I found myself in a similar situation years ago being a fan of 845 and 211 amps and struggling to find the a more powerful amp using them to pair with my speakers of choice. After much hunting, I couldn't find anything that made sense beyond 50-55w. That led me to consideration of OTL amps using 6AS7 and other amps using 6C33. Atma-sphere and BAT respectively. IMHO both are worthy of consideration if your tastes run to 845 & 211, but you're looking for something that can drive a bigger load. I preferred both to most other higher power designs I've heard running the typical 6550s, EL34s, etc. Cheers,
Spencer |
Hi Spencer
Thanks for your reply! Yes indeed thats a genre of amplifiers that I have not explored yet! Have heard tt BAT amps are pretty good! The 6c33 are high current tubes....may sound different from the normal EL34 that I am used to. With high current 50-55w they might be able to drive my speakers without any issues.
The other ones i am considering are the cary 211 FE monoblocks, but those are more pricy. And another 845 tube amp driven by 300b which sounds truly interesting...but those are made in japan hence i wont be able to test them out/demo them myself...which is unfortunate.
Regards
Ben |
A Crown XLS1502 (525wpc@4ohms) will sound far better than any tube amp driving those current-hungry KEF's! And at $449 it is the cost of a pair of 211/845's! |
Hi Jasonbourne52
Thanks for your input. Not sure if you heard that combo before of crown + kef ref 5....
Either way am asking for the 211/845 tube amps for the kefs. Tubes are the way to go for me at least!
Thanks |
Ben, I am not sure if Kara is still making amps, but I have the utmost respect for http://www.dehavillandhifi.com/. They specialized in your wheelhouse and when I had the right speakers, their 845s really sang! They played around with some other tubes GM70 or something like that, trying to keep that magic with higher outputs, but I haven't heard those...I guess they never found much audience, but perhaps others with firsthand experience could chime in about that approach for your needs. Yes, the 6C33 are a good option to consider and quite a robust tube. Not the bargain of the 6AS7s used in the Atma-Spheres, would you should also read up on. They have sold a ton of amps for a reason! Cheers, Spencer |
Those Kefs like power. I think you would love the sound but hate bass performance. I had run Art Audio Quartets which are 45w 845 monos for almost 18 months. I am the importer. They are Incredible amps but they would not handle bass at reference levels and I would not recommend them with those speakers.
Maybe bi-amp. An 845 for mids and treble and a 200w SS for the bass?
The is probably above budget but mention it anyway. For an alternate pure tube amp, you would love the sound of the KR Kronzilla. It is a much more powerful tube but pricing stings a bit. The list for the Kronzilla DXL monos is $44k but they are truly amazing amps and are 140w. They don’t come up used often but they could be had for $15k to $20k used. Might be an Interesting option.
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@thegreenman Unless you are in a small room there is simply now way any SET is going to do that speaker justice and the other way 'round. Don't do it! Your speakers need a bit of power, being rated at 90dB. KEF rates the speaker at 8 ohms, but the fact that it employs dual woofers in parallel and a look at the impedance curve (published by Stereophile) shows that in the bass region, its really a 4 ohm load. So in that region, its actual efficiency is more like 87dB rather than 90 (Sensitivity is 2.83volts at one meter; converting to efficiency, which is a more useful spec for tube amps, you get 2 watts into 4 ohms, subtract 3dB to get back to 1 watt, you get 87dB)! So a tube amp with no feedback (like most SETs for example) will be incompatible with this speaker; even if the amp made enough power (which no practical SET does). On this speaker, it would be bass shy. The speaker expects the amp to behave as a voltage source (putting out constant voltage regardless of load) but SETs being tube amps with no feedback behave as a power source (they try to put out constant power regardless of load). If you want to know more about this see http://www.atma-sphere.com/en/resources-paradigms-in-amplifier-design.htmlIf you want to put a tube amp on this speaker, get one with some power; I would recommend 60 watts as a minimum. Run it on the 4 ohm tap. Keep the speaker cables short (monoblocks are helpful in this regard). |
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Bel Canto SET80
use 845R power triodes and output
70Watts per channel. This is why this amp won't work with the KEF: http://www.atma-sphere.com/en/resources-paradigms-in-amplifier-design.htmlThe Bel Canto is a Power Paradigm device; the speaker is a Voltage Paradigm device. Anytime the two technologies are mixed, you run the risk of a tonal anomaly. In this case, it will be bass shyness. |
op
listen to ralph (atmasphere) and scott (verdant)
211/845s won’t go well with big kefs...
you want low watt sweet single ended amp sound to play at real volumes, you need to hunt HARD for the right speakers... i still have a set of gordon rankin’s lovely 300b wavelength cardinal xs’s from 20 years ago... still can’t find a speaker i like enough and can live with to use them as the main amps |
thegreenman OP
845/211 tube amplifiers with kef reference 5? You should be fine with P/P 845 or 211’s, or even SE ones with the speakers being 90db, and if the amps have a 4ohm tap, and you don’t want to go too loud with the SE’s. The 8ohm tap will give more watts but "could" a problem in the bass. https://www.stereophile.com/images/1017KEF5fig01.jpgThe impedance peak at 2.5khz will be bought back down by the increase in -phase angle around there also, so a fairly flat 4’ish ohm impedance will be seen by the amp This is what Stereophile had to say Fig.1 shows how the impedance and electrical phase vary with frequency. While the impedance lies above 8 ohms in the low treble, it remains between 4 and 5 ohms throughout the midrange and bass and in the top octaves. The minimum value was 3.3 ohms between 90 and 100Hz, but as the phase angle is generally benign, the Reference 5 should work well with tube amplifiers from their 4 ohm output transformer taps. Cheers George |
You should be fine with P/P 845 or 211’s, or even SE ones with the
speakers being 90db, and if the amps have a 4ohm tap, and you don’t want
to go too loud with the SE’s.
The 8ohm tap will give more watts but "could" a problem in the bass.
https://www.stereophile.com/images/1017KEF5fig01.jpg
The
impedance peak at 2.5khz will be bought back down by the increase in
-phase angle around there also, so a fairly flat 4’ish ohm impedance
will be seen by the amp
This is what Stereophile had to say
Fig.1
shows how the impedance and electrical phase vary with frequency. While
the impedance lies above 8 ohms in the low treble, it remains between 4
and 5 ohms throughout the midrange and bass and in the top octaves. The
minimum value was 3.3 ohms between 90 and 100Hz, but as the phase angle
is generally benign, the Reference 5 should work well with tube
amplifiers from their 4 ohm output transformer taps. What George is saying here is bad advice. The Stereophile comments apply only to tube amplifiers capable of acting as a voltage source (IOW, employing feedback). Since 99% of all SETs are zero feedback, they will tend to behave as a power source rather than a voltage source. Since the design of the speaker clearly is expecting a voltage source (and Stereophile clearly shows this in their impedance curve measurement) you'll encounter a tonal issue (weak bass or brightness, depending on how you look at it) with such an amp. One other thing to keep in mind with all SETs! You can't run them up to full power like you can with most push-pull amps; to really get the most out of any SET the speaker should be efficient enough that the amp never needs to make more than about 20-25% of full power. If this rule is broken, the SET will be making quite a lot of distortion at higher power. Almost any SET has about 10% THD at full power. If you keep the amplifier power under 20% its going to be a lot less- typically under 0.5%. When you push the SET harder, the additional distortion is perceived by the ear as 'dynamics' since the higher orders are showing up, initially on transients. The ear uses the higher orders to sense sound pressure- hence 'dynamics' but its really just distortion. Its just not a good match. If working with a tube amp of that power, (60-70 watts) a push-pull amp employing feedback is the way to go. |
What George is saying here is bad advice. That’s wrong you’ll encounter a tonal issue That’s just what sets do, look at ANY SET into the Stereophile simulated speaker load frequency response graph, most sets act like tone controls. thegreenman OP As I had 805 sets drive just that same speaker off the 4ohm taps, like I said the max loudness wasn’t quite there, but it sounded great, for tube set. The Kef looks like a benign 4ohm load to an amp when impedance and combined -phase angle is taken into account. Cheers George |
Peaks in SPL are usually at lowest frequencies. I have ne problem driving less efficient speakers with a 45w 845 push-pull to reference levels because I never pushed the limit in terms of SPL because the speakers rolled off at 60hz. And to Ralph's point, my amps were Push Pull and not SETs. Pushing a SET to hard doesn't sound as good. I have done a direct comparison of the Art Audio Carissa vs. Quartets. With efficient speakers, Carissa kills the Push-Pulls but as efficiency drops, the Push Pulls
That will ne be the case with the Reference 5s. You will have peak output of about 100dBs before the amp clips. This is going to mean VERY flabby bass.
Seriously, wouldn't it make more sense to bi-amp. Get a great 845 for mids and treble and power the bass with a nice, SS amp. Get a used Krell or Chord power amp, even Musical Fidelity to pair with it and the net result will be brilliant.
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That will ne be the case with the Reference 5s. You will have peak output of about 100dBs before the amp clips. This is going to mean VERY flabby bass. Yes as I also said the bass is the problem unless there’s a 4ohm tap, then ultimate loudness is reduced Seriously, wouldn’t it make more sense to bi-amp. Get a great 845 for mids and treble and power the bass with a nice, SS amp. Get a used Krell or Chord power amp, even Musical Fidelity to pair with it and the net result will be brilliant. Yes this would be the best way, put his 845 on Ref 5’s mid/highs terminals, and just a cheap Class-D for the bass, a number of configurations could be done being able to even triamp. Cheers George |
That’s just what sets do, look at ANY SET into the Stereophile simulated
speaker load frequency response graph, most sets act like tone
controls. Sheesh! The Stereophile simulated speaker load ignores the fact that SETs do not function a voltage source (Voltage Paradigm) devices. As a result they will 'act like a tone control' (more accurately, will exhibit a tonal anomaly) on speakers that expect the amp to behave as a voltage source (which is most speakers). But! If the SET is running on a speaker **designed** for this sort of thing (IOW the speaker is a Power Paradigm device too, which is *all* speakers made before 1955) then there will be no tonal issues and the SET can be neutral other than the coloration brought on by the lower ordered harmonics, which audiophiles call 'warmth' or 'bloom'. Speakers that fall into this category will often have controls on the rear to adjust the speaker to the voltage response of the amp (midrange and tweeter level controls). But some speakers, like Coincident loudspeakers, are simply designed to expect a high output impedance of the amp and don't need the controls. Put another way George is spreading misinformation, apparently out of a misunderstanding of how tube amplifiers behave. Yes as I also said the bass is the problem unless there’s a 4ohm tap, then ultimate loudness is reduced This statement is false. Loudness or sound pressure is a function of power output. If the amplifier is making the same power into 8 ohms as it does into 4 (which is what the taps are for) then the sound pressure will be the same since its power will be the same if properly loaded. Now if the speaker is 4 ohms and you use the 8 ohm tap to drive it, you may find that there is less sound pressure on that tap because the power tube is now loaded at an impedance well below optimal. This will cause it to run hotter since some of the power it makes will be absorbed by the tube itself, and because that is the case there will be less output power available to the speaker (and it will be higher distortion). |
thegreenman OP
Don't listen to Ralph, it won't be a disaster like he's making out, he's got a bee in his bonnet, over something. They will work up to a point as verdataudio and I outlined.And very good if you just use them for the mids and highs, with a cheap class-D on the bass.Maybe he's got some sort of other agenda with his soon to be released Class-D and got you in his sights. Cheers George |
it won't be a disaster like he's making out, he's got a bee in his bonnet, over something. 'Something' is misinformation. In case there is any question, I am a manufacturer of tube amplifiers that employ zero feedback. I know all too well that such amps don't work on speakers of this type. You're not seeing me recommend our amps here. That should tell you something. I just don't like to see people flush $$$$$ down the loo for nothing. If the speaker is bi-amplified, then an SET might work on the top. But you'll have to try it with a loaner- you might find that even with bi-amplification (and by that I mean also using an electronic crossover) that the SET still doesn't have enough power even if it can handle the load. Again, to get the most of an SET, it should not be used past 20-25% of full power. |
Dear All,
Thank you so much for your replies. Sorry for the delay as I was heavily bogged down by work. Am grateful to each and every of your replies.
Especially to atmasphere, thanks so much for sharing your views from a tube amplifier designer/manufacturer point of view on SET. I never knew that SETs are not meant to be pushed past their 20-25% mark. Still trying to process and understand some of your more technical comments but am very grateful for your sharing.
Am curious, how about push-pull 845 amplifiers in monoblock configuration? Eg 50w class A, each channel driven by 2 845 or 211 tubes? Would those be sufficient to drive the kef reference 5?
Thanks |
Hi Verdantaudio,
Thanks for your replies as well! I did consider bi-amping but was worried about the matching of the sound. Heard a steve guttenberg video where he was trying to match a tube for high/mid and solid state class A for bass, and sounded bad. Haha hence I am holding that off for now though I agree technically its a feasible option! :)
Heard mcintosh mc901 demos though and agree those sound wonderful! But definitely out of my price range :pp
Cheers
Ben
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Hi Sbank
Thanks for your suggestion! Will keep a lookout for dehavillaudio! Now they dont have 845 tube amps but I will keep a lookout for those! :)
Thanks! |
Am curious, how about push-pull 845 amplifiers in monoblock
configuration? Eg 50w class A, each channel driven by 2 845 or 211
tubes? Would those be sufficient to drive the kef reference 5? If the amp uses feedback you'd probably be alright. The feedback is to allow the amp to behave as a voltage source. |
Dear @thegreenman : I know that you ask for tubes that is where you are sticked.
I know very well all the deficiencies tube alternative has that can’t in true gives us the kind of sound that puts us nearer to the recording ( to what the recording microphones pick-up. ) and with out doubt SS is the way to go.
J.Atkinson ( Editor in chief of ST. ) not only is a trusty professional reviewer but even a recording engeneering and he makes the audio product professional measurements in that magazyne.
Well he made very good review to your Kef 5 and did it using SS MBL amp ( Ayre preamp. ) and he did it for very good reasons. Atkinson was in the old times a tube lover till he learned.
You own very good speakers so it’s up to you and if you want to stay nearer to the recording and to achieve that we need to stay away from tubes, no matters what.
Btw, like you I was a tube lover for 10+ years till I learned by my self because the corrupted AHEE just does not permit it. Pity.
Regards and enjoy the MUSIC NOT DISTORTIONS,
R. |
You going to have limited output with a 50w PP 845 even with feedback. Again, the issue is going to bass distortion during peak dynamic moments at low frequencies when you push above 100dB. Most of the time it will be just fine. |
Hi Atmasphere,
Thanks so much for your input! really appreciate them! sorry may be slightly laggy at some times as some days are really bogged down by work.
All the best and stay safe! :) |
Hi Rauliruegas
Thanks for your opinion! Haha somehow or other have heard many solid state systems, and ultimately I think it depends on what you are looking for/chasing in your system. To me, I think I am truly in love with tube sound, and ultimately am chasing after that as my end goal! Good tube sound just makes you want to close your eyes, savour the sound and smile :)
Stay safe and enjoy your music! :)
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Hi Verdantaudio
Thanks for your opinion! Haha luckily usually I listen at around 85db, so I shouldnt push past 100db I hope! (bar the occasional drum note :p)
I will keep updated if I do upgrade my amplifiers to another tube amp :)
Enjoy the music :) |
