Among many outrages foolishness that are so common among the people who going high-end audio one of the most ridicules is use of Single-Ended Triodes and low sensitivity speakers. The people who have db-meters between their ears instead of brain are under impression that compatibility between amplifier and speaker could be described ONLY by power rating and load sensitively. When they consider they have a correct ratio? When they have enough volume for a given listening space. Nothing could be further from truth - volume is hardly in the picture.

I have seen many times when Morons claimed that a given SET was  able to play “even too loud” still the Morons failed to note that the amplifier sounded like it was driving too heavy load. Since most of the people outs there in complete denial about the subject I will give a very brief survival guide for recognition of SET-to-speaker compatibility (here and below it will call it the Compatibility

Mostly, and very contrarily to common practice, disregard the assessment of the Compatibility by looking at LF clipping. Yes, when a SET runs out of power it clips LF. However, different topologies of LF enclosures handle that clipping-sound differently and different output stages behave differently at max power and at max currant in output transformer. So, the observing of bass is not an objective incaution of the Compatibility. BTW, there are few other reasons why bass should not be a target of attention but I will not dive in this article into those reasons.

The most objective indication of the Compatibility is observing the MF. In this area a SET is far always from any saturations in output transformer, the dimension of the room is way less critical and sound is very easy identifiable for own sensitivity-power compatibility. So what to listen while you are listening?

1) Mechanical sound in upper MF. In 90% of all cases if you drive 95dB speakers with 20W SET than it is might be “loud enough” but at the same time the upper MF sound mechanical. Have you head bad turntable setups when tonearms sound mechanical? It would be the same.

2) The “sculpture in wall effect”. The upper MF do not sound as independent sound but rather as relief over the entire range. Any “space” information in upper MF non present.

3) The “Wet Fur Effect”. Arming with “Wet Fur Effect” you will be able after 5 seconds of listening to draw a collusion if a given speaker is “too dead” for a given SET. (In the past a number of “big names”, seeing as I discarded setups after a few seconds of listening, made a conclusion that I was too superficial and did not even listen the playback enough. Well, there are reasons why I consider most of the audio’s “big names” as pathetic Morons)….

Anyhow, what is the “Wet Fur Effect”? Look how the hair of your fuzzy women looks like if she did not wash them long enough. They are not fluffy and if they not feel this way but at least then look greasy. OK, let do not put women in uncomfortable position and let make more politically correct and more illustrative example.  It will be juts for the sake of association.

Take (hypothetically only!) your Cat or if you are less lucky your dog. Dump her in bathtub, wash he with soup. Then dry your pet with towel. Then put your pet on a middle of carpet and looks at her fur. It is wet and it is not stick out as it should. Now begin to dry your pet with hair blower for instance. The dryer the pet’s fur will be the more distinctive and the more spatial each individual practical of hair will be. The very same is with upper MF and SET amplifiers.

Any low sensitively, dead speakers/driver sounds like wet fur in upper MF. In fact in many cases increase of SET power without increasing the load sensitivity DOES NOT improve situation. I do not why but it was what I have observed. Driving a 92dB for instance speaker with 2A3, or 45, or 300B SET makes upper MF sound like your Pet is submerged under bottom of the Marianas Trench…. even though in some cases YOU HAVE ENOUGH VOLUME.  Increasing SET powers to 211, 845 or to 6C33C do improve bass and sound generally but it does not dry out your pet. I’m not well familiar with sound of 50W-100W SET amplifiers and I might not speculate. However, regardless of the speaker class and type, moving speaker up in sensitivity instantaneously removes moisture from the pet’s fur, making the upper MF to sound as they should.

If I may add, from experience, following and including Romy's post above:

1) In cases of established incompatibility with a average power SET, more output energy (55W), will not completely clear the above 2) and esp. make 3) less "muddy" or "sticky" if I understand it correctly. It will remain flat & wet and will not go significantly louder either -- in case you wondered. There is still no Compatibility.

2) Average sensitivity or higher, speakers may still not offer compatibility -- check following 1) & 2) above. Already 1) should give immediate indications and you won't need to consider 2 or 3. If inconclusive, just change the volume level (and/or move closer to the speakers if necessary -- which probably means the spkrs are too insensitive, see below my "3").

3) Average or higher output SET ("+W"). 
One feels the speaker may be compatible but the results from the MF & upper MF check are strange. Maybe a higher watt ("+W")capability can deliver the goods?
In this case, take note of the upper midbass with the inconclusive SET. Try the +W. There may be compatibility if lowMF is now improved. The MF checks 1) & 2) above should fall into place automatically and consistently. The amp-spkr combo is OK. If the lower MF to MF region is NOT improved, then there is no chance of compatibility (i.e. don't spend too much time checking it out) despite any other improvements, and one is best off buying the cheapest SET as a fashion statement.

4) Another quick check -- maybe 1b': "The camouflaged midbass"
If you hear a nice, euphonic, sweet, honey, whatever, midrange sound with lots of nice "midbass" information right from the start, you may immediately conclude that 1) is satisfied. Forget it. Most MF is recessed & upper MF non existant. You don't need to consider 1-3 above.


Indirectly on topic
5) An indicator of SET sonic performance can often be had by using a planar/ribbon etc speaker. Take note of the sound as in MF checks 1 & 3, above, and disregard 2). (I don't know why, admittedly, but it works in very many cases.)
BTW, I don't like planars, nor ribbons, so can only recommend these as a possible convenient tool (since many people seem to drive such spkrs with SET, so they are available for testing).

BTW, Eduardo de Lima has some thoughts on amp-spkr interfacing  here seen as an equivalent circuit (the Glass Audio articles).

What even more interesting is the relation between sensitivity power. Evan a quadruple increase of power is no compensation for decrease sensitivity. There are many objective justifications why “power does not help”: flux modulations, thermo desertions in drivers, compressions many others. Still, the most fascinating is non-linearity of sensitively vs. power relation. Here I made up juts out of my mind a graph that indicates my visualization of it. Do not be over anal about the exact numbers in there and about what it means “exactly”. It doe not have exact meaning, it rather what Thomas Mann called “truth of moon-light” (when he counted Jacob’s Jews)

Gray Line represents a behavior of a powerful PP that with increasing of power practically linearly dries out the fur of your Cat. The Blue line is how I feel SET behaves.  I know, it is might look for some of your too hypothetical but in fact it is much less hypothetical then you might think. The point is that beefing up you amp increasing its powers is not as necessarily a good direction for getting “better” sound out of a SET. Still, I have no experience with powerful SETs. I have head some SET around the powerful transmitting tubes and some “paralleled SET” (that I’m not convinced that is a good idea to begin with) but in all those situations the general result was very poor and there not conclusive enough to alters my vision and SET’s needs.

Hello all,

Some time ago, I bought a pair of very early production ML2s for an ongoing horn project (see "Note at end").

Rather than just let the ML2s sit and wait for the horns to get done, I of course tried them out with my "normal" 89db/watt@1m speakers (Verity Audio Parsifals with their bass modules), which I had been driving for years with a pair of M1.1s (a very nice match).

Results of the ML2 Verity Audio experiment :
I was not expecting it, but according to my references at that point (still in my pre-horn life) the ML2s drove the 89db/watt@1m Verity Audio speakers quite well. Without going into detail, I can easily understand why people who have never heard these amps mated to a high sensitivity speakers would insist they are a good match for certain "normal" speakers. In fact, the results were satisfying to the point that, until the horns are done, I decided to continue letting the ML2s drive the VA Parsifal speakers.

That's the way things were for quite some time...

Until one day...

I had been very patient, waiting to complete more of the horns, but one day I just couldn't stand it any longer... Though I only had a couple of Upper-Mid horns done, I decided to take the time to un-hook my "normal" 89db/watt@1m speakers, clear a space, and connect the ML2s to this pair of horns (Vitavox S2s into 400Hz Tractrix).

I positioned and connected the horns (high-passing the drivers at 1kHz), switched on the ML2s, loaded a Patricia Barber CD (JUST KIDDING !!!), and sat back to listen.

To make a long stroy short, both cats immediately left the room until I replaced the tubes... And then the sound was fantastic!

It is true that I was only getting part of the frequency spectrum (above 1kHz), but damn! ... Amazing... I was first struck by the total absence of sonic fog and inertia... You know how you feel when you finally manage to get a couple really good nights of rest... Well the drivers now sounded like they were performing as a person who has had this sort of recharge... Alert and ready, without being overly jacked up on caffeine.

The sound is now simply free, and seems to have its own energy or life force. Over all, it is more inviting to explore music when presented this way. Sound imaging is really strong.

I say is, because though these horns are designed to deliver only Upper-Mid-Range, what they deliver is of such quality that I have still not disconnected them (been listening to a lot of violin, soprano, trumpet etc. while working on the other horns).

I now understand why Romy is so addicted to "content-loaded music".

jd*

Note at end :

I bought the ML2s to use as a development/reference tool while constructing this horn system. The idea being that I would first use them to dial in the horns, and later as a reference, to which I would compare and evolve a 5-channel version of the Super Melquiade DSET amps.

The M1.1s are now happily driving a pair of 15 cubic foot, sealed concrete Lower-Bass enclosures ; together they will produce everything below 45Hz in the future system : integration is courtesy an SMS-1.

jessie.dazzle wrote:

I bought the ML2s to use as a development/reference tool while constructing this horn system. The idea being that I would first use them to dial in the horns, and later as a reference, to which I would compare and evolve a 5-channel version of the Super Melquiade DSET amps.

Jessie, it might not be exactly on the subject but I still would like to point out that you are doing very correctly by keeping ML2 as a reference. With all accused limitations of ML2 this amp is very much a reproduced sound reference about the way in which it joints notes. It is not juts harmonics but also some freakish dynamic accents within the harmonics… The  ML2.0 in that area is absolutely superb. In fact if exist any 125dB-130dB sensitive acoustic system then ML2 might be very interesting to play on it and I presume then some of the ML2’s issues might be less evident with very high se4nstivery of load.

So, if/when you make Milq then I highly advise to have your ML2 around. I kept ML2 for a half year after Melquiades was made.  You will see that ML2 will be beneficial for having a good reference regarding that tones/notes jointing. You see, Milq will be more contrasty, more colorful, more dynamic and more articulate. When you will have Milq up and running then that new for you “more everything” will give to you a lot of initial excitement. However, after a while you might fell saturated with this “more everything” and could find yourself with to a collusion that too much “more everything” ads unnecessary sensationalism to music. Then it will be a good idea to switch back to ML2 and to observe how ML2 does. Sure you will observe a few things that you already will not like but also, l you will see that very interesting ML2's NOTES JOINTING INTEGRITY. From there you might consider to set Milq a little bit down, it will be very ease to do by loading the output stage a littlie harder. Eventually you will be able to dial your speaker very prices to have the “proper” (means acoustic-like) tone jointing. Do not worry that by setting Milq down it might “loose” anything. Milq will have a LOT of spare reserve: two stages, no feedback and very fast but at the same time very idiosyncratic driver. So, the word of wisdom: keep ML2.0 for a while. You will/might experience some benefits for re-commissioning ML2 from time to time…. At least how it was with me....