The PHLUX cartridges address these problems very successfully. But customers have asked us for a solution so that they can use existing (non acitive) cartrdidges - especially those models known and admired for archive work (like the Shure V15).
For those customers, we have invented the PHLUX-AI. Instead of activating the cartridge, we have activated the interface (AI). This secures all the advantges of the PHLUX cartridges without active electronics in the cartridge or headshell. You can use a completely standard setup, and any connecting cable - the electronics in the PHLUX-AI compensates for all the shortcomings of the standard arrangement.
PHLUX-AI is particulaly valuable when used with moving-magnet cartridges, but there is also a moving-coil version.
Our tests have revealed that the PHLUX-AI is the first really innovative phono preamplifier in a generation!
The advantages of the PHLUX-AI are the following:
*Depending on mechanical nature of cartridge. But - if the mechanical system can respond up to 50kHz - the PHLUX-AI will recover amd amplify it!
The PHLUX-AI operates as a Maxwell bridge which compensates for the complex cartridge impedance and the complex impedance of the connecting cable and termination with complex impedances inside the PHLUX-AI unit.
A Maxwell bridge is a modification of the Wheatstone bridge. It is named after James Clerk Maxwell, who first described it in 1873.
After the unit is energised, or for a few seconds coming out of STANDBY mode, the CAL/PLAY light will flash as the bridge calibrates. During this period, outputs are muted. This allows for a very wide range of cartridges and cables. After that, the signals un-mute and the switches on the front adjust the fine-balance the bridge. See the USER INFORMATION for instructions on switch selection.
We wanted the advantages of the PHLUX cartridge, but we have a policy to use Shure V15 cartridge for archiving. With the PHLUX-AI we get the low-noise, level and extended bandwidth of the PHLUX cartridge using our precious Shure cartridges in our preferred headshells....
Here are the technical results in the frequency and time domain. Note how the cartrdige response, when coupled to the PHLUX-AI has less than 1dB variation from 10Hz to 100kHz: compare that with the ±3dB variation due to cable loading via the classic MM interface. Also note the time domain response, which rings due to unequal group-delay in the normal interface. This is eliminated with the PHLUX-AI. Oscillograms of the squarewave response of real cartridges, compared with the PHLUX-AI (with MM cart') are given.
In this section we have a demonstration of the PHLUX-AI, compared with a standard RIAA preamplifier.
Here's the results from the moving-magnet cartridge coupled with a standard RIAA preamplifier.
And here's the PHLUX-AI interfacing the same cartridge.
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Here, the same two files as in the example above are arranged to play simultaneously. A button ("Toggle") enables you to switch between the two recordings; enabling you to A/B compare the MM cartridge via a normal interface with the Phædrus Audio PHLUX-Active Interface.
Track 1 is the PHLUX-AI: track 2 the MM via standard interface.
There are several ways to set the fine bridge-balance switches on the front-panel of the PHLUX-AI preamplifier.
1. It is entirely possible to calibrate the bridge-balance by ear, provided you are methodical. In fact, this is an excellent approach. It should be noted, this is a fine balance adjustment, the tonal differences are subtle.
Set up the equipment and play a disc you know well, monitoring via the internal RIAA or iLOOP outputs. Select position II (both switches out). If the sound is a little “lean” (bass light), select position I, by depressing the left-hand button. If the sound balance is a little “rich” (bass heavy), select position III, by depressing the right hand button.
If you feel unsure about setting the bridge-balance by ear, Method 2 and 3 represent the engineer’s approach.
2. Consult the manufacturers’ information regarding the cartridge coil resistance and inductance. Once you have these figures, substitute the figures in the following equation,
Fine balance value = Coil inductance (in mH) / coil resistance (in ohms)…. Eq1
Select the fine balance switches according to the following rubric:
3. 
We have not always found that cartridge specifications are entirely reliable (due to manufacturing changes and different approaches to measurement), if you, or an engineer friend, can measure the coil inductance and resistance with a component bridge (as illustrated), then these values should be substituted in equation 1 to derive value mH/R, and used to select the fine balance setting accordingly.
4. Finally, ask us. We have an extensive cartridge database and can advise.
a. Ultimately, method 1 (by ear) is the easiest - and often the best - because the appropriate setting may compensate for an overall tonal-cast in the cartridge mechanical response.
b. Note that the position in which both buttons are IN is invalid. Once the left-hand switch is IN, the unit remains in balance setting I, irrespective of the position of the right-hand switch.
c. The Proster LCR Meter Digital Capacitance Inductance Resistance Tester: available from online retailers at a very reasonable price.
Size: PHLUX-AI: 112 × 50 × 225 mm (W-H-L)
Preamplifier Supply: DC input on screw locking connector.
Power: The PHLUX-AI preamplifier is designed to be compatible with European Commission's Regulation (EU) 2023/826 with the new rules from 2025. Consumption is less than ½ Watt in off/standby. The unit is intended to remain energised.
Sensitivity @ 5cm/s recorded velocity: Nominal 5mV RMS (-44dBu)
Input load: Active (Bridge-node)
Gain: See options. Nominal 0dB to iLOOP output in base version
Frequency response: ±1dB from 20Hz to 50kHz
Distortion: 0.005% THD at maximum output level
Dynamic range (wrt nominal sensitivity and un-weighted): 82dB iLOOP, (RIAA), and MAIN output
Maximum input signal: Nominal 85mV RMS (active)
Headroom (wrt nominal sensitivity): 25dB
iLOOP function: Cartridge level output for connection to subsequent RIAA preamplifier
iLOOP frequency response: ±1dB from 20Hz to 30 kHz
iLOOP output load: 47kohms (non-critical). Suitable for feeding any MM input
Phædrus Audio reserves the right to change specifications without notice.
Address all mail to sales@phaedrus-audio.com
