Tannoy Westminster amp matching question.

The amp you want for these is definitely tube! However the efficiency is slightly on the low side as far as SETs go- but of course a lot depends on your room size and listening habits.

My speakers (Classic Audio Loudspeakers model T-3.2) is about the same efficiency (98 db). I find that while I can play them with 5-10 watts, the simple fact is that the amp is straining if I push things at all. So I see 30 watts as being a good minimum power level.

There are good number of tube amps that make that sort of power. SETs in that size are rare though, and lack the bandwidth that the speaker has. So my recommendation is some sort of push pull triode amplifier. Our S-30 amp does well on that speaker and you should be able to find a used one for that price.

Push-pull triode amps can be rare. A small ultra-linear amplifier might be a good choice also. Two vintage examples of that are the Dynaco ST-70 and the Marantz 8B. Dynaco is still making the ST-70. Tannoy recommends 50 watts minimum. With that kind of power you would never clip the amps in most rooms.

Awesome speaker!

Borg7x9, unless you are in a small room listen to what Bvdiman is saying, or you could be making an expensive mistake.

SETs have certain properties. One is that they essentially make no distortion at low power levels. This is unusual- most amps have **increasing** distortion below a certain power level. This is why they have that 'inner detail' that is part of the description of any SET.

The 2nd thing about SETs is the lushness. This comes at slightly higher power levels and has everything to do with the 2nd harmonic distortion that appears at moderate levels. As we can see, the human ears does not mind too much about this distortion.

The final aspect of all SETs is what happens above about 1/4 to 1/3 power. The higher ordered distortion components begin to appear. If the speaker has enough efficiency, this will only occur on louder transients. However, on these transients are also the higher ordered harmonics, which, it happens, that the ear uses to determine how loud a sound is.

The result here is that the SET appears to have far more 'dynamics' because of these loudness cues than it should for such a small amp. You will hear people talking about this all the time.

However, as you can see this is all based on how the amp distorts. The problem you are up against is that you actually need some power. The speaker you have has got bandwidth, and that is something that higher power SETs don't have. To be really successful with an SET you need a horn-loaded speaker with about 103 db at a minimum! That way you have a moderately-powered amp (12 watts, no more) that might still have some bandwidth. Its a trick!

However, SETs are not the only amps that have distortion going to unmeasurable as power is decreased. There is at least one OTL that does that as well. I think there are a few push-pull triode amps as well. The trick here is how the driver circuit is designed. This is a feature you want, because its that first watt that gets you that 'inner detail'. The issue is you need power and bandwidth too (if you really want to hear what the speaker can really do).

I agree with Charles1dad:

Your speakers deserve the best quality amp you can afford.

There are very few SETs that will fill the bill- you can count them on one hand. OTOH there are a number of push-pull amps (including at least one OTL) that will suit that will give the the inner detail, power and bandwidth. BTW all of the ones I am thinking of are zero feedback.

Borg7x9, if brightness is something that bothers you in a system (I know it does for me....) then you will want to avoid amps that employ negative feedback. Feedback will make any amplifier sound brighter.

Remember how I mentioned that the ear uses the odd ordered harmonics to tell how loud a sound is? Negative feedback in an amplifier will reduce most forms of distortion, but will increase the odd orders slightly. By 'slightly' I really do mean by trace amounts - 1/100ths of a percent. But our ears are so tuned to this issue that it is safe to say that using negative feedback violates a fundamental rule of human hearing- how we detect the volume of a sound.

Charles1dad, I think you might misunderstand me on something. Although what I said about distortion in the SET is perfectly true and should not be a matter of debate, it is incorrect to assume that I don't appreciate what a good SET can do.

However I am of the opinion that people try to get away with using SETs on speakers that are not efficient enough! The result of this is that they never find out what the amp was capable of nor what the speaker could do. If you have a speaker that has the right efficiency, SETs offer some of the more transparent and musical setups around. **But the speaker must have the efficiency.**

This is why horns have become more popular in the last 20 years. The Tannoy of the OP, IMO, does not have the efficiency to allow most SETs to strut their stuff. IMO/IME The JOTA (not sure if that one is made anymore; might be available through the UK designer) and the VIVA are good choices of higher power SETs. But in general the idea of a 'high power SET' is nearly oxymoronic although there are a few out there. None of them IMO have the 'magic' of a 45 or 2A3, which require 6-10 db more efficiency than the Tannoy has.

'high power' SETs are expensive! That is why I have been recommending something that offers as much of the 'magic' of an SET, but will also have enough power to do the job.

Atmas do you design to what you think sounds great, or is it a case of trying to please some of the people, most of the time ?? I expect in this industry(at this end of the industry) that its driven by passionate artisans who are designing towards their ultimate personal taste.

I'm looking to improve the performance of the circuit all the time. Until you asked this question, it never occurred to me to try to go for a sound that someone else likes. First off I don't have any idea how I would get into their head to really know what that was :)

So I just try to get as much performance as I can, doing it according to the design principles that have guided me now for several decades. To that end: eliminate sources of distortion (some examples of distortion sources are transistors, pentodes and transformers), particularly the kinds of distortion that the human ear finds objectionable. I don't care so much about what distortion if the ear does *not* care, so I do place a value on listening!

I go for simple circuits; a lot of people are surprised to learn that our OTLs have a simpler signal path than even SETs have (only one stage of gain).

I agree to a certain degree with Charles1dad in that what works for you is fine- that is what works for you. But to that I add that that is in your experience, and what I have found is that no-one has experienced everything. There is always room for improvement. So really its more a matter of if its 'good enough'.

One thing that I find interesting is that we audiophiles use much the same language to describe sound ('soundstage', 'relaxed', 'dynamics', etc.) but this language fails to convey the intensity of the experience. So as a result on the Internet two audiophiles can use the exact same expression although one is describing a $600 transistor amp and the other a $50,000 tube amp. Their experience is worlds apart but the language makes it sound like its exactly the same.

So we still have to audition stuff- no way around it.

Have a good holiday!

The underlying assumption you imply is that high powered solid state has a sound - well that's not true, its going to be speaker dependent.

I find the main 'sound' of most transistor amps the is the slight presence of odd-ordered harmonics, which manifests to the human ear as 'brightness'. The human ear is more sensitive to odd ordered harmonics than just about anything else due to the fact that it uses them to determine how loud a sound is. However I do agree that not all speakers work with all amps and there is indeed a speaker dependency! For more on that see http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php

My point was that you need an amp that is driving the speakers properly and with over 20 years experience with Tannoy 15" drivers in various cabinets, I do believe that many folk incorrectly assume that you only need a few watts because of the high efficiency.

Agreed. I regard the Tannoy has being moderate efficiency rather than high efficiency. You need some wattage.

I believe that controlling the 15" driver, which has been specifically designed to be phase coherent through the crossover point at 1k, is paramount to maintaining that design intent.

For this you don't need high power- you need good bass extension out of the amp. In fact the driver in the Tannoy seems to be happier if the amp has a lower damping factor rather than higher, typical of a lot of speakers with efficiencies in the upper 90s or higher. My speakers are 98 db with dual 15" drivers, yet they are easily 'controlled' by a 5-watt amp, even if that 5 watts is really not enough power to satisfy.

Art80342, I've heard that the BAT and the Tannoys are not the best combination. Overall though the speaker is very tube-friendly.

Driving a 600 ohm load is an unusual task for most home audio preamps. We make the only tube preamps that can do it. There are a few solid state units too, but as you found out just because its a transistor unit does not mean it can drive this kind of load.

I think its important for a preamp to be able to drive such a load, but practically speaking it would be a lot easier for you if the amp was modified to have a more traditional input impedance. The way it is set up right now it kind of sounds like there is an expectation that it will be used with professional broadcast/recording studio gear. There is no reason why an amp like this can't have a 100K input impedance, which would increase your options quite a lot.

Borg7x9, it should not be that big a deal to change the input impedance of the amp. It may be that it has an input transformer- this is not all that strange in the world of SETs. It might be that the transformer has to be replaced. That is not all that hard- I am sure Lundahl or Jensen makes a suitable transformer.

If the input impedance is set by a resistor it will be a piece of cake!

Our preamps can drive higher impedances with no worries.

An amp with a 600 ohm input is designed to be used with a preamp with a transformer output (like professional gear in the old days).

FWIW our preamps can drive that load but have a direct-coupled output rather than a transformer.

It is the immense size of the coupling cap at the output of many tube preamps that also limits the abilities of said preamp. When you are driving a 600 ohm load, the cap has to be at least 120uf (FWIW 30uf cuts off at 8 hz) in order to not have phase shift problems in the audio passband.

Look at what the output impedance of the preamp is at 20Hz and compare that to the 1000Hz figure and you will see what I mean! If you want the preamp to play bass without coloration, the two figures should be exactly the same.

By the time the cap gets over about 3-5uf, it is offering significant coloration at all frequencies due to inductive effects and increased dissipation factors due to its size.

In the old days, to drive a 600 ohm load with tubes, you needed an an output transformer in the preamp. Of course such transformers have problems of their own. But we developed a patent (we are an OTL manufacturer after all) that allows direct-coupling. Even if driving a 100Kohm load, getting rid of the output coupling cap in the preamp is an easily-heard increase in transparency.

We found that our little amp with 30 watts sounded fine on them but our next amplifier up with 60 watts did the job a whole lot better. I am really of the opinion that the speaker is a lot happier with a little power behind it. Most SETs IMO just don't have the power.