Positive Feedback Logo

KECES S300+ Stereo Amplifier

08-05-2023 | By Dean Waters | Issue 128

Dean Waters on the hardware:  First contact with the KECES S300+ Stereo Amplifier

I've been given the wonderful opportunity to listen to and evaluate the KECES S300+ dual-channel Class A / Class AB hybrid amplifier. What a marvelous experience! First time I've had goosebumps listening to recorded music since I can't remember how long. This is an exceptional amplifier. A hands-down new favorite of mine. It's beautiful in both appearance and sound quality. A stunning achievement from KECES worthy of being proud of.

Beautiful, bold, and stately.

In the box you get the amp, a standard power cable, a 3.5mm trigger cable (for remote power on/off) and a user manual.

Back view from above

Built like a tank!

Some of the internal circuitry, showing the level of audio craftmanship involved.

Back panel


See HERE for KECES's complete specification summary.

Some details

The KECES S300+ provides 130w of power at 8 ohms continuous and a peak of 240w. This is more than enough unless you're driving truly giant speakers. Or you're trying to fill a small arena or large church. Even when I crank up the volume as loud as I can stand it, I'm still at just under 50%. Any louder than that and the neighbors will put a "For Sale" sign in the yard. I detected no noticeable distortion even at crazy-loud listing levels. The S300+ handles this with ease. If you have 4-ohm speakers, you get 225w per channel continuous power (300w peak).

There are three distinct "modes" that the S300+ can operate in:  Stereo, Bi-Amp, and Bridged. The Stereo mode behaves like any normal 2-channel amplifier. Hook up left/right inputs and connect left/right speakers to the outputs and voilà!, you're done. If you have one S300+ and two speakers, this is the mode you will use. If you're lucky enough to have TWO S300+s, you get to pick from the other two available modes. In either Bi-Amp or Bridged modes, each S300+ will drive a single speaker.

Bi-Amp mode requires speakers with separate LF and HF terminals. In Bi-Amp, you'll provide a single input (RCA or XLR) to each S300+. You then connect the left speaker output of each S300+ to the speaker's LF terminal and the right speaker output to the HF terminal. Bridged mode also uses one S300+ for each speaker, but with much more power (as if one S300+ isn't enough). Bridged mode provides a whopping 410w at 8 ohms to a single speaker. Guaranteed to drive your neighbors crazy. Bridged mode and Bi-Amp are similar in that each amp drives a single speaker. The primary difference is Bridged doesn't separate LF and HF and more than doubles the raw power.

The S300+ is a split-personality as far as amplifier class is concerned. There is a bias switch on the back of the unit that allows the S300+ to function as an AB class amp ("Low Bias"). Flip the switch to High Bias, and the S300+ will dedicate 5w per channel as pure class A. In my listening, the High Bias setting smoothed out the sound just a touch over the straight AB Low Bias setting. Delightful. The sound is wonderful and about as smooth as you can get.

Class AB amps are quite inefficient power-wise, and Class A amps are even less efficient than that. There is a price to pay for this inefficiency: Heat! The S300+ runs HOT. After one hour of High-Bias listening, the top surface of the unit measured in at 123.6° F, 43.4° F. over ambient room temperature. Running in Low Bias Class AB yielded a surface temp of 119.8° F. Just a few degrees cooler. The aluminum chassis is 4mm thick on all sides and has large heat-sinks on the inner sides to help dissipate all this heat.

In Low-Bias mode running as a Class AB amp, the S300+ measured a power draw of 91.6 watts at idle. In High-Bias mode running as a Class A/Class AB hybrid, the S300+ had an idle draw of 116.8 watts. In either case, most of that power draw is being converted into heat due to the natural inefficiencies of Class A and (to a lesser extent) Class AB amplifier designs. Personally, I think it's worth the extra heat and energy to have sound this good!

The chassis is solid (and heavy!). The black brushed aluminum finish, curved edges, gold name plate on the front, and wide sturdy feet make this a highly attractive unit. This would be a welcome addition to just about any décor. Just make sure to place it in a well-ventilated area. There is a red/blue power LED just above the power button. Red turns to blue when switched on. The blue power LED is …… bright! Crazy bright. If you listen to music in a dark room, you won't need a nightlight. Chances are you'll either put a post-it note or a piece of semi-transparent tape over the LED. That's a shame because other than that the unit looks great. Oh well.

Put it in a window and passing ships can use it as a navigation aid!

There is a somewhat heightened noise floor with this amplifier. You won't notice it unless you are right next to the speaker with nothing playing in a very quiet room. The noise presents as a light "hiss" with a peak near 12kHz. I was able to reduce the noise floor somewhat by upgrading the power to an RSX Power8 power distribution box and upgraded power cables, compared to the included standard power cable plugged directly into the wall outlet.

Ambient room noise with the S300+ powered off. Measured 1" away from the speaker.

Same measurement with the S300+ powered on. The peak on the right-hand side of the graph is just over 12kHz. This is measured using the included power cable plugged directly into the wall.

Listening experiences

I fell in love with the S300+ almost immediately. I would characterize this amp, above all else, as revealing. For the first time ever, I was able to hear what my speakers were capable of. I began my journey with the S300+ by hooking it up to my iFi iDSD Pro Signature DAC as a source and a pair of JBL S312 speakers. I've owned these speakers for about a decade now, and I have no idea what I paid for them when I bought them. I always thought they were "good," "acceptable," "decent" speakers. Certainly adequate, if nothing to write home about.

That changed! And boy howdy, did it ever. Twenty minutes in and I found myself saying, "I had NO idea these speakers could do THAT!" It's weird to think that I fell in love with my speakers after listening to them for 10 years. But there you have it. The S300+ brought to life all that the speakers could offer. In the final analysis, I'd say that's about the highest praise I could give an amplifier. Turns out my DAC has a noise floor of its own. Never knew until now. My old amp was never good enough to reveal the limitations of the DAC. Did I mention that this amp is revealing?

After about 10 hours of listening over three days, I took the amp over to a friend's house and hooked it up to his pair of SVS Ultra Tower speakers. He's had these speakers for a long time and is familiar with how they sound. He was astonished at the difference. He, too, was saying "I didn't know that was possible with these speakers." He raved about the increased clarity compared to his old amp. We spent about 2.5 hours listening to Verdi, Widor, Disney, The Mamas and The Papas, The Beatles, and The Vocal Majority. We were in HiFi heaven. I didn't have the heart to take the amp back immediately, so I let him keep it for a few days….

After we had listened to the SVSs, we then drug out his pair of JBL ES80s and swapped out the SVSs for these for comparison. We were instantly disappointed. Not in the S300+ mind you, but in the ES80s! Just as the S300+ revealed what the SVSs could do, it also revealed what these ES80s couldn't do. Again, I go back to the word "revealing." With the S300+, you'll either fall in love with your speakers, or you'll want to throw them off a cliff. (Hopefully the former!)

All told, I have only about 20 hours of use so far. I think it's just starting to break-in, so some of my comments should be considered to be provisional. As is sometimes the case with higher end gear like this, it gets better with continued use. At least that's what my ears are telling me. (Think "bloom"!) In addition to all the aforementioned titles above, I've also been enjoying the remasters of Andre Prévin's recordings of Shanker, Gershwin, Prokofiev, and Tchaikovsky. It's a real joy to listen (and re-listen) to these on a better version of my own speakers thanks to the KECES S300+.

Some final thoughts on the KECES S300+

Remember to place this amp in a very well-ventilated area. I have mine sitting on a credenza about a foot away from the DAC. Nothing else nearby. I would advise against putting this into any type of fully or semi enclosed cabinet. If you do plan on putting it somewhere other than out in the open, a small quiet low RPM fan wouldn't be a bad idea. I'm thinking about placing a spare 140mm PC fan on top of the unit just to assist in the convective airflow for cooling.

If you're facing a choice to either upgrade your speakers or upgrade your amplifier, choose the latter. Upgrade the amplifier first. As the KECES S300+ shows, you likely have no idea what your current (or new) speakers can do if your amplifier is sub-par compared to the true capabilities of the speakers.

KECES S300+ Stereo Amplifier

Retail:  $3499



2F., No.4, Ln.163, Xinyi Rd., Banqiao Dist., New Taipei City 220636, Taiwan

[email protected]