KECES S4 PRE-AMPLIFIER / S300+ POWER AMPLIFIER REVIEW

Keces is a brand from Taiwan and in this HiFi review, Oscar Stewart takes a listen to the Keces S4 Pre-Amplifier / S300+ Power-Amplifier costing €3990 apiece.

Keces may not be one of the big names in HiFi, however, they have been making a range of power conditioning and power supply products since 2002. A few years ago, in 2017, they released a DAC/Pre-amplifier and since then have gone on to make a couple of power amplifiers along with a small integrated amplifier too. The S4 pre-amplifier is their latest model which features a DS Audio optical cartridge compatible phono stage, and the S300+ is the newest power amplifier in their line-up, with quite a few tweaks over the standard S300. 

Keces is based in Taiwan and aims to build affordable HiFi components that are compact, well designed and with excellent build quality. The S4 and S300+ are both priced at €3990 each, so let’s see how they sound. 

BUILD QUALITY AND FEATURES OF KECES S4 PRE-AMPLIFIER / S300+ POWER AMPLIFIER

The build quality on both units is excellent, but Keces do go for a more utilitarian look with the solid black enclosures made from CNC machined aluminium. They use 4mm thick aluminium enclosures to keep RFI interference at bay, along with aiding in cooling the units’ inner-workings. All the inputs on the S4 are of excellent quality, including Neutrik XLR connectors, and the included remote is also made from machined aluminium. The S300+ also uses Neutrik connectors and one of the upgrades over the standard S300 is the inclusion of WBT-0703Cu speaker terminals – these are excellent quality terminals. Both products have some heft to them, especially the S300+, yet they are compact compared to most full-width products allowing for easier placement in your setup. 

Feature-wise the S300+ is a class A/AB power amplifier with 26dB of gain, a simple power button on the front with LED indicator along with another LED status indicator showing which mode it is in (High/Low bias). It has both XLR and RCA inputs along with 12v trigger support and it can be used in stereo or bridged mono mode if you wish to use a pair as monoblocs. Power-wise in stereo mode you get 130Wpc continuous power @8Ohms, and 225Wpc continuous @4Ohms (going up to 410Wpc @8Ohms in bridged mono mode). Peak power it can hit up to 240Wpc into 8Ohms and 300Wpc into 4Ohms, but wattage isn’t everything – it can handle up to 45 amperes of peak current per channel. Keces put a lot into creating a power amplifier with ample current for demanding speakers and this amp should easily drive most speakers it is likely to be paired with (price-wise) in a domestic setup. Damping factor is extremely high, 4000 at 20Hz, providing excellent control over the drive units of your speakers, it also boasts very low distortion (0.04% THD+N at full power). It is stable down to 2Ohms and one of its biggest features is the High / Low Bias modes – in High bias, the first 5w of power are delivered in Class-A and after this it slowly moves into Class-AB operation. The S300+ features a full dual-mono design with separate power supplies for each side and stage, it uses a JFET input stage and MOSFET driver stage. 

The S4 features a separate power supply / pre-amplifier housing which are joined by the included 4-pin XLR cable, this reduces power supply noise within the pre-amplifier. The pre-amplifier has 2 pairs of balanced XLR inputs and 1 pair of RCA line inputs, there is a built-in low-noise MM/MC compatible phono stage alongside a DS optical cartridge EQ stage. The latter is quite interesting. DS Audio cartridges are becoming increasingly popular, so having this built into the S4 can save you some money if you are thinking of getting a DS Audio cartridge in the future. For outputs you get one pair of balanced XLR outputs, 2 pairs of RCA outputs along with a 4-pin XLR headphone output on the front – thanks to the built-in dedicated headphone amplifier. There are two buttons on the front for dimming the lights and muting the pre-amplifier, along with a switch to change between headphone amp and headphone + pre-amp output. The volume knob acts as the power button and pressing it in will turn the pre-amp on, internally the S4 runs in single-ended, zero feedback Class-A operation with fully symmetrical, dual-mono construction. This allows for complete separation of the L/R sides for lower crosstalk and noise, it also uses a R-2R ladder resistor volume control with 128 steps that are logarithmically tuned for perfect channel balance, no matter the volume level. The S4 has 20dB of gain for line/XLR inputs, 25dB for MM cartridges, 72dB for MC cartridges (with multiple loading options) and 32dB for optical cartridges. 

The S4 and S300+ are an ideal pairing, you can wire them up with the 12v trigger and have everything turn on with the remote for the S4, making it an easy system to live with in a domestic HiFi system like mine. One downside I have found that the LED’s on the front of the S4 power supply and S300+ amp are very bright and this is distracting in a dark room. I did manage to fit some LED dimming stickers over them which brought them down to a much better level of brightness and much less distracting. 

SOUND QUALITY

I’ve been using this combo being fed by an iFi NEO Stream fed into the iFi NEO iDSD 2 then into the S4 via XLR balanced cables. I also hooked up the NEO Stream direct to the S4 using iFi’s premium 4.4mm to XLR cable,

I also have a Rega Planar 3 paired with a Classic Audio Ltd Spartan 5 running into the RCA inputs on the S4. The S4 is then running balanced cables into the S300+, I am running Tellurium Q cables throughout the system and my main speakers are Bowers & Wilkins CM8’s. 

Due to the high gain of both the S4 and S300+, when using these together you may hear a tiny amount of noise through sensitive speakers when you have your ear next to them with nothing playing. This is inaudible when playing music though, and it also means that this isn’t the best pairing for uber-efficient speakers as even on the lowest volume it may be too loud in some situations.

I have mostly been listening to this combo with the S300+ in high-bias mode, to my ears it has better sound quality over low-bias and, due to living constraints, I don’t listen at particularly high volumes meaning most of my listening being fed by the 5w of class-A power that this amp can output. It is an effortless and smooth sound; this is one of those setups that straddles that line of being technically brilliant without drawing attention to itself. It’s not warm, however, it never outputs a harsh or clinical sound either and on my subjective sound spectrum this combo has a tiny tilt towards warm-neutral. In low-bias mode there is a shift towards a slightly more neutral character, and I find that low-bias causes the S300+ to sound slightly less engaging and enjoyable. I feel this is an amp that was voiced to be used in high-bias mode. 

Silverstein – True Romance, one of my favourite Silverstein songs, Shane’s vocals cut through with great clarity and tone, the bass kicks in with great articulation, control and depth. If you’ve listened to a system that runs in class-A you will recognise the effortless delivery that the S300+ offers, however, this is also a powerhouse of an amp and even when switching over to class-AB operation at higher volume doesn’t rob this amp of any of its core character. This is a setup that lets your speakers shine, it’s one that will compliment the right speakers by giving them ample current and drive without sound etched or harsh. This pre-power combo does what any good pre-power combo should – deliver clean and clear sound without drawing attention to itself. The treble is crisp yet well extended and every instrument is well placed within the soundstage. 

Having this setup in your system gives you a chance to fine-tune the source components, the transparency of this pre/power combo allows you to distinguish with ease between downstream components (when paired with good speakers of course). The pre-amplifier and power amplifier are the heart of many systems, as much as a system is only as good as its source material, the pre/power combo can make or break a setup. The S4 / S300+ can easily sit at the heart of a modest system and it simply delivers in the sound quality department. Since having this combo in my personal setup (which has had a lot of component changes over the years) I’ve found myself not worrying about if the amp is well-matched, or if the pre-amp is influencing the sound. I’ve found myself enjoying my speakers a lot more and know that this pre/power combo will do justice to other speakers I am tempted to try in the future. 

I did have a listen via the internal MM phono stage and much like the rest of the pre-amp, it delivers a clean and natural sound, the internal phono stage is more than enough for most setups and it does take a very good phono stage to improve upon the internal one. As a headphone enthusiast, I also spent some time listening to the headphone output – the headphone output on the S4 is really good, not quite enough to fully do justice with the HiFiMAN Susvara but more than capable enough with easier to drive planars and dynamic headphones. The S4’s headphone output did a great job with the Meze 109 Pro, it stands out as clean and natural sounding, and also handled my Beyerdynamic DT880 600Ohm headphones with ease. 

Architects – Downfall, the crushing sound of this song is delivered with weight and power, Sam’s cathartic vocals have grit and are filled with emotion. The guitars occupy their own space and the chugging riffs cut through with great definition, cymbals crash around yet never sound fatiguing or brash. Kick drums hit with authority, the high damping factor allowing the drivers to do their job without overhang, perfect for fast articulate music like this. 

The opening section of Ascensionism by Sleep Token is a slow piano melody with vocals, there is a deep black background to this track and the music comes out of the imaginary abyss with such ease and composure. Vocals are nuanced and perfectly balanced, after a minute or so the track changes with a heavy bass beat coming in and trap-like vocals, the shift in genre is handled with ease. This track shifts again about 2/3rds of the way through into metal and the sound remains articulate and engaging throughout – a brilliant system test track. 

The S4 / S300+ do a great job at tying a system together – the beating heart between your source and speakers of choice. I’ve had amps that have not been a good pairing with certain speakers, others that are less fussy but can sometimes sound a little boring, and then you get the amps that have a clearly audible voicing that works well within certain setups. This combo though, doesn’t fit into any of those categories in my opinion, it is transparent and allows you to hear plenty of detail without sounding clinical, it’s natural and balanced without sounding boring (there is plenty of power for dynamic swings in music), and the voicing here is subtle allowing it to pair with many different components with ease. 

QUIBBLES

Tiny bit of noise when nothing is playing with sensitive speakers, the high gain may not be suitable for high sensitivity speakers and the LEDs on the front of the units are too bright.

CONCLUSION

HiFi Systems are about synergy and (at least in my system) the S4 / S300+ have great synergy between all my components. This isn’t an overly coloured setup that will magically tame a bright setup, or clean up a muddy setup, it does however, deliver sound in an engaging and effortless way. Keces may not be that well known but they should be considered if you are looking for a setup at this price point as they offer up a lot of value for money. 

AT A GLANCE

Build Quality And Features:

Solid 4mm aluminium chassis

Well designed for longevity

High-quality components throughout

Sound Quality:

Smooth, effortless and transparent

Engaging with plenty of power on tap

Value For Money:

Considering the build quality, features and sound quality the S4 and S300+ both represent great value for money

We Loved:

Size, sound and build quality

Price to performance

We Didn’t Love So Much:

High gain means it won’t be suitable for high-sensitivity speakers

LEDs on the front are a bit bright

Elevator Pitch Review: Keces know what they are doing when it comes to offering up excellent sound quality for a reasonable price, this combo may look a little industrial yet the effortless and natural sound it puts makes for an enjoyable and engaging listening experience. The subtle voicing means this setup will pair easily with other components and happily sit at the heart of a system providing plenty of power and current for even complex speaker loads. 

Price: €3990 for the S4, €3990 for the S300+

Oscar Stewart

SUPPLIED BY KECES

SUPPLIED SPECIFICATION

S4: 

• Input – MM/MC*1 / Optical*1 / RCA*1 / XLR*2
• Input Impedance

MC: 56/100/220/470/47K

MM: 47K

OPT: More than 10K

RCA/XLR: 170K

• Output – RCA*2 / XLR*1 / Headphone XLR-4pin
• Total harmonic distortion (THD+N):

MM<0.02%, MC<0.05%, OPT<0.04%

RCA<0.0015%, XLR<0.0015%

• S/N R:

MM: 78dB A-Weighted

MC: 70dB A-weighted

Optical: 75dB A-weighted

RCA: 110dB A-weighted

XLR: 110dB A-weighted

• Gain:

MM: 52dB / MC: 72dB / OPT: 32dB

RCA/XLR: 20dB

• Power Requirement:

Standby: 0.5 Watt

Maximum: 90 Watts

• Casing – All Aluminium
• Dimension (WxDxH) – 300x279x66mm*2
• Weight:

Net Weight 4.5KG(Power) / 3.5KG(Pre)

Shipping Weight 10KG

S300+

• Power Output:

130 watts x2 @ 8 ohm continuous output power

Maximum 240 watts x2 @ 8 ohm

225 watts x2 @ 4 ohm continuous output power

Maximum 300 watts x2 @ 4 ohm

BTL: 410W x1 @ 8 ohm

• Power bandwidth:

5Hz – 160kHz, +0/-3dB

10Hz – 20kHz, +0/-0.1dB

• Current capacity – 45 amperes peak per channel
• Total harmonic distortion (THD+N):

<0.04% at full power

<0.004% at 60 watts

• S/N R:

110dB, input shorted, IHF A-weighted

101dB, input shorted, unweighted

• Inter-channel Crosstalk:

>100 dB at 1kHz

>82 dB at 20kHz

• Gain – 26 dB
• Input sensitivity :

Unbalanced: 1.6V

Balanced: 0.8V per leg

• Input Impedance:

Unbalanced: 50k ohm

Balanced: 100K ohm

• Damping Factor – 4000 at 20Hz
• Power Requirement:

Standby: 0.5 Watt

Maximum: 1000 Watts

• Casing – All Aluminium
• Dimension (WxDxH) – 300x279x133mm
• Weight:

Net Weight 14KG

Shipping Weight 16KG