Using circuitry pioneered in the ADAMANTINE and LOCKDOWN preamplifiers, and combining Phædrus Audio's unique signal processing for LP replay and stereo enhancement, the Phædrus Audio FLIGHT is our reference-quality, all-analogue phono preamplifier for real-time replay of records.
A checklist for the FLIGHT preamplifier.
As the perfect partner to the Phædrus Audio FLIGHT we are introducing the PHLUX-III active cartridge. With a hand made wood and brass body made by a recognised luthier, the PHLUX-III incorporates new amplifier technology with a bandwidth from DC to 2MHz. The stylus is a nude, square-shank, Shibata type.
Type: Phono preamplifier for: Phædrus Audio PHLUX active cartridges; or moving coil types in voltage mode.
Size: Two boxes: 220mm × 170mm × 55mm (L × W × H).
Phono cartridge input load: Active: or ≅100Ω (MC).
Input level: 10µA nominal; 5cm/s velocity at 1kHz, or 5mV at 5cm/s velocity at 1kHz, or 500µV at 5cm/s velocity at 1kHz
Transfer function: I or V → V; Overall - RIAA 3180µs, 318µs, 75µs curve. Non-inverting on pin 2 or XLR.
Output level: 0VU (standard recording level) = -10dBV. Max output = +24dB re. 0VU (+15dBu).
XLR polarity convention: Pin 2 is “hot”¹
1. According to AES 14 standard for professional audio equipment — Application of connectors, part 1, XLR-type polarity and gender. In turn, based on IEC 60268-12 Sound System Equipment Part 12: Application of Connectors for Broadcast and Similar Use, International Electrotechnical Commission, Geneva, Switzerland.
Phædrus Audio reserves the right to change specifications without notice.
Phædrus Audio believe we can benefit from treating the signal from the cartridge as a balanced signal.
The drawing (below A, B, & C) illustrates a normal turntable wiring arrangement. The cartridge coils are earth-free or "floating" (B). The right-hand signal appears across the red/green wiring pair: the left-hand signal across the white/blue pair.
Here we'll use the convention that RIGHT means the "hot" (positive) connection to the right-channel coil, and RIGHT means the "cold" connection. (With a similar convention for the left-channel signals and colours.)
These four, signal-carrying wires make their way along the arm-tube and pass out of the moveable part of the arm to a fixed termination arrangement (C).
Very often these wires are terminated so that the "cold" side of the cartridge connections RIGHT and LEFT) are commoned with the earth connections to the arm tube and the main-bearing sleeve (purple wire) as shown at C (straps A, B or both).
This is the only strategy possible if the the signal is to be sent to the preamplifier in an unbalanced (coaxial) signal cable, as shown at C. But it is non-ideal because various earth-borne leakage currents flow in the same conductors as the signals. This can result in hum and noise.
A better strategy is to wire the turntables with a high-quality balanced-cable which has a twisted pair of signal conductors and an overall braid and connect the signal to the preamplifier via a three-pin XLR connector. High-quality microphone-cable, right, is a good solution.
The cable is connected so that the the cartridge connects as a "floating" (balanced) signal and the braid connects the frame, bearing and arm earthing to the preamplifier earth.
Importantly, no connection is made between the "cold" signal side(s) of the cartridge (RIGHT and LEFT) and the frame connections or arm earthing in the deck itself.
The balanced connection is then brought to pin 2 and pin 3 of the XLR connectors so that RIGHT and LEFT connect to pin 3 respectively: and RIGHT and LEFT connect to pin 2. This is illustrated in the diagram at D.
By wiring the signals in this manner, the advantages of balanced signals are obtained — because any earth-borne currents are kept entirely separate from the signal currents.
A further advantage of this cabling scheme is that it enables us to get rid of the little earthing wire arrangement which is common with most turntables (at C). so, this also makes for neater cabling.
Many cartridges have an electrostatic screen around the electrodynamic motor which is connected, by convention, to the RIGHT signal terminal as shown schematically at B in the above drawing. An inadvertent extra earth connection is possible if the cartridge fixing screws make a further connection to the metal cartridge body — although this depends on the arm grounding scheme and if this connects to a conductive headshell (red star in drawing B above). The resulting ground-loop from the double-connection to the cartridge is something to watch out for as it can cause hum problems.
Some cartridge manufacturers helpfully make the connection between the metal screen and the right-hand signal "cold" via a metal tab which affixes to the RIGHT signal terminal of the cartridge. Shure Brothers always made this a feature of their cartridges, as shown left.
This tab may be carefully teased away from the connector pin if the screen is connected via another circuit. If your cartridge doesn't offer this provision, you will have to look at Nylon fixing screws or some other means to avoid the double-ground connection.
A word of warning: even greater problems arise if this electrostatic screen isn't connected to signal ground at all. So, if your cartridge does have a ground-strap, only disconnect it if you are sure the cartridge body is securely earthed via another circuit. The strap may be easily damaged during the process and difficult to reïnstall once removed.
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