You can hardly enter five forum threads on budget audio without seeing the Lepai LP-2020A+ mentioned. At about 20 U.S. dollars (30 with an AC adapter included), this compact and 20 WPC advertised amplifier looks like a solid deal.
However, despite its popularity, actual information about it seems scarce, aside from the occasional teardown or two. It’s built around a Tripath TA2020-020 class D amplifier chip, which, with its fine specifications and almost 90% efficiency, is what allows for this fantastic power to size ratio.
However, class D amplifiers require far more attention to detail in the circuit board design and component selection than traditional class AB chip-amps (like the classic LM3886). Did Lepai get it right? Does the LP-2020A+ live up to the specifications quoted on the box, or perhaps even the ones quoted in the TA2020-020 datasheet?
Let’s find out! (The less technically minded may want to skip to the verdict)
The LP-2020A+ was powered by a 5 A industrial switchmode power supply. THD+N measurement was done with an HP 339A, low-passed at 30 kHz. A 4/8 Ohm switchable resistive load was used.
Output impedance/damping factor was calculated by setting a loaded voltage of 5,51 V (8 Ohm) and 5,2 V (4 Ohm) and observing the voltage change when the load was disconnected. A VCC of 13,5 V was used for all tests, 13,4 V was the lowest voltage observed.
The results (updated 9.12.2012):
More spectrums (HF noise is included in the unweighted ones):
- 5 W (8 Ohm) unweighted
- 5 W (8 Ohm) unweighted, band limited 20-20 000 Hz
- 5 W (8 Ohm) 10 kHz A-wtd.
- 5 W (8 Ohm) 10 kHz unweighted
- 5 W (8 Ohm) 20 kHz unweighted
- 10 W (4 Ohm) A-wtd.
- 10 W (4 Ohm) unweighted
- Unweighted noise floor (shorted input, volume dial at 12 o’clock)
- A-weighted noise floor (shorted input, volume dial at 12 o’clock)
Sadly, but perhaps not surprisingly, the Lepai did not fulfil the claimed 20 W/ch at <0,05 % THD.
It starts distorting after about 9,6 W into 4 Ohm and 5,6 W into 8 Ohm. It doesn’t show on the THD+N measurements, but the clipping waveform during mild clipping is unorthodox and in my opinion rather intrusive. It causes a popping sound in the tweeters of my test speakers.
It does however far surpass its specification of 80 dB SNR, measuring in at 90,1 dB A-weighted and 87 dB unweighed from 20 Hz to 20 kHz.
Absolute noise measures in at roughly -76 dBV(a). This is 10 dB higher than higher-end amplifiers I’ve measured, and can be audible on many speakers – it is very obvious on mine. If noise above the audible spectrum is included, the numbers falls considerably; if measured unweighted from 10 Hz through 30 kHz on my HP 339A, the noise floor is at roughly -66 dBV. For comparison, that’s nearly two orders of magnitude above the -84 dBV of the Luxman L-120A that resides in my system.
There is also a constant 200 mV P-P noise at about 160 kHz. Even with the low-pass filters in place, this somehow caused the 339A to go haywire when measuring at very low levels (<250 mW). This noise is probably not an issue in everyday use.
A more noteworthy detail about the LP-2020A+ is that it seems to have a considerable notch in the frequency response above 10 kHz, even with the tone controls disabled. After investigating the issue, I was able to conclude that the notch was not present at the input of the TA2020-020 amplifier chip.
I’m not certain about what causes this anomaly, but I’d wager that it has to do with the way Lepai have designed the output filter. This could very well be an audible problem with this amplifier.
The high-frequency anomaly aside, the LP-2020A+ seems to be flat throughout the frequency spectrum down to about 40 Hz, rolling off by 1 dB at 17 Hz.
Build quality wise, you do get what you pay for – the design has a fair few cut corners that deviate from the design guidelines in the TA2020-020 datasheet, in order to reduce component count. The electrolytic capacitors are of varying Chinese brands not renowned for their quality, the potentiometers are pretty nasty and power supply filtering is … minimalistic. All in all, it’s still better than I expected. Soldering quality is decent and the aluminium case is solid.
However, something that struck me about my unit was this:
Yes, there was an almost millimetre-thick gap between the chip and the heat sink! The over-temperature protection would kick in after a few minutes of heavy 4-Ohm loading. Thanks to the efficiency of the TA2020-020, this would probably not have been noticeable in every-day use. However, one must wonder what it does to the chip lifespan.
I entered this with a hunch that the Lepai LP-2020A+ would not deliver its advertised performance. The TA2020-020 chip that it’s built around is rated for 20 W into 4 Ohm at 5 % THD. Despite that, it is still a very decently performing amplifier for the price as long as you stay within its limits. 5 clean Watts per channel into 8 Ohm might not sound like a lot, but for casual near-field listening with small bookshelf speakers it should still be plenty; “normal” background listening level is generally only around 0,1 Watt!
The biggest issue with this unit is the build quality. The casing is good quality extruded aluminium, but the quality control and above all the potentiometers (volume control, bass and treble) are of atrocious quality. The unevenness and scratching of the volume control can be fairly bothersome, especially when close to zero. Since the volume control is connected to adjust the gain of an op-amp rather than simply attenuate the input signal, a bad connection in it can lead to very loud popping and oscillation.
Sound quality wise, there isn’t much to comment on. There is a slight notch in the treble that could colour the sound, but it is a minor issue in this market segment. Other than that LP-2020A+ has a background hiss that’s 10 dB (twice as loud) higher than the considerably more costly amplifier I usually have in my system. Depending on what speakers are used and how sensitive one is to background hiss, this could be an issue, and probably the biggest sound quality concern with the Lepai.
All in all, would I recommend it? The answer is a resounding yes! While it’s hardly “audiophile quality”, you aren’t going to find a better 5-watt-per-channel amplifier for the price – and with proper stereo amplifiers often costing several hundred Dollars, this little Lepai introduces a whole new standard for budget amplification.