Tube Amp for Martin Logan Speakers

George, the 4.7 number appearing on that page is a specification, not a measurement. On the same Manley page an output impedance of 1.5 ohms is specified, which is confirmed by TJN's measurements in the review you linked to. On the same Manley page, and also in the manual, the statement "optimized for 5 ohms" appears. Maximum output power, input sensitivity, and frequency response are all specified for a 5 ohm load. The 5 ohm power rating is higher than the 8 ohm power rating, for the same distortion level.

I see no reason to assume that the 4.7 number is accurate and the 5 ohm number is not. As I said, the converse seems much more likely.

Regards,
-- Al

All depends on which way you look at it Al.
Saying it's "optimised" for a 5ohm speaker does not mean it's a 5ohm tap.
But giving figures as exact as in 1/10th's, 4.7 for damping and 1.5ohm for output to me is far more exacting.
And from these two figures the tap is closer to an 8ohm tap than 4ohms.
Whatever the case, the way your seeing it, or me, it's not the ideal amp for what the OP has.

Cheers George

Atmasphere. I have indeed used the Zero's on many occasions, as I mentioned in my post. So my opinion IS based on experience, not on any wish to derail this thread, as you insinuate. My experience with them was as I indicated - yes, they allow amps that would otherwise struggle, to drive speakers that present too hard a load for them. An analogy would be saying that your standard 4 cylinder commuter car is capable of 200+mph. But only when towed by a Nascar ! Then claiming that there's no difference in the experience vs not being towed. By their very nature, the Zero's must add/subtract something from the sound. I'm sure their are many happy Zero owners out there. There must be, as they sell. But, I suspect those owners would be better off educating themselves, then spending the money on a better matching between components in the first place. I have yet to hear a system that benefitted (sound-wise) from their use. Your assertion that they "solve a problem" is correct, technically. But at the cost of sound quality. If sound quality is not a priority, then sure, buyers have indeed got their mismatched components to "work" together. But only that. The degradation of sound quality is obviously secondary to them. As a manufacturer, I would have thought your emphasis would be on making sure your amplifiers were matched with speakers that show them at their best ? Surely you're doing your products a disservice, by suggesting the Zero's as a bandaid panacea for buyers ? Just my 2c worth !

With a measured damping factor of 4.7 and an output impedance of 1.5ohms it's closer to an 8ohm tap than a 4ohm tap.
But all this can change with a bit more global feed back to raise the damping factor and lower the output impedance.

George, this may come as a surprise but increasing feedback does not affect output impedance. It stays the same, and the proof is simple.

Your assertion that they "solve a problem" is correct, technically. But at the cost of sound quality. If sound quality is not a priority, then sure, buyers have indeed got their mismatched components to "work" together. But only that. The degradation of sound quality is obviously secondary to them. As a manufacturer, I would have thought your emphasis would be on making sure your amplifiers were matched with speakers that show them at their best ? Surely you're doing your products a disservice, by suggesting the Zero's as a bandaid panacea for buyers ?

Tradeontheweb, sounds like you and I are more on the same page than different. Whenever someone calls me and is interested in one of our amps I always ask about their loudspeakers to see what I am up against. Sometimes they have speakers that they don't want to sell that are IMO not all that compatible. Sometimes they won't work even **with** the ZEROs. But if they will work, I suggest them. Quite often they ask 'doesn't that defeat the OTL aspect of the amplifier?' to which the answer is 'No.'

That is because the ZERO has such a low turns ratio due to its only going from 16 ohms down to 4 ohms or so. It also does not have to block DC; between the two that gives it more bandwidth than most amps. You have to start with an amplifier that already has a low-ish output impedance and puts out no DC...

People also ask if it degrades things as you allude to, the answer to that is "The ZERO is a problem solver and there will be no tradeoff whatsoever, if not it is either not being used properly or does not need to be used at all."

Now its the former in that last statement that needs some looking into. For example, you can set the ZERO up to run only a certain portion of the loudspeaker. An example might be a speaker that has a 4 ohm woofer array but is 8 ohms in the mids and highs, and the speaker can be bi-wired. In that case you can recover some of the lost impact in the bass by using the ZERO only on the woofers.

There are those cases where a person has a speaker that is so inefficient and/or with an adverse impedance curve that there is nothing for it; then I let them know that:

If you want a tube amplifier, your tube investment dollar in whatever amplifier that is will be best served by a speaker that is higher impedance and/or higher efficiency.

The ZERO only comes in when it is obvious that a person is simply not going to budge on their loudspeakers and that is that.

Again, the ML ESLs have a very low impedance as they want more of the solid state market; to use them successfully with tubes the ZERO is an excellent option. The reason for this is simple- a tube amp using a set of ZEROs still has an excellent chance of sounding better than transistors for all the reasons that have been debated about tubes and transistors in the last 50 years. The ZEROs don't change that.

If one looks at the Zeros as a type of adapter, its not that complicated to determine the value case by case, which will vary widely.

Some cases they will add value, but only when an adapter is what is needed to make two devices not designed to work well together work well together.

But clearly if starting from scratch, in most cases, one will be better off NOT using an adapter, especially one that costs big bucks in order to bridge a gap.

FRom the perspective of an amplifier vendor whose product plays by a different set of rules than most, there are surely many good applications of the adapter.

However, if speaker maker and amp maker play by the same set of rules, there should be no need for an adapter if they dd their job well. IF they didn't, they will probably go out of business and no adapter will help save them.