Предусилители — VTL TL7.5 Series III

The TL7.5 Series III is the Reference line preamplifier of the Californian maker VTL Amplifiers, and it was the company's first preamplifier in the Reference family. It is split into two boxes - a Control chassis holding the power supplies and control logic, and an Audio chassis carrying the signal circuits and every input and output jack. VTL designed it as the matching front end for its MB-450 Signature monoblocks and its S-400 and Siegfried Reference amplifiers.

Key specs that matter

Two 12AU7 tubes are used. Four input pairs accept XLR or RCA, and four more pairs are RCA only, two of which are tape inputs. Outputs are two balanced pairs, two single-ended pairs and two buffered RCA tape outs. Gain is 19.2 dB to the balanced outputs and 13.2 dB to the single-ended outputs, whichever input type is used. Output impedance is 25 ohm, reaching at most 150 ohm at 10 Hz, and input impedance is 50 kohm with a 20 kohm minimum. Response is 1 Hz to 100 kHz within +0 and -1 dB. The maximum output below 1 percent distortion is 30 V into 10 kohm or more, and 10 V into 600 ohm. Channel separation is above 100 dB at 1 kHz and above 80 dB at 20 kHz, and the unit draws 150 W. Both chassis are 44.5 cm wide and deep, 10.2 cm high for the Control unit and 15.3 cm for the Audio unit, which weigh 14.50 kg and 17.24 kg.

Engineering and use context

VTL uses a fully differential, balanced topology. Tubes provide the voltage gain with less than 2 dB of negative feedback, and a solid-state buffer supplies current. For Series III VTL revised the power supply around current-sourced shunt regulators and redesigned the high current stage with normally-on FET devices, running it with zero global negative feedback. Selected capacitors and a bi-directional RS-232 interface were also added. The Control unit contains multiple precision-regulated supplies and links to the Audio unit through two control cables and a power cable, and the two chassis must not be stacked. A Mon/Proc button can set any input to unity gain for a home theater processor, and the handset switches power and sources and controls level, mute, fade, balance and polarity. The unit has no phono stage.

Pairing

Four 12 V trigger outputs on the Control chassis can switch power amplifiers on and off, and a rear IR receiver accepts an external remote extender.

Alternatives

VTL's TL5.5 Series II is a single-chassis preamplifier from the same maker.