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Per my recent post I have been looking for speakers. The new (vintage lovers sin- I know) KEF LS50 have been getting a lot of praise and no one has said anything negative about the speakers. Sensitivity has been measured at 84.7db and the 8 ohms impedance does not dip below 4 ohms. In fact, I am surprised no one has mentioned the KEF LS50 at the Speakers forum per my post there.My KT-66 based amp uses Dynaoo A431s that measure 5.6K PP at 8 ohms (not 4.3K ohms per reports) and has a stiff 1/2 amp power supply. So, the amp should drive the speakers well enough at moderate listening levels and maintain reasonable power tube loading during speaker impedance dips.
Anyone here at AA used a tube amp with the KEF LS50? I am also looking at Maggie 1.7s.
Edits: 01/24/15Follow Ups:
Maybe there is a way to re-wire the drivers in the KEF to make it more tube friendly, i.e., raise the impedance across the bass and midrange, at least.
I did something like that with my Sound Lab 845PX speakers. SL uses two transformers (one for bass, one for treble) to achieve full range. Thus there is a passive RC type crossover on the input side of the transformers, and the secondaries are re-combined to drive the panel full range. But this resulted in a horrible impedance dip in the mid-range (around the 550Hz crossover point). Not much of a problem for a massive SS amplifier, but a real kludge for my tube OTLs. Taking an idea offered by someone else, I ditched the dedicated treble transformer in favor of a really well made full-range transformer made in Australia. This allowed complete elimination of the passive crossover network formerly driving the SL treble transformer. Now I run the SL bass transformer in parallel with the full-range transformer, using only an air core inductor to roll off the bass transformer. No capacitors or power draining, impedance lowering resistors, anywhere. After the mod, I measured Z of the speaker. From 50Hz to 5kHz it does not go below 20 ohms. I can drive the speaker to very loud levels with no more than 50W, probably less, from my OTL amplifiers. (The Australian transformer by itself did not have enough oomph to drive the bass frequencies by itself; you still need the SL bass transformer to help out.) The subjective improvement in sound was so huge that I shed tears of joy, literally if only briefly, maybe one tear in each eye.
!
The Mind has No Firewall~ U.S. Army War College.
Disclaimer, I don't know enough to make this post but I'll try and point you in the right direction.
Take a look around at places that sell all the big name drivers (not finished speakers but raw drivers).
You will be hard pressed to find anything rated as low, in db/watt at 1 meter, as many popular consumer speakers.
Gee, why is that? How does adding a crossover, cabinet, and some more drivers suddenly make a big decrease in db/watt rating? Well if done right it doesn't. But today we want more out of smaller. So speaker companies are playing games.
They reduce the output of a driver where it is happy operating at to make it seem to have a flat response when forced to play outside it's optimum range. Take a smallish driver forced to play lower bass. The cone has to move so far that the voice coil is now partially outside the influence of the magnet. In short part of the voice coil is just burning amp wattage, and creating heat, while doing nothing else. Driver impedance goes to hell. The cone might not even have the ability to acoustically load with the air any more.
But hey, what do they care. It is small and sexy and the wife approves. Plus you have tons of solid state amp watts to waste. Here is to hoping your ears can't tell the difference. After all most of these brands are the most popular, so they have to be good, and it is more likely your ears are deffective.
Figure music is ten octaves from 20 to 20khz. Truthfully it is a hard act for most drivers to reproduce three octaves, nice and flat, and with constant impedance.
Work backwards...20khz to 10 khz is one octave....10 to 5kz is two....5k to 2.5kz is three. That means the tweeter should be crossed around 2.5khz. Midrange should go from around 2.5kz to 312.5 hertz. Woofer should go from 312.5 to 39 hertz. A subwoofer is needed below that.
An uber dollar full range might play down to 125 hertz, and with enough work 5-10khz, but you still need a woofer and a tweeter.....and probably a subwoofer.
Having heard the difference....I don't think a 500-1,000 watts is a ridiculous amount of power for low bass....and you just can't get that at a reasonable price from tubes.
And before I get jumped on....they are certainly drivers out there capable of extended range that makes a two-way a viable option. Most are vintage, costly, and don't really play 20-20khz.
That is why I use a full range driver with a filtered super tweeter. No crossover for me. 16 ohms and 98 db sensitivity.
GEO, with no offense intended, how do you reconcile the lack of low bass with your current speakers with the comments made about the sound quality of some other systems? Your speakers will fall way short of a full range system and as such they won't give you a correct impression of the bass available with a particular amp. Do you use a second system to compensate?
Are you talking about sloppy power supply design? Go back and find an instance where I said someone's amps sound bad. I have not heard them. I believe I said perhaps the reason someone may like the sound of the amps is because of the design. As for my listening taste, the speaker are fine. I listen to acoustic jazz in a 14 x 22 room. Solo Piano up to Nonets, generally. I had a subwoofer but never used it. I have a 15" electro-voice in my basement but have never set them up.
Edits: 01/25/15 01/25/15
Thanks for the clarification. I have never made or thought of making a soft, soggy or slow power supply. No power supply of mine would be described as sloppy or wobbly. I go for the critical plus 20% plan.
I'm convinced that the second coming didn't happen in Montana.
No problem.
That is why I like a single drive and maybe a super tweeter if need be.
..
I would have understood if you objected. After all there are speakers, like Altecs (and others), that don't need threee drivers to get the job done. One might argue they aren't 20-20khz but I'll be the first to admit they are solid choices for use with tube amps. Wish I had known better and found some while they were still affordable.
!
The Mind has No Firewall~ U.S. Army War College.
Obviously, just kidding. :)
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Buy Chinese. Bury freedom.
If only they made this in a more compact and less expensive,far less expensive speaker system.Argh argh..What a set tho eh?
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
I have of IMF SACMs and I have other British speakers in the past and I can tell you they use complicated networks and they are inefficient AFAIC.They have a laid back sound that typical British and I always felt the B&Ws were more detailed..
The 1.7s will be much more satisfying and they respond very well to the type of amps that you and I like.
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
PP EL84, PP 6V6, PP WE421A, KT66, KT88.
16X24 room at normal levels.
The big Duce is perfect but 12 watts is fine unless you want to blow the doors off.
You are wasting your time and money. Tube amps need 94 dB 1 watt, 1 meter or higher speakers minimum, for best results. Ideal for a tube amp is 99 dB or higher. Good solid state is what those speakers need !!Jeff Medwin
Edits: 01/24/15
I heard those KEFs at a local dealer running with a Prima Luna EL34 tube amp. It was okay. Tell you the truth, I was underwhelmed. Maybe it would have sounded different under different circumstances, I don't know. I have Magnepan MG12QR at home that I have run with Dynaco Stereo 35, Stereo 70 and a couple of other tube amps and I think it sounds "better" than the KEFs running on the Prima Luna at the dealer. FWIW. Maybe I didn't give the KEFs enough of a chance.
Edits: 01/24/15
You may be a lot better off on the 4 Ohm taps with those speakers, which reduces the available power otherwise.
A dip to 4 Ohms on an 8 Ohm speaker isn't exactly tube friendly.
Exactly and you also have to derate the claimed sensitivity by 3 dB. :> (
IMO, a KT66 based amp and those KEF speakers are poor mates.
Eli D.
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