A few weeks ago, I received a Konaki KO-3691D Class D subwoofer amplifier ($499.00) to evaluate. Well, the product has been tested, and I came away impressed at the performance for the money.
The KO-3691D is a high power single channel amp, designed to drive subwoofers at any load impedance between 4 and 1 ohms. Power output is rated in the owner’s manual at 500, 900, and 1250 watts into 4, 2, and 1 ohm respectively. As you’d expect with that much power available, the amp isn’t going to fit in your pocket. The KO-3691D is moderately sized, measuring about 20”x 9.5”x 2.5”. Cosmetically the amp is pretty good looking; the sides of the heatsink are chrome plated, as are the removable end caps that hide the wiring connections and controls. Getting really good chrome plating means endless part polishing, which in turn is expensive. For this reason, you don’t see many chrome amps, and if you do, the chrome usually is quite appalling. And while the Konaki’s chrome isn’t going to be confused with a Harley-Davidson part, it’s pretty darn good. The top of the big Konaki amp is a thick piece of aluminum, with a traditional brushed finish, anodized black. In the center of the top plate is a digital voltmeter which provides information on the supply voltage to the amp. The cosmetic treatment results in a combination of understated elegance and enough chrome plating to provide the impressive ‘bling factor.’
I removed the hex head screws that retain the end bells, and had a look at the amps connections and controls. On the connector side of things, all the power and speaker wiring is done on one end of the amp. The power connectors will readily accept 4 gauge power cable, which is what a high power amp needs. Four terminal speaker connections two positive and two negative, were generously sized as well to accept up to 8 gauge wire. The amp comes with four 35A ATC style fuses, which are also mounted on the end panel beside the main power connections. The opposite end of the amplifier is where the RCA input and output connections are made, and where all the adjustable controls live. In terms of control and adjustment features, the Konaki amp delivered a very competent selection, in addition to the usual gain and crossover functions, there is also control for bass EQ, a switchable (in/out) variable subsonic filter, a phase switch, and a wired remote level control. A bright blue LED lights up when the amp is on, and a red one provides an indication of a protection issue. Of course the voltmeter on the top of the amp also illuminates in blue when the amp turns on.
I moved the Konaki amp into my listening room and connected it to my reference system. For this session, the amplifier was connected to a 2 ohm 12-inch subwoofer in a sealed enclosure. With the crossover set at about 100Hz, and the subsonic filter turned off, I spent a while listening to the amp with a variety of different musical genres. During the listening, I had to continually remind myself of the amps relatively economical price, because it sounded good enough to be compared with amps costing quite a bit more. Of course there was plenty of power, and the KO-3691D drove my reference sub with authority and good control. The remote level control worked well, and I played around a little bit with the other controls. The bass boost worked about as you’d expect, but I got a surprise when I engaged the subsonic filter. With the filters control pot set to 15Hz, I flipped the switch to on, and the output seemed to double! In fact, the difference was drastic enough to startle me. I experimented a bit, but it seems like the subsonic filter switch causes additional gain to be applied. This is not a problem if you know about it when you set the gain, but it can be quite a surprise if you’re not expecting it.
Throughout my listening, the only minor complaint I had other than the subsonic surprise was a small amount of pop noise when the amp turned on and off. Not enough to do any harm, and some people may never even notice it, but it was there.
Read on for the Results
On the Bench
Moving from the listening room into the lab, I connected the Konaki to my 16,000 watt load bank, and my 900 ampere DC power supply. Then the Audio Precision was fired up, and I began to exact the numbers out of the KO-3691D. All in all, it measured reasonably well and better than I had expected for a 500 buck piece. The actual power numbers fell a touch short of the advertised power at 2 ohms, but the difference was so minimal, it would not be audible. At 1 ohm, many Class D amplifiers have enough inaudible noise that they exceed the 1.0% limit generally used to determine maximum undistorted power. This was also the case here, so I have included power measurements that were taken at clipping, not prematurely limited by inaudible noise.
I also was able to verify the additional output caused by engaging the subsonic filter, with the frequency set to the lower limit, the amount of boost added was 6dB!
Overall, this is a nice amp with a lot of bang for the buck. Yes, there are a couple of minor technical glitches with noise and the subsonic filter, but the Konaki amplifier is designed to offer high power and reliable performance at a low price, and it does that job well. You could spend a lot more dough on a more famous brand, and end up with much less actual performance.