Spartacus is a statement. Demonstrating what can be achieved with modern directly heated triodes, advanced magnetic materials and the application of 21st century technology to a classic concept.
It is an engineering overkill in all aspects understated by the slim chassis.
A rebel in the world of “good enough”.
- Custom current production tubes for long life
- KR PX25 input/driver tube
- EML 520v3 output tubes
- 70w for ample power reserves
- Current sourced shunt regulators on output and driver for stable power allowing explosive dynamics and transparency even when handling the hardest loadsLow noise for subtle dynamics
- Transformer input and output for galvanic isolation
- Auto bias for compensation of tube ageing and correct operation
- Microprocessor controlled operation for safety
- Special filament heating circuit for harmonic richness and tube protectionSelectable gain and speaker impedance for interoperability
- Highest quality torque binding posts protecting your cables
- No electrolytic capacitors in power supply to avoid ageing
- Made in Bulgaria of all places – to puzzle the world – inexplicable!
Spartacus features one of the simplest possible signal paths with absolute zero feedback (wire-vacuum-wire-vacuum-wire). To achieve simplicity while delivering exemplary performance, each device in the signal path had to be the best possible.
Emission Labs and KR Audio manufacture a special breed of tubes called Directly Heated Triodes. They are the most linear amplifying devices and some of the very best audio tubes ever made.
It is a fact that the distortion of triode vacuum tubes compared to solid-state devices is orders of magnitude better.
Apart from the low distortion level, the type of distortion they produce is 2nd harmonic. To go further we employ a technique to eliminate the little distortion they would generate by running two of them out of phase so that they cancel out each other’s distortion. For this to work we designed a driver stage that would supply the two output tubes with exactly the same signal in phase for one and out of phase for the other by using another super linear DHT – the PX25. It is loaded with a perfectly symmetrical phase split transformer with independent windings providing separate bias to the output tubes. Not a popular approach to design, at the voltage and currents involved, as it is extremely difficult to produce. But rewarding when done.
The most linear DHT tubes have considerably low voltage gain and require high input voltage for full power.
Again we implemented an input solution with the cleanest possible voltage gain – a step-up transformer with switchable ratio.
Spartacus has one of the most sophisticated power supplies.
To reduce power supply noise we use a choke input full wave tube rectifier arrangement. This eliminates switching noise and this topology keeps the voltage on the reservoir capacitor bank constant. In our case, this allows for a considerably smaller capacitor bank using of the highest quality film capacitors. Power supplies operate best when the load presented is constant – namely, with constant current sourced shunt regulators. A constant current source is a device that passes the exact same amount of current no matter what happens on either end by varying it’s voltage and a shunt regulator that will try and keep a constant voltage across itself by changing its conductivity no matter what follows this.
At the voltages we operate it in, this has become possible only very recently.
We use a special technique to supply power to the heaters (filaments) of the tubes. Following a separate winding, rectifier and capacitors is a voltage regulator supplying an electronic choke isolating the filament from the DC source and counteracting modulation of the heater current by signal going through it. It is complicated but small things make a big difference.
As tubes age and cannot stay perfectly matched we designed a servo circuit that keeps the current in both output tubes constant and matched to a predefined reference. As tubes age and cannot stay perfectly matched we designed a servo circuit that keeps the current in both output tubes constant and matched to a predefined reference.
We use microprocessor control to make sure all is switched in the right sequence and that all separate systems function as expected.
In case of malfunction in any of the subsystems the amplifier shuts down to protect the tubes.
The chassis to house all of the above had to be a masterpiece itself. Milled from solid aluminium billets.
We have the power supply mounted on a mid level plate of this structure with the control board on top and the transformer and choke hanging below bringing the center of gravity low enough so the signal transformers can be mounted on the top plate to avoid magnetic interference.
The top and mid plates link the front and back plates forming a protected cavity housing for all the sensitive electronics.
There are no screws visible on the chassis. And the chassis feels like a solid block.
1 unbalanced RCA connector
1 balanced XLR connector
Output Power up to 70W in 4Ω or 8Ω
Power supply 115 or 230V
Power consumption 380W
Weight 35 Kg
Dimensions 210W x 440D x 420H mm
1x PX 25 amplification
2x EML520B-V3 amplification
Г-811 (G-811) shunt regulator
СГ-13П (SG-13P) voltage reference
2 х 6Д22С (6D22S) rectifier
Operating Manual http://thraxaudio.com/pdf/Operating_Manual_Spartacus.pdf