hen thinking about headphone amplifier, we usually mean small or even portable devices, often integrated with digital-to-analogue converters. As examples, we could use iFi Audio products, such as Micro iDSD Black Label and Nano iDSD Black Label, but also Luxman DA-150. These are devices that fit both the beginner and advanced-user systems. We make an exception to this rule for tube headphone amplifiers, such as our reference Ayon Audio HA-3 with 45 triodes in the output stage or presented during the last High End Show in Munich V16 Single Ended by Octave featuring KT-family tubes.

The Luxman P-750u is still different. It comes to us in a large box, that reminded me of the one I received the Luxman L-550AX MARK II in, an integrated beast working in class A, delivering 40W per channel into 4 Ω load. It turns out that such a large box is not at all exaggerated – I knew it once I picked it up. The Luxman integrated weighed less than 24 kg, and the P-750 weighs more than 13kg! And although the headphone amplifier is lower, the width is the same and it is deeper. It is a mechanically and electrically refined device that is not an "addition" to company's lineup, but an equivalent product, possibly even an apple of Luxman engineers eye.

| P-750u

The device has a very solid mechanical construction. It's built on the basis of a steel chassis, features also a cover made of a thick, bent steel plate. And only the thick front is made of aluminum. The engineers made sure that eddy currents would not form in the chassis, electrically separating the upper wall and connecting it to the chassis only in one point, and the whole was placed on feet made of high-carbon steel, characterized by excellent vibration damping.

The front wall is not empty at all – there is a large volume knob, smaller one for balance between the channels and two more, which allow user to change sensitivity and inputs. Two buttons with amber LEDs are used to change outputs and to activate "bypass". Knobs are made of aluminum, knurled, so the amplifier is pleasant to use. When changing the input or output you will hear nice clicks of three relays - this is the output muting circuit, which works together with the output stage protection system.

The P-750u is a balanced design, from input to output. However, it is also possible to use combinations of balanced and unbalanced inputs and outputs, which is possible because of use of a circuit that symmetries or de- symmetries signal. The idea is to amplify signal always in a symmetrical circuit, no matter what signal we deliver to it or expect at the output.

There are three headphone outputs:

• a standard stereo jack (unbalanced) ø 6,3 mm,
• a stereo pair of balanced 3-pin XLR
• 1 x 4-pin XLR balanced

The latter features widely spaced sockets (18 mm) so that you can use cables with thick plugs. There is also a "pass through" output delivering signal straight from the input. It allows user to insert this headphone amplifier in the existing system between the signal source and the integrated amplifier. At the XLR inputs there is an absolute phase switch - by default, the amplifier is wired in "American" way, with pin 3 "hot", i.e. according to the standard introduced by the inventor of this type of link, the American company Cannon. In Europe, the AES standard was used, ie with the "hot" pin number 2 and for a long time it has been de facto a standard. Luxman gives you the option of choosing between them.

The inputs are activated by a small, solid switch on the front panel. After switching, the amber LED lights up at the relevant socket / sockets. The device is also equipped with a step sensitivity switch, which adjusts the gain to the headphones used. It works together with LECUA, known to us from the integrated amplifiers of this manufacturer, advanced volume control system. The amplification takes place in the three-stage Darlington system, with parallel input circuits and three pairs of output transistors; the input features integrated circuits, but the gain section is completely solid-state. The very low distortion level is achieved via usage of a variant of the patented by Luxman, feedback system called ODNF.

LECUA – LUXMAN Electrically Controlled Ultimate Attenuator, is a highly precise attenuator featuring switched resistors. It has 88 steps - from 0 to -87 dB - and changes the volume without compromising the quality of the signal. At a given volume level, the music signal passes through only two resistors. Due to its design, there is no deviation in it, caused for example by the aging of the resistance track, so it will serve well for a very long time, also maintaining a precise balance between the channels.

ODNF – Only Distortion Negative Feedback, it's an original amplification feedback circuit that achieves a high-speed primary slew rate, ultra-wide bandwidth and low-level distortion by feeding back only the distorted elements of the audio signal from the output amplification circuit. The design of the P-750u has resulted in even lower output impedance and a higher signal-to-noise ratio, due to a paralleled first stage and a Darlington-equipped second stage amplification circuit. The P-750u features the very latest version of ODNF, Version 4.0, offering improved accuracy in detecting distortion by using a triple-paralleled input stage error detection circuit.

The device features an enhanced high capacity power supply, contributing to the considerable weight of the P-750u. It is based on a large OI transformer with three secondary windings for: output stage, control stage with LECUA system and for a microcontroller controlling systems and protection circuits. High-speed Shottky diodes and large filtering capacitors cooperate with them. The output section is not regulated, because it resembles the output of a classic power amplifier - 4 Ω in class A is half of what the 300B tube offers! In turn, the driver and the LECUA system are supplied with regulated voltage.

It is a very solid, well-made device, delivered with a detailed instruction which includes a block diagram of the device. Replacing the previous model, the P-700, the reviewed device is currently the top headphone amplifier in Luxman's lineup.

BALANCED OUTPUTS

The Sennheiser IE 800 S headphones we have recently tested feature a balanced connector called the Pentaconn Connector. It is a headphone plug with a diameter of 4.4 mm with five separate contact elements - the tip, three rings and ground. It was developed by Japan Electronics and Information Technology Industries Association (JEITA), a body similar to the German DIN organization. Thanks to the support of the household appliances market leaders, such as Sony and Sennheiser companies, this plug has a chance to become a standard for mobile devices.

In the world of "big" audio this standard is not used and should not be expected to. Currently, four types of balanced headphones plugs are used. The most common are two three-pin XLR plugs, featured in the tested Luxman, with separate plugs for left and right channel and two unbalanced big jack plugs ø 6.3 mm, which we know for example from the D/A converter and headphone amplifier Chord Hugo TT. We rarely encounter a four-pin XLR plug, in which separate signals for the left and right channel are carried out, and for example, in their devices, ASUS uses two "mini" XLR male connectors - see the Essence III.

The P-750u headphone amplifier was compared to two other amplifiers used in the "High Fidelity" reference system: Ayon Audio HA-3 (tube) and Bakoon HPA-21 (transistor, current output); both offer unbalanced outputs. The source of the signal was Ayon Audio CD-35 HF Edition SACD player (RCA input) and Lumïn T1 audio file player (XLR input). In both cases, I used Acoustic Revive cables, RCA-1.0 Triple-C FM and XLR-1.0 Triple-C FM. To power the amplifier I used the Acoustic Revive Power Reference Triple-C cable.

Listening sessions were performed using three headphones: HiFiMAN Edition X V2 i HE-1000 V2 and Sennheiser HD800. All three models featured Forza AudioWorks Noir Hybrid HPC cables. For HiFiMAN I ordered them in a new configuration with LEMO plugs. These are one of the best currently available ones.

Together with cable I received three types of adapters:
| LEMO→ Furutech big jack,
| LEMO→ 4-pin XLR Furutech,
| LEMO→ 2 x 3-pin XLR Furutech.

Thanks to them I could assess amplifier using all of its outputs – I will describe differences between them. For the Sennheiser I have an earlier version of Forza AudioWorks Noir Hybrid cable, but with a 4-pin XLR adapter which allowed me to use HD800 with two Luxman outputs: Furutech big jack and 4-pin XLR Neutrik.

Recordings used in the test (a selec- tion)

| Compact Disc/SACD

• Blade Runner, soundtrack, reż. Ridley Scott, Atlantic Records/Audio Fidelity AFZ 154, „Limited Numbered Edition | No. 2398”, SACD/CD (1982/2013)
• Bogdan Hołownia, Chwile, Sony Music Polska 5052882, Master CD-R (2001)
• Dire Straits, Dire Straits, Vertigo/Universal Music LLC (Japan) UICY-40008, Platinum SHM-CD (1978/2013).
• John Coltrane, Coltrane, Prestige/Analogue Productions CPRJ 7105 SA, SACD/CD (1956/2012)
• Nat ‘King’ Cole, The Nat King Cole Love Songs, Master Tape Audio Lab AAD-245A, „Almost Analogue Digital”, Master CD-R (2015);

| Tidal

• Aretha Franklin, A Brand New Me: Aretha Franklin (with The Royal Philharmonic Orchestra), Rhino/Atlantic/Tidal, MQA Studio 24/44,1 (2017)
• Art Blakey & Jazz Messengers, Three Blind Mice, Blue Note/Tidal, FLAC 44/1/16 (1962/?)
• Four Tops, Four Tops – Second Album, Motown Records/Tidal, MQA Studio 24/192 (1965/?)
• REM, Automatic For The People, Warner Bros./Tidal, MQA Studio 24/192 (1992/2017)
• Robyn, Do It Again, Arts & Crafts/Tidal, FLAC 44/1/16 (2014/?)
• Steve Wonder, Intervisions, Tamla/Tidal, MQA Studio 24/96 (1973/?)

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Japanese issues available at

The thing you can hear from the very beginning, from the first album, the first track and which stays with us to the end, regardless of what we say about this amplifier, it's the perfect control over the headphones. The best ones need a lot of power, regardless of whether they are planar-magnetic or dynamic designs. The Luxman amplifier controlled all my cans perfectly, even over such a difficult model as the HE-6.

With the HE-1000 v2 I set the input sensitivity to "mid" - with jazz and hi-res tracks the volume knob usually operated in the third quadrant, which is probably the optimal setting. In turn, with strongly compressed music, such as Röyksopp and Robyn, and their Monument, played from Tidal in various versions, the knob was in the second quadrant. So I tried to reduce the sensitivity of the system and switched the knob to "Low". The sound became more effortless, but the drive disappeared, which is so important here. Although - theoretically - I should listen to club music, rock, pop, etc. in this way, in the end, all auditions with HiFiMAN headphones were carried out in the "Mid" position.

| Outputs – comparison

Comparison of outputs in the tested amplifier was enlightening. Each of them sounds different; of course, the output does not "sound" itself - it modifies the sound, but I will use this type of terminology to make it simple. The fact that the unbalanced output will sound differently than the balanced one could have been expected, but it was completely surprising that both types of balanced outputs behaved differently.

Let's start with the basic difference, i.e. between the stereo jack and both types of XLRs. I would not like to generalize it, I am talking about this particular device now, but there is no doubt that the balanced output is the right one. If I did not carry out such a comparison, it would not be so obvious, because also with the jack at the end of the cable, the headphones sounded great with Luxman. But listen to the same cans with XLR plugs and there will be no coming back.

Sound with the latter is fuller and denser. It is also more natural, and this is because the hardening of the upper midrange disappears, which earlier "pushed" the sound towards the listener. The correction is not big, but so clear to me that after hearing a better version I did not want to go back to the previous one. The foreground is placed in a bit bigger distance from listener - we are talking about headphone “perspective”, of course - which is a step in the right direction. In this way, everything goes in the direction of naturalness and softness - but the softness of the live event rather than artificial softening.

This was to be expected. It's not that the headphone amplifier MUST be balanced, because my Ayon Audio HE-3 is single-ended and it sounds great. However, when it comes to solid-state amplifier, it will deliver much better performance via symmetrical output. These differences will be even clearer if amp is fed with balanced signal. Playing music from the RCA inputs and via XLR balanced output was very satisfying. The transition to the XLR in and out, however, resulted in additional advantages such as additional deepening of the sound and richer tone.

Much smaller differences occurred when I compared balanced outputs - 4-pin XLR and 2 x 3-pin XLR (for simplicity I will use the names: 4XLR and 3XLR). But they were also unambiguous and repetitive. Especially for this part of the listening session I prepared myself a playlist on Tidal, composed of such different tracks as Robyn, additional tracks from the Currents B-Sides & Remixes by Tame Impala, as well as Art Blakey & Jazz Messengers with the album Three Blind Mice. And then I listened to several Master CD-Rs from the Ayon player.

The conclusion was surprising, but I'm sure of it: these seemingly equivalent outputs sound different. For now, this is still a preliminary assumption, I will have to listen to a few other amplifiers with both types of balanced outputs, but for the Luxman P-750 I can say that: 4XLR input sounds lower and deeper, has a darker top, 3XLR sounds "higher" and more spatially. It's hard to say which is better on the absolute scale, but with the HiFiMAN headphones I preferred the 4XLR output because it gave me a denser colors. I would not be surprised if you chose 3XLR for its better selectivity and detail. It is important that we have a choice.

| HiFiMAN HE-1000 v2 | X Edition v2

I've already said a lot about the Luxman-HiFiMAN combination. It's an amplifier that controls all cans perfectly, just like my Soulution 710 power amplifier controls all speakers. This is an absolute control, but “enlightened”, i.e. without unnecessary cruelty, with proper attention towards the "subjects". Because Luxman delivers a very creamy sound. Planar headphones can play analytically, especially HE-6, but also the HE-1000 v2 are not too warm. Luxman does not care about it, meaning it is not a problem for it, because too bright top with these headphones only appears when they are not properly driven/controlled. It is not the case here.

The listener's attention is focused in the middle of the band, and with Tidal in the lower middle. The upper trable and lower bottom are present, the differentiation of recordings is clear, but we do not get fleshy bass like from DJ headphones. Luxman focuses more on the flow of sound, on connectivity, rather than on sound filling in the style of my Harbeth M40.1 speakers. If I had to compare this setup to something, it would be YG Acoustics Carmel 2 or JBL Studio Monitor 4429. It's a great, fast sound that includes everything we demand from a headphone listening. It's just a bit limited on both band's extremes.

| Sennheiser HD800

As expected, the Sennheiser require less gain, so the sensitivity knob has been moved to the "Low" position. Also in this case the advantage of the balanced output was clear and probably even more important, because the HD800 sound with Luxman "higher" than HiFiMAN. It's a sound nicely distanced from us, very smooth. I've said this before about planar headphones, but it was also repeated with the Sennheiser and - listened for comparison - AKG K701.

The Luxman sounds incredibly silky, smooth, nice. It is not as rich and saturated as with HE-3, but I did not even expect it. It's a different type of sound for people looking for total control, aligned bandwidth, high resolution. That comes at the cost of fleshiness and three-dimensionality of the sources. The Japanese amplifier shows everything from a some distance, rather "in front" of us, while maintaining the pace&rhythm. Jazz sounds fantastic, because the amplifier organizes the sound, sets the hierarchy of importance. Also, the classical music sounds equally good, because we have smoothness and a good perspective. But also the latest Eminem album, available on Tidal in MQA Studio 24/44.1, was surprisingly rhythmic, pushing forward.

In lesser recordings, as for example - unfortunately - those from the Charlotte Gainsbourg's Rest, which not even the encoding in MQA Studio 24/44.1 was able to improve, the upper midrange will be a bit too strong with the Sennheiser. The solution is then the lower volume level. However, if the source signal is of high quality, Luxman behaves like a gentleman, controlling the presentation, striving to convey it in the most honest way possible. This was the case with, for example, Neil Young's (MQA Studio 24/96) and R.E.M. (24/192) albums.

MICROTEST

Forza AudioWorks
NOIR HYBRID HPC

Headphone cable

The Polish company Forza AudioWorks manufactures some of the best headphone cables. Period. I have been using their products for years and have never regretted it. Since I've been using my HiFiMAN HE-1000 v2 headphones with the latest version of its top Noir Hybrid HPC cable, I wanted to share some thoughts about it with you.

The cable is made of high purity 8 strands of 26AWG cryo 7N UPOCC copper/silver hybrid wire in semi-Litz geometry with PE insulation. In total, there are 56 individual strands in 7 groups. The new version uses additional insulation of a hand-wrapped Java cotton. 4x2 geometry has been chosen to minimize EMI noise without the need for shielding. The cables are divided using an aluminum splitter with a company logo made on CNC machines. The cable can be bought terminated with almost any plugs on headphones and amplifier ends. There are also numerous adapters available, which allows user to use this cable with almost any headphone output.

I have used Forza AudioWorks headphone cables for several years and consider them unique designs. They're great mechanically - nothing ever loosened, unscrewed, unsoldered, and I use headphones every day. And they sound better than most other cables I know. Compared with the standard HiFiMAN cable, the Noir Hybrid HPC sounds lower, richer, more resolving. The sound is more reliable and natural with it. All parts of the band some more vibrant, cleaerer and although the energy is higher with it, the sound - paradoxically - seems milder. The sound attack is slightly rounded with it. This is an effect that can be heard, for example, with a piano. On the other hand the dynamics, which is related to energy of the sound, is excellent.

The price/performation ration of this cable is truly exceptional. You can try to find something better and companies such as Crystal Cable guarantee it. But it will cost you much, much more. Here and now, Forza AudioWorks Noir Hybrid HPC meets all my expectations.

Price: 239 EUR/1,5 m/Furutech/HiFiMAN
forzaaudioworks.com

Summary

The P-750u is one of the best headphone amplifiers on the market and only specialized tube designs from top high-end range offer clearly more in terms of resolution, differentiation and richness of the sound. Even they do not do much more when it comes to the naturalness of sound and its smoothness. Sound of Luxman is very silky. What you do not get is fleshy bass and lit treble. But as always, it's a matter of priorities. Luxman will drive and control any headphones you throw at it. In fact it is even more than just "driving" – it will lead every cans where it wants and where the music leads it. It's a great example of thoughtful engineering and natural sound.

Technical specification (according to manufacturer)

Nominal output:
2 x 4 W RMS/8 Ω | 2 x 16 W RMS/16 Ω
Frequency range: 10 Hz - 170 kHz (-3 dB)

Input sensitivity/impedance:
In. RCA → out. jack: 1 V/15 kΩ
In. XLR → out. XLR: 2 V/40 kΩ

THD:
In. RCA → out. jack: <0,003% (1 kHz/8 Ω/1 W)
In. XLR → out. XLR: <0,002% (1 kHz/16 Ω/1 W)

S/N (A-weighted):
In. RCA → out. jack: > 113 dB (A-weighted)
In. XLR → out. XLR: >116 dB (A-weighted)

Power consumption: max. – 40 W | idle we. – 27 W
Dimensions (W x H x D): 440 x 92 x 400 mm
Weight: 13,3 kg