Are you PAYED BY THEM?
Most all tube amps use output transformers with impedance taps that work just fine into 4 or 6 or even 16 ohms!
The Zero is of NO VALUE to most tube amps!
No- I have no financial relationship with Paul Speltz or his company. He just makes a good product that I believe in.
The latter statement is false when the loudspeaker has lower impedances nor is it limited to tube amplifiers (see below). It turns out that on almost any tube amplifier employing an output transformer that when using the 4 ohm tap, bandwidth (particularly in the bass) is reduced and distortion is increased, while total output power goes down slightly. It will be found that the transformer runs warmer too (this is where the loss in output power goes- it is used to heat the output transformer). This is because nearly all output transformers are less efficient into their lowest impedance tap. This is not only measurable but is also audible and that's as real as it gets.
How many people use Zero’s anyway?
And those that do not, do just fine IMO!
There are lots of tube amps that will sound fine on ML speakers without Zero’s.
Turns out that the ZEROs are used in many installations that don't involve OTLs. Some of the Martin Logans have impedances at 20KHz of only 0.5 ohms. That's a problem for most tube amplifiers even though there isn't much energy up there its likely you will hear a rolloff or power will be limited or both. The ZEROs solve the problem easily.
Paul Speltz has a letter from Steve McCormick which states that while Steve's amplifiers can double power form 8 ohms to 4 ohms quite easily, they actually sound better driving 4 ohms through a set of ZEROs. Although power is cut in half (8 ohm power), its a simple fact that all amplifiers including solid state amplifiers like those of Steve McCormick *sound better* into higher impedances because they make less distortion.
Martin Logan has always made ESLs, and ESLs traditionally have their best combination when used with tube amplifiers. This has been the case since ESLs were developed in the 1950s. However what ML recognized was that the transistor amplifier market is much larger than the tube market, so to make their speakers work with solid state better (greateer sales), they set up their matching transformers (similar to an output transformer in a tube amp- all ESLs have them) so that the speaker presents a 4 ohm load or less to the amplifier. This makes them an often very difficult load for a tube amplifier even if it has a 4 ohm tap, since with any ESL the impedance curve varies by about a 10:1 value from 20Hz to 20Khz. So a four ohm ESL will have about a 0.4 to 0.5 ohm impedance at 20KHz (Sound Labs, which have a maximum of about 30 ohms in the bass, tend to be about 3 ohms at 20Kz but can be as low at 1.5 ohms depending on the setting of the Brilliance control).
The thing is, impedances like this are not really all that great for solid state either, especially with less expensive solid state amps that might lack for heatsink area. So a set of ZEROs can put them in much more comfortable (read: cooler running) territory! Plus they will have audibly and measurably less distortion. Now ESLs tend to be very fast and detailed loudspeakers, so if you can reduce distortion the speaker will reveal that very quickly by sounding smoother and more detailed. This is because the human ear/brain system converts distortion into tonality, and the distortion we are reducing by using the ZEROs is going to be the higher ordered harmonics which audiophiles call 'bright' and 'harsh' because of how the ear/brain system reacts to them.
Now I mentioned that ML wanted to make their speakers more drivable with solid state by keeping their impedance low. To give you an idea of what is meant, look at a Quad ESL 57 or 63, or a set of Sound Labs. These ESLs have much higher impedances in the bass region- anywhere from 30 ohms (Sound Lab) to as much as 95 ohms (ESL 57). Solid state amps have troubles making power into those impedances and this is in the bass region where most of the power demands exist. So ML's solution was to reduce the impedance.
To further illustrate, in the case of a Sound Lab, if using solid state usually people use amps that make 400-600 watts into 8 ohms. In the case of 600 watts, what will happen is that into 30 ohms of the Sound Lab ESL in the bass region the amp is going to make slightly more than 150 watts at full power. what this means is a tube amp of only 150 watts can keep up with a 600 watt solid state amp on a set of Sound Labs. Do you see the problem? That is why ML went for much lower impedances and that is why the ZERO is such a handy problem solver when working with them.
