Tube Amp for Martin Logan Speakers

Atamsphere, here's another link:

12-28-09: Audiokinesis
Unsound, obviously I should have
made it clear which part of my
response was about things an owner
of existing speakers could do, and
which referred to something that
would have to be done during the
design stage.

In my opinion using an autoformer is
something a speaker owner would do
to make his speakers more compatible
with OTL amps.

If we're just looking at the design
stage, then yes it is easier to
smooth the impedance curve by
lowering it. But if the end goal is
compatibility with OTL amps, for
example, lowering the impedance
curve can be counter-productive.
Some of the design choices that lead
to a medium to high, and smooth,
impedance curve need to be made
before the crossover design stage.
For example, I can't expect to build
a 2.5-way system using two 8-ohm
6" woofers and end up with an
OTL-friendly design.
Audiokinesis (Threads | Answers |
This Thread

I'll try to find more as my time
permits.

Ralph, George and Mapman .... I have no dog in this fight, but I have read the several posts and would like to suggest that much of what everyone has written has merit. Let me suggest to my fellow hobbyists that you aren't really disagreeing with each other, but you are talking past each other and just getting frustrated.

I think Ralph would agree, and has said as much in other threads, that a high'ish output impedance amp might not mesh well with a low'ish sensitivity speaker that has a roller coaster impedance curve. Indeed, one could expect sonic colorations as a result of the interaction between the two components behaving in according with various electrical principles, e.g., Ohm's Law.

That may be why Ralph says that an autoformer might aleviate some aspects of the "non-optimal" (whatever that means) impedance match in such cases. George, I gather your point is that sticking an autoformer into the circuit is just a "patch" for an underlying issue that maybe shouldn't be an issue in the first place.

If that is a fair restatement of your view, I too happen to be biased (pun intended) against sticking gizmos into the circuit based on a few anecdotal experiences of my own. In the two or three cases I put "artifacts" into the signal path, I had dismal outcomes. I am not saying one would have a similar result with autoformers. Just that I am dubious based on past experiences. And even if they work, I am not sure I would want to shoe-horn an amp and speaker together if the two components weren't a good fit in the first place. But that's just me.

If we can all agree that I fairly restated the dilemna, let me suggest that perhaps one way to view OTL amps is kinda like SETs. That is there are audiophiles who swear by SET amps. But, ... they recognized as a threshold matter that a SET amp will not be a good match with a low sensitivity speaker that has a roller coaster impedance curve. That's why some have suggested matching a speaker like a Daedalus with this type of amp. I suspect that an OTL would perform beautifully being matched with a Daedalus speaker.

Hey ... to a lesser extent, I've got amp/speaker issues too. My ARC Ref 150 amp is driving Paradigm Signature 8 v3 speakers. This is **not** a match made in heaven. The S8s have wild impedance and phase angle curves. Paradigm advises that the S8s should be driven by a high-power/high current SS amp. Oooopss. I blundered. But not that much. I've found some sonic solitude by using the 4 ohm taps (as of late), which seem to have smoothed out the rocky impedance road and improved bass response. Having a 1040 joule power supply "don't" [sic] hurt either.

In short, if everyone takes a minute to re-read the other folks' posts, I think you'll wind-up agreeing with much of what has been written.

IMHO.

Btw, I'm rocking with the Best of Pat Benatar CD. Having a ball!! :) :)

Quicksilver, Quicksilver, Quicksilver, Quicksilver, and Quicksilver.... any of the larger variety will do a splendid job.

Bruce, I am a moderator on another site that is unrelated to audio. In that regard they put me through some training so that I could spot posts that went beyond the pale. I don't see Unsound doing that- he attacks the argument, not the person (which is how its done). IMO debate is fine and healthy- and is what forum sites are for. In the end, the debate can help people gain education or at least viewpoint on a subject.

George is different that he attacks the person (look for the word 'stupid' in his last post) and he will often negatively engage in topics just so he can get a rise out of other posters. That is one of the definitions of trolling. (As a side note its also pretty evident that he does not know what he is talking about WRT the ZEROs.)

This site does not employ a 'Report' function so its pretty hard to alert moderators when this sort of thing is going on- they have to encounter it on their own.

Unsound- I see that you reposted some earlier comments I made and one from Duke; I don't see exactly why though. Could you elucidate?

Ralph, as I have come to better appreciate, there are very few if any perfect solutions to audio technical issues. It seems that EE/designer folks like yourself make judgments and compromises to achieve a certain balanced product that has market value within its market niche.

For that reason, I think that it is imprudent to think in absolutes. Having said that, I believe that if one is looking to invest significant sums into their rig, they can avoid obvious pitfalls and clear mismatches, for example, matching a low powered SET amp or a high'ish output impedance tube amp with a low sensitivity rock n' roll impedance curve speaker, like my Paradigm Signature 8s.

(It's only through dumb luck that my Ref 150 can do a decent job driving these beasts. Should have picked another speaker, or kept the speakers and opted for a top drawer SS amp like a Pass or Ayre.)

So, I share your view. We are adults and should be polite, albeit a little tongue-in-cheek humor from time-to-time is ok by me. :)

By the way, I thought the primary focus of your comment about using ZEROs was with respect to matching one of your OTL amps with ESLs like Martin Logans which have extremely low impedance specs at high frequencies. Quite honestly, if I loved ML ESLs, I would have some agita matching that transducer with pretty much any amp, SS or tube, unless the amp was rock solid stable and wouldn't distort driving juice into a .5 ohm load.

Btw, btw, after having read your posts again, I changed the output taps on my Ref 150 from 8 ohms to 4 ohms ... again. Although gain was clearly reduced because I was using the 4 ohm taps (about 2.5 db less than the 8 ohm taps), I think it quite possible that the amp was producing cleaner power (i.e., less distortion).

Bass is clearly more extended and tighter. No surprise there since the output impedance off the 4 ohm taps is less than the 8 ohm taps (therefore higher DF). Plus, speaker impedance in the "power zone" (say 60 Hz to 700 Hz) is for the most part 4 to 5 ohms), ergo a better impedance match for the amp where it is being called upon to deliver most of its juice. Imaging was less forward (probably because midrange/treble was less emphasized as a result of higher impedance), so I turned up the gain and imaging came back. In short the rig plays louder, but not as harsh (i.e., maybe less distortion).

Regards to all,

Bruce

P.S. Back to audio business, I just bought a JVC hi-rez redbook CD of Tango music from Acoustic Sounds. I'll report back with comments. I'm trying to keep track of good hi-rez CD label. So far, +1 for MoFi.