"Ruby STD" Preamp Line Stage
 5687WB – NOS JAN PHILIPS USA military dual Triodes
 12B4A – NOS JAN GE USA military Triode
This preamp uses the latest development in grounded grid configurations which surpass all our previous designs. In addition to this new circuit configuration, while lab experimenting we happened to stumble upon an observation of stupendous consequences that would have seemed impossible beforehand. We have not only managed to simplify the circuit using less parts, but have allowed 3 useful and necessary functions to be performed by one passive component.
As a consequence we can with certainty state that this line stage is the fastest possible using tube circuits. While it would be possible with solid state devices to reach these speeds, very few of the ultra high end solid state line stages that we are aware of approach this extreme bandwidth in actual performance. Not only is it flat from 20 Hz to 250 KHz but extends way out past 1,000,000 Hertz. As always the three stages are non-inverting maintaining absolute phase.
While the grounded grid configuration is known for its extremely wide bandwidth, this circuit has moved the bar way beyond the capabilities of any other tube configuration, including grounded grid circuits from other manufacturers. [ OK, we only know of 1 other > [ Transcendent Sound ]
The buffered output is capable of driving two pairs of outputs to accommodate bi-wiring or bi-amping. All stages are DC coupled and only one Teflon signal capacitor is used in the output stage for DC blocking. No feedback and mirror image circuitry is implemented in the audio section for best channel separation.
The parts quantity is the lowest count yet achieved, using a superior Grounded Grid circuit over previous designs. This allowed us to use the highest quality parts while limiting cost due to the lower parts count and without resorting to using two chassis to implement this design, while at the same time exceeding the specifications of all previous line stages in the past. No tube product could hope to compete with the Ruby STD unless they copied the circuit and parts verbatim. The circuit cannot be simplified further and the parts cannot be substituted including the tube types. We have finally achieved the criteria of Einstein’s thoughts that ... “things should be as simple as possible, but no simpler.“
We chose to append this Ruby with the abbreviation “ STD “ meaning this is the STANDARD circuit by which all other tube circuits will be compared to and for which none can duplicate it’s sonic attributes without outright cloning it. This is undoubtedly fighting words for all challengers, at all price points, come what may. There are no words to describe the majestic sound when operated with appropriate legendary products.
A Toroid power transformer is employed to eliminate mechanical hum and contain the magnetic field from radiating to surrounding areas. A choke LC filter is used for the 300 Volt plate supply that effectively reduces ripple and noise to zero.
Because our unique circuit operates with very low power requirements, it wasn’t difficult to build the perfect DC power supplies needed for this exceptional line stage. The use of pure DC 12 Volt power to the filaments insures that no AC ripple [120 Hz] will effect the audio signal.
- Machined aluminum plates [1/4” & 1/8” thick] bolted together with stainless steel machine screws is used to construct the preamp chassis. This provides excellent shielding from external radio frequency fields.
- Custom plated brass designer knobs with a Titanium look and notched indentation allow for precise settings. These knobs have dual hex set screws to secure to the shaft that insures accurate calibration and smooth reliable operation of switches
- The stepped ELMA dual Volume control has 24 gold plated contacts with surface mounted 0.1% precision resistors to maintain channel balance to within +/- 0.05db
- Selector and Tape Monitor switches control relays and are not in the signal path
- Tape Monitor switch can also function as a processor loop
- Balance control uses a sealed Electroswitch with silver plated contacts and 1% Vishay precision resistor networks
- NKK toggle switches for Tape monitor, Muting & Power on functions
- Noiseless TOROIDAL power transformer
- Non magnetic stainless steel and brass hardware is used throughout
- Automotive high gloss paint finish
- Polished Brass Handles accentuate the aesthetics of the front panel
- Herbie’s tube damping isolators are used to restrict microphonics
This preamp is hand built and each component is soldered by hand to insure a good solid joint. The double sided printed circuit board [ PCB ] has been manufactured with the highest quality standards in the industry.
It has full solder masking on both sides of it's premium glass epoxy board with white silk screening that identifies parts and there placement for fast efficient hand soldering and assembly. These boards are held elevated from the surrounding metal chassis to avoid capacitive coupling between components.
High quality Teflon coated Silver plated OFHC copper wiring is used in all analog wiring to and from the circuit board. Dual timing circuits control power up sequence and muting on power up.
AUTOMATIC POWER SEQUENCING & MUTING
To allow for extended tube life a 30 second delay is applied before the high voltage plate supply is engaged. To allow circuit stabilization and quite operation a 90 second automatic muting is activated during power up. Muting is accomplished using a double pole relay that shorts the preamp outputs. When disengaged the muting circuit is not in the signal path.
|FREQUENCY RESPONSE: [ reference to a sine wave at 1KHz @ 2 Vrms output ]||+/- 1 dB 9 Hz to 1.25 MHz|
|GAIN:||12 db [ 4 x ]|
|INPUT IMPEDANCE:||45K ohms minimum|
|CHANNEL BALANCE CONTROL:||11 position for +/- 5 dB adjustment in 1 dB steps|
|ATTENUATION:||24 position stepped volume control [ -60 dB to 0 dB]|
|OUTPUT IMPEDANCE:||450 Ohms|
|RATED OUTPUT:||3.5 Vrms [ maximum = 15 Vrms ]|
|OUTPUTS:||2 pre-amp outputs, 1 tape output, 1 line level output|
|INPUTS:||4 line level inputs, 1 tape input|
|FUNCTION:||A processor loop can also be used using the tape in/out connection|
|POWER REQUIREMENTS:||115/230 Volt 50/60 Hz 51 Watts [ 64 VA ]|
|NET WEIGHT:||15 LBS ( 6.8 KG)|
|SHIPPING:||18 LBS ( 8.2 KG.)|
|DIMENSIONS:||15” W x 10.875” D x 3 3/4” H|
|LIMITED WARRANTY:||[ TUBES & COMPONENTS ] 5 YEARS PARTS & LABOR|