Amplifier for the KEF LS50s

[SlydZ]

The LS50 requires a fair degree of current to run well. From Amir’s review...
The KEF manual recommends an amplifier of 25 - 100W. I’d further recommend an amplifier than can deliver at least 50W into 4 ohms.

The problem is that there are so many people who say that the LS50 need much more. I don't know what I should believe

In this review the author says that even the XTZ Edge A2-300 is in his opinion a little underpowered for the LS50 (from sound experience):

(9:40)

The XTZ specs:
2 x 460 W (1% THD, 2.7 Ω) / 2 x 300 W (1% THD, 4 Ω) / 2 x 150 W (1% THD, 8 Ω)

The KEF LS50 Wireless has a 200W amp per speaker.

I think I will try the XTZ, the form factor is really good and I think there should be enough power

 

[Angsty]

More power rarely hurts; what matters is current vs Watts to deal with impedance issues. Look again at the impedance curve in the review.

I doubt an amp that puts out 300W into 4 ohms is insufficient. My NAD is rated at 150W into 8 ohms and I’ve never run out of steam at sane volumes.

 

[SlydZ]

More power rarely hurts; what matters is current vs Watts to deal with impedance issues. Look again at the impedance curve in the review.

I doubt an amp that puts out 300W into 4 ohms is insufficient. My NAD is rated at 150W into 8 ohms and I’ve never run out of steam at sane volumes.

I can't imagine that either, that this is not enough. Do you have another amp recommendation ~500 USD/Eur (less would be better ) or do you think the XTZ is worth a try ? For my taste its a little bit expensive, because the LS50s are at 660€ and the XTZ is at 500€. I think its a wrong ratio. I would like to test the Behringer A800, but they are at the moment not available

Another option would be a NAD D3020 V2. This amp is im comparison to the XTZ muss less powerful, but there are a lot of recommendations for LS50 + NAD D3020 combo. NAD 3020 V2 would cost 400€ in comparision to XTZ + Pro-Ject Phono amp 600€

 

[Angsty]

I’m not familiar with XTZ and I tend to be old school in my amplifier preferences; I like classic Class AB designs. I have not purchased an amp in years; I already have several I like.

Parasound has an excellent reputation for reliable, well-performing Class AB amps. The Parasound NewClassic 2125 is around this same price range. It has a peak current output of 35 amps and a rated power of 225W into 4 ohms.

https://www.audioadvisor.com/mobile/prodinfo.asp?number=PAC2125V2

You may need to find another distributor for Europe.

 

[audiophile]

there are a lot of recommendations for LS50 + NAD D3020 combo

I used NAD D3020 (first version) with LS50s in the past and think it's not a good match. This combination lacks bass, and at a louder volumes high frequencies sound distorted.

 

[digitalfrost]

Do you have another amp recommendation ~500 USD/Eur (less would be better ) or do you think the XTZ is worth a try ?

If you want lots of watts for cheap, I would also look at the Crown amplifiers:

https://www.audiosciencereview.com/...ds/crown-xli-800-power-amplifier-review.9420/

https://www.audiosciencereview.com/.../crown-xls2502-stereo-amplifier-review.10627/

https://www.audiosciencereview.com/...-and-measurements-of-crown-xls-1502-amp.6062/

I'd probably choose the XLS 1502.

 

[Objectivist01]

Greetings!

I decided myself for a pair of LS50s. In Germany, they cost only 660€ a pair right now. And now I am at the most difficult part of finding a suitable amp for the speakers.
I am listening mainly in near field. When I don't, listening distance lies at around 4 meters. My taste of music is wide, but I mainly hear techno (both chill and hard) and prog rock (mainly the yes, pink floyd).
First off, I don't care if the amp is integrated or if I have multiple parts lying around. I have enough space for both options. I would not like to spend more than a 1000€
The amp/amp combo should have:

• phono stage (either built in the integrated amp or in a preamp/phono preamp)
• digital input
• high wattage (100W+ 8 ohms) to power the rather hungry ls50s

to this point it's rather easy to find a good amp. Now here's the first question: Since class D amps have that clean polish, they would fit harder acid techno very well, whereas with prog rock a little bit more sweetnes to bring out the e-gitarrs wouldn't be bad. So it's either A/B or D if I'm right? What class would you recommend?
Now the second more difficult point: Since I like listening through headphones, when I don't want to disturb my neighbors, a nice headphone output either on the integrated or the pramp would be very nice. I really would not like to have to buy another Schiit Modi + Magni stack which would cost another 300€. So the amp should preferably have a nice headphone output.

So with all that in mind, I stumbled upon the Pro-Ject Amp Box DS2 + Pre Box DS2 digital stack. Have any of you heard them before? Would you recommend them? It's class D judging by weight and size.

Regarding seperate components, the cheapest viable power amp I found was the pro-ject mentioned before. Now buying a preamp from a different company wouldn't make much sense, would it? So I think the Pro-Ject stack is at this price point my only option.

As of integratd amps, there are loooooaaaaaads.

So now I'd like you to correct any mistakes I made in this post, and help me find a suitable amp option.
Thank you very much for your time and help!

The ls50s has very good exaggeration or transparency of midrange. I would choose an amp with very good midrange detail not to compensate but to make a wonderful midrange focused system. My pick would be atoll in 50se. With ls50 its hard to get a neutral system, why not make a beautifully singing vocal foucsed system?


Edit: this is not a kind of recommendation which this forum members are happy with. So ignore this post.

 

[detlev24]

[...] I don't know what I should believe [...]

The LS50 has a given sensitivity of 85 dB/W/1m, which reduces to ~75 dB/W/1m as shown by amirm's measurements. [Since 2.83 V produce exactly 1 W, for such an 8 Ω loudspeaker.]

Starting from the worst case, with 1 W power, the LS50 would produce 75 dB SPL in 1 meter distance - over the limiting part of its bass region. 10 W would provide 85 dB/1m, 100 W -> 95 dB/1m [and 1000 W -> 105 dB/1m]. Such a small loudspeaker will distort heavily [= audibly] at 95 dB SPL bass output, for sure, and the 200 W you mentioned for the LS50 Wireless, would still allow for peaks of 98.01 dB/1m; in this worst-case scenario.

Then, there is the amplifier's limiter [LS50 Wireless], that will kick in earlier on the sub-bass region...

The choice should rather be an amplifier, that does not distort audibly when forced to provide peaks of 100+ W at 8 Ω; but this really should not be an issue with power amplifiers, like the chosen XTZ model [unless, if of poorly internal design]. In practice, "room gain" will help to reduce the 'power required' on the low end. // In case you pair the LS50 with subwoofer(s), you basically would not be limited by amplifier choice(s) at all.

Just as an addition [source: KEF.com], the following measurements. The lower graph shows distortion levels over a range of 85-100 dB SPL. There are 4 curves in each color, so one can safely assume:

• red = 100 dB SPL
• blue = 95 dB SPL
• green = 90 dB SPL
• black = 85 dB SPL

The indicated frequency range on this graph, most probably, is 20 Hz to 5 kHz.

 

[Eetu]

The ls50s has very good exaggeration or transparency of midrange. I would choose an amp with very good midrange detail not to compensate but to make a wonderful midrange focused system. My pick would be atoll in 50se. With ls50 its hard to get a neutral system, why not make a beautifully singing vocal foucsed system?

What makes you say this particular amp has "very good midrange detail" opposed to some of the amps discussed here previously? In any case, the specified THD of 0.05% (at 1khz/10W) does not look good. That's -66db.

 

[SlydZ]

Thanks for the recommendations and your explanation detlev24. To be honest I only understand half of it ;-) but its very interesting! I think that this is the point that some reviewers recommended amps with so (or too) much power to provide these peaks.

I pulled the trigger to the XTZ Edge A2-300. Perhaps I will compare the XTZ to the Berhinger A800. The XLS 1502 would be an alternative, too, but with 370€ "only" 130€ less than the XTZ. In this case I pay the extra because of the better form factor and convenience (auto off...). The Behringer A800 are at ~180€. For this price the size and look is ok.

Whats the best way in generell to adjust the gain/limiter at amps like the XTZ? Play music, max volume at preamp and than turn the gain at the amp up to the max. enjoyable volume? I ask because I was wondering if it could happen, that the amp cut some peaks off when the limiter is "active".

 

[Objectivist01]

What makes you say this particular amp has "very good midrange detail" opposed to some of the amps discussed here previously? In any case, the specified THD of 0.05% (at 1khz/10W) does not look good. That's -66db.

That’s not a neutral amp, just like ls50. It has bit exaggeration in the midrange. Though my personal preference never would go for ls50 as it’s already a colored sound. So, objectively there is nothing to achieve even if you have a perfect amp in the chain with a ls50. So atleast add beautiful midrange distortion to it to make it sound that way. I am pretty sure it won’t meaure wel as I can hear it’s not flat.

 

[Eetu]

That’s not a neutral amp, just like ls50. It has bit exaggeration in the midrange. Though my personal preference never would go for ls50 as it’s already a colored sound. So, objectively there is nothing to achieve even if you have a perfect amp in the chain with a ls50. So atleast add beautiful midrange distortion to it to make it sound that way. I am pretty sure it won’t meaure wel as I can hear it’s not flat.

Have you considered changing your user name to 'Subjectivist01'?

And wouldn't it be smarter to buy a neutral amp so you can EQ the mids if you like (and add distortion while you're at it..)?

 

[VintageFlanker]

The ls50s has very good exaggeration or transparency of midrange.

How the midrange may be exaggerated and transparent in the same time?!

With ls50 its hard to get a neutral system

No, no, no, no... It's very easy to find a "neutral" system when we're talking about electronics: that's the all purpose of ASR: we know which amp/DAC/preamp are transparent by measurements. This isn't some cooking forum where we're arguing about synergy of seasoning to obtain good meal.

 

[Objectivist01]

How the midrange may be exaggerated and transparent in the same time?!

No, no, no, no... It's very easy to find a "neutral" system when we're talking about electronics: that's the all purpose of ASR: we know which amp/DAC/preamp are transparent by measurements. This isn't some cooking forum where we're arguing about synergy of seasoning to obtain good meal.

Then ls 50 shouldnt be in the chain in the first place. Personally i dont like the system inrecommended. But ls50 fans may like it . I am not dumb to not notice that this forum strives for accuracy more than anything. It was my mistake to recommend that amp. I take it back.happy?

 

[Objectivist01]

Have you considered changing your user name to 'Subjectivist01'?

And wouldn't it be smarter to buy a neutral amp so you can EQ the mids if you like (and add distortion while you're at it..)?

yes
I am wrong. I take it back. But i wont change my name for you .

 

[detlev24]

Thanks for the recommendations and your explanation detlev24. To be honest I only understand half of it ;-) but its very interesting! I think that this is the point that some reviewers recommended amps with so (or too) much power to provide these peaks.

[...]

Whats the best way in generell to adjust the gain/limiter at amps like the XTZ? Play music, max volume at preamp and than turn the gain at the amp up to the max. enjoyable volume? I ask because I was wondering if it could happen, that the amp cut some peaks off when the limiter is "active".

Bottom line is, I would not be too concerned of such subjective recommendations. Those people would wonder, if they actually measured the provided W + the loudspeaker's distortion at their listening levels.

No, I would not even try to push the LS50 to its limits! Everything above 90 dB SPL would hurt my ears, for sure, due to its rising distortion levels. The LS50 is, by its physical limitations, not made for a deep bass reproduction at high SPL. If you want that, extend your setup with a properly crossed-over subwoofer. This way, you would take the load off the LS50, as the 5.25" LF/MF-woofer would not require to reproduce the lowest frequencies anymore; which you would be "routing" to the subwoofer(s). If you would force the LS50 to its maximum woofer excursion and beyond; you might as well break the woofer permanently.

To make it more obvious, one example, regarding the distortion graph I posted above. If we take the two green lines, which are supposed to be at 90 dB SPL. The horizontal grid lines must be spaced by 5 dB then. This gives, in case of a 60 Hz tone: Difference between fundamental [upper green curve] and distortion levels [lower green curve] = ~24 dB. By application of the formula to calculate THD in %, this would equal ~6.3 % distortion at 60 Hz and 90 dB SPL. At just around 40 Hz, distortion would therefore reach 100% (!) and also passing 60 Hz it would rise again; until it finally decreases when passing 90 Hz. // For this example, theoretically, only 32 W at 8 Ω would be required to reach 90 dB SPL in the LS50's bass region [1-meter distance; 1 loudspeaker. Two combined, as usual, would provide roughly +3 dB output].



The threshold of audibility in the bass region, which extends up to 250/300 Hz, lies at roughly 10 % THD. Hence, lower amounts are most welcome.

 

[Ron Texas]

I'm using a Crown XLS 1502. It might seem like overkill, but the built in high pass filter is handy for sub integration.

 

[maty]

The LS50 requires a fair degree of current to run well. From Amir’s review...



The KEF manual recommends an amplifier of 25 - 100W. I’d further recommend an amplifier than can deliver at least 50W into 4 ohms.

Futhermore, if you get an integrated amplifier with a phono input, you can eliminate the phonobox.

Better idea: more than 100 watts (THD 0.1%) at 4 Ohms. It has only true 83 dB/W/m.

With KEF Q100, and true 85 dB/W/m (THD 0.1%) -> at least 80 watts at 4 Ohms.

 

[digitalfrost]

This gives, in case of a 60 Hz tone: Difference between fundamental [upper green curve] and distortion levels [lower green curve] = ~24 dB. By application of the formula to calculate THD in %, this would equal ~6.3 % distortion at 60 Hz and 90 dB SPL

As we can see from the impedance graph

The KEF LS50 is bass reflex port is tuned around 60hz. This is also the reason why in your distorition graphs, the distortion goes down around 60hz, and then rapidly rises below (since the air volume in the box is no longer damping the movement of the driver at these frequencies).

Therefor it is advisable to cross the LS50 over either with 24dB LR if using the standard sub/sat frequency of 80hz, and/or to increase the highpass the LS50 to 100-120hz, to get the level below 60hz low enough.

Or you could plug the BR ports. In either case, LS50 like higher/steeper highpass filters.

 

[AudioPersona]

I'm using a Crown XLS 1502. It might seem like overkill, but the built in high pass filter is handy for sub integration.

So I recently bought myself a pair of ridiculously low priced LS50 speakers and was trying to figure out the right amp to go with them. After reading a little (but not enough), I decided that the Crown 1502 was a good fit for the money.

The next step was to upgrade my old focusrite scarlett 2i4 and make full use of my Tidal HiFi membership with the MQA and all that. SMSL M500 seems to fit and although it's not perfect, it has the features I'm after and is not too expensive. Happy days and all cool right?.. No, not cool. Totally uncool in fact.

The Crown 1502 has internal AD-DA which is used in order for the DSP to work. That AD-DA is locked at 48khz and cannot be bypassed. That means that you're always limited by the quality of the Crown's internal AD-DA and can never playback anything at a sample rate above 48khz. This rules out any benefit from sample rates above 48khz and makes higher rated DACs pointless.

The high pass filter comes at a price which is too high for my use case.

As a result, I'm returning my Crown 1502 and buying a Hypex Ncore NC252MP based power amp. I'm likely going for the Audiophonics MPA-S250NC XLR. I think the XTZ EDGE A2-300 would also be a good option. Ideally I'd DIY myself a Hypex NC400 amp but that's way more money and enters the realm of diminishing returns on investment.