Speaker Impedance, Tenor OTLs, and Watt Puppies

Generally, is it better to match Tenor OTLs, or any low wattage tube amp, with 8 ohm speakers, rather than say, 4 ohm speakers? I do not clearly understand the impedance factor concept, but have been told that 8 ohm speakers are easier to drive, and also that speaker ohm stability is important. Are Watt Puppies a poor match for the Tenors? I know they will sound good, but are the Watt Puppies performance being maximized?
When using an OTL(like the tenors) it is more important to choose a speaker with the proper impedance and sensitivity. I am not familiar with the Wilson specs. but if they are 4 ohm and high sensitivity say 94dB@1watt/meter you would probably be OK, but they typically work better with high efficency 8 ohm or higher stable load type speakers. Other tube amps aren't as particular, I use a BAT VK-60 powering a 6 ohm 85dB speaker with out any problems. There are many here who know a lot about OTL's I am sure they will offer there opinions as well. ~Tim
Let me give you my two cents form what I learned about Tenor OTLs, or OTLs in general, when it comes to speakers.
OTL amps like an easy load, so an 8 Ohm speaker is easier to drive than a 4 Ohm, but what is more important is the impedance behaviour.
They like a rather linear impedance curve, so if a speaker has huge impedance spikes, say up to 30 Ohm or more and dipping down to 2 Ohm, like my Martin Logan Prodigy┬┤do, they are not a good match and hard to drive for OTLs
I am also looking into these amps and next to the Piega P10, whci a friend drives with Tenor, I am interested in a German made speaker which has an Air Motion Transformer for the treble (I saw it for the first time at the High end show in Frankfurt/Germany)and it is an 8 Ohm speaker, whose impedance varies between 6 Ohm and 10 Ohm, with a 93 dB sensitivity. So this speaker would be a very easy load for any OTL amp like the Tenor.
I would also look into the von Schweikert DB 100 speakers if I were you. I have discussed this speaker with Mr. von Schweikert and according to him, it would be a wonderful match for any OTL.
Hayden, one thing you need to remember is that the Tenors only output 55 watts into 4 ohms, but 75 watts into 8 ohms. then if that is reduced to 3 ohms you are probably looking at less than 50 watts. so the output power of the amp is affected by the impedence.

then the stability of the amp is affected by the change in impedence since there is no output transformer to regulate and stabilize output.

think of impedence as the size of a garden hose. high impedence is a very thin hose....it doesn't take much water to fill and pressurize the hose and it is easy to keep up the pressure. now consider a very large garden hose which is like low impedence....to keep up the pressure it takes lots of water and power to drive the water. without trying to explain the whole impedence picture; an OTL amp is like a water pump designed to work ideally in a medium size hose but that struggles with the bigger hose. also, this pump has a hard time changing speed of flow if the hose changes size.

as you already know, the Watt/Puppy 6's sound great on the Tenors....they just have limited dynamics and can get hard on the peaks or go into soft clipping if pushed. so a marginal match still works with the Tenors....but why have a marginal match when speakers exist that are a very good match with the Tenors?
Thank you Mike. You used a good analogy to clearly explain three concepts: the difference between high and low impedance; impedance stability and output; and amplifier matching with the correct impedance. The problem is should you match your speakers to your amplifier or the other way around
you will read a good review about tenor and watt/puppy
macth at soundstage(june)
adsal, i did read that review.

Hayden, the choice of which comes first, the chicken (speakers) or the egg (amps) is classic. my 2 cents in this case is that for the closest to the musical event an OTL is the best amplifier and no matter what speakers are used only an OTL offers the level of musical satisfaction that i want, especially the Tenors.

in my experience 3 or 4 different speaker systems that are quite a bit different all sounded their best on the Tenors.

Comments are spot on. I'm curently evaluating the Tenor 75wi with a pair of SF Amati Homage (4ohm, with a maximum of 7.8 ohms, but a value below 6 ohms in the midrange and below 4 ohms in the bass and high treble -- Stereophile measurements).

Some other things to add into the equation:

1. Voltage output and gain of your source gear if you are going to run direct, or even through a preamp. If the source doesn't have enough gain (i.e. my CJ Premier 15 phono pre) or voltage output, then you tax an amp already at it's edge driving a speaker below 8ohm.

2. Size of listening room and average level of loudness you like. Some listen in the 80-85 db range. Some in the 95 db range and up. This also impacts whether an OTL like the Tenor will "be a good match" for something like the Watt Puppies. (i.e. my listening room effectively is my entire 1300 sq ft open live/work loft, which makes things a little more difficult).

3. Do you already own the Watt Puppies? Sunk cost is an issue, and one that people will react to differently.

The way to describe the "poor match" is taking a speaker rated at 4ohm, and driving it using the 8ohm taps on a "normal", transformer based tube amp design. The 4ohm tap will provide more cohesion throughout the freq range, tighter bass and mid-bass, with more control over the drivers. Going off an 8ohm tap, you will get more "air", "sparkle", and maybe some more detail. Different people prefer different sounds. For instance, some folks with 8ohm speakers will drive them from a 4ohm tap, and some will drive it from an 8ohm tap.

Hope this helps,

Tom H
You must consider the damping factor when matching OTLs with speaker loads. I do not know what the output impedance of the Tenors is, but low output impedance is generally not the strong suit of OTLs. If you get low impedance speakers, or ones that swing low in the bass freq's particularly, then the damping factor of the amp can be seriously compromised. Generally speaking, higher impedance speakers will present a more controllable load for OTLs.
Mikelavigne, you state: "..this case is that for the closest to the musical event an OTL is the best amplifier... "
I would totally agree with you, was it not for the Kron Double Kronzilla SET amps. I have heard from very two reliable people, that the Double Kronzilla Monoblocks ($35000,00) are even better than the Tenor. And if you read here how the tubes are made (it takes about 120 man hours for one tube and Bohemian artisan glass blowers make the glass shell) I tend to believe these audiophiles. Read here if you like, it is in English
I was almost 100% set on Tenor amps, but since I heard of the Double Kronzilla and an audiophile using two pairs to drive his ML Prodigy, I am going to audition this set up first, before I will decide which amps to buy. He and another auduiophile who knows both amps as well, the Tenor and the Kronzilla told me that the Kronzilla will beat the Tenor by quite a margin, when it comes to reproducing music life like.
Had you ever had a chance to audition Kronzilla amps, or have you heard from people about these amps? As you know I always value your opinion.
Tekunda, i refuse, on general principle, to buy anything called "Double Kronzilla".....the name is just too "out there". i couldn't brag all over the web on my great "Double Kronzillas".....the name "Tenor" sounds much more classy and dignified.

i, of course, am joking....eventually i will hear a better amp than the Tenor 75Wp....could be the Double Kronzilla....heck, some people prefer the Lamm ML2. my opinion is that ON THE PROPER SPEAKER, the best OTL can't be bettered.....and at this moment, the best OTL to my ears is the Tenor.

maybe out there is someone who has heard the Double Kronzilla (could they have come up with a sillier name?) and the Tenor on speakers correct for the Tenor, and they could share with us their opinion.

one last point, the Prodigy is an electrostat that is not OTL friendly. it would be the last speaker to compare OTL speakers on. the Prodigy is 4 ohm and drops to one ohm. any conclusions reached on the Prodigy regarding the Tenor are not meaningful to me. also, even though the Prodigy is an excellent speaker (i know you own them), the dis-similar driver designs limit the potential coherence of this hybrid design, and render meaningless the Tenor's top to bottom excellence. with the Prodigy you need horsepower, and lots of it. don't get me wrong, i like the performance of the Prodigy, it has earned it's awards. but find an OTL-friendly speaker to compare the Tenor and the Double Kronzilla.
Mikelavigne, I agree, the name Kronzilla is silly at the first look, but what else can you name your products if your last name is Dr. Kron and you design the biggest, baddest audio tubes in the world? I have not yet seen a Kronzilla tube in real life, but I was told it is monstrously tall. So Gonzilla-Kronzilla, its not toooo far fetched.
I know that the Prodigy is not a good match for the Tenor at all and the guy in Germany has auditioned the Tenors on different speakers (if I am not mistaken on a new desgin called the Ascendo, www.ascendo.de)
But you are right, there will always be something better eventually. I was only intrigued by the idea of Bohemian artisan glass blowers and 120 man hours to build one tube.
So for me, it is more a piece of art and once Dr. Kron, who is not a young man anymore, will die, his designs might die with him.
My brother, whom I help to build a system, might indeed buy the Ascendo speakers with a apir of DoubleKronzilla
(he opted for Tenor and Piega at first, but he now could get an good deal on the Kronzilla and since the Ascendo are very OTL and SET friendly speakers, 8 Ohm, between 6 and 10 Ohm impedance swings and 91dB sensitivity, it would be a good match to test the Tenors.
The problem is only what to do with the pair of amps, which looses the audition. It is kind of tough to sell these kind of amps on the used market.
Anyway, I just bought two Wolcott amps for my Prodigy. That made a huge improvement. Especially the soundstage and transperency has greatly improved now.
So now I have time to look into analogue stuff, since my system is now at a point, where I would benefit from a nice turntable.
Tekunda, art is art, and sound is sound. make sure if you spend big bucks for amps (even with a great discount), that you get solidly engineered amps (which the Krons may well be).

i have done "biggest and baddest" before, i had the Mark Levinson #33 monoblocks, 365 pounds each of muscle. the 33s literally dwarf any other amp. while i have nothing bad to say about them, i have heard 5 amps in my room since then that i preferred to them. none of those amps had the visual majesty and "wow" factor of the #33s, but i can say i won't ever own the #33s again.

your Wolcotts are an excellent choice for your Prodigys.

i think your intention to get a vinyl setup is great, go for it!!
Mikelavigne, you are absolutely right, art is art and sound is sound, but wouldn't it be wondeful, if you could combine both?
If you had the choice of two equal performing amps, wouldn't you go for the visually more appealing?
And by saying biggest, baddest, I did not mean that I need muscle amps, the Knrozilly "only" have 80 watt, which is still a lot for a SET amp.
But with biggest, baddest I strictly meant the size of the tubes. These tubes are really stunning looking monsters and will visually impress anybody and if the sound is also very impressive, it would make the Kronzilla a very good amp indeed. But do not worry, I have not taken on a dealership for the Kronzilla amps now, my cables are giving me enough trouble already (-: ) Just kidding of course.