Living Sounds Audio Discovery Warp-1 power amplifier Measurements

Sidebar 4: Measurements

I performed the measurements of the LSA Discovery Warp 1 with my Audio Precision SYS2722 system. The Warp 1 runs cool—after 3 hours of testing, the chassis was still at room temperature. Because the amplifier has a class-D output stage, I inserted an Audio Precision AUX-0025 passive low-pass filter between the test load and the analyzer. This filter mitigates noise above 80kHz and eliminates noise above 200kHz that would otherwise drive the SYS2722's input circuitry into slew-rate limiting. Without the filter, 378mV of ultrasonic noise with a center frequency of 454kHz was present at the amplifier's output terminals. The level of the noise was not affected by the amplifier's gain setting (see later). I used the Audio Precision filter for all the tests other than frequency response.

The LSA Warp 1 has four gain settings, labeled "0dB," "6dB," 14dB," and "20dB," these selected with internal DIP switches. The default setting is "6dB," in which condition the voltage gain at 1kHz into 8 ohms was 27.4dB with both the balanced and single-ended inputs. The "0dB" setting, which TF had found optimal with his Benchmark LA4 preamplifier, reduced the gain by 6.1dB. The other two settings respectively increased the gain by 7.9dB and 13.8dB compared with the "6dB" setting. The Warp 1 preserved absolute polarity, ie, was noninverting, with all the gain values and both input types.

The LSA's single-ended and balanced input impedance is specified as 47k ohms. I measured 47.4k ohms at 20Hz and 1kHz for the single-ended inputs, decreasing to 41.5k ohms at 20kHz. The balanced input impedance was 49k ohms at low and middle frequencies, 44k ohms at the top of the audioband.

Fig.1 LSA Warp-1, frequency response at 2.83V into: simulated loudspeaker load (gray), 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta), and 2 ohms (green) (2dB/vertical div.).

Fig.2 LSA Warp-1, small-signal 10kHz squarewave into 8 ohms.

Considering it's a bridge-tied load design, with two output stages in series with the speaker in each channel, the Warp 1's output impedance at low and middle frequencies was relatively low, at 0.11 ohms. However, the impedance rose above 1 ohm at the top of the audioband, which led to the amplifier's small-signal frequency response at 20kHz rolling off by 1dB into 4 ohms (fig.1, cyan and magenta traces) and by 4dB into 2 ohms (fig.1, green trace). Into our standard simulated loudspeaker, the variation in response in the audioband, due to the Ohm's law interaction between the amplifier's source impedance and the impedance of the simulated speaker, was +1/–0.3dB (fig.1, gray trace). The LSA amplifier's response into 8 ohms (fig.1, blue and red traces) peaked sharply between 40kHz and 50kHz, which correlated with some critically damped overshoot in the Warp 1's reproduction of a 10kHz squarewave into 8 ohms (fig.2).

Fig.3 LSA Warp-1, spectrum of 1kHz sinewave, DC–1kHz, at 1W into 8 ohms (left channel blue, right red; linear frequency scale).

The Warp 1's channel separation (not shown) was excellent in both directions in the midrange, at >100dB, though it decreased to 62dB at 20kHz. The unweighted, wideband signal/noise ratio (ref. 1W into 8 ohms with the auxiliary filter and measured with the single-ended inputs shorted to ground) was very good, at 72.1dB (average of the two channels). This ratio improved to an excellent 83.7dB when the measurement bandwidth was restricted to 22Hz–22kHz, and to 88.3dB when A-weighted. Spectral analysis of the low-frequency noisefloor while the LSA amplifier drove a 1kHz tone at 1Wpc into 8 ohms (fig.3) revealed that AC-related spuriae were absent.

Fig.4 LSA Warp-1, distortion (%) vs 1kHz continuous output power into 8 ohms.

Fig.5 LSA Warp-1, distortion (%) vs 1kHz continuous output power into 4 ohms.

The Warp 1's output power is specified as 150W into 8 ohms (21.8dBW) and 250W into 4 ohms (21dBW). With our usual definition of clipping—when THD+noise reaches 1%—I measured a clipping power of 110Wpc into 8 ohms with both channels driven (20.4dBW, fig.4) and 165Wpc into 4 ohms (19.16dBW, fig.5).

Fig.6 LSA Warp-1, THD+N (%) vs frequency at 20V into: 8 ohms (left channel blue, right red), 4 ohms (left green, right gray).

Fig.6 shows how the percentage of THD+noise varies with frequency into 8 and 4 ohms at 20V (equivalent to 50W into 8 ohms and 100W into 4 ohms). I couldn't examine the THD+N percentage into 2 ohms at this voltage, as the amplifier muted its outputs after just 3 seconds and the red "Amp Fault" LED illuminated. This happened after 3 minutes with the amplifier driving the same voltage into 4 ohms, for an output of 100W. The distortion into the higher impedances was very low in the bass and midrange but rose considerably in the treble.

Fig.7 LSA Warp-1, left channel, 1kHz waveform at 50W into 8 ohms, 0.011% THD+N (top); distortion and noise waveform with fundamental notched out (bottom, not to scale).

Fig.8 LSA Warp-1, spectrum of 50Hz sinewave, DC–1kHz, at 50Wpc into 8 ohms (left channel blue, right red; linear frequency scale).

Fig.9 LSA Warp-1, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 100Wpc peak into 4 ohms (left channel blue, right red; linear frequency scale).

With this very low distortion level, the harmonics' contributions to the waveform (fig.7, bottom trace) are obscured by the residual audioband noise. Spectral analysis, however, indicated that the third harmonic was the highest in level, at just –97dB, right (fig.8, red trace) and –101dB, left (blue trace), although this graph indicates that the second harmonic and higher-order harmonics are also present. With the Warp 1 driving an equal mix of 19 and 20kHz tones at 100Wpc peak into 4 ohms (fig.9), the 1kHz difference product lay at –100dB (0.001%), though the higher-order products at 18 and 21kHz were almost 30dB higher in level.

LSA's Discovery Warp 1 offers respectable measured performance and relatively high power in a small, cool-running package.—John Atkinson

LSA Electronics
89 Kahana Makai Rd.
HI 96761
(770) 667-5633

cognoscente's picture

Thank you, good to know, so nice to read .this brief history about amp types.

I was never a believer in tube amps, they have limited listening hours and lack control and detail. And I was never a believer in class d amps, which sound too cold and artificial. I swear, swear, by toroidal transformer class a/b amplifiers.

Until I was able to buy a new Nad C298 class d amplifier as a real bargain. And this Nad is already a bargain compared to the Nad Master series or competing amplifiers from Primaire or T&A with the same Purifi Eigentakt module. Of from Purifi of couse. Anyway, the Nad C298 now replaces the power amp section of my Hegel H360, which only serves as a USB receiver, proprietary re-clocking and preamp. DA conversion is done via the HoloAudio Spring 3 3.

It was immediately clear, the Nad C298 sounds fresher, clearer, more detail, more crips and attack and with a tighter bass. You can better hear the piano strings vibrating, the fingers sliding over the strings. Then you would say it also must sounds more tangible, more "live" present (in-the-room), more real with all those extra details? But that's the funny thing about human hearing. So no. It sounds also clinical, the feeling, the emotion is gone. In other words, the music is gone. At the Nad, like all the sets of my audio friends, you listen "to a set" and not to "live" present music (in the room). Your ears tell you. I'm exaggerating to make my point, you have to sit down (and listen carefully) to hear the difference, but still, then the difference is obvious. As if the Hegel is squeezing detail to provide more power, to sound more muscular, more mature, more "live" present, while the Nad is doing the opposite, as if it squeezing the power in the bass to bring out more detail to the surface. To sound fresher, younger. I say my Hegel H360 sounds like a Ford GT while the Nad sounds like a Porsche 911. Which one is more fun to drive? It just depends on what you prefer. I can switch with both power amps available. Still, I almost always choose the Porsche. I'm more of an audiophile than a music lover after all. I want to hear everything. The art of omission! Not really I'm afraid.

Probably a (for me) priceless class a/b amplifier can offer the same freshness, clarity, detail with the same crips, attack and tight bass as this Nad while retaining the musicality, the emotion and live (in-the-room) feeling, perhaps but as said that is unattainable and that's why I don't even want to know. I'm happy with my Porsche. And Bugatti ... whatever

Kursun's picture

Would you believe toroidal transformers are actually inferior to EI transformers?

This hobby of ours, hi-fi, is a hobby of prejudices!

Ortofan's picture

... record review, or little more than an advertisement for this product?

How did it perform/sound compared to the Benchmark amp?

The B&W 808 speakers have a minimum impedance of 4 ohms and can handle up to 200W on a continuous basis. The LSA can't sustain even 100W into a 4 ohm load without shutting down.

The LSA can't meet its rated power output, doesn't have a load-independent frequency response and has relatively high levels of IMD. The designer needs to go back to the drawing board.

If the amp contains special Coilcraft inductors that are supposed to remove/filter class-D switching noise from the audio output, then why did JA1 need to use an Audio Precision AUX-0025 passive low-pass filter between the test load and the analyzer. Either the filter built into the amp functions as claimed, or not.

As stated above, if you're in the market for a class-D power amp, then choose the NAD C 298, instead.

Kursun's picture

-"If the amp contains special Coilcraft inductors that are supposed to remove/filter class-D switching noise from the audio output, then why did JA1 need to use an Audio Precision AUX-0025 passive low-pass filter between the test load and the analyzer.

Filter was used during NAD C 298 tests too:
-"The C 298 has an output stage operating in class-D, so I inserted an Audio Precision auxiliary AUX-0025 passive low-pass filter between the test load and my Audio Precision SYS2722 system (see the January 2008 "As We See It"). This filter eliminates RF noise that could drive the SYS2722's input circuitry into slew-rate limiting, and I used it for all the tests other than frequency response."

Long-time listener's picture

"Class-D amplifiers started to appear in audiophile-grade components about 10 years ago..."

Interesting -- I recall auditioning a pair of Jeff Rowland digital monoblocks about 20 or more years ago.

Ortofan's picture

... TacT Millennium, introduced in 1998. That amp later became the Lyngdorf Millennium. It incorporated technology from Toccata Technology. Toccata Technology was eventually acquired by Texas Instruments.

Two members of the Toccata Technology team were Lars Risbo and Claus Neesgaard. They went on to work at TI.

Subsequently, Lars Risbo - along with Bruno Putzeys and Peter Lyngdorf - co-founded Purifi, of which Claus Neesgaard is a co-owner.

JRT's picture

If you want to try a TI TPA3255 based amplifier, consider trying the Fosi Audio V3 and 48VDC 5A switch mode power supply (avoid the 32VDC supply). At the online store at the Fosi Audio website, that bundle is priced at a penny under $110 and there is also a $10 off coupon, free shipping, and 24 month warranty. So it comes in at under $100 direct to your door.

That is a relatively recent addition to Fosi Audio's line, but has already received numerous favorable subjective reviews. And for objective measurements, Amir has posted a review, also very favorable, at his ASR discussion forum.

Here is a Google websearch on the subject:

Here is another Google websearch specific to the youtube website:

It is useful to consider amplifier output signal voltage. Loudspeaker sensitivity is most usually specified as a voltage sensitivity relative to 2.83 Vrms pink noise signal across the loudspeaker input terminals, with output measured as B-weighted SPL with the propagation distance normalized to 1 meter. Amplifiers most usually are designed ro provide a constant gain in voltage (not power) when operating below significant clipping, often represented as 1% THD+n, which can also be stated as -20dB THD+n.

With 48VDC 5A supply, Amir measured -74dB (.02%) THD+n at 141 Wrms into 4 Ohm load, corresponding to 23.75 Vrms across that load.
(141*4)^(1/2)= 23.75 Vrms
And relative to 2.83 Vrms that is
20*log(23.75/2.83)= +18.5dB

At 1% (-40dB) THD+n, 160 Wrms continuous into 4 Ohm, corresponding to 25.30 Vrms.
(160*4)^(1/2)= 25.30 Vrms
And relative to 2.83 Vrms that is
20*log(25.30/2.83)= +19.0dB

And for 20ms IAW CEA-2006/490A (suitable for headroom for brief crests in the music signal), at 1% THD+n, 190 Wrms into 4 Ohm, corresponding to 27.57 Vrms.
(190*4)^(1/2)= 27.57 Vrms
And relative to 2.83 Vrms that is
20*log(27.57/2.83)= +19.8dB

For $100 the Fosi Audio V3 might be sufficient in some applications, but don't expect Purifi modules at that price.


That said, if you want to spend $1.1k on a two channel stereo class D amplifier, then I would suggest that there are other better alternatives than anything utilizing the TI TPA3255 chipset.

For example, investigate some offerings from Buckeye Amplifiers, all prices direct, with free shipping. Buckeye's "Purifi 1ET400A Amplifier, 2-channel" is $1095. And their "Purifi 1ET400A Amplifier, Monoblock" is priced at $750/each, $1.5k/pair.

The new (currently on backorder) Buckeye "Hypex NCx500 Amplifier, 2-channel" for $1095 with free shipping. That uses a new improved Hypex module in competition with the Purifi Eigentakt modules.

Buckeye's "Purifi 1ET7040SA Amplifier, Monoblock v2" is priced at $950/each, $1.9k/pair. That uses Purifi's newer improved higher current module, etc.

There are some very good amplifiers from NAD using the older Purifi 1ET400A modules, such as the C298 priced at $2.4k MSRP. Safe and Sound is currently advertising some factory refurbished units priced at $1.8k. But for only $100 more I would rather have the Buckeye monoblocks with the newer modules, higher current power supply, etc.

Ortofan's picture

... approvals from the relevant regulatory/safety agencies?
Photos of the amps do not appear to show the markings that would indicate those approvals.
Skipping that step is one way to reduce the cost of a product.

JRT's picture

Depending much on the device (consumer electronics are not medical devices or aircraft radios) the markings can be self-certifications of compliance to governmental regulations and/or industry standards, and do not necessarily require any validation with third party qualification testing or qualification testing by any regulatory agency.

That said, below is an image of the 48VDC 5A external switch mode power supply sold by Fosi Audio, and included in the $109.99 ($99.99 with $10 off coupon) Fosi Audio V3 48V bundle. Notice the CE Marking and FCC Marking. The amplifier itself is a low voltage device, does not directly connect to powerline voltages.

Ortofan's picture

... UL/CSA safety approvals for the amplifier unit itself?

afgverhart's picture

It is always interesting to read all these comment from people who - I think - have never heard this amplifier in real life. Well, I did, actually, I own one after having owned nCore 400 mono blocks as well as a Purifi Eval 1 design. The Warp does indeed not have this typical class D top end that other class D designs tend to have. And yes, I have heard them all, well most of them at least.

My Warp One has been driving Dynaudio Contour 3.4 LE, Dynaudio Confidence C2 Platinum, Focal Scala Utopia Evo and most recently Dynaudio Contour 60i comparing it with a NAD M22 and a Hattor nCore class D design. The Warp One was the best sounding amp, again. It sounds detailed (but not too), with black backgrounds, it separates instruments excellently and best of all: it sounded most natural. The Warp has a flow to it - some call it PRaT - that I have not heard better from any class D design. and the bass reproduction is sooo nice and layered. It’s addictive.

My advice: don’t have yourself fooled by the above comments or measurements, but just listen to it before forming an opinion on it.


Poor Audiophile's picture

"but just listen to it before forming an opinion on it."
That should always be the case IMHO.

JRT's picture

This Living Sounds Audio Discovery Warp-1 power amplifier has a reset switch on the rear panel.

When was the last time you had an amplifier in need of a reset?

What makes this amplifier vulnerable to a control failure in need of a reset? What is the behavior during that failure? What happens if the consumer fails to push the button?

Ortofan's picture

... circuit breaker, rather than having a fuse.

David Harper's picture

in need of a reset? My schiit Vidar amp when driving my magnepan LRS speakers often shuts down due to current/thermal overload. It's no big deal I just turn it off and on again, turn the volume down a bit, and it's good to go.

Delius T's picture

So, he is out of jail?

Mark Schifter of AV123 Indicted by Grand Jury on Five Counts