Douk Audio A5 2 Channel TPA3255 Stereo Amp, 300 Watts x2 Mini Hello-Fi Audio Energy Amplifier Class D for House Theater System, Passive Bookshelf Tower Audio system with Excessive-Go Filter + 48V Energy Provide

Sound impressions, comparisons, and op-amp rolling results
I will spare the specs and features of this amp, as you can read them yourself, and focus on what you came here for:  how does it sound?[UPDATE: just went through various op amps and the SX52B discrete opamp is by far the best. These are about $14 each on ali*xpress and will transform the A5 into the next level. SparkOS SS3602 are also excellent, but these are almost double the amp’s price, and the SX53B’s get you there for a fraction of the cost. For a total of $128 ($99 for amp and $24 for op amps) this is an unbelievable setup.]Compared to other impressive Class-D amps coming out of China (Aiyima, Fosi, etc) this one is among the best. Very open and detailed, if a tad analytical (a common characteristic for Class-D amps) but below I discuss how this can be improved.The default configuration is crisp, clean, and very detailed. I focus on acoustic jazz, symphonic/chamber music, and opera, so for me midrange purity, soundstage, and imaging are critical. The soundstage here is excellent– a bit narrow vertically, but very good imagining and placement otherwise. This is a very, very good amp, period.I have compared this with Aiyima A07, and the A07 max, which also use the TI-5532 op-amp and provide a socket for trying out other flavors. While these amps have similar sound characteristics, the Douk Audio A5, has the advantage of a high-pass filter, a slightly better design circuitry, and an easily accessible op-amp socket via the removable glass (acrylic) cover.  I did not care as much for the A07 max (sounded a bit thin to me) and this unit and the original A07 sound much more similar to the A5.I tried upgrading this with various op amps, with mixed results.  The LM4562 and OP275 chips seemed to create some muddiness in the midrange (particularly in orchestral passages) that did not sound right; the MUSES02 chip diminished much of the treble region, seeming to remove the delicately brushed cymbals from jazz trios altogether.  I have yet to test out the SparkOS SS3602 on this, but so far this unit has not played very nice with alternate op-amps.  My favorite at this moment is the original 5532 that it came with.  Which is to say, it sounds excellent.To bring back some of the warmth missing from Class-D amps, rather than swapping op-amps, the best bang-for-your-buck upgrade is a tube buffer.  When I coupled the stock A5 with a $35 tube buffer (FX-Audio Tube 01) and two  JAN 5654W tubes ($20) it took everything to the next level.  I would put this up against my much more expensive audiophile amps.So, in short, get this amp.  Most can listen to it as is and get much pleasure and enjoyment out of it.  If you are itching to follow an upgrade path,  spend $55+ in a tube buffer/preamp and see if that does it for you.  The quality this amp provides is simply amazing for its price.

Sonido de alta fidelidad
Excelente producto

Includes post-filter feedback (PFFB), high pass and variable level aux output
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.