Thrax Audio Dionysus Silver Pre Amplifier
Dionysos is a remote-controlled transformer-coupled vacuum tube line level amplifier.
The control amplifier is the centerpiece of every high-end audio system. It is responsible for source selection, signal conditioning and volume control. It has the task to match the output of your source to the input of your power amp. Its output stage has to drive any power amplifier through any length of cable with optimal quality via balanced or unbalanced lines.
The input of Dionysos provides optimal loading for the source component to develop its full potential, allowing it to extract the maximum amount of information while keeping all noise picked up along the way out of the signal chain. During our research and evaluation of the various approaches possible we settled for a transformer. A transformer provides complete isolation from the rest of the system, rejects common mode signals much better than any active solution, stops EMI/RFI and ensures a truly balanced differential input, while having very low DC resistance.
The volume control of Dionysos adjusts the level of the input signal to the value required by the power amp without burying low level information in noise while transferring enough power to properly drive the amplification stage without affecting its operation.
Potentiometers and resistor ladders, as sophisticated as they might be, have a fundamental flaw. They operate by unnecessarily dumping the excess signal across a resistor. It is like driving a car with fixed engine power (signal) and adjusting the speed with the brakes (resistor) wasting most of the engine power! Our solution is fundamentally different and as simple as it gets. We use a transformer with various winding ratios and we switch between them. In the example above it would be illustrated by a gearbox, transferring all the power of the engine at all speeds. In other words remains in CONTROL at all volume settings.
The gain stage is realized by the use of a single low noise vacuum tube loaded with a transformer, making the output of the control amplifier low impedance, DC free, truly balanced, isolated from noise sources and decoupled from other components in the system. This is the absolute optimum driving signal for the following power amplifier's input stage.
To further reduce the astonishingly low noise floor of the unit the active circuit is disabled below a certain volume setting and the attenuator is connected directly to the output providing low impedance noise free signal.
The power supply of Dionysos uses a choke input rectifier arrangement. This eliminates switching noise and any other disturbance that originates before the choke, so the power reaching the reservoir capacitor is perfectly clean. As signal modulates the power supply of all devices we opted for a very unique way of regulation getting rid of the problem entirely. Dionysos uses a current sourced shunt regulator. Meaning the current consumed at any given time is kept constant avoiding any variations and making any intermodulation impossible while the shunt element passes all signal currents getting rid of any energy storage devices (e.g. capacitors) that might affect the sound allowing all the finest textures to be rendered unaffected by signal amplitude.
All this is governed by a microprocessor switching to the appropriate combination of relays and monitoring the unit’s status and incoming commands. The chassis is milled in-house from solid plates of different thickness aluminum that are interlocked together to form a ringlike rigid structure. We have the power supply mounted on the left sidewall of this structure and the signal transformers on the right side, crossed by two semi-flexible bars on which the motherboard and its heat sink are attached via vibration isolating Gel bushings. The top and bottom plates link all sides of the ring with the flexible bars and the feet made from conductive plastic on flexible screws. There are no screws visible anywhere on the chassis. And the chassis feels like a solid block protecting the circuitry from the environment both mechanically and electrically.
4 pair unbalanced RCA connectors,
2 pair balanced XLR connectors
2 pair unbalanced RCA connectors
or 2 pair balanced XLR connectors
Volume control range
Minimum gain: -46dB
Maximum gain: +18dB
32 (first 10 steps passive)
Max output level
115 or 230V
17 W x 15.75 D x 4.75 H inch
1 x 6H6П (6N6P) indirectly dual triode