KECES S125 Power Amplifier Review – My Daily Driver

Overall Score 94/100
Sandu Vitalie Amplifiers

My Video Review:

Few months ago when I was building a secondary speaker setup, I decided to try a medium sized power amplifier that had all the right ingredients that were mandatory for me as an oversized toroidal transformer, an all discrete circuitry and of course some of that Class-A magic for an undisputed naturalness, easiness and control of the driver. I didn’t want to spend a fortune and KECES S125 kicked all those boxes for me. It so happens that at that time I’ve tried several power and integrated amplifiers of different manufacturers but the little S125 always stuck in my head. It simply sounded the way I wanted and it literally obliterated some of its competition. In the meantime, I’ve returned back some of those amplifiers and S125 remained as my daily driver for the last few months or so. I should state that I’m using it for more 3 months now and I enjoying the hell out of it, I’ll try to be as objective and descriptive as possible so you could better understand its voicing and working principles.

KECES might be new to you, but it isn’t for me. I have already tested their tiny but incredibly natural sounding E40 integrated amplifier, I’ve tried their detailed sounding S3 DAC + Preamp combo and I’m still using their BP-600 passive power conditioner in a small desktop setup to shoo away those nasty gremlins living in my power lines. With every single component, I was surprised the most about their low price-points and good sound performance and the unit I’ll will be testing today is exactly that kind of product. S125 is being sold in the USA by their official distributor for only $1099 right here. In Europe it will cost you €1399 and you can buy it from different places, here is an example. Although its price seems pretty low considering its design philosophy and power ratings, its sound performance is far from low-end. This one remained at my place and a lot of amps were returned back and that should tell you how I feel about it.

I’m a little sad that not a lot of people know about this Taiwanese brand, you can’t spot them at the biggest audio shows around the world and that is a strong cause people aren’t talking about it, but I assure you…it deserves your attention in full. If you have a chance to try one of their products, please do so.

Unboxing & Package Contents

S125 came double boxed with lots of foam around it for protection. I was surprised at first by the weight of the smaller box, it already suggested that a huge transformer was sitting in there somewhere. S125 was wrapped around with spongy bag as an extra protection measure during shipping. Inside the box you will also find a heavy-duty power cable, a warranty card with the serial number stamped on it and a user manual in English where you can find all its specs and features. That is basically it, it is only a power amplifier, so don’t expect a remote, it either works or not, it’s really that simple.

Design & Build Quality

Quite a lot of modern integrated and power amplifiers aren’t using thick aluminum cases anymore, I never liked those cheap looking punched-steel cases, even established manufacturers as Cambridge Audio, Hegel, Onkyo, Yamaha, Anthem, Sony, Schiit Audio and many others are still using such cases. KECES is having a different philosophy as even their cheapest products as E40 integrated or the BP-600 passive power conditioner are using absolutely the same case with the unit that I am testing today. S125 is having a thick aluminum case, with just two panels attached on top and under the unit.

I also like that all KECES units are looking more or less the same, building a very strong brand identity is important as you don’t need to approach them or check their logo to recognize them. Go tell SMSL about this, they still don’t have a clue about brand identity…

Being a power amplifier working mostly in Class-AB and spitting few Watts in Class-A, S125 is dissipating a lot of heat, KECES left some open holes on the base of the unit and on its top case. Those lines are perfectly aligned, so that air could move freely in and out of the case. I really like this simple but clever approach of dealing with heat. S125 is one of the hottest amplifiers I’ve tried and it needs a bit of space to breathe, please don’t put anything on top of it.

I like its simple matte black stealthy look and it seems that my lady likes it too, since in few months she never asked me what is that thing and why we need it. It has only a blue LED just above the power button, it’s dimmed and you can barely see it in the night, so WAF factor is through the roof in this one.

It’s moderately big and at not super heavy, at 12 kilos (or 26.5 pounds) and 30 cm wide, it even fits in simple TV benches like those from IKEA. It has solid metal feet with small silicone inserts to absorb micro-vibrations and all its connections on the back are tightly secured, exactly what I would expect from a high-quality product. When you see it first it looks small and cute, but its fully packed with electronics, with a huge 1KV transformer in the middle.

Controls & Connectivity

S125 is simple to use and it’s a straightforward amplifier. There is just a single On/Off button and a blue LED on its face plate and everything else is located on the back. There you’ll find your left and right speaker terminals, a pair of unbalanced RCA and balanced XLR inputs, a 230V or 115V voltage switch, an AC inlet and two switches. The first one lets you select the Balanced or the Unbalanced input and the second one is your stereo or bridged mode. That’s right folks, if you need Mr.Olympia power for your inefficient speakers, you can use two of them bridged for a huge power output like 360 Watts in 8 Ohms and somewhere around ~650 Watts in 4 Ohms – mind you this is continuous power and not maximum power for high dynamic swings.

It’s important to mention that KECES included an Overload and an Over Temperature Protection circuit. No matter how hard you push it to its limits, it will shut down by itself to cool down or to save your speakers from any further damage. I’m spotting 5 fuses inside it and that makes me extremely happy as it should resist huge current spikes too.

Tech inside S125

I can’t deny the amazing power efficiency of the latest Class-D amplifiers that are being released lately, most of the mid-level stuff already moved to this working principle, but the super inefficient power draining Class-A amplifiers are still very desirable, especially when it comes to high-end audio. Class-A amps are still very popular among speaker lovers and head-philes thanks to their instant power delivery and amazing driver control. There is however a huge difference between designing a 5 Watt or a 500 Watt fully Class-A amplifier, the later one would look more like a side-by-side fridge that should be connected to a nuclear power plant for the best results. Different ways have been developed so than an amp could look more like a box and not like a fridge and still offer a bit of power in that magical sounding Class-A.

That is mostly why class AB amplifiers like the unit I am testing today are operating in Class-A at low power levels and then move to Class-AB at higher power levels. After an exchange of emails, KECES mentioned that it offers about 3 to 4 Watts in Class-A and then moves to AB at higher power output. There is one legendary designer that believes the first watt is the most important one, I’m no audio engineer but I’m going to agree with Nelson Pass on this and KECES seems to also agree with that.

Most of the current production integrated and power amp makers started moving to Class-D with their newest creations, on the other hand KECES thinks that you can’t preserve natural harmonics with a design like that and that is precisely why their E40 integrated and their S125 are quite different sounding compared to a lot of mid-level amplifiers that are being released today.

Another interesting aspect is that S125 uses a fully discrete input to output circuitry with no op-amps in its signal path. I can’t count all those J-fets / output transistors, but I see a lot of them and some of the bigger ones are directly glued to some huge heat sinks to cool down and prolong their lives. KECES used a single 1KV (1000VA) toroidal transformer and about 40.000 μF sitting in some big capacitors will be filtering all that power. KECES also added DC Servo circuits that will be dealing with the source noise with the help of negative feedback – this is crucial if you using a noisier analog or digital source.

As for the power, as its name suggests, it will provide a continuous power of 125 W in 8 Ohms, 225 in 4 Ohms, if you bridge two S125 working as a team, you’ll get 360W in 8 Ohms and somewhere around ~650 Watts in 4 Ohms and of course a zero channel cross-talk, since there are two units instead of one. Do note that its current output peaks at 30 Amperes per channel and with some very inefficient speakers it could enable its overload protection mode.

All in all, the spec sheet looks really promising, it is more like amazing to me and it’s something I would normally see in much higher priced amplifiers.

Test Equipment

I used it mostly in tandem with a Matrix Audio Element X and with an Audiobyte HydraVox + HydraZap, both can be used as DAC + Pre units and I was curious to hear how will they perform with the S125. Element X already incorporates a hybrid analog/digital preamp section so for about a month they worked together without a preamp. Later on, I have added the Benchmark HPA4 as a dedicated preamp in my system to see if I can further improve the listening experience. I used the Buchardt S400 loudspeakers and sincerely, S125 is a bit of an overkill power amplifier for speakers of this size and sensitivity. With all that said, even with small speakers like these, an amplifier with a bigger power reserve will always awake better dynamics, will have a better diaphragm control (especially of the low-end) and you will be unleashing their maximum potential.

Enough with the talk, I’m eager for some music so let’s play some.

Sound Performance

I. Preliminary Impressions

S125 is already playing sweet tunes for a few months now and I do feel that I’ve formed a very solid opinion about its performance. I have swapped in and out quite a few amplifiers in this period of time with the same speakers, so I could better understand all its pros and cons. In the end lots of amplifiers went back and S125 remained as my daily driver and that already tells a story about its performance. Buchardt S400 may have a small cabinet and a pretty high sensitivity numbers, but the passive radiator on the back will start pounding your chest only with serious horse power, feed them fat juicy watts and that passive driver on the back will be drawing a bigger picture, immersing yourself much deeper into your music. S400 sounded mellow and plain boring with little to no depth with three amplifiers, they sounded considerably more alive and ass-kicking with a KECES E40 and absolutely amazing with other three amplifiers: Hegel H190 ($4000), KECES S125 ($1099) and with the Kinki Studio EX-M7 ($2598). The latest ones are looking like overkill amplifiers for a small book-shelf speaker like S400 and to some degree that is true, but I can assure you that an absolute control of the drivers, an instant start and stop of their drivers and some of the punchiest dynamics were achieved only with these three wild horses.

I put the Element X working as a streamer and a DAC, I used the Benchmark HPA4 as a line-amplifier and S125 was doing all the heavy lifting. The hardest task of an amplifier is to perfectly control, sustain and decay a bass note. Long After You Are Gone by Chris Jones (Tidal / Spotify) is a track that you would never use to check the bass performance of your stereo setup. I beg to differ as this track offers some of the nicest bass layers coming from a single guitar. S125 was immediately pumping more air around me and I felt it heavier and denser with every single note, low-end was breathing, it was pulsating and S125 was considerably improving its sustain. A longer bass note can be sustained only with powerful amplifiers, that are capable of bigger voltage and current swings. I was so amazed that after returning back the Hegel, S125 sounded so very alike, that I thought it was made in Norway, in the same factory. It was pumping dynamics, it was pushing and pulling back those notes and I was simply taking an audiophile beating in plain sight.

H190 is known for an incredible transient response thanks to its huge damping factor, somehow the S125 was sounding as engaging and as hard hitting in a very believable and natural way. Naturalness is something that not a lot of amplifier possess, solid state amplifiers are sometimes boring sounding or just want to impress with an uneven frequency response. S125 by comparison sound neutral, but with a correct rendition of neutrality as nothing really stands out in the frequency response and yet everything is perfectly balanced as in real life.

Hearing my music with an exploded view where I would pick any tiny sounds I wanted was also something that S125 was really good at. I’m using it in a bigger room - an open space of about 35 square meters (~377 square feet) and I felt that music sounded always big and airy and everything was coming from different angles. S400 are not having a sweet spot, so I started moving around the room and no matter where I went, the pin point location was spot on and I could easily focus on anything I wanted.

II. Noise Floor

S400 may not be a high-end speaker when it comes to details and transparency but it will show you if there is a dirty background with your amplifier. My former Burson Bang power amp had a bit of residual noise even after being connected to a high-end source. Element X in its streamer and DAC mode already takes care of the digital jitter and sends clean signals to the HPA4 and then to S125, so take that into consideration. The good part is that S125 incorporates simple but effective DC servo circuits that should kill the unwanted noise coming from your source with the help of negative feedback. I approached my speakers and went almost full power on the preamp and all I’ve heard was an absolute silence coming from these speakers. There is nothing I dislike more like a dirty and muddy sounding amplifier, that increases the noise floor and completely kills the enjoyment factor at higher listening volumes.

With S125 I could go as high as I want and it will still provide a complete silence between passages and a transparent black background. I didn’t use it with a passive power conditioner since both my KECES BP-600 and Plixir Elite BAC400 can’t offer a continuous power of 500W that S125 is eating non-stop, so the clean sound is coming from the S125 alone. That makes me very satisfied as sometimes I like to crank that volume higher and I can do that safely with this unit.

III. Transparency & Resolution

Compared my some of my former integrated and power amplifiers, S125 is a resolute and quite a transparent sounding unit, but don’t expect the last drop of transparency out of this one. It uses discrete components alright and of course that translates into a clear detailed sound with a see-through transparency, but it wasn’t as crystal-clear sounding as that $2598 Kinki Studio EX-M7 or $4000 Hegel H190. While listening to Scotty by Allan Taylor (Tidal / Spotify) the piano player gently touches its pedals and usually those barely audible sounds can be heard with a transparent sounding setup. I didn’t need to close my eyes to hear them, they were rendered clear and were positioned on the far left, like they were coming from the wall and not from the speakers, like they weren’t part of this song.

I did hear additional details compared to my own integrated and power amplifiers I’ve used in the past and it delivered them in an easy non-aggressive way. S125 genuinely doesn’t force the listener on some particular parts in the FR, it presents your music in an effortless and engaging way. I’m actually so much behind this review, because after pressing play, I am forgetting that I need to take some notes. I had absolutely the same feelings about the Kinki EX-M7 where it mostly wanted to impress with its easy-going nature, with its naturalness and with an incredible grip over the speaker drivers. All other technicalities, although being there as well, were not asking for spot lights. If you expect the last drop of transparency out of this one…that will not happen.

Most of the Class-A and AB amplifiers will impress you more with their smoothness and naturalness and less so with sharp details and that is happening in here too. At a high 113 dB signal-to-noise ratio, you will still need to go way past your comfortable listening levels just to hear a very small increase in harmonic distortion. When it comes to things like distortion, in most Hi-Fi setups your speakers would be that bottle-necked and not the unit I am testing today.

IV. Transient Response

Now, this is where those 3 to 4 Watts are showing their muscles, outplaying a lot of amplifiers like my former Cambridge Audio Azur 851A and others. S125 is a fast sounding unit, it will instantly increase those dynamics and if needed, it will stop the diaphragm in an instant. My former bass tests proved that it renders it in a fast way, in can sustain a bass note for a longer period and it can decay it slowly and naturally. On one hand it has everything you could desire in an amplifier, including enough power output, control and punch, but all that comes at the cost of a less transparent sound. I can go on and on with a lot of tracks but I would arrive at the same conclusion. I’m mostly into energetic music and I kept going back to this unit, because it knows how to impress a transient nut as myself. Speed of delivery was great, the same can be said about the kick in the chest that followed. Bass slam was outstanding too and with some particular music that becomes addicting.

For the record, I was toe tapping with smooth old blues too, thanks to its energetic and punchy delivery. I like a lot that it doesn’t alter the imperfections of my music, the grain and the needle noise of the older recordings is still there and I can hear them vividly, but they don’t bother me as much. Those aren’t as sharp sounding and will not ruin my listening pleasure. I’m very fond of some electronic music bands which I’ve grown-up with and when I’m testing a brand-new amplifier or speakers, I would always test their limits with such music. The impact, the scale, the layering that followed, with notes jumping off the walls and bumping into my body in a ruthless way, was something that I will never forget with my old electronica. S125 was truly made for this kind of music and will show its true form and identity.

V. Soundstage & Depth

It proved that it knows how to push bigger amounts of air for a nicer impact and when it does that, music is also expanding and is nicely filling the room. A nice power reserve and a huge headroom on tap, will always have a positive impact on depth and stage size, it happened so many times and S125 is no different. When it comes to how much air it can move around, compared to all amps I’ve tried before, S125 is easily in my top 3 list.

I’ve observed that Class-A amps are borrowing few best traits of tube amplifiers as their easy-going nature and their expanded soundstage. S125 offered an exploded view of my music with a distinct space between each and every note. It surprised me that even crowded passages started sounding uncluttered and much deeper too.

Some of the blues and jazz recorded in smaller studios weren’t claustrophobic sounding at all. Case in point, Sweet Sixteen by Junior Wells (Tidal / Spotify) was simply playing with my imagination and the notes were jumping from left to right and vice versa. The note placement in the room was spot on and I could easily appreciate the distance between each instrument. Junior was staying exactly in the middle, but everything else felt like disconnected from this track, switching places and making me turn my head left and right. S125 really shined with this track by increasing the stage size and depth by a decent amount and in the end, it played nicely with smooth blues too and I was ready for more.

VI. Frequency Response

After swapping a lot of amplifiers in a span of just few months, the biggest difference between all of them was their tonality and frequency response. S125 stood out immediately with its robust and powerful bass delivery, with a natural and full-bodied midrange performance and with a calmer top-end, rounding the notes past top-octave for longer listening sessions. It is a bass and midrange beast with just a small drop in the upper registers. There is another unwritten rule that Class-A amplifiers are rounding the top-end for a smoother music delivery and that was felt immediately with this one.

Bass was always delivered raw; without too many warnings it will be hitting your chest ruthlessly. It goes deep, it goes fast and it hits with a pretty nice force. I felt it with my chest, my neighbors felt it too, I’m told they are listening only to high-quality music and it doesn’t matter if they want that or not…Bass stood out even from the first days without too much burn-in, it grabs your attention and it will put butterflies in your stomach. It is not a bass heavy amplifier, it has the right amount of it, it is quite linear but executed really well.

Midrange was also delivered in higher quantities, S125 is a linear sounding unit that slightly shifts towards warmth. While listening to a lot of acoustic music, I felt heart-warming midrange and natural rendition those tones. Everything that is tied to the midrange like most of the acoustic instruments and voices will be pushed forward a bit. You will not find dryness, thinness or plain brightness in this one, it is mostly on the opposite camp with its tonality. There is indeed a small increase of the midrange density for a livelier and colorful musical experience. Not going to lie that I really enjoy this kind of sound.

Treble is considerably smoother and it rolls-off a bit in the upper treble. I still hear it loud and clear, I hear its textures, I hear the outline of the cymbals, but their intensity is lowered. There is a much lesser ringing in the treble compared to few Class-D amplifiers, the sharpness is definitely toned down a bit. Some might like this kind of sound; others might want additional texture and sharpness. It might sound like some gibberish non-sense, but…it reminds me a lot about the naturalness of the R-2R DACs - S125 is having the same voicing and the same calmer top-end performance that I truly adore in R2R digital designs. It has a relaxed top-end and a smoother presentation, so listening to modern over-processed and over-mastered music is a non-issue anymore, it smooths out those dips or rises and makes them more manageable.

Overall, I’ve heard lots of naturalness, a linear performance with a gentle roll-off in the treble, it was visceral and vivid sounding most of the time and on rare occasions it was even disappearing from the acoustic chain with that intoxicating liveliness.

VII. A Comparison

All amplifiers I’ve mentioned before were returned back, so I can’t make a direct comparison with any of them, but I will just say that S125 is only by a hair behind the Hegel H190 when it comes to body slams and treble extension, everything else felt more or less the same. H190 is considerably more expensive, it is almost 4 times the price of S125, but it also has a dedicated DAC section, a streamer and it’s a full integrated amplifier with a preamp section too. I was really surprised about this, since I had them side by side for a couple of weeks and with my eyes closed, I could differentiate them only with fast energetic music or with treble oriented music, where H190 was not rolling-off the upper treble at all. Kinki Studio EX-M7 is still on loan, it is also a lot more expensive, but what the hell, let’s do this comparison.

KECES S125 (MSRP $1099) VS Kinki Studio EX-M7 (MSRP $2598)

Both are power amplifiers only, both are working in Class-AB mode, however the very first watts of S125 will be delivered in Class-A. S125 is considerably smaller in size and offers less power output as well. As its name suggests S125 will offer 125W in 8 Ohm and M7 will double that number to 250W. S125 is considerably simpler inside, it is relying on a single 1000VA toroidal transformer, compared to 4 toroids on M7 (2 bigger and 2 smaller ones). M7 is also using two pairs of high-performance Exicon mosfets. For power filtering and storing, M7 is again taking the lead with a lot more capacitors. So even at this point, it is clear that M7 is a higher-class device as all its internal components, weight, size and price are suggesting.

In terms of features, EX-M7 again outperformed the smaller fellow by offering DC filtering, GND and Earth posts, Link and Float possibility and most importantly an amplifier/speaker protection circuit which is vital in an expensive setup. In its defense, if you add another S125 to the chain, they can work together as a team in dual-mono mode offering some juicy 360 Watts of power in 8 Ohms and a zero crosstalk, vastly outperforming a single EX-M7.

In terms of overall tonality and frequency response, both are more alike than different, going for a natural approach to music reproduction. They both excel in terms of bass and midrange presence with a slight difference that S125 felt less extended in the treble region. In terms of sheer power, control and punch, M7 was better and no matter the music is being played, it always wanted to impress myself by throwing better dynamics and more air around every note. Yes, more air, meaning better depth and wider soundstage size. Even with such small speakers, the difference was there and it was undeniable and easy to spot. Would I be happy with a just a S125? Yes, of course, it is still my daily driver and I love it to bits, but when it comes to ultimate performance, that trophy is for the M7 to take.

Another key point that was felt much later on is the detail and transparency. With higher quality recordings, there was simply a bit more of everything, slightly more bass layers, more guttural voices, clearer guitar plucks, more string vibrations and a better treble performance. M7 felt more transparent and also offered a higher degree of micro-details.

I’m sure that in a less revealing system, the difference would be much smaller and of course, in a more revealing system with harder to drive speakers, the difference would be bigger, so it obviously depends on your particular setup.

All in all, Kinki Studio EX-M7 was a better unit, but it also costs more that two times the price of S125 and since I own one, buying a second S125 and bridging them together for an unlimited headroom is very, very appealing to me. You can never have too much power, isn’t it?

Conclusion

Not a lot of time was needed before it started blooming and showing its true form. After about one week of burn-in, KECES S125 was already pumping back and forth those drives like it was a child’s play for it. It is very important to have a balanced FR and a natural tonality in your setup. My DACs are all super linear sounding top-to-bottom, HPA4 is colorless too, I needed a bit of soul in my speaker setup and S125 brought exactly that in my room. It worked flawlessly in this particular setup and if you are searching for more body hits, for more low-end, for more guttural and soul-grabbing voices, then S125 seems like a very good choice. My sources and preamp are extremely extended in the treble region, so again S125 with its calm treble rendition, made the final performance closer to live-music, it wasn’t producing sharp tones and it wasn’t ringing at all in there too.

S125 was always organic, warm and full bodied, fast and impactful sounding - if these words resonate with your taste, then you should strongly consider it as a serious sounding power amplifier at a mid-fi price.

I’ve got the confirmation that it indeed costs only $1099 in the US and at that price I’m going to call it a giant killer amplifier. It really plays in the big boy category with just a mid-fi price tag attached to it. If you are living in Europe, it will cost you €1399 – but even at this price I find it extremely competitive or dare I say better than its competition. It will remain my daily driver and it is getting my stamp of approval!

PROS:

  • Simple, minimalist design, nice looking too
  • Small footprint, works nicely with TV benches
  • Unbalanced and balanced outputs, can be bridged for some Mr.Olympia power
  • Amazing dynamics with fast paced music
  • The punch and the body slams are truly visceral
  • Sounds big and decompressed, good scale and depth
  • Quite 3D sounding, accurate pin point location of all the notes
  • Linear FR with a gentle roll-off in the treble
  • One of the nicest bass and midrange renditions I’ve experienced from a power amp
  • No background noise at high volumes
  • Very good tonal balance
  • One of the best valued power amplifier right now

CONS:

  • It’s hot after about an hour or so, needs proper ventilation
  • Don’t expect the best transparency and details, it’s coming close but it’s not there yet
  • Rolled-off in the treble (could a PRO for some)

ASSOCIATED EQUIPMENT:

  • DACs: Matrix Audio Element X, Audiobyte HydraVox + HydraZap, Flux Lab Acoustics FCN-10, Burson Conductor 3X Performance
  • Integrated Amps: KECES E40, Hegel H190 (gone), Cambridge Audio Azur 851A (gone)
  • Power Amps: KECES S125, Kinki Studio EX-M7
  • Preamplifier: Benchmark HPA4
  • Loudspeakers: Buchardt S400, KEF LS50W (gone)
  • Headphone Amps: SparkoS Labs Aries, Benchmark HPA4, Flux Lab Acoustics FCN-10, Burson Conductor 3X Performance
  • IEMs: FiiO FA9, FH7, Meze Rai Penta, Rai Solo & many others
  • Portable headphones: Sennheiser Momentum 2, Meze 99 Classics
  • Full-sized headphones: Audeze LCD-4, Erzetich Phobos, Erzetich Mania, Hifiman Arya, Quad ERA-1, Kennerton Wodan, Magni & Gjallarhorn, Fostex TH909
  • Interconnects: QED Reference (x2), Aune AL3
  • Speaker cables: Kimber PR8, Audioquest Type4
  • Power Cables: Isotek EVO3 Premier (x3)
  • Balanced Isolation Power Conditioners: PLiXiR Elite BAC400, KECES BP-600

Overall score 94/100

Value 100/100
Power Output 92/100
Resolution 92/100
Dynamics 95/100
Frequency Response 93/100
Stage Size 93/100
Build Quality 95/100
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