Not enough power?


Hi everyone,

I'm trying to sort through an issue with my system as I have it configured.  I've added a couple of pieces recently, and the results have been quite good.  However, there is one major problem - I don't seem to be able to generate reasonably high SPLs.  The system is as follows:

Source: VPI Traveler with Clearaudio Maestro V2 (4.2mv output)
Phono Stage:  LFD LE/SE (39db gain, not adjustable)
Integrated Amp: Sony TA-A1ES (80wpc into 4 or 8 ohms, switchable between the two)
Speakers:  KEF LS50 (84.5db sensitivity, 4 ohms min.)
Listening room 15x12ft.  relatively easy to pressurize.  

The system sounds fantastic.  However, I am using the volume of the Sony set between 70-80% of max, and I'm still only generating peaks of 80db (avg around 65db) at the listening spot (7 feet away).  If I push it much higher than that the sound starts to thin out quickly.  Interestingly, I had a similar problem a couple of years ago when I first tried the KEFs (and returned them) with a Hegel H80, which also puts out 80 watts per channel.  My initial thought is that the KEFs just need more power.  However, the various reviews of the LS50 use similarly powered amps with no comment about power problems.  

Don't know whether I should be looking at a more powerful amp.  The sliding class A sound of the Sony is phenomenal, but perhaps the topology just doesn't draw enough current?  Maybe the KEFs just need more kick?   I will be trying a pair of MM De Capo BEs, which in theory should be much easier to drive (although I just read a review where they were measured at just 86.7db sensitivity rather than their 92db as claimed).  

Any thoughts would be greatly appreciated.

Thanks, Scott
smrex13
I think I agree with your suspicions in saying some of what your describing may lie in the Sony’s power section being less than adequate for the Kef’s. However I noticed they match it with the same Kef’s during one review I read, they speak more positively about the mating. I was not able to find detailed specs but was less than highly impressed with the Sony's power amp from what I did find. I have De Capo’s and while they sounded quite good on one of the NAD 326 BEE integrated amplifiers they really came alive when I got a larger Bryston hooked up to them.
Could be the phono preamp output. Try hooking up a cd player.
Meerizistar - yes, I noticed that review, too.  They didn't seem to have any problem with the Sony driving various speakers, including the LS50s. 

Leads me to believe that gs5556 is probably on to something.  I checked the Clearaudio website, and the output of the cart I'm using is only 3.6mv, not the 4.2mv I listed above (that was for V1 of that cart).  I would imagine a higher output cart might be just what I need, or a LOMC with an appropriate SUT. 

Will bring my CD player home from my office system and give it a go with the Sony to see if I have similar issues.  

Thanks for the help,Scott
According to the KAB phono gain calculator, you're right on the money with the phono pre-amp.  Which suggests that either the LFD is not putting out enough voltage (defective) or the amp/speaker interface is the issue.  The fact that the Sony is spec'd at the same wattage for 8 or 4 ohms, plus your experience with the Hegel, and the low sensitivity of the KEFs all point to the amp/speaker match-up not being optimal.  The S-phile measurements show impedence dips to 4 ohms at the low end and 5.3 ohms at the high end and also notes " the combination of 5.3 ohms and –41° at 135Hz, a frequency where music often has high energy, will make the speaker work at its best with a good, 4 ohm–rated amplifier."  I'm no techie, but most solid state amps put out more power into 4 ohms than 8, the "more robust" being able to double their power output as Ohm's Law suggests.  No idea what is happening with that 4-8 ohm switch, but you might try it at the 8 ohm setting.  If that does not work, I think you need a beefier amp that "doubles down" into a 4 ohm load. 
 
Yes it is not a high current design. 2 thousand can buy a lot more capable amplifier in that respect. If you want something new look at a Roksan for one example. I had the K2 BT paired with some difficult speakers other amplifiers struggled with, I was impressed with its power and musicality. In some cases I didn’t feel a strong need to biamp it when I thought I might. I have a feeling one would tame the Kef’s and sound great doing it. I’m not trying to lead you in any other direction, these are just some thoughts to consider.

I followed up to finish that review this morning. Dare I say it I thought there might be something fishy going on prior to. But not so much as It goes on to be less than fully impressed by the Sony’s output during closing comments.

I don’t base a lot on reviews but they can be helpful in some ways to gain a certain feel for things. Then again they can also leave you more confused about a product. Before indulging in the review I had already formed the opinion leading in the same general direction. It more or less confirmed my initial impressions.

It could very well be a combination of the two. If you do go by way of another amplifier with more gusto you may be very happy with the LFD phono and the Kefs. Theres never a shortage of things to keep it interesting. 



i believe that the issue with your system is that your power amplifier is inadequate for your KEF LS50 speakers. Looking at the impedance & phase plots of your LS50 on Stereophile I see that your speaker has some really crazy phase ups & downs making it a challenging load for your amplifier (or any amplifier for that matter). Couple this with the rather low sensitivity of 84.5dB/2.83V/1m & it means that you basically need a high current amplifier to drive this speaker if you want it rock. Looking at your Sony integrated amp I don't see it as being a high current amp - it's not high/tall enough & it's too lightweight. This Sony is more of a life-style product than a serious amp for hard-to-drive speakers like the LS50. This is also confirmed when you wrote 8W/ch into 8 or 4 Ohms. So, while it might have 80W to offer, it has very little current to offer. If you cannot get high current into a low impedance you will not get a high enough voltage. And its voltage you need to generate pistonic motion of the speaker drivers to generate the SPLs you are looking for.
Either get rid of the Sony amplifier OR get rid of the LS50. These items are mismatched. 

Thanks to everyone for your input.  Yes, I've quickly come to the conclusion that the Sony is not a good match for the KEFs (perhaps made even worse by a slightly lower than average 3.6mv output mm cartridge).  As I mentioned, I just picked up a pair of MM De Capo BEs, and the Sony can definitely drive those better (still need to have the volume at the halfway point for background listening, but it will get louder than the KEFs).  The De Capos are fascinating - I haven't heard anything with their clarity before - but I'll avoid jumping to conclusions before I give them a good listen over several weeks.  I think the Sony will be moving on soon for something with a higher current capability.

Best, Scott
Smrex13

Check the speaker impedance switch on the back. Make sure it's set for the right setting for the KEF's. Also, the manual says to turn off the head phone impedance selector when listening to speakers. See if that helps. 

When the sound "thins out", as you say, the power supply is not supplying as much juice as the output transistors could use. The bass goes first. Years ago, I bought my Dad a 90 wpc Pioneer receiver, which is now on my TV. At higher volumes, I lose the bass compared to a separate amp with 65 wpc.