PHONO PREAMPLIFIER WITH LCR RIAA EQUALIZER
Multi-input microprocessor controlled vacuum tube phono equalizer with LCR correction.
Built-in moving coil step-up transformer
Programmable gain and loading per input
Switches ground plane with input selection preventing ground loops
Balanced and unbalanced outputs
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 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, unless the grounding option on the RCA inputs is engaged referencing all to the system ground. Switching the ground plane only to the active input ensures there are no hum loops or induced ground noise even with multiple turntables. The input stage is a super low noise D3a German Post tube. Loaded by a constant current cascode it provides the necessary gain and output impedance to feed the custom built passive LCR RIAA correction following it.
Equalization is realized through the use of constant impedance LCR filters using coils wound with OCC wire and copper foil capacitors. This way the input stage sees a constant load (resistor) at all levels and frequencies, 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. All this is governed by a microprocessor switching the appropriate combination of relays and monitoring the unit’s status and incoming commands.
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.
The chassis is milled in-house from solid plates of different thickness aluminium 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 machined plastic on flexible screws to prevent scratching and allow for use on uneven surfaces. There are no screws visible anywhere on the chassis. And the chassis feels like a solid block.
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.