Hector TVC preamplifier in passive mode: an owner’s review

An owner who had always run his tube monoblocks straight from a DAC added a Hector passive preamplifier to his system in 2025. He wanted to set the volume from his chair without hearing the preamplifier itself. Below we summarise what he heard, what he compared Hector with, and why a transformer volume control behaves differently from the resistor-based passives he had tried.

This review is summarised and translated from an owner’s review on an online marketplace. It is the subjective view of its author, not a measurement or a claim of Demograf Audio.

The system and the brief

The owner listens through a pair of 70 W class A2 tube monoblocks on GU-48 tubes and four-way loudspeakers with 12-inch woofers. Before Hector, the amplifiers were connected directly to his DAC, and the volume had to be set separately on each monoblock.

He had one requirement for a preamplifier: it should have no audible influence on the signal. He spent about a year talking to different designers before choosing. He had set out looking for a passive preamplifier, and his Hector is one: a transformer volume control (TVC), with no gain stage of its own. In his review he described it as transformerless; in fact it is a transformer-type passive preamplifier, as the reply to his review pointed out.

Built to order

Like every Demograf Audio instrument, his Hector was made to order. The details, from the connectors to the colour of the indicator light, were agreed with him, and he spoke directly with the designer.

What changed with Hector in the system

Volume from the listening seat

The first change was practical. With Hector the volume is set by remote control, where before he had to walk to each monoblock and turn its control in turn.

Bass at low volume

He turned the volume control on each monoblock fully up and left it there, which, as he notes, takes that control’s resistor out of the circuit. Hector now sets the level. His 12-inch woofers had sounded weak at low listening levels; with the monoblocks at maximum, the bass came through even when he listened quietly.

Micro-dynamics and timbre

With Hector in the chain he heard more micro-dynamics. What mattered most to him was what he did not hear: no loss of tonal balance and no loss of fine dynamics compared with the direct connection. In his words, everything sounds excellent.

Compared with other preamplifiers

vs a Japanese passive preamplifier

Before Hector he tried a Japanese passive preamplifier with a conventional volume control. To his ears it made the sound thinner.

vs a tube line stage

A tube preamplifier he tried coloured the sound strongly. With Hector he heard none of that colour, only better dynamics and more bass.

vs no preamplifier at all

His reference was the DAC driving the monoblocks directly. Against it he heard no loss, and he gained the remote control, fuller bass at low volume and the added micro-dynamics described above.

Why a transformer volume control behaves this way

A resistor passive, whether a potentiometer or a stepped attenuator, is a voltage divider. Its output impedance changes with the setting and rises towards the middle of its range, where it can interact with cable capacitance and the amplifier’s input. A transformer volume control sets the level by selecting taps on a transformer winding. Because a transformer changes impedance as well as voltage, the output impedance the amplifier sees falls as the volume goes down, and the load on the source becomes lighter.

Owners moving from a resistor passive to a TVC commonly report fuller dynamics and bass at low volume, which these impedances partly explain. This owner’s experience fits that pattern, though one system proves nothing on its own. A passive also adds no gain, so it suits systems in which the source delivers more level than the amplifier needs for full power, as is common with DACs of about 2 V. Our guide to passive and active preamplifiers explains gain structure and impedance in detail.

Summary

For this owner, Hector solved a practical problem, remote volume for a pair of monoblocks, without the cost he feared. He heard no change in timbre and no loss of fine detail, and he gained bass at low listening levels and a little more micro-dynamics. The two other preamplifiers he tried, a Japanese passive and a tube line stage, both changed the sound in ways he did not want.

His is a single report from a single system. Anyone considering a passive preamplifier should first check that the source has enough output and that the amplifier is sensitive enough, as our guide describes.

Which Demograf Audio piece fits

Hector is a preamplifier in two versions, tube and solid-state, built on a transformer volume control on a Swiss stepped mechanism in a wooden chassis; the passive-only version has no mains connection. Its TVC is inspired by the Stevens & Billington TX-103 passive volume control. For volume from the listening seat, as this owner wanted, there is a relay-switched TVC version with remote control. The active stage is solid-state or tube, with EL8, AL4 or ML6 tubes, and a dual-mode unit switches between passive and active. Balanced XLR inputs and outputs are optional.

As a source, the Reference Tube DAC pairs naturally with a passive preamplifier, and for vinyl the Ulixes phono stage (solid-state as standard, tube to order) provides the gain a passive cannot. Every Hector is made to order by Dmitriy Gubchenko and covered by a one-year warranty (extra warranty available: +1 or +2 years).