20 euro ZK-MT21

But to the point. We came across one of these mini amplifier modules, priced at just 20 euros, on the amazon.de online store. The price of 20 euros combined with 2 x 50 W + 100 W power, adjustable subwoofer crossover frequency and level, bass and treble controls, Bluetooth connectivity and good reviews, piqued my interest so much that I had to order one. The product seems to be sold on many channels under different “brands” but the model is all the same ZK-MT21. The brand of our version was WANGCL. The price seems to vary between 10-40 euros depending on where you buy it.

To be precise, the ZK-MT21 is not “just” an amplifier module, but its delivery also includes separate cover and base plates and their mounting hardware. With these, it becomes a mini-sized 2.1-channel desktop amplifier.

There is also an almost identical parallel version of the amplifier with the model number ZK-TB21, which has, at least in theory, a higher-quality TPA3116 class D amplifier circuit manufactured by Texas Instruments. The “basic model” uses the Chinese CS8673e circuit. By the way, the promised power is 2 x 40 W + 80 W, when the Texas power is “really” 2 x 50 W + 100 W. But more on power later.

In the ZK-TB21, some components are also “higher quality” and there is also a separate screw terminal for the power, while the MT21 only has a plug connector (if that makes any difference). This model with the TI circuit was only 8 euros more expensive than the basic model on Amazon, but since we had already ordered the cheaper version, we’ll go with it. In addition to Bluetooth, the amplifier also has one line input with a 3,5 mm connector.

The operating voltage of the amplifier modules is 12-24 V, and the power supply is not included in the price. It can easily cost much more than the amplifier itself. It is also worth noting that the operating voltage produced by the power supply, as well as its current delivery capacity, naturally affects the amplifier's power. The manufacturer's declared power is stated with a 24 V / 5-9 A power supply. We bought a 24 V / 5A power supply for the module in Finland. It was cheaper and cost 34 euros.

How in practice?

The amplifier was easy to “assemble”. When installing the potentiometer knobs, you had to think for a moment that the knob pointer points in a logical direction in relation to the adjustment range and function of the potentiometer in question. For example, the middle position of the tone control potentiometers is not otherwise marked in any way and the potentiometer also does not have a middle notch, so you go by eye and hope that the zero point of the adjustment is approximately in the middle of the potentiometer's adjustment range.

Then just plug in the speakers: Main channels to 8 ohm speakers (Aurelia Aniara) and as an “emergency solution” the old Epos ES14 floorstanding speaker, also 8 ohm, was allowed to act as a subwoofer (there was nothing else available at the time).