PrimaLuna EVO 300 Integrated Amplifier Triode On The Side

Triode On The Side

If HFN readers care to pop over to PrimaLuna's US website they'll discover the brand is very realistic about the limitations of triode mode operation. This includes low power output, limited bandwidth, higher distortion and output impedance, despite the 'elegance' of SET amplifiers retaining a cult status among audiophiles prepared to select from a limited pool of very high sensitivity loudspeakers.

PrimaLuna, in common with other progressive brands, offers switchable ultralinear (UL)/triode modes on its integrated and power amps. Indeed, with its 'AutoBias' facility and ability to accommodate almost any choice of pentode or tetrode, PrimaLuna's EVO series is one of the most flexible in this regard. The EL34 pentodes fitted here are perfectly suited to triode adaption – the control and suppressor grids are disconnected (or linked to the cathode) while the screen grid is coupled to the anode (plate) typically via a 100ohm resistor. This is performed on-the-fly with relay muting to protect ears and speakers!

High quality output transformers are specified, along with moderate use of feedback, squeezing the amp's output impedance down from the 5-8ohm seen in other designs [HFN Feb '21] to 2.86-3.65ohm in UL and 2.28-2.68ohm in triode mode (20Hz-20kHz). However, while this certainly confers better bass control, it will still influence the overall system response according to the impedance trend of the attached speaker. Into a non-reactive 8ohm load, the UL mode offers a more uniform –0.1dB/10kHz to –0.35dB/20kHz treble response against the slightly 'sweeter' –0.25dB/10kHz to –0.85dB/20kHz of triode mode. PM

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Supplied by: Absolute Sounds Ltd
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