Интегральные усилители — VTL IT-85

The IT-85 is the only integrated amplifier in the current catalogue of VTL, the Vacuum Tube Logic company based in Chino, California. It combines a fully active tube line stage with a push-pull EL34 power section on one chassis, and it is the integrated counterpart of the ST-85 stereo power amplifier. VTL chose an active preamp with gain over the approach of a high-gain power stage behind a passive volume control.

Key specs that matter

Output is 60 W per channel into 8 ohm and 80 W into 4 ohm from a class AB1 push-pull tetrode stage. The tube line-up is four EL34 output tubes, four 12AT7 for the input and driver stages of the power amp and two 12AU7 in the preamp section. Five pairs of single-ended RCA inputs are labelled CD, Tape, Tuner, Aux 1 and Aux 2, and a sixth pair acts as a processor loop that drives the power amp directly. Line input sensitivity is 180 mV at 20 kohm, while the amp input needs 575 mV and presents 135 kohm. Output impedance is 1.55 ohm at the speaker terminals, 16 ohm at the headphone jack and 400 ohm at the pre-out. Small-signal bandwidth extends from 0 Hz to 60 kHz at under 0.2 percent THD at 1 W. Idle consumption is 200 W and full power draw 600 W. The case is 40 cm wide, 28 cm deep and 17.75 cm high, with a weight of 29.5 kg.

Engineering and use context

Since the input impedance of the power section is known inside a single box, VTL left out the output buffer a separate preamp would need and connected the two stages directly. A buffered pre-out and a fixed tape output are still provided. The quarter-inch headphone socket is fed from the tube output stage through the output transformer, and plugging in mutes the pre-out, while a front selector switches between phones and speakers. In processor mode the internal preamp is skipped, and an external surround decoder controls the level of the front left and right channels. A remote handles volume and mute, and after power-up the preamp stays muted for about 30 seconds with a blinking LED. Bias is checked at measurement points near the back edge of the chassis and set with trimpots to between 275 and 300 mV DC. There is no phono stage, as VTL preferred to keep high-gain circuitry away from the power supply fields.

Pairing

VTL gain-matched the ST-85 to the pre-out of the IT-85, so the pair can bi-amp speakers with split terminals, one amplifier on the bass of both channels and the other on the treble. A TP-2.5i or TP-6.5 Series II Signature phono preamplifier from the same maker covers vinyl playback.

Alternatives

VTL offers no other integrated amplifier, so the IT-85 has no in-brand alternative in this category.