Speaker Impedance, Tenor OTLs, and Watt Puppies

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.

Hayden,

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