Hey,
This is a short review of the Serene KTE preamp from Holo Audio. I won't get into the build etc, there are enough videos about that stuff out there. This review is purely about sound.
To know how the Serene sounds as a pure preamp i connected my May directly to the Envy via RCA and also to the Serene via XLR and the Serene to the May via XLR. I matched the volume on the Serene (-6db) and can now switch between input 2 and 3 of the Envy to directly compare the chain with and without the Serene. Headphone is my (veiled, huehue) Susvara, tubes are Elrog TM's and Melz 1578.
It sounds absolutely identical. There is not a single trait i am able to tell the inputs apart. Everything sounds exactly the same. So i spare the time listing the common traits, because i am not able to tell that there is a Serene in between one of the inputs of the Envy. I can't even hear a very slight warmth which Goldensound was describing in his review.
As a preamp, it's supergood. It's super clean, transparent, and just acoustically invisible. If you want a preamp that colours the sound, this is not it, get a warmer class A or tubeamp for that. For me it does exactly what i want. If i had to nitpick, i would have liked more outputs and less inputs, it does have 2 XLR and 3 RCA inputs, but only 2 XLR and 1 RCA output, so three amplifiers are the limit that you can connect your Serene to. Well, maybe i'll get more sources in the future, who knows.
The knob and remote are both clicky and very satisfying to use, i love it. I use two inputs (May and another DAC that handles my PS5) and (currently) two outputs, the Envy at XLR 2 and the Mass Kobo 475 at XLR 1. If i keep my Rebelamp it gets plugged into the RCA out again.
The Mass Kobo is connected via an adapter cable, dual female 3pin XLR -> female 4pin XLR and then a short adapter that handles the male XLR -> 4.4 male that goes into the unit. That way i can use the Serene also as a headphone amp via the XLR1 out.
How is it? The Serene as a headphone amp? It's average.
It would be very good, if it didn't have one major drawback. Everything is truly impressive, it sounds super clean and transparent. It is always dead silent, so silent that i thought i'm losing my mind. When i connected my most sensitive IEM (Trifecta) via a 4.4 -> XLR adapter to the Serene, i could hear absolutely nothing, as if the unit was off. What the heck. Not even the Mass Kobo can achieve that, i have a very minor background noise even when i use it with batteries. It's just spectacular how low the noisefloor is, i never had anything that sounded so black.
The sound itsself is as described dead neutral, no warmth, but no brightness or harshness either. I really enjoyed it a lot with my Valkyria, it made me realize that it is not as dark as i originally thought. It's still a dark headphone, but it has some very enjoyable sparkle, it's not completely muted in the treble as i have experienced it with some tubes (with the Western Electrics in the Envy it gets too warm and dark).
The Serene is truly perfect as judging a headphone without any colouring, no sharpness, no added warmth, just pure extension on both ends, and it plays the headphone exactly as it would sound on a dead neutral amplifier without having a drawback like being lifeless, soulless, or in any way negative. Except one trait which i'll get get to soon.
How much power has it? It seems decent, but maybe my one major gripe is affected by the thought that it may not have that much power for being a good headphone amp. I think it can power every headphone decently except the truly demanding ones (1266, Susvara, OG HE-6, probably Tungsten etc).
The texture of the sound is perfect, soundstage is good, separation is fantastic, it sounds very revealing and the noisefloor ist just jaw droppingly black. So, what is my problem with the Serene as a headphone amp?
It massively lacks dynamics. When i was listening to the Valkyria on a piano album, everything sounded perfect. Then i switched to some metal and thought: "Huh, that sounds soft, why is that the case when the Valkyria is one of the two hardest hitting headphones in existence?".
I tested it with IEM's, actually also a soft experience. The Mass Kobo is very dynamic, i immediately noticed the difference, suddenly my music was way more engaging again. If that comparison would be the only failing point, the option to use it as a direct headphone amp would be still decent in my opinion. I have my 500€ Rebelamp here, and the dynamics are the same as with the Mass Kobo, it easily beats the Serene. I know that the Rebelamp is somewhat specialized in a very punchy and also warm sound (the Serene sounds way cleaner, better separated etc), but the dynamics are just something the Serene is lacking, and the difference is huge in my opinion compared to the Rebelamp. I guess a Schiit amp for the same or slightly higher price as the Rebelamp will also outslam the Serene hard.
I really like good dynamics (who would have thought that with my headphone selection, a shocker, i know). There is a reason i dislike Stax and DCA headphones.
While the Serene does everything else perfectly, the dynamics are in my opinion so lackluster that i would not call the headphone amplifier output "good". It's decent at best. If you're the guy that does not need strong dynamics, you may be fine with it, for me it's such a drawback that i'll use it only sparingly as a headphone amp, for example when i don't care for dynamics in an album or when i want to judge a headphone without any colouring from the amp. The transparency is impressive, the noisefloor is truly non-existent, but the punch and slam are so weak that i would highly suggest getting a 300-500€ amp, a Schiit unit / or a Rebelamp if you're planning on using the Serene as more than just a testing tool.
Maybe it had to be done this way, maybe you can only achieve such impressive technical aspects by sacrificing one thing, but for me that aspect of the headphone out is almost a dealbreaker. By the way, this complete lack of dynamic is not bound to the volume, it will have plenty of loudness for 99% of headphones. Also, this problem is only present with the headphone out aka XLR1 -> directly to your headphone / IEM, it's not like the final amplifier you're using the Serene with will suddenly drop in dynamics, that's not the case. It's only when you use the Serene as a final amp yourself that you'll notice that.
Maybe i sound too harsh, i know all of my amps are extremely punchy. The rebelamp is warm, compared to the Mass Kobo muddy and less separated / clean, but it's exceptionally punchy. The Mass Kobo 475 has the same very nice dynamics, but now you also have a nice musicality added which sounds clean, the muddyness of the Rebelamp is gone and the warmth is reduced. Of course my Envy with any tubes is highly dynamic, i also can't really test it with worse tubes since i don't have any.
So now i'm thinking that every amp i own is exceptionally punchy, maybe that is the case. However, the Serene's headphone out via XLR1 is so lackluster in that regard that i can hear it immediately, even with IEM's.
For me the experience of the Serene as a preamp is truly perfect, as a headphone amp that one flaw is so severe for me, that i would get a cheap headphoneamp which sounds (way) less clean to trade in some punch and slam. For me that also explains why you have to go out of your way to use the Serene as a headphone amp, the manufacturer clearly gave the preamp function the whole focus, otherwise it would have a standard headphone out at the front. I'm not going to punish the Serene in this review too much for that fact though, how would you rate for example a Chord Dave which might be a 10/10 DAC that has a headphone output which may not sound that good (haven't heard it, it's just an example)?
If you want a headphone amplifier, get a Bliss or something else.
As a preamp, the Serene gets my full recommendation.
