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FLUX Mentor - teardown, inside pictures and a few measurements

trl

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Hello,

I had the opportunity, for about a week, to listen and test the newest member from the FLUXLAB-ACOUSTICS headphones amplifier line, the MENTOR headphones amplifier. The manufacturer, an Ukrainian company, specifies an extreme output power on 32 Ohm in mono mode of “only” 33.5W RMS per channel, while in 300 Ohm (mono mode) of “only” 6.4W RMS per channel. I really wanted to see if this huge amount of power is for real or is it only in the specs, so I was grabbing my PicoScope and a 33 Ohms / 50 Watts resistor to test this in one of the below paragraphs.

I found inside very good quality “guts”, like the toroidal transformers with an outer shield to minimize electromagnetic radiation (probably G.O.S.S. or similar), electrolytic capacitors like Cornell Dubilier SLPX, Nichicon MUSE and SAMWHA, relays from OMRON, PANASONIC and TAKAMISAWA etc.. A “dual mono” design on both linear power supplies and on the two amplifiers could be easily spotted. Choosing four bridge rectifiers for the power supplies, one for each dual-rail, should help in dealing with higher current loads (especially for the PCB traces and the ground plane that will split the current better), but will also deliver a smoother DC output. Dual bridge rectifiers will also help if the secondary coils of the power transformers are not delivering a perfectly identical output voltage too.

IMG_6154.jpg

Inside Flux Mentor, top view

IMG_6159.jpg

For big electrolitic capacitors per each main power supply

IMG_6162.jpg

There's an interesting op-amp on each channel that is sand-off, not sure what it is for.

Everything inside this amplifier screams “quality”, from the way the PCB looks to the thick cables and the components used. I like when I see several bridge rectifiers that separate the stages, I also like seeing multiple relays designated for protecting parts of the circuitry, I also see a nice ground plane too.

IMG_6171.jpg

Several smaller bridge rectifiers that power the logics inside the Mentor headamp

Volume control is relay-based and contains 64 volume steps. The volume control circuitry uses Panasonic fast signal relays with low contact resistance, while the dual-gang ALPS potentiometer from the front-middle only acts as a “rotary knob” that controls the relays.

IMG_6155.jpg

Custom-made toroidal transformers

The toroidal transformers are custom-made by the Torenergo company from Ukraine and are 2 x 31 VAC @ 0.3A, so we won’t be able to drive speakers with this amplifier. :) In contrast, the VOLOT headamp was using the same 2 x 31 VAC transformers, but rated @1.2A, hence the higher output power of VOLOT over the MENTOR, well...at least when used in stereo mode.


The beefy output stage operates in Class A and is created around the complementary silicon power transistors NJW0281G (NPN) and NJW0302G (PNP) (similar with the well-known Toshiba 2SC5200 and 2SA1943) that came in TO-3P package and are able to continuously sustain up to 15 amperes (30A peak) and dissipate up to 150 watts each. The regulated voltage across the output stage is 70 V, so a rather high output voltage is to be expected at headphones output, which translates in a high output power. These transistors are usually seen in powerful speaker amplifiers like 2 x 150...250 W, but also in powerful bridged versions like the 500 W kit presented here. A nice PDF file containing a DIY amplifier schematic can also be read here as well.

The remote control is big, bigger than the one from my Samsung TV, which is odd given the low number of controls, but interesting at the same time. It’s also fully made of aluminum, so it’s heavy too, much heavier than I expected it to be. I do like it’s expensive and stylish remote control look and feel. There is no plastic in this remote control, probably this is why it’s heavy, although the feeling in my hand is pleasant.

IMG_6177.jpg

Rather big, but somehow luxuriant remote control

IMG_6178.jpg

Inside the remote there's a rubber disc that acts as shock attenuator for the back plate

I was using my PicoScope to measure the output voltage of this headamp and 33 Ohms / 50W resistors to measure the output power too. I won’t care about the stereo power, but more about the mono/bridged power, to see if manufacturer specs or 33 W / 32 Ohms can be achieved or not or if this huge amount of power spec’d is peak power or continuous power. For seemingless bridged mode operation there’s need for two such amplifiers and synchronization cables that are sold by the manufacturer, then one unit becomes primary and the other secondary.

When using Low Gain, in Mono/Bridged mode, I managed to get up to 20.18 Vrms output voltage and 44 Vrms in the Medium Gain; on High it’s the same as on Medium, so High Gain can probably be used when connecting low-voltage audio sources on the inputs, maybe for non-balanced RCA connections. I was using 4 Vrms on the balanced input fed by my Topping D90 MQA source DAC.


Flux_Mentor_bridged_NoResistor_LowGain.png

20.18 Vrms in Low Gain, no load resistor connected


Flux_Mentor_bridged_NoResistor_MidGain.png

44.42 Vrms in Medium Gain, no load resistor connected

With 33 Ohms resistors connected, on Low Gain, MENTOR headamp was able to deliver a clean 20.10 Vrms, meaning 12.24 Watts.

Flux_Mentor_bridged_33Ohms_LowGain.png

20.18 Vrms in Low Gain with 33 Ohms resistor connected as load, meaning over 12 Watts per channel

Getting to Medium Gain I managed to get a clean and stable signal of almost 32 Vrms, meaning over 30 W of continuous power when used in Mono/Bridged mode!

Flux_Mentor_bridged_33Ohms_MidGain_07.png

31.68 Vrms in Medium Gain with 33 Ohms resistor connected as load, meaning over 30 Watts per channel

More than that, I was able to push it even further, until 40 Vrms, but I’ve noticed that after 37 Vrms there was a protection in place that kicked in (I was able to hear a relay kicking in) and the signal started to become squared (distorted).

Flux_Mentor_bridged_33Ohms_MidGain_02.png

37.07 Vrms in Medium Gain with 33 Ohms resistor connected as load, meaning peaks of 42 Watts per channel

That tells me that with music sine-waves this headmap has peaks up to 48-50 W per channel @33 Ohms resistive load, which is impressive and overkill at the same time for a headphones amplifier, but this probably makes it the most powerful headphones amplifier of all times.

Flux_Mentor_bridged_33Ohms_MidGain_03.png

39.80 Vrms in Medium Gain with 33 Ohms resistor connected as load, meaning peaks of 48 Watts per channel

I was wondering why would anyone need such amount of power coming from a headamp and I’ve noticed that a new pair of headphones appeared on the market: Tungsten from Mod House Audio, with an average sensitivity of only 76 dB/mW @ 135 Ohms, so 12 dB less sensitivity than ABYS AB1266 (50 Ohms) and 7.5 dB less than Hifiman HE-6 (50 Ohms). I guess these headphones should be driven without problems by a couple of FLUX Volot headlamps (in bridged mode).

The below measurements are done with my E1DA Cosmos ADC fed by Topping D90 MQA. I was only using 1 kHz sine-waves to check quickly how the SINAD looks when FLUX Mentor is used in Mono/Bridged mode.

1kHz_Bridged_LowGain_4.5V.png

@ 4.5 Vrms scale I got a SINAD of 110.7 dB.

1kHz_Bridged_LowGain_10V.png

@ 10 Vrms scale I got a SINAD of 114.6 dB in Low Gain, 109.6 dB in Mid Gain and 108 dB in High Gain.

When connecting the 33 Ohms resistors I got a SINAD of 87.3 dB, identical with the THD (probably due to higher second order harmonic), which translates in 0.004% distortions, a bit better than manufacturer’s specs of 0.006%. However, increasing the value of the output resistance will instantly lower the THD and increase the SINAD.


1kHz_Bridged_LowGain_4.5V-33Ohms.png

With 33 Ohms resistors attached @ 4.5 Vrms scale I got a SINAD of 87.3 dB.


Listening with any of my headphones on this powerful headphones amplifier was done on the lowest gain, even with my 600 Ohms Beyerdynamic cans I haven't felt that I need more "juice" than the Low Gain was able to offer me. I can't say much about the output sound given that it sounds and measures very well to be as transparent as any other of the headamps I have. It sounds powerful, it can drive any cans out there and it has a power reserve that inspire confidence to the owner, so no more headamp upgrades should be required for a long time, unless some headphones manufacturer will ever decide to create headphones that will require an insane amount of power to surpass Mentor's bridged 30-40 Watts @ 32 Ohms. :)
 
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ObjectiveSubjectivist

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That's another great device from Flux. Extremely powerful but not leaving performance behind. Seems to be good match for something like Modhouse Tungsten
 
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trl

trl

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That's another great device from Flux. Extremely powerful but not leaving performance behind. Seems to be good match for something like Modhouse Tungsten
My guess is that this was the main reason why they made this amp for.
 
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trl

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Just realized now that for getting peaks to reach to 115 dB SPL with the Modhouse Tungsten cans we'll need an amplifier able to output at least 8 W per channel (we still need some power reserve too), which should suit THX reference levels and nobody should ever complain of needing more power to drive these cans. Most of us we're not listening to peaks over 105 dB SPL (meaning an avg. of about 85 dB SPL), so probably all powerful headamps tested here on ASR should do the work well with these cans, but looking forward for some measurements to happen, perhaps @amirm will soon get a pair of Moodhouse Tungsten to have them tested. Meanwhile we can stick to https://forum.headphones.com/t/modhouse-tungsten-measurements-official-discussion/22645 which shows pretty good measurement results.

Tungsten_115dB.png

However, worth mentioning that with FLUX Mentor headamp the Tungsten will be driven to insane levels to above 120 dB SPL, so prior to inserting any headphones in this powerful headamp double check for Gain setting (start from the Low gain) and turn the volume knob to 9 o'clock or so, then hit the Play on your source.
 

Doodski

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Nice. They spent on good crimpers and did everything really pro level nice. Good to see. :D
 
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Sokel

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Nice. They spent on good crimpers and did everything really pro level nice. Good to see. :D
I love this PRP (I guess) resistors red color (I do love their precision too) .
 

AnalogSteph

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IMG_6162.jpg

There's an interesting op-amp on each channel that is sand-off, not sure what it is for.
I'd think that's responsible for the power amp input stage. Looks to be a dual opamp, and I'm pretty sure I've seen that face before... if I had to place my bets I'd say that's an RC4580I. Used as poor man's fully differential opamp, I guess? (Would explain why what little distortion is there unloaded is domanent H3.) What follows must be inverting, as the capacitor as between pins 2 and 6, the inverting inputs. Either way, the opamp is clearly not the bottleneck, the output stage seems to have some current-related symmetry problems instead (distortion mechanisms #5-7 may be worth checking for).
 
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trl

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@AnalogSteph thanks for the comment, I was thinking myself the same, those two op-amps are probably placed in the input stage there.

The THD measured is even better than the manufacturer stated, so the THD H2-H3 distribution is per design. I'm sure that THD can be lowered, but I don't think the manufacturer is interested on this, mostly because the actual THD is way below the THD of the headphones. Also, increasing the output voltage above 10V RMS will lower the THD even more, so SINAD will get even better for both loaded and unloaded scenarios.

I'm personally impressed by the huge amount of power this amplifier can deliver when used in bridge-mode and I consider it as an "end-game" headamp for most folks looking for a very powerful headamp. Also, I'm glad to see that in Ukraine the audio electronics department is still in business due to the ongoing war from there.
 
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trl

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I measured MENTOR with real headphones, both balanced, just to see how the graphs look like.​

1kHz_Balanced_LowGain_2.7V_AKG_K701_resized.png

Mentor in balanced-mode driving AKG K701 (62 Ohms) balanced - 96.5 dB SINAD
[2.7 Vrms @ full scale]



1kHz_Balanced_LowGain_4.5V_Beyerdynamic_DT880_600_resized.png

Mentor in balanced-mode driving Beyerdynamic DT880 (600 Ohms) balanced - 109.2 dB SINAD
[4.5 Vrms @ full scale]

 

Cbdb2

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Why would anyone spend $3000 for a headphone amp when you can't tell the difference with a $100 Amp?
This is just unnecessary over engineering to separate audiophools from there money.
 

Cbdb2

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And I didn't have to read much before there snake oil BS started:
"We have also used an Ultra Pure Oxygen Free Copper (UP-OFC) power cable with additional shielding from Neotech from the AC Inlet socket to the power transformers. This has allowed us to achieve a more focused sound in the low-frequency range and more punch in the mid/high range.
 
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trl

trl

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Why would anyone spend $3000 for a headphone amp when you can't tell the difference with a $100 Amp?
This is just unnecessary over engineering to separate audiophools from there money.
If you know a headamp costing only 100 USD and having relays-array volume control, both balanced and unbalanced Inputs and Outputs and at the same time to be able to output peaks close to 50W @32Ohms then I'd be happy to buy a couple of these, at least.

We need to understand that sometimes other things might matter more than pure performance like SINAD:
- warranty on a specific continent (or worldwide)
- size (many folks want equipment that can be racked or at least stacked on top of others)
- color
- look and feel
- no. of Inputs & Output etc.

After all, the above teardown/review is for the most powerful amplifier from this planet (when bridged), so kudos for the Flux Lab Acoustics team for delivering such a great product in these times of war!
 

Cbdb2

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If you know a headamp costing only 100 USD and having relays-array volume control, both balanced and unbalanced Inputs and Outputs and at the same time to be able to output peaks close to 50W @32Ohms then I'd be happy to buy a couple of these, at least.

We need to understand that sometimes other things might matter more than pure performance like SINAD:
- warranty on a specific continent (or worldwide)
- size (many folks want equipment that can be racked or at least stacked on top of others)
- color
- look and feel
- no. of Inputs & Output etc.

After all, the above teardown/review is for the most powerful amplifier from this planet (when bridged), so kudos for the Flux Lab Acoustics team for delivering such a great product in these times of war!
Blah blah blah, you cant hear the difference. Why does anyone need 50 watts for headphones, thats ludacrous. None of the other things you mention are worth 10% of the price of that ridiculous audiophool amplifier.
 
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