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In Reply to: List speakers suitable for OTL amps. posted by The Killer Piglet on September 23, 2006 at 12:10:51:
Easy to Drive Speakers (works with M-60) that work without the ZEROs:-a short and very incomplete list-
Quad 57s and 63s, Classic Audio Reproductions, Spendors, ProAc Response series, Merlins, Lowthers, most horns, Talons, JM Labs, nearly all 'full range driver' speakers, Silverline, NHT, Coincident, Wilson Audio, ZU Druids, Gallo, AvantGarde, Reimer, Soliloquy, Vandersteens, IOW if the speaker is 8 ohms in the woofer region and 89 db or more it will probably work...Works without ZEROs but need more power (MA-1 or MA-2):
Avalon, Sound Lab, Wilson Audio, newer Quads, Magnaplanars, Appogee, MBL (easier to drive than you would think!), Audiostatic, bigger Vandersteens, Kharma, Cabasse, Meadowlark
There's a bit of crossover (no pun blah blah) in this list depending on models in the manufacturer's lineup. As you can see, in the bigger amps 4 ohms isn't such a big deal.
ZEROs can help smaller amps with lower impedances and often the MA-1 too. Anytime you can get the impedance up the amp will make less distortion, but you can run into tradeoffs so the general rule is 8 ohms=0 ZEROs :)
Follow Ups:
What about Tannoy? I'm considering Yorkminsters....Just thought I'd get the question in while the thread was active.
-there's a lot that I missed.
I hesitate to disagree slightly, but in my experience with Sound Lab M1s, they have a dip in impedance to about 4 ohms at 500Hz and then go down as low as 2 ohms at high frequencies. I found a tremendous benefit to using Zeros with my MA240s (about the same power as MA1) driving M1s. Without Zeros there is a noticeable midrange "suck-out". With Zeros, it's "all good". Also, Apogees and Magneplanars?????? These are 2-ohm and 4-ohm speakers, respectively.Somewhere I once read in Paul's writings that the Zeros were designed to work with amps producing up to 150W. When one uses Zeros with MA2s (rated at 220W) or other high power tube amps, do the Zeros themselves limit the power made available to the speaker? I once queried Paul about building a pair of "high power" Zeros, but he never responded.
Hi Lew-yes, there is some varience in the Sound Labs!! Depending on the vintage, ZEROs can help a lot. I recently heard a *new* set of A-1s running with MA-1s and the tonality was utterly neutral with a presentation stunning in its overall musical nature- I totally get why the speaker has such a following!
Paul Bolin based some of his comments on the MA-1 in his review several years ago while using Appogee Duetta Signatures, which are 4 ohms and arguably the best of the Appogees. Other Appogees, like the old Full Range, need either ZEROs or the Atma-Sphere Z Music device to work with almost any tube amp.
The people at Magnaplanar maintain that the best they ever heard the MG-20s was with MA-2s. MA-1s make a good showing on them too. To do well with M-60s the ZEROs are required.
Ralph,does using the Speltz Zero box make an OTL amp an effective non-OTL amp? (one has inserted a transformer/autoformer between the amp & speaker effectively making it an transformed amp). One could/does lose the true benefits of an OTL amp as the "purity" of the technique - OTL directly driving a loudspeaker - is lost?
Thanks!
The effectiveness of the ZERO is the fact that the amp driving it already is comfortable with a 16 ohm load. Most tube output sections are driving between 1000 and 5000 ohms. So the result is something that has not been done before- in effect the gestalt amplifier is not an OTL but it is not working inside the conventional transformer-coupled constraints either. This would not be possible if you did not start with an OTL to begin with.On speakers where the amp is uncomfortable (for example, M-60s driving Magnaplanars) this allows the amp to work quite well where it would not have done poorly before- in such a case there are no trade-offs. In the case of 8 ohm speakers there are trade-offs, but then you don't have to use the ZERO unless you want to- with a regular tube amp you have no option. So its something different- something that works. We generally recommend the ZERO if the amp is working with less than 8 ohms, and do not if the amp has 6 ohms or more to deal with.
With our larger amps 4 ohms is not a concern, although the ZERO is sometimes helpful with the MA-1 and speakers less than 4 ohms. If you look at the ZERO as a problem solver then you get a better idea of what its about.
nt.
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