Solid State Power Amp Reviews

Linn Klimax Solo 800 monoblock power amplifier Measurements

Sidebar 3: Measurements

I performed a complete set of measurements on one of the Linn Klimax Solo 800s (serial number 1593390) with my Audio Precision SYS2722 system. I preconditioned the Solo 800 by following the CEA's recommendation of running it at one-eighth the specified power into 8 ohms for 30 minutes. At the end of that time, the temperature of the top panel was just 81.6°F (27.6°C) and that of the side-mounted heatsinks only slightly higher, at 89.0°F (31.7°C). The Linn amplifier runs cool, especially considering its high rated power.

The Linn amplifier's balanced and single-ended inputs both preserved absolute polarity. (The XLR jack is wired with pin 2 positive.) Linn doesn't specify the Solo 800's input impedance—I measured a reasonably high 7760 ohms from 20Hz to 20kHz for the balanced input, 9930 ohms at 20Hz and 1kHz and 9600 ohms at 20kHz for the unbalanced input. The voltage gain at 1kHz into 8 ohms was 22.4dB balanced and 28.44dB single-ended; these values are close to the specified impedances of 22.6dB and 28.6dB, respectively.


Fig.1 Linn Klimax Solo 800, frequency response at 2.83V into: simulated loudspeaker load (gray), 8 ohms (blue), 4 ohms (magenta), and 2 ohms (red) (1dB/vertical div.).


Fig.2 Linn Klimax Solo 800, small-signal 10kHz squarewave into 8 ohms.

The output impedance, including the series impedance of 6' of spaced-pair cable, was a relatively low 0.17 ohms at 20Hz and 1kHz, rising slightly to 0.187 ohms at 20kHz. As a result, the variation in the frequency response with our standard simulated loudspeaker (fig.1, gray trace) was minimal, at ±0.12dB. The response into resistive loads was flat in the audioband, not reaching –3dB until 90kHz into 8 ohms (blue trace). The rise in output impedance with increasing frequency means that into 2 ohms, the output was down by 3dB at 63kHz. With its wide small-signal bandwidth, the Linn's reproduction of a 10kHz squarewave into 8 ohms featured very short risetimes (fig.2) with no overshoot or ringing.


Fig.3 Linn Klimax Solo 800, spectrum of 1kHz sinewave, DC–1kHz, at 1W into 8 ohms (linear frequency scale).

Although low-level ultrasonic noise was present in the Solo 800's output—this was not affected when I connected the grounding terminal on the amplifier's rear panel to the Audio Precision's chassis ground—the unweighted, wideband signal/noise ratio (ref. 1W into 8 ohms), taken with the single-ended input shorted to ground, was a good 65.6dB. This ratio improved to an excellent 95dB when the measurement bandwidth was restricted to 22Hz–22kHz and to 99dB when A-weighted. Spectral analysis of the low-frequency noisefloor while the Linn drove a 1kHz tone at 1W into 8 ohms (fig.3) revealed very low levels of both random noise and of AC supply–related spuriae.


Fig.4 Linn Klimax Solo 800, distortion (%) vs 1kHz continuous output power into 8 ohms.


Fig.5 Linn Klimax Solo 800, distortion (%) vs 1kHz continuous output power into 4 ohms.


Fig.6 Linn Klimax Solo 800, distortion (%) vs 1kHz continuous output power into 2 ohms.

Linn specifies the Solo 800's maximum power as 400W into 8 ohms, 800W into 4 ohms (both powers equivalent to 26dBW), and 1.2kW into 2 ohms (24.8dBW). Stereophile defines an amplifier's clipping power as when the THD+noise reaches 1%. With that criterion, the Solo 800 slightly exceeded its specified powers into 8 ohms (410W, 26.1dBW, fig.4), into 4 ohms (805W, 26.05dBW, fig.5), and into 2 ohms (1260W, 25.0dBW, fig.6). These high clipping powers were achieved even though the wall voltage had dropped from 117V AC with the amplifier idling to 113.6V AC at clipping into 2 ohms.


Fig.7 Linn Klimax Solo 800, THD+N (%) vs frequency at 20V into: 8 ohms (blue), 4 ohms (magenta), and 2 ohms (red).

The downward slope of the traces at low powers in figs.4–6 is due to actual distortion lying beneath the random noisefloor. therefore examined how the THD+N percentage varied with frequency at 20V, which is equivalent to 50W into 8 ohms, 100W into 4 ohms, and 200W into 2 ohms. The THD+N percentage was very low into 8 ohms (fig.7, blue trace) but slightly higher into 4 ohms (magenta trace) and 2 ohms (red trace). The THD+N percentage doesn't rise at the top of the audioband, which suggests that the amplifier has commendably wide-bandwidth open-loop gain.


Fig.8 Linn Klimax Solo 800, 1kHz waveform at 50W into 8 ohms, 0.0028% THD+N (top); distortion and noise waveform with fundamental notched out (bottom, not to scale).


Fig.9 Linn Klimax Solo 800, spectrum of 50Hz sinewave, DC–1kHz, at 50W into 8 ohms (linear frequency scale).


Fig.10 Linn Klimax Solo 800, spectrum of 50Hz sinewave, DC–1kHz, at 100W into 4 ohms (linear frequency scale).

The distortion waveform was predominantly the third harmonic (fig.8), with no crossover distortion spikes at the waveform's zero-crossing points. The third harmonic lies below –100dB (0.001%) into 8 ohms (fig.9) but rises to a still-low –84dB (0.006%) into 4 ohms (fig.10).


Fig.11 Linn Klimax Solo 800, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 100W peak into 4 ohms (linear frequency scale).

Even at a peak power of 100W into 4 ohms, the high-order intermodulation products with an equal mix of 19 and 20kHz tones all lay at or below –90dB (0.003%, fig.11). Commendably, the second-order difference product at 1kHz lay close to –120dB (0.0001%).

The Linn Klimax Solo 800's measured performance is one of the best I have encountered, offering very high power with extremely low levels of noise and distortion. Wow!—John Atkinson

COMPANY INFO
Linn Products Ltd.
Glasgow Rd.
Waterfoot, Glasgow
Scotland, UK G76 0EQ
helpline@linn.co.uk
+44 (0) 141 307 7777
linn.co.uk
ARTICLE CONTENTS

COMMENTS
georgehifi's picture
Submitted by georgehifi on May 6, 2024 - 11:50am

Nice to see a ClassA/B amp without Class-D switching noise filtering needed when it's being measured.

"how could Linn get so much power out of an amplifier that weighs a teeny bit less than 60lb, is relatively small, and manages to run at a stable, cool temperature without the use of a fan?"

SMPS (money and weight saver) and Class-A/B (low bias=cooler)

(not a lover of the SMPS especially in source equipment)
Go near one with a old AM portable radio that has no auto mute if it tuned in off channel, tune it in down around 600khz off channel, turn up the volume and hear what horrors come out of it.

Cheers George

hb72's picture
Submitted by hb72 on May 7, 2024 - 12:41am

am in the camp of those who try to eliminate all SMPSs from the A/C circuit that feeds the hifi system. But, if I understand correctly, provided all components, sources, pre & power-amp are powered by SMPS, that noise on A/C would not be an issue to the hifi system.
Correct?

If I understand correctly, it is the mix of Lin and SM PSUs that is problematic, as lin PSUs are less good in filtering noise on A/C from entering the DC section. High Quality SMPS provided.

tx
hb72

georgehifi's picture
Submitted by georgehifi on May 7, 2024 - 1:53am

They radiate not only through wiring but also airborne radiation.

Cheers George

hb72's picture
Submitted by hb72 on May 7, 2024 - 3:51am

Some suppliers of external SMPSUs allegedly provide useful filtering on DC & AC side and also usefully grounded housings (ifi); here is where a low (HF) impedance power cable comes handy :). I would assume the same for companies like Linn, wow have the SMPSUs integrated in their source and amp components.
Point being: (aside of their way faster voltage control) SMPSUs are said to be much better in isolating the DC side from AC side noise, while LinPSUs apparently are far less so, and thus more prone to AC side noise passing through to DC side; OTOH they are less noisy on AC side so, one would think this warrants limitation to linPSUs, or, otherwise, to SMPSU driven components only.
Is there anyone who can confirm such considerations from real experience?

SNI's picture
Submitted by SNI on May 12, 2024 - 11:47am

The reasons why you have to use filters for measuring class D amplifiers, maybe somewhat different from what most people think.
Using an AP analyzer for Class D measurements, several issues has to be considered.
First thing is, that you don´t want to put illeagal signals into an amplifier with limited bandwith. That makes no sense.
A class D amplifier is intended to amplify audio signals, not signals made for measuring purposes, hence i.e. square signals will not be of any use.
Second thing is, that you need to filter out the carrier wave. The reason for this has nothing to do with class D, but with the way he analyzer works.
If you want to look for very low noise and distortion levels, the AP analyzer will adjust its sensitivity for that purpose. That would not be possible with a carrier wave @ several V at the output of the class D amplifier @ ~500 KHz. The analyzers input stage would be damaged.
And it is worth noting, that a carrier does not affect the audioband at all what so ever.
Also worth noting is, that most class D amplifiers are actually real DC amplifiers without any kind of servos or like. They can just do frequencies down to DC by nature.
As a small extra, class D amplifiers has no crossover distortion.

Regarding SMPS there is at least 17 different types in existence.
Some of those are relevant for audio, and a lot of them are not.
On top they can be regulated or not, as well as they can be PFC SMPS, where PFC stands for Power Factor Correction, meaning less noise on the AC side, and increased efficiency.

Anyways what I´m trying to say is, that IMO nothin can be said generally about SMPS. There are to many different types, which easily gets mixed up.
Needed filters for class D amplifiers, has nothing to do with performance or sound quality, it is the analyzer, that is in need for filtering, not the amplifier.

But still the Linn amplifier presents very good results.
Almost as good as i.e. Toppings 800USD 56W Pch amp.

georgehifi's picture
Submitted by georgehifi on May 12, 2024 - 4:00pm

SNI: "Needed filters for class D amplifiers, has nothing to do with performance or sound quality, it is the analyzer, that is in need for filtering, not the amplifier."

JA: was measuring these Class-D's way back with the AP analyzers without filtering at first and showed what was coming out of the amp for real which was ugly!! Fig-2 and then started using the AP filtering to make them more acceptable to look at Fig-3 even though it was not representative of what the speaker was really seeing which is what's in Fig-2
https://tinyurl.com/2b88paus

It is possible that these HF switching frequency oscillations riding on that square wave "can" cause an amp to become unstable, and cause it to ring/oscillate and punish tweeter voice coil over time, has happened a friends Watt/Puppy 7's tweeters which sounded "off" with his Nu-Force Ref Mono's and the reason when I dismantled them for new voice coil replacement, the old voice coils (both) got severely "blued" with heat and he's not a loud listener

Cheers George

CG's picture
Submitted by CG on May 6, 2024 - 11:55am

Two questions...

Do the in-spec production units sound different than the not in-spec pre-production units?

What kind of notch filter is used to measure the distortion waveform? With distortion products below -100 dBc, that implies that you need a notch depth of well better than 100 db. (I'm guessing that it's part an analog notch in the APx555 and a lot calculated in the '555, but I want to see what I can do to come close at home.)

JRT's picture
Submitted by JRT on May 7, 2024 - 7:04am

Thank you for another interesting review and measurements.

At $90k/pair, I simply wouldn't want to accept the opportunity costs on these.

I would very much like to see review and measurement of monoblock amplifiers providing good implementation of Purifi's 2nd gen Eigentakt 1ET9040BA module. I have seen comments from Buckeye Amplifiers that they will be bringing their new 1ET9040BA based monoblocks to demonstrate at the MWAV (midwest audio visual) trade show in Kansas City in late June. Their target price is $1050/amplifier shipped direct, (so $2100/pair, which is $87,900 less than the amplifiers that are the subject of this review).

Note that -120dB is 0.0001%

My current understanding of the model number is:

1ET9040BA

1: single channel
E: Eigentakt
T: ?
90: = 90 volts peak at maximum output
40: = 40 amps peak at maximum output
B: bridged
A: amplifier

edit 05/14: Purifi has posted a link to the datasheet, now openly available to consumers at their website. The module is also now available (EUR 598.00 VAT excluded) at their online store, as well as an engineering eval/demo kit (EUR 696.00 VAT excluded).

Link:
https://purifi-audio.com/

I have no profit motive in any of this, nothing to personally gain or lose by it. ...am merely exhibiting some enthusiasm.

Anton's picture
Submitted by Anton on May 7, 2024 - 8:34am

I can tell you before they even get built how the subjective review would go, but seeing JA hit those with his measuring tools would be way cool.

David Harper's picture
Submitted by David Harper on May 8, 2024 - 11:40am

Like you I, to, can predict how the subjective review will go. It will feature imaginative and evocative descriptions of sound which will challenge the intellect and cause the reader to abandon all reason in his pursuit of audiophile bliss.

supamark's picture
Submitted by supamark on May 8, 2024 - 2:03pm

Including prior Eigentakt, Ncore, and Ice power amps - but not any of the GaN FET amps, it will sound grey and harsh in the treble. They all sound like the worst of 80's digital. The closest analog would be the vinyl version of Eric Clapton's Crossroads anthology, which was edited/mastered digitally and sounds like grade A (or gray) dog crap. I also don't get why people like DSD, but different strokes.

I would like to hear one of the better GaN FET amps (and their higher switching frequency) to see if it "fixes" class D.

Bias alert - I prefer class A amps with minimal/no global feedback. And MOSFETs over BJT's in the amps I've heard.

Yes, the puns were intended.

JohnnyThunder2.0's picture
Submitted by JohnnyThunder2.0 on May 7, 2024 - 12:50pm

get you all hot and bothered instead of the love of music and subjective listening tests tells us all we need to know about you. If I were you, I'd take the $87,000 you've saved buy buying those black boxes you like and travel to NY or Chicago or Vienna and listen to real orchestras and music. PS - are you getting kickbacks from Buckeye or Purifi ? Very interesting that at Apoxna there were 100x more tube amps demonstrating music than little black boxes w class D modules.

Anton's picture
Submitted by Anton on May 7, 2024 - 3:30pm

Can't crap on it unless you've heard it, right?

Put this with cheapie with a pair of DeVores, Klipsch, and have a comparo!

I would love to see that.

JRT's picture
Submitted by JRT on May 7, 2024 - 4:32pm

I suspect that Andrew Jones' new MoFi Electronics SourcePoint 888 ($5k/pair) 3-way floorstanding loudspeaker might work well in combination with well engineered amplifiers utilizing Purifi's 1ET9040BA module, depending much on the surrounding components (input buffer, SMPS, ventilated case, etc.).

I recall some mention of Erin Hardison ordering/buying a pair of SourcePoint 888, so I expect to see, eventually, a subjective review and a set objective measurements (he uses Klippel nearfield scanner) with associated commentary on his Erin's Audio Corner website and YouTube channel.

edit: Stereophile posted a video on their YouTube channel, with Andrew Jones describing his new SourcePoint 888.
To watch the video, copy/paste the following link into your web browser address window.

http://www.youtube.com/watch?v=vJzNjsWtmnU.

Ortofan's picture
Submitted by Ortofan on May 14, 2024 - 8:13pm

... the live sound of a "real orchestra and music" as heard in a concert hall in "NY or Chicago or Vienna" as a reference point.
Have you not read J. Gordon Holt's writings in that regard?

JohnnyThunder2.0's picture
Submitted by JohnnyThunder2.0 on May 16, 2024 - 8:49am

and orchestral reproduction. I was suggesting that with all that money he would save by buying inexpensive equipment to travel to different cities to experience an orchestra live - in an audience, as an enriching life experience, not as a point of comparison with home audio. I was making a point about the love of music and life vs. equipment and measurements. That's all.

JohnnyThunder2.0's picture
Submitted by JohnnyThunder2.0 on May 7, 2024 - 4:03pm

with your point....That would be interesting. M

georgehifi's picture
Submitted by georgehifi on May 8, 2024 - 12:56pm

Nice to see an amp again that almost doubles it's "tested" wattage from 8 to 4 to 2ohms again which means it's got a pair.

Cheers George

supamark's picture
Submitted by supamark on May 8, 2024 - 1:46pm

I would like the sound of *first* amp JA tested a fair bit more than the second amp. The difference is in the amount of global feedback - which is almost certainly why the first amp had more ouput power; way less feedback. This is clearly visible in the power vs distortion curves.

If the first amp tested is also the one of the ones JVS listened to, there needs to be a follow up to see how the sound is changed.

georgehifi's picture
Submitted by georgehifi on May 8, 2024 - 5:46pm

"amount of global feedback - which is almost certainly why the first amp had more output power;"

Amount of feedback, local or global doesn't influence output power or current ability much at all. But it does influence distortions and damping factor.

Cheers George

supamark's picture
Submitted by supamark on May 9, 2024 - 10:05am

That's the approximate difference in power. If removing global negative feedback from a 1 Watt headphone amp can add 6 dB (4x) gain (Schiit Asgard 2), then I think an approximately 4% drop in power is quite plausible in a 400 Watt amp.

Also, the way the feedback is added fitfully is probably audible with the right playback material... mfg's need to stop chasing SINAD, anything over ~100 dB s/n is weiner waving since microphones top out in the mid 80's s/n wise. The mic is just the start of the signal (to noise) chain, plenty more noise is added along the way (and some of it intentional).

georgehifi's picture
Submitted by georgehifi on May 9, 2024 - 12:55pm

supamark: "If removing global negative feedback from a 1 Watt headphone amp can add 6 dB (4x) gain (Schiit Asgard 2), then I think an approximately 4% drop in power is quite plausible in a 400 Watt amp."

Yes increasing or reducing feedback will effect "the gain" (sensitivity) of any amplification device be it a buffer/preamp/or poweramp, not the wattage or current ability of it.
It will not give the device the ability to give any more or less maximum wattage/current (power) than it had originally, it will just have "less gain", and the need for more or less voltage from the sources before it to drive it to those maximum wattages/currents "powers"

Cheers George

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