Phono Preamplifier with LCR RIAA equalizer

The phono preamplifier is responsible for extracting the last bit of information from the cartridge by providing optimal loading while maintaining very high noise immunity. After vastly amplifying the input signal and applying the standard RIAA equalization it interfaces at line level with the rest of the system via balanced or unbalanced lines. The LCR method used to apply the RIAA correction is very rare due to complexity and cost.

Orpheus 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
  • Programmable ground arrangement for large systems
  • Balanced and unbalanced output
  • Programmable absolute phase per input
  • Shunt regulated constant current PSU for lowest noise and best dynamic behavior
  • Choke input tube rectifier for lowest switching noise
  • Custom vacuum encapsulated signal relays for ultimate sound and reliability
  • Modular construction
  • Microprocessor controlled
  • Interlocking solid aluminum chassis
  • High reliability and MIL spec parts

Orpheus uses two tube gain stages with zero feedback and 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 and 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 BeeWax impregnated paper capacitors.

This way that the input stage sees a constant load, making its behavior predictable at any signal level.

The power supply of Orpheus uses a choke input full wave tube rectifier 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. In our case, this allows for a capacitor bank made with vibration resistant military paper in oil capacitors to last a lifetime.

All this is governed by a microprocessor switching the appropriate combination of relays and monitoring the status and incoming command.

The chassis is milled in house from solid plates of different thickness aluminum that 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.


  • Tube compliment:
    - 2 x D3a amplification
    - 2 x 6C4П amplification
    - 1 х 6Ц4П rectifier
  • Inputs
    - 2 x RCA and 1 x XLR – MM or MC phone cartridges
  • Output
    - RCA or XLR
  • Power consumption: 50W
  • Dimensions: 432W x 400D x 120H mm
  • Weight: 15 kg
  • Finish: Black or Silver anodized aluminium