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5. Output section mode: Solid-State / Tube / Tube+
The Pro iDSD (just like the Pro iCAN) is a one-of-a-kind product that is able to switch between:
'Solid-State' - a purely solid-state J-FET based circuit of fully-discrete Class A topology.
'Tube' - the J-FET circuitry is switched to an all-valve Class A section based on 2 x GE5670.
'Tube+' reduces available negative feedback to a minimum. As a result, a greater amount of the
tubes natural harmonic distortion is produced (even order harmonics dominate).
When switching, there is a momentary pause as the circuit switches over.
The audio circuit is a development of iFi's revolutionary 'TubeState' design. It is fully-discrete, fully-
balanced with either tube or J-FET input switchable, bipolar second stage and mosfet-buffered bipolar
Class A power stage (with Class AB for low impedance headphones and very high levels). The circuit is
fully DC coupled.
Please note that, due to the wear on the cathode of tubes after an extended period of time in solid-
state mode, the tube heater element will automatically power down and turn off the tubes. If the tube
heater is shut off when switching to tubes, they will need to warm-up again (as if the whole Pro iDSD
itself was powered up from cold). Music will continue to play via the solid-state section until the tubes
are ready.
This ensures maximum longevity for the NOS General Electric 5670 tubes.
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