Lepai LP-2020A+ mini-review and measurements

Thanks goes out to a friend for donating this amplifier for testing! (You know who you are)

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.

The specifications printed on the box (that’s apparently used for two models)

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 test set-up

The test set-up

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):

lepai_results

A-weighted spectrum captured at 5 W into 8 Ohm.

More spectrums (HF noise is included in the unweighted ones):

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.

The LP-2020A+ exhibits this behaviour during mild clipping. Picture taken at 0,3 % THD+N.

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.

There is a constant noise present at about 160 kHz.

Scope view of a 20 kHz sine wave at 5 W into 8 Ohm. The HF noise can be seen as the abnormal thickness of the trace.

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.

Captured at the output, this curve shows that the frequency response peaks at about +1,6 dB at 30 kHz, and is up by over 1 dB at 20 kHz.

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

The LP-2020A+ freed of its case

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:

My LP-2020A+ had very poor heat sink mounting.

Thermal paste was scarce.

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.

Verdict

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.

Image gallery

Front

Rear

Top

Preamp and tone amp op-amps (JRC 4558)

Output low-pass filter. The blue capacitors are 47 nF.

The Tripath TA2020-020 amplifier chip

Solder side

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24 thoughts on “Lepai LP-2020A+ mini-review and measurements

  1. Finally! A review of the LA-2020A+ with actual *DATA*. Thank you!!!

    As a thought, if you want people who haven’t taken at least a basic EE class to make it through the first couple of paragraphs: You might want to include a jargon-free summary, or at least point them to the verdict. ;)

    • That’s a good thought; in hindsight I regret not doing so to start with.

      Anyhow, thanks for the comment, I’m glad you liked the review.

  2. “good quality cast aluminium,”
    It’s extruded aluminum, not cast.

    Also it seems like I’ve seen a bigger capacitor used on the left hand side of these things… Are they cutting corners?

    • “It’s extruded aluminum, not cast.”

      Oh, I’ll fix that!

      And yes, they have used a bigger bulk capacitor before. My unit came with a 2200 µF cap installed while I have seen units with a 3300 µF one from factory. However, given an even half reasonable power supply, 2200 µF should be good enough by a wide margin.

      • Oh, I don’t know that much about electronics… I’m just eagerly waiting for my lepai to arrive.

        Though now I’m wondering where the hell Bukang is located seeing as the printed board says its made there.

    • Wow this is great… Got my LP-2020A+, only it wasn’t a 2020A+. Took it apart and it had 2020B+ printed on the board and it has no Bass/Treb bypass switch.
      After using it a little over a month I touched it to turn it off yesterday and heard a lot of static discharge. Turned it on the next day and all I get now is nasty sounding static.

      Ծ_Ծ

      So now I’m in the market for another cheap amp after wasting $21 dollars…

      • The LP-2020B is an older (and much worse) revision of the unit. While the A+ revision hardly has much build quality to brag about, the older revs are nothing short of horrid.

      • Ouch! Well I discovered that little chip labeled JRC is red hot.
        I don’t like the bass/treb mixers so I may go another route.
        I was looking at some TOPPING’s but they’re a bit much.
        The SMSL are cheaper but I don’t know how good they are.
        Just too many models to research…

      • That JRC chip is the input buffer or tone control op-amp. If you’ve got the know-how, you could just bypass it, or replace it with any off-the-shelf op-amp.

        To be honest, if you’re considering spending money approaching a Topping (about $ 100), I think you might be better off with a cheap Cambridge Audio or Audiosource amplifier. These little class T things are mostly just good for the ultra-low end in my opinion.

      • Don’t know how to bypass that. I’m trying to stay compact and cheap. < $50.
        It's for my Desktop PC which does all my multimedia and I don't want anything needlessly drawing wattage when it's not in use (or in use) and these Class T amps, as far as I know, are more efficient in that aspect.

  3. I can see that un-American mains going through your amplifier measurements. :P

    Do you have the capability to do more thorough testing? As in a sweep of THD+N, and IMD tests.

    • Do you have the capability to do more thorough testing? As in a sweep of THD+N, and IMD tests.

      Yes and no; I can use the ADC of my sound card for measuring stuff with reasonable accuracy as long as I’m using a mains-isolated signal source like the signal generator in my HP 339A. That’s fine for any test that only requires a single static or stepped-frequency sine wave. However, if I use the DAC in my sound card to put out a test signal, I set myself up for a ground loop between the amplifier’s inputs and its outputs. That makes testing single-ended amplifiers unreliable, and testing BTL amplifiers impossible.

      If I had another good quality DAC at hand, doing IMD and sweep tests would not be a problem, but sadly the fun-time budget doesn’t allow for that at the moment.

      I hope that answers your question.

  4. Hi – I got one of these a month or so ago, it’s powering a pair of Whafedale Diamond 9.0’s (86dB / watt) as both desktop (near-field) and in-room for movies & music (room is c. 11′ wide by 17′ long, 8.5 ‘ celiing).

    So far, so good – goes as loud as is possible without risking eviction, and doesn’t leave me yearning too much for my sweet Rotel RA820BX4 integrated (which is languishing in storage) too much.

    The fact that I can just leave the Lepai on 24/7 is convenient ( 10KHz) notch in the FR you report – I can’t interpret your graphs, could you tell me exactly what frequency this notch is at so I can experiment with some test tones?

    • My comment got truncated for some reason.

      What I’m interested in knowing is exactly where the >10KHz notch in the amp’s FR is – I’d to play around with some test tones and see how audible it is.

      Thanks.

      • The relevant curve is here: http://ffseb.files.wordpress.com/2012/11/freq_notch.png

        The mean (“0 dB”) level is at about -1,65 dB. At 10 kHz, the level is up by roughly 0,4 dB. At 20 kHz, it’s up by about 1,2 dB. I strongly doubt you’d be able to detect this with your ears; your speakers have much larger FR irregularities than that. The poor damping factor of the LP-2020A+ is also bound to cause larger variations than that.

      • Thanks!

        Damping factor – hadn’t thought of that.

        I have noticed that with some music the Lepai + 9.0’s sound quite life-like and rewarding, other times less so, and I get an urge to turn the volume up, but doing so doesn’t really improve the experience.

        When I think about it, I think it’s modern, heavily compressed (‘loud’) CD’s that sound OK, but older, more dynamic ones (and vinyl recordings I’ve done)) don’t sound so good.

  5. I’m going to attempt to tune a mediocre piano and want to drive my older HP frequency counter with the microphone built into my new Korg CA-40 Chromatic Tuner. The Korg’s built-in mic outputs on the tuner’s 1/4″ output jack. Will this Lepai amp amplify a very low mic level signal enough to where I could use it as an input to the freq. cntr.? Right now the freq cntr doesn’t trigger with just the output of the Korg. I’m wanting a cheap means of amplification that would provide a dependable signal so I can tabulate the piano’s 88 key string frequencies and input them into a spreadsheet so I can at least try to recover back to normal if my foray into piano tuning (probably) fails. The idea is to solve freq. cntr. trigger problem and then still have a nice little audio amp for other (to be determined) uses. Thanks for your thoughts. I don’t know the impedances or line levels involves,

    • If you wanna amplify a microphone signal, you want to use a microphone preamp. The LP-2020A+ is far too noisy to be at all usable in that application.

      • Thank you, I can see that now. I hadn’t realized that mic outputs and instrument outputs were in the 1 – 3 mv range. I also have since used my laptop mic to record piano keys A0 (leftmost key) and C4 (middle C) and watched the waveforms on the headphone output with my old Tektronix 465 scope. The strings have such strong harmonics that my frequency counter wouldn’t be able to sync on the note’s fundamental without some sophisticated band pass filters. It surprises me that our ears can make sense of analog signals. My guess is that the ear is an audio spectrum analyzer of fantastic capabilities. Then in a different realm, there’s that eye…

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