Amplifier matching to KEF LS50 speakers

[dave2010]

I have a pair of KEF LS50 Metas. Hardly used so far, but finally got round to tidying up the living room (slightly) before Christmas, so we can have a fire in there and use it. I'm just letting the fire die down before giving up for the night.

I'm using a Marantz PM7200 to drive the speakers. Just thought I'd check the specs of the amp tonight, and it seems that it's around 95watts in AB mode, but only 25 watts in A class mode. KEF recommend fairly powerful amps - I'm assuming this one is powerful enough, though should I avoid the Class A mode?

Also, are there any significantly better matches for these speakers - say at under £1k? Alternatively any price - and I'd look around for a good deal if I felt it would be worthwhile. It may be that I've already got good enough kit in this price bracket. I'm just curious as to what amps others might recommend.

So far I neither like, nor dislike this combination, but I've not really pushed these hard or with any really good source material.

These do not compare with the live concert I went to recently - but then I wouldn't expect them to. I did buy the CD of the piece played though - so could try that. It's this one - https://www.amazon.co.uk/Quatuor-Pour-Temps-Quartet-Time/dp/B00FKPBAXG/ref=sr_1_3?keywords=chandos+messiaen+quartet&qid=1639265056&sr=8-3 and yes - I did get the CD not a download.

[walpurgis]

If the Marantz amplifier sounds and works OK, even in Class A mode, then just use it. I don't see a problem there.

Or, if you want bags of sophisticated power at a sensible price, you could consider a Quad 909 or QSP power amp with a decent passive pre-amp, I'd expect the Rothwell Indus for sale in our Private Exhibitions section would suit nicely.

[Macca]

Sensitivity is 83dB so depends on what levels you want to play at as to how much power you need - but they are pretty insensitive for modern speakers, even small ones.

25 watts won't be enough if you want to crank it up a bit since it won't take much volume to clip the amp on peaks. Also distortion is very high in the bass so not a speaker I would recommend if you want to rock out, unless using with subwoofer(s) and a high pass filter.

Impedance low point is 3.7 ohm, the Marantz should be able to cope with that, although it might still be slightly sub-optimal.

[AJSki2fly]

I have a pair of KEF LS50 Metas. Hardly used so far, but finally got round to tidying up the living room (slightly) before Christmas, so we can have a fire in there and use it. I'm just letting the fire die down before giving up for the night.

I'm using a Marantz PM7200 to drive the speakers. Just thought I'd check the specs of the amp tonight, and it seems that it's around 95watts in AB mode, but only 25 watts in A class mode. KEF recommend fairly powerful amps - I'm assuming this one is powerful enough, though should I avoid the Class A mode?

Also, are there any significantly better matches for these speakers - say at under £1k? Alternatively any price - and I'd look around for a good deal if I felt it would be worthwhile. It may be that I've already got good enough kit in this price bracket. I'm just curious as to what amps others might recommend.

So far I neither like, nor dislike this combination, but I've not really pushed these hard or with any really good source material.



You may find this helpful after a bit of a read. http://www.sengpielaudio.com/calculator-efficiency.htm

Matching speakers can be confusing there are several things to bear in mind.

Firstly most people in a domestic environment are not likely to listen to more than around 85-90dB measured at the listening position. So what doe that mean, well a speaker nowadays is calibrated with a fixed voltage of 2.83v(I think) giving a 1 Watt load on the amplifier used and the measuring microphone is at 1m from it, and the measured dB is the quoted sensitivity, I think I have that right, others will correct me if not.

So looking up your speaker spec it is :=

Crossover frequency 2.1 kHz
Frequency range (-6dB) 47 Hz - 45 kHz
Typical in-room bass response (-6dB) 26 Hz
Frequency response (±3dB) 79 Hz - 28 kHz
Harmonic distortion (90dB, 1m) <0.4% 175 Hz - 20 kHz
<0.1% 300 Hz - 10 kHz
Maximum output 106 dB
Amplifier power (recommended) 40-100 W
Nominal impedance 8 Ω (min. 3.5 Ω)
Sensitivity 85 dB

So at 1m distance with the specified voltage your speakers will produce 85dB, so what does this mean you may ask. Well every additional metre you move away from the speakers then you will need to double the power to maintain the decibel output of 85dB(dB will drop 3dB for every metre away from the speaker), so if you sit 3m from your speaker to maintain 85db will require a further doubling on power output from the amp. I would not panic too much about this though because most peoples listening levels mean their amplifiers are on average going to be used at around 1-5 Watts.

But the next bit is quite important, as the frequency of the tone/signal(music) is lowered, for example if we ask a speakers to produce a 40hz frequency then its efficiency drops dramatically and the load increases on the amplifier, this is why KEF quote a minimum sensitivity of 3.5 Ω(ohms), at a low frequencies the speakers will be down to around 3.5ohms. You could work out what the load at 40hz to produce 85dB would be using the calculators in the link.

So in simple terms as you turn up the wick(volume on the amp) the load induced on the amplifier will get greater the higher you go, and this is worse the lower the frequencies being produced are.

In relation to your KEFs, they are not particularly efficient speakers, being measured at 85dB, running your amp in class A at normal listening levels should be fine, but if you start whacking the volume up high say for a party or because you want to see how the neighbours react, or feel an orchestra in full flow at a 100+dB then I would be more cautious and use class B, obviously class B in itself has issues of inducing some level of distortion.

I hope this is of some help, amp and speaker matching is not straight forwarding at all, I had mismatch issues with a 300B amp and my speakers and in the end moved to a pure class A amp that could produce very high watts at low loads, the result was better low end and higher listening volumes if I wanted them. If you ask any hifi buff who is into low watt output valve amps they will tell you straight away efficient speakers are the key to purity of sound and higher volumes, especially in the low end. However there are other things to consider the listening environment, room size, how loud you like to listen to music, and how far you want to be from the speakers when listening.

The Power amps Geoff suggests would give you better flexibly driving the speakers, and others are good as well. But if you like the Marantz and are happy to run in class A at reasonable volumes it should fine, but I do believe it can become less defined and controlled in class AB which is true of most AB amps.

[Macca]

Good post - should mention that with a pair of speakers running you can add another 3dB so an 83db speaker is really 86dB with two channels.

I have a 100 watt class A power amp here doing nothing if anyone want lots of watts and class A operation. It's big though and you won't need any other form of heating in the winter months.

[Haselsh1]

I use KEF R5's which are also a bit difficult in the low frequencies down around 3.7 Ohms but my class A power does a good job.

If it sounds good then maybe it is good ?

[wee tee cee]

audiolab 6000a or poweramp croft 7.

I only have problems with 57s....brutal impedance curve makes majik smoke with ss amps

[Old boy]

Currently using a Cambridge audio 851W with my LS50 sounds great and only cost a grand great bang for the buck.

[hifinutt]

Not easy to find better than your speakers at under a grand ...possibly b@w 706s2 in the sale , possibly something from allchris ??? Probably best to stick with what you have as kit is hard to sell

[dave2010]

Currently using a Cambridge audio 851W with my LS50 sounds great and only cost a grand great bang for the buck.Sounds a good idea if I needed that much oomph - but around £1k used - https://www.ebay.co.uk/itm/265439076698?mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5338353466&toolid=20006&4236=%26customid%3Ds%253AGS%253Bgc%253ACj0KCQiA2Na NBhDvARIsAEw55hiHeYYsaPzqZsoArLTmM-xvrc5-AT9CISIrgT_k1I9gEC86uNBXHkIaAu7hEALw_wcB%253Bpt%25 3A1%253Bchoc%253A2&customid=s%3AGS%3Bgc%3ACj0KCQiA2NaNBhDvARIsAEw55hi HeYYsaPzqZsoArLTmM-xvrc5-AT9CISIrgT_k1I9gEC86uNBXHkIaAu7hEALw_wcB%3Bpt%3A1% 3Bchoc%3A1&gclid=Cj0KCQiA2NaNBhDvARIsAEw55hiHeYYsaPzqZsoArLTm M-xvrc5-AT9CISIrgT_k1I9gEC86uNBXHkIaAu7hEALw_wcB or £1600 new. Also that's just for the power amp, so would need a preamp as well. That wouldn't necessarily be a problem for me, but right now I'm just exploring the Marantz PM7200 with these and it seems pretty good. Some CDs now sound like they have "real" instruments - though some still sound very artificial - even if they were recorded very recently.

Some interesting suggestions are emerging in this thread so far.

[Firebottle]

I only have problems with 57s....brutal impedance curve makes majik smoke with ss amps

Just to be accurate it's not the impedance curve it's the level of capacitance presented to a less than optimally stable amplifier, this usually causes the amplifier to oscillate at high power at high frequency, leading to majik smoke.

The LS50 has low impedance at the mid bass region with a brutal phase change at 100Hz.

http://www.stereophile.com/images/1220KEF50fig01.jpg

[Macca]

QUAD 303 was intended to replace the QUAD 2 valve amps as a partner for the ESLs and that's solid state and doesn't like low impedance loads. But it's a great combination.

The LS30 Meta is a much better speaker than the original LS50 but it's still not an easy load so based on the comments about the sound being a little artificial I would be looking for a more compatible amp than the Marantz - or some of the suggestions above which IMO won't fully cut it either.

This is what the magazines don't tell you - at least not since the 1990s - most amps are rubbish at driving tough loads.

Class D amps don't seem to have problems with low impedance or abrupt phase shifts, maybe look at one of those?

[Old boy]

Best amplifier I’ve listened to with KEF Ls50’s is the Hegel H590 simply stunning combination sadly it is bloody expensive.

[hifinutt]

Yes heard a Hegel 120 the other day with similar size speaker and it was impressive. I can imagine the 590 but be special but jolly expensive

[dave2010]

Yes heard a Hegel 120 the other day with similar size speaker and it was impressive. I can imagine the 590 but be special but jolly expensive
The Hegel stuff does seem rather pricey - see https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313&_nkw=hegel&_sacat=0
The 120 which is listed right now is at £2100+postage and extras.

I'm still not over convinced about these KEFs - sometimes I like them, and sometimes I don't really. Perhaps these work better with some music, some recordings than others. I've really not given them a lot of attention - had other things to do. It's not helped by my live music experiences. Quite often initially live music doesn't sound "as good" - the ambience is often not quite right, the volume levels perhaps not either, plus the actual sound of the instruments. After a while one can be drawn in to the music, and that happens in a way which is quite rare when listening to recordings. Later one realises that actually most recordings and reproduction equipment can only give a pale imitation of live sound - even with its faults. Generally listening at "realistic" levels in a domestic environment is not a good thing to do, either.

Whether the KEFs would sound better with a different amp I'm not sure - but for me it probably wouldn't make sense to spend more than the speakers cost - though maybe other people do just that.

[hifinutt]

you could get a brand new one for less than that one on ebay , most times you can get a minimum of 5-10 % off new which would make it less

might be tempting to try this one too

https://www.hifiwigwam.com/forum/topic/156707-fs-hegel-h200-integrated-amplifier/

[Macca]

you could get a brand new one for less than that one on ebay , most times you can get a minimum of 5-10 % off new which would make it less

might be tempting to try this one too

https://www.hifiwigwam.com/forum/topic/156707-fs-hegel-h200-integrated-amplifier/

That's a lot of amp for the money he's asking, weren't they about £4K new?

[hifinutt]

yes not sure about new price but yes they do seem cracking value

there are a few on ebay about that price too

[Macca]

$4500 USD in 2010, can't find a UK price.

[Pigmy Pony]

That Hegel looks a bit of a beast at 25kg (55lb in old money). I want one, but I'd need to offload my others first.

[hifinutt]

Glad you mentioned that 25kg weight , that won't be coming here at that weight !! Good for someone though