The PHLUX cartridges address these problems very successfully. But a few customers have asked us for a solution so that they can use existing (non-active) cartrdidges - especially those historical models known and admired.
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.
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 and 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 and cartridge compatibility.
See Afterword 14 for a taste of the technical description of the preamplifier as it will appear in the new edition of the Needle-drop Handbook.
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....
It may seem illogical to have a PHLUX option for this preamp'. The reason is, commited PHLUX active cartridge users want to be able to enjoy the high-performance WV2 RIAA preamplifier option with its enormous amplification and headroom. Therefore, a version of the PHLUX Active Interface is available with PHLUX phantom power.
Here are the technical results in the frequency and time domain. Note how the cartridge 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 as they trace a zig-zag groove, compared with the PHLUX-AI (with MM cart') are given. Note how the transient response of the MM cartridge via the PHLUX-AI is better than either MM or MC.
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 with valve-based Neumann WV2 RIAA stage.
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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 MM via standard interface.
Standby/CAL-PLAY
The right-hand Standby/CAL-PLAY switch is straightforward. When the unit is not in use, this switch should be in the out position. Depress this switch when the unit is required for use. The green front-panel LED will flash for several seconds as the bridge-circuit calibrates.
I, II, III
The buttons on the left-hand side of the panel operate in various ways, depending on the configuration of the PHLUX-AI preamplifier. The most important rôle they play is in fine bridge-balance when operating with moving magnet cartridges.
They play other roles when the unit is in different configurations:
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.Note a
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.Note b
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:
Here's a calculator to help you...
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 colleague or friend, can measure the coil inductance and resistance with a component bridge (as illustrated),Note c 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.
When the PHLUX-AI has either the PHLUX or MC option installed and the WV2 RIAA option, these switches are used to select various record deëmphasis characteristics.Note d The switches positions are as follows:
c. The Proster LCR Meter Digital Capacitance Inductance Resistance Tester is illustrated: available from online retailers at a very reasonable price.
d. Note that when the unit has either PHLUX or MC options fitted, but the WV2 RIAA option is not fitted, the left-hand switches are inoperative.
Size: PHLUX-AI: 112 × 50 × 225 mm (W-H-L)
Circuit: First- and last-stage of Neumann WV2 playback equaliser for the AM-32b lathe
Performance as of MM. Phantom supply provided at input connector.
Specifications
PHLUX-AI Preamplifier
Preamplifier Supply: DC input on screw locking connector.
Power: The PHLUX-AI preamplifier (even when valve RIAA stage is fitted) 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 30dB to OUT: 0dB to iLOOP output in base version
Frequency response: ±1dB from 20Hz to 50kHz
Distortion: 0.05% THD at maximum output level
Dynamic range (wrt nominal sensitivity and un-weighted): 87dB iLOOP and MAIN output
Maximum input signal: Nominal 130mV RMS
Headroom (wrt nominal sensitivity): 28dB above standard recording level
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
Options
Moving coil cartridge option
Gain: 53dB to OUT: 65dB when RIAA fitted
Sensitivity: Nominal 500µV RMS (-64dBu)
Dynamic range (un-weighted): 96dB iLOOP and MAIN output
Frequency response: ±1dB from 30Hz to 20kHz
Distortion: 0.1% THD at maximum output level (1kHz)
Valve (tube) based RIAA output - replaces iLOOP output with equalised, line-level output
Valve type: Medium-μ Electronic Tube™ triode model
DC bias: 1.5V LEDs in place of Neumann's nickel-cadmium STABILYTs
Gain (to RIAA output): 45db/65dB (MM & PHLUX/MC) at 1kHz; RIAA curve
Dynamic range (un-weighted): 96dB iLOOP and MAIN output
RIAA response accuracy: Exactly emulates WV2 transfer function (RIAA)
RIAA IEC amendment: Not implemented; two-pole rumble filter implemented: -1dB@30Hz; -3dB@22Hz; -15dB@10Hz; -40dB@3Hz
RIAA Neumann Pole or eRIAA: Never existed and not implemented
Maximum output signal level:+26dBu output
PHLUX active cartridge option
Appendix - ZWEIKANAL-WIEDERGABEVERSTÄRKER WV2
TWO-CHANNEL PLAYBACK AMPLIFIER WV2
The Neumann WV2 is a vintage Zweikanal-Wiedergabeverstäker (two-channel playback preamplifier). The unit was originally designed for professional vinyl mastering and playback systems. Introduced in 1958, the WV2 was built for demanding, professional use and had a price tag to match. (DM1288 is equivalant to about €5000 today.) Today, the mono WV1 and stereo WV2 are considered the Holy grail of phono preamplifiers, coveted by enthusiasts seeking the best audio fidelity.
Why is this preamplifier so highly regarded?
Here is our circuit analysis which underwrote our implementation of the important characteristics of the Neumann WV2 in the PHLUX-AI preamplifier. These are explained.
Finally, there is our translation of the German manual.
The "core" of the WV2 amplification and equalisation circuitry is illustrated below. The three stages may be considered to be: the input transformer; the first-stage triode stage; and the equalisation stage. The third-stage operates by employing frequency-selective feedback around a high-gain pentode stage. Both valves are EF804 pentodes, Rö1 strapped as a triode. These two stages, along with the output stage and transformer account for the rather special performance of this circuit.
The rare BV33 transformer was made by Haufe for Georg Neumann company in Berlin. Neumann used this transformer in various broadcast studio preamplifier/equalisers. The transformer has a massive 1:50 step-up ratio and was designed to be used with the Neumann DST-62 moving-coil cartridge and other units by Ortofon and EMT. Remember, this was the period when the only high-quality pickups were moving coil types tracking at downforces (say 60mN) which are eye-watering today! The modern moving-magnet type cartridge is a relative newcomer in the world of vinyl replay. The originators of the moving magnet principle were ELECTROACUSTIC GmbH in Kiel, Germany. They patented the idea in 1957 and licensed the concept to Shure Brothers Inc., who remained adamant supporters of the moving-magnet cartridge type.
One of our objectives in developing the PHLUX-AI preamplifier was to support the mechanically superior (but electrically inferior) moving-magnet cartridges. This is the origin of the active bridge input stage of the PHLUX-AI preamplifier. See the Needle-drop Handbook for more information. In the PHLUX-AI the transformers are replaced by a unique electronic stage with noise which betters the performance of the original WV2.
The RIAA (or DIN) equalisation stage is built around an EF804 pentode stage. This configuration was very common in both high-quality domestic replay amplifiers, and professional units - for example, the BBC's broadcast AM16/1 Disk Reproducing Amplifiers (See BBC Engineering Division's Technical Publications Department Technical Note AM16/1).
The midband gain of the pentode stage is very substantial (more than 40dB). Yet, the closed-loop gain of this stage (at 1kHz) is only 6dB. A great deal of loop-feedback is therefore present and distortion is therefore very low: about 0.02% on the basis of a 50mV RMS signal from the pickup. Similarly, the bandwidth of this circuit is extended, with a -3dB point at about 200kHz.
This stage is clearly not the origin of any bandwidth restriction or distortion which we might conjecture has an effect on sound quality. Moreover, given that this circuit operates at a relatively high level, it has very little effect on noise performance either. It's "magic" lies in its implementaion of the equalisation. This we analysed and measured carefully and we have implemented an exact copy of this in the EQ in the PHLUX-AI unit.
Unlike the second-stage, this stage uses a pentode valve, but with g2 and g3 strapped to the anode, so that it operates as a triode. (The technique of connecting both the screen-grid and the supressor-grid to the anode is an old Neumann trick - used for example for the VF14 valve in the U47 microphone). No data exists of the EF402 operating in this mode. And this is especially important in this context because it is röhre 1 which dominates the performance of the WV2 unit in terms of: bandwidth (-3dB at 40kHz); noise (mostly mysterious - and unpredictable - flicker noise); and distortion (around 0.2% for a maximum signal from the pickup.)
We measured these effects carefully (with a range of tubes of different age) and have implemented the same performance in the Electronic Tube™ stage in the PHLUX-AI preamplifier RIAA option.
Note that the cathodes of both Röhre 1 ans 2 are biased with batteries. These are the infamous nickel-cadmium STABILYT components, developed by Neumann. These ensure a "solid" DC condition at the cathodes of both circuits. Rather than use batteries of any sort, we use LEDs.
The output stage of the WV2 preamplifier is a E88CC triode driven transformer stage with an anode load formed of the Bv32 choke. The whole stage is "wrapped" in feedback so that the closed-loop gain of this stage is 0dB. Maximum (unloaded) output from this stage is about 20V RMS (27dBu). This huge output level is matched in the PHLUX-AI preamplifier.
A translation of Neumann's German manual for the WV2 follows.
AREA OF APPLICATION
The WV2 playback amplifier is used primarily in recording studios as part of high-quality stereo record playback systems as well as in the record industry for calibrating stereo record transfer systems and as a control amplifier.
The outputs of the WV2 playback amplifier allow the connection of all common loudspeaker amplifiers and control instruments.
The WV2 playback amplifier is designed to raise the low audio frequency voltages, as they are emitted by high-quality dynamic stereo pickups - e.g. the NEUMANN stereo pickup DST - to the standard level of + 6 dB (1.55 V) that is usual in studio operation and at the same time to equalize the frequency response of the sound recording so that a linear frequency curve is produced for the output voltages.
The playback amplifier is designed and constructed in accordance with DIN 41190, also in a version WV2, for rack installation, size 2U. It can be supplied for a 19" rack width on request.
The WV2 consists of two identically constructed, four-stage, multiple negative feedback voltage amplifiers and a common power supply.
Each amplifier unit has a potentiometer for setting the desired gain. These potentiometers are primarily used to adjust the two channels to the same output level. The operational volume control, however, should be carried out using a suitable downstream dual level control outside the amplifier.
To avoid overloading the input stages at higher input levels, the inputs of both amplifier units can be made approximately 20 dB less sensitive using a common switch.
The two channels of the amplifier can be set - also using a common switch - to three different equalizer frequency responses, which below 1000 Hz correspond with high accuracy to the recommendations of DIN, RIAA or NARTB (see curve representation). The curve is characterized by frequency-dependent elements with the time constants 318µs and 3180µs.
Normally the amplifier is set to the DIN frequency response in switch position "A" and to the RIAA frequency response in switch position "B", i.e. the elements that are decisive for the treble reduction are characterized by the time constants 50µs (DIN) and 75µs (RIAA). The reduction of the higher frequencies can be changed separately in the device for each switch position by turning the correspondingly marked trimmers. The setting range is indicated in the curve display. This enables exact equalization of all currently used cutting characteristics. The switch position "Measure" results in a linear frequency response above 1000 Hz, which is intended for playing measuring records and for calibrating stereo record cutting systems.
The output transformers each have two equivalent secondary windings and can therefore also be used as differential transformers, e.g. if the lateral and vertical components of the voltages are to be obtained individually from a 45° recording.
Üpertragungsbereich (transmission range, passband): 30 - 15kHz
Frequenzgänge (frequency response): gem. Kurvendarstellung (see curves)
Eingangsanpassung (input adjustment): 1) Dynamic pickups with internal resistance of 10 - 20Ω
2)For negative feedback amplifiers GV2
Ausgangspegel (output level): +6dBu (1.55V RMS, +2VU)
Ausgangsquellwiderstand (Output source resistance): 35 Ohm
Abschlusswiderstand (terminating resistance): >200 Ohm
Verstärkung bei 1kHz (gain at 1kHz): 50/70dB, umschaltbar (switchable)
Eigenstörspannung (self noise voltage): <1.5mV
Klirrfaktor (distortion): <0.4%, 40 to 10kHz
Übersprechdämpfung (crosstalk): >40dB
Konstruktionsausfuhrung (design execution): DIN 41490 or 19" rack
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