Thrax Orpheus MK3S, the LCR valve phonostage

Single input micro processor controlled phono stage based on tube gain stages and LCR correction. 3 separate inputs with two different loading via Lundhal step-up transformers.

Features

Built-in step up transformer
Programmable gain and loading
Accepts both balanced and unbalanced input signals on RCA and XLR connectors
Switches ground plane with input selection preventing ground loops
Balanced and unbalanced output
Programmable ground arrangement for large systems
Programmable absolute phase per input
Choke input rectifier for lowest switching noise
Shunt regulated constant current PSU for lowest noise and best dynamic behaviour
Modular construction
Microprocessor controlled
Interlocking solid aluminium chassis
Orpheus uses two tube gain stages with zero feedback and a passive LCR equalizer with 2 inputs on RCA and one 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 or induced ground noise.
The input stage is a super low noise D3a German Post tube used as a triode. Loaded by a constant current cascode it provides the necessary gain and output impedance to feed the custom passive LCR RIAA correction following it.
The switchable input transformer interfaces to MC cartridges and has selectable gain and loading impedance.
The equalization is passive and 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.
The equalization is realized through the use of constant impedance LCR filters using coils wound with OFC wire and silver capacitors.
This way the input stage sees a constant load, making its behavior predictable at any signal level.