Thrax Dionysos
Line level PreAmplifier – remote controlled In a sentence: Dionysos is a single ended single triode stage transformer coupled remote controlled line level amplifier.
 

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The line level amplifier (or control amplifier as some call it) is still the centerpiece of each high-end audio system. It is responsible for source selection, signal conditioning and volume control. It has to match the output of your source to the input of your power amp. It’s output stage must be able to drive any power amplifier through any length of cable with optimal quality via balanced and unbalanced lines.

The input of a pre-amplifier has to provide 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 on the way out of the signal chain. During our research and evaluation of the various approaches we settled for the most obviously "perfect" one - a transformer.

Advantages:
Inductive loads are very well received by almost all output topologies.
It provides complete isolation from the rest of the system.
It stops EMI/RFI and ensures truly balanced differential input.
To be fair, transformers have disadvantages - expensive and few know how to make them properly.


volume photoThe volume control of a pre-amplifier has to adjust the level of the input signal to the value required by the power amp without burying in noise the low level information and transferring enough power to properly drive the amplification stage without affecting it's operation.

Potentiometer and resistor ladders, as sophisticated as they might be, have a fundamental flaw. They operate by dumping the unnecessary signal across a resistor. It is like driving a car with fixed engine power (signal) and adjusting the speed with the brakes (resistor)!

Our solution is fundamentally different and as simple as it gets. We use transformer with various winding ratios and we switch between them. In the above example it will operate as a gearbox, transferring all the power of the engine at all speeds. In other words CONTROL.

The output has to provide an absolute optimum driving signal for the following power amplifier's input stage. This would include: low impedance, DC free, truly balanced, isolated from noise sources and the other components in the system. The solution yet again is a transformer. As a bonus it is the perfect load for vacuum tubes.

The power supply of Dionysos uses a very well-known but very rarely used arrangement. We use a C core transformer with a gap in the core to prevent any saturation of the core from distorted mains or a DC component in the mains. As the power transformer is in the same case we chose a design that has two identical sets of windings (essentially two transformers) on the same core. This way all the nasty magnetic and electrostatic leaks cancel each other out, and it does not influence any of the other components in the chassis.

To reduce power supply noise further instead of the normal arrangement of bridge rectifier and electrolytic capacitor bank we use a choke input full wave tube rectifier arrangement. This practically eliminates switching noise and anything that comes before the choke stays there. The other beauty of this topology is that the choke keeps the voltage on the capacitor bank pretty constant. In our case, this allows for a considerably small capacitor bank opening the possibility to use vibration resistant military paper in oil capacitors for the job that would last a lifetime.

chassis photoThe chassis to house all of the above had to be a masterpiece itself. Milled from solid plates of different thickness 6061T651 grade aircraft certified aluminium are interlocked together to form a ring like structure.

We have the power supply mounted on the left sidewall of this structure and the signal transformers on the right side. Two semi-flexible bars on which the motherboard and its heat sink are attached, which then support this ring. The top and bottom plates link all sides of the ring with the flexible bars and the feet made from carbon doped plastic on flexible screws. There are no screws visible anywhere on the chassis. And the chassis feels like a solid block.

The ergonomics. It does not matter how advanced a technology is, if it is not useful. We have tried to anticipate all the possible needs of our clients. The Dionysos has 4 inputs on RCA connectors and 2 inputs on XLR connectors. All inputs are balanced differential unless the grounding option is engaged on the RCA inputs. As we switch the ground plane when switching inputs there are no hum loops and induced ground noises, allowing for large setups with multiple sources powered from different mains outlets in the house. It applies for the outputs as well. For those that use bi-amping we have accommodated 2 sets of outputs active simultaneously. It might be considered legacy but we have implemented a buffered tape output that could be disengaged when not in use. We also have a level set function programmable on any input allowing the preamplifier to be in the loop of home cinema processors when the music and cinema systems share amps and front speakers. Controls are as simple as possible and self-explanatory, but we have also added an absolute phase switch with memory for each input. All functions are available on the supplied remote.
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