble compression driver delivers a broad +3.8dB boost through presence and treble. This alone will mean the Diapason/JBL combination will exhibit significantly more 'sizzle' and bite than an equivalent Jadis/MA-based system. PM