Thrax Audio introduction & Tech pt.3

GAIN

Finally, we reached the gain stage. The decision was to use the most linear device with zero feedback for this task, a vacuum tube, more precisely a triode vacuum tube. Contrary to general perception tubes are the most linear voltage amplifying devices, more than an order of magnitude better than transistors. They also have a very linear relationship of distortion and amplitude. Their harmonious distortion spectra makes them the most suitable for audio signal amplification. Most distortion artifacts are masked by the human ear internal working mechanism and are virtually and literary inaudible

Dionysos uses the simplest possible signal path with just a single tube with absolute zero feedback. The tube is configured with a transformer load giving the Dionysos' output the same abilities as to its input. It can float relative to its ground plane. This is just as important for the gain stage as for the input as we have to supply uncontaminated signal to the inputs of the power amplifiers referenced to their own ground planes undisturbed by the Dionysos power supply and inner workings.

Transformer coupling also greatly reduces EMI/RFI interference coming in through the signal cables (acting like antennas). Gain stages are sensitive to radio interference and it's best to avoid exposing their inputs or outputs to connections outside the screened box. Many designers use input buffers and output buffer stages to provide that isolation but this already raises the number of stages defeating the goal of simplicity and augmenting the sensitivity to RFI/EMI. Transformer coupling deals with this isolation beautifully without any extra complication.

Now that you are at ease that we have taken care of the faintest of signals and their delivery to your power amps let me tell you about another feature not found elsewhere.

When you adjust the amplitude at the input of the gain stage you can vary the output signal level but what you end up doing is that you reduce the signal at the output of the preamplifier but the noise floor of the gain stage is a constant as it is after the attenuator. It will remain there no matter how much you attenuate the signal, so you end up reducing the signal to noise ratio of your source each time you lower the volume. Yes this is correct. The active output stage will have a noise floor that you just can’t go below. That is a very serious limiting factor to almost all known line level pre-amplifiers on the market.

It is obvious and yet most designs are like that.

Then the obvious solution is the attenuation to happen after the gain stage. There are those who do that as we do in the Libra line level 300B pre-amplifier. In the Dionysos we have a more interesting solution.

We switch the gain of the tube stage using the same principle of the input attenuation. This allows us to optimize the gain/noise relationship maintaining the highest signal to noise ratio through the attenuation range. The used tube is low noise on its own but still, going from zero noise to some is a big jump. By using different transformer ratios we attenuate the tube signal including its noise but we have the ability to vary the amount of signal going to the tube with the input attenuation keeping the tube stage in its optimal for maximum signal to noise/distortion performance. This is achieved by switching the ratios of the tube stage output transformer. To go even further in order to supply such low level signals without any rise in the noise floor we revert to our most elegant and simple solution to extend that range.

We remove the gain stage of the pre-amplifier as contributor to noise and we use the inductive attenuation to reduce the output impedance of the source. Ah?!! What did I say.

Thrax is the ONLY company whose pre-amplifier goes from active gain to being an entirely passive device below a certain attenuation level. The noise contributed by gain stages is taken out of the equation with that of the attenuation remaining at as much as a 300Ohm resistor.

Staggering revelation but it explains why connecting a Dionysos between your super DAC with integrated volume control and your super power amp makes them sound even better.

No one else does that! And now you know why Dionysos is here for 20 years with no peer.