PHONO PREAMPLIFIER WITH LCR RIAA EQUALIZER
Orpheus Signature is our ultimate take on the subject of phono equalization.
Thrax uses the very rare LCR type of equalizing circuit as the core of a feature and functionality rich pure tube phono preamplifier. Most notable features are:
Built-in moving coil step-up transformer
Programmable gain and loading per input
Switches ground plane to the active input selection only preventing ground loops
Balanced and unbalanced outputs
Programmable ground arrangement for large systems
Programmable absolute phase per input
Choke filter for lowest switching noise
Active elements on a suspended platform with high damping and low resonance.
Nanocrystal inductors and OCC wiring
Shunt regulated constant current PSU for lowest noise and best dynamic behavior
Interlocking solid aluminum chassis
Orpheus is a modern masterpiece that uses only two vacuum tube gain stages with zero feedback and a passive LCR equalizer between them. Moving coil sources are handled by a built in step-up transformer taking advantage of its balanced differential nature. Switching the ground plane only to the active input ensures there are no hum loops or induced ground noise even with multiple turntables.
The switchable input transformer interfaces to MC cartridges and has selectable gain and loading impedance, while MM cartridges connect directly to the grid of the input tube. The equalization is passive and of the constant impedance type. The next stage is another super low-noise tube loaded by a transformer to bring the signal up to the necessary level and provide complete isolation of this sensitive circuit from the following components. The filter is out of any gain loops and sits between the two gain stages protected from any unpredictable influences.
Equalization is realized through the use of constant impedance LCR filters using coils wound with monocrystalline wire on toroidal nanocrystalline cores. This way the input stage sees a constant load (resistor) at all levels and frequencies, making its behavior predictable like a resistor at any signal level.
The power supply uses choke filter arrangement. This eliminates switching noise and any other disturbance that comes before the choke. The other benefit of this topology is that the choke keeps the voltage on the capacitor bank constant. All this is governed by a microprocessor switching 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 aluminium that are interlocked together to form a ring-like structure dissipating unwanted vibrations while the circuit board is suspended on gel dampers internally to “float” immune to interference.
Orpheus Signature is the ultimate tool for the analog lover with multiple sources as it presents unprecedented flexibility with a sound like no other.
SILVER ANODIZED ALUMINUM
BLACK ANODIZED ALUMINUM
Introduced in 2011 for the first time, the unit featured an XLR input allowing balanced cable runs for specific tonearm/cartridge combinations.
In 2017 a revision was made to the loading of the first tube and the coupling of the LCR circuit allowing the gain a few extra db of amplification. At this stage we also removed the rectifier tube replacing it with a pair of silicon carbide diodes and a better magnetically and electrostatically shielded power transformer. Those units are known as v2. Unfortunately for second hand buyers there are no visible differences between the first and second generation units. Signal path components are the same but v2 has a significant sonic advantage.
Current 2020 v3 has no XLR input on the back and a few changes to the power supply, shunt regulators and components used to push the performance even further. Also, now available officially at a substantial premium is a SE version with a silver input transformer, Teflon/copper capacitors and an OCC output transformer on 50u GOSS (built on order). These units are indicated with an “SE” marking on their serial numbers.