Douk Audio A5 2 Channel TPA3255 Stereo Amp, 300 Watts x2 Mini Hi-Fi Audio Power Amplifier Class D for Home Theater System, Passive Bookshelf Tower Speakers with High-Pass Filter + 32V Power Supply

The Douk Audio A5 is my first foray into the intriguing new landscape of small class D amplifiers from China. As someone who got into "hi-fi" in the 1970s, I have always equated amplifier power with amplifier weight and size. Beefy power required heavy massive amplifiers. It was just an inarguable fact. Seeing the recent proliferation of these toy sized amplifiers definitely piqued my curiosity about whether these things could seriously be considered to be in the same league as traditional audiophile amps.I recently bought a pair of Elac Carina BS243.4 bookshelf speakers and found them to be power hungry. I had been using a Monoprice Pure Tube amp to drive them but the 10 watts per channel was insufficient to drive these speakers with any authority. I was looking for some additional clean power to be fed by the Monoprice amp (Love the sound of this amp!) working as a preamplifier, and wondered about one of these amps from Aiyima, Fosi, and Douk, etc. While I know the power ratings on these units are exaggerated, I was impressed with the measurements and reviews I saw online. With this Douk A5 on sale for only $85, I figured it was worth a shot.To say I was blown away by the sound of this amplifier is a huge understatement. The performance is incredible regardless of the price. When taking the price into account, it is truly absurd! In addition to the plentiful power, it managed to preserve the holographic imaging and soundstage of the Monoprice Tube amp. I remember reading some reviews that compared the Douk A5 favorably to multi-thousand dollar amplifiers, and thinking "Aw come on, that is ridiculous". Well I have now been thoroughly enlightened! I think there is a generational paradigm shift underway in the area of home audio amplifiers to the great benefit of audiophile consumers. These tiny class D amps with PFFB technology are the real deal!The only downside I can think of is the appearance of these amps are so cheap and toy like. You are not going to impress anyone with the looks of these as compared to a large, heavy, fancy, stylish, conventional class AB or class A amplifier. But how much are you willing to pay to impress people?I had ordered this with a standard 32V power supply and was curious what the performance increase would be like with the 48V power supply. So I ordered one. Performance was definitely raised a notch with more controlled and robust bass. I could really crank up the sound with the 48V power supply (71 watts @ 6 ohms -> 110 watts @ 6 ohms). However it makes the amp run HOT as the chassis serves as the heat sink. I removed the glass panel on top and replaced it with a piece of steel mesh but it is still very hot. Hopefully this does not affect the lifespan of the unit.Bottom line -This amp is a mind blowing value. As I listen to my system while I type this review, I am still having trouble reconciling the incredible sound I am hearing - with visual disconnect of seeing this tiny little unit being responsible for it.

I found the sound of the Douk Audio A5 stereo amplifier to be natural sounding and dynamic. Although not noted in the provided product documentation, my understanding is that the Douk Audio A5 amplifier features post filter feedback (PFFB) for improved sound. PFFB can result in an amplifier achieving overall flatter frequency response that is less affected by speaker impedance changes across the audio spectrum. The right knob is the volume control. This control doubles as the power switch. There is no power indicator LED on the front panel of the A5.There are 3 multi-segment LEDs inside the A5 amplifier. These LEDs can be configured via dip switches located inside the unit to provide Red, Green or Blue illumination (or any combination of these three colors) to the inside of the A5 amplifier. There is a clear insert in the top cover of the A5 that can be easily removed to access the dip switches and the A5's other circuitry. There are two swappable op amps inside the A5 amplifier that can be changed if desired. On the rear of the A5 there is a 3.5mm output connection labeled Aux Out. I confirmed that the A5's Aux Out level is variable, full frequency. (Douk Audio could have labeled the 3.5mm connection as Pre Out or Sub Out.) The Aux Out level is controlled by the volume knob setting on the A5.The left knob on the front of the A5 lets you activate and adjust the high-pass filter. When switched on, the high-pass filter can be set anywhere between 30Hz and 200Hz. (Note that there are no conventional bass or treble tone controls on the A5.) The high-pass filter only affects the speaker level outputs and has no effect on the Aux Out's audio. Even without a subwoofer the A5's high-pass filter can be useful if you desire to roll off the lowest bass frequencies that are sent to the speakers.The A5 comes with a Douk/Nob Sound branded power supply rated at 32 volts and 5 amps. The included A5 documentation states the A5 is capable of 300 Watts x 2 @ 4 ohms. With the stock 32V/5A power supply I estimate the A5 is able to deliver ~50 Watts per channel output @ 8 ohms. You can substitute a 48 volt, 10 amp power supply so that the A5 would be able to deliver its maximum power. The case of the A5 amplifier, when used with the stock 32 volt power supply, runs about the same temperature as the Aiyima A07 Max with that amplifier's stock 36V/6A power supply. The A5's case temperature reading was ~82F, in standby and 90F when in use. In comparison, the Fosi Audio TB10D amplifier's case measured 72F, in standby and in use. [Update: I measured the standby power consumption of the A5 amplifier. Plugged in, not switched on, the power consumption measured 0.3 Watt. Powered on, no input signal, 4.7 Watts.]