Tube Amp for Martin Logan Speakers


Hi, I love tube sound through my Martin Logan Aerius-i fronts and Cinema-i center. I currently have a Butler 5150 which is a hybrid, but it busted on me and would cost $700 to fix. I've had china stereo tube amps that were pretty good and gave true tube sound, but not enough drive for higher volumes. I live in condo, so not like I can blast music anyways but still. I got the Butler because I wanted 5 channel tube sound for home theatre (The piercing sound from my Denon 3801 receiver was not pleasant to my ears). It appears there are only three multi-channel tube amps around, from Mcintosh, Butler 5150, and Dared DV-6C. The latter two are hybrids, and the last one was one of the worst tube amps i've ever heard. I have no clue why 6Moons gave the Dared a 2010 award, but maybe it's because it produces only 65W.

So since multichannel tube amps are hard to come by, and they tend to be hybrid, I was thinking maybe it would be best to get three true tube monoblocks to power my fronts. Thing is I wonder if they will be underpowered for my speakers, and not sure which ones are decent for the price. Maybe China made ones would suffice, and they still go for pretty expensive price. I'm wondering if anybody knows of a decent powerful tube monoblock that is affordable, because I can't pay $3000 per block. or maybe best to just repair my Butler. Thing is, I'm not confident that it is reliable. The tubes are soldered in which is weird, and i've taken it to a couple repair guys who both said that the design is not good, because it's very tight inside and more susceptible to being fried from DC voltage areas. it's too sensitive.

Any suggestions for tube monoblocks, even if china made ones? the holy grail for me would be Mcintosh tube amp, but they are hard to come by. Thanks.

smurfmand70
George, not having ever used the ZEROS, I can't speak to their pros or cons. Having said that, as I mentioned in one of my posts above, I tried a couple of gizmo tweaks in the signal path in various places and was disappointed. So, I suppose based on those experiences, I would be biased (pun) against inserting **any** artifact in the signal path .... unless my back was up against the wall.

For that reason, I would shy away from using ESL speakers with wacko impedance and phase angle curves, even if ZEROS would enable my amp to drive them. At one point, I was wondering whether picking up a pair of QUAD 2805s would be worthwhile. After doing some reading about their impedance curve, I decided against it.

Hey ... there's a lot of amp ball-busting speakers out there. The impedance and phase angle specs of some "fav" dynamic speakers are killers. So I happen to concur with the parts of your last post that counsels caution when matching amps and speakers.

As I also said above, it is only through dumb luck that my ARC Ref 150 seems (??) able to do a good job with my Paradigm S8s. Talk about amp ball-busters. I think the reason the combo works is because (i) I use a self powered sub woofer to pick up some of the low end load, (ii) the S8s are spec'ed at 92 db sensitivity, (iii) the Ref 150 is rated at 150 wpc, and (iv) the Ref 150 can presumably deliver serious current because it has a beefed up capacitive power supply of 1040 joules.

Btw, I currently use my amp's 4 ohm output taps. Output impedance is probably on the order of .5 ohms or so. If correct, the "actual" damping factor is probably 8 or 10'ish in the S8's bass region (60 Hz to 500+ Hz) because the S8's spec'ed impedance is about 4 or 5 ohms in that frequency corridor. That is clearly better than if my amp had an output impedance of 4 ohms, in which case the DF would be about ONE (1) .... not so good.

Finally, I think there is more we agree about than not. Hopefully, we'll all read each other's comments more carefully to avoid talking past each other.

Cheers,

Bruce
With the Quad 2805's your AR Ref 150 would be fine on the 4ohm tap as they are below 1ohm output impedance, maybe not so on the ML Monolith's

http://www.stereophile.com/content/audio-research-reference-150-power-amplifier-measurements

Cheers George
Thanks George. Very interesting plots for the Quads and MLs.

Looking at the Quads, I see the bass impedance spike is literally off the chart. Heck, it's almost an open circuit. I don't know, .... schlepping around a 75 amp to a dealer ... auugh. I ain't gettin' the warm and fuzzies.

The MLs have one of the flatest phase angle plots I have ever seen. Even still, I would be concerned that my amp might be challenged driving the MLs because its impedance is incredibly low in the treble region, almost a short.

So here, if I blundered into a combo involving the MLs and the Ref 150 and my back was up against the wall, ZEROs might help. So ... if impedance was doubled, the bass region impedance wouldn't be outrageously high. But jeez, impedance in the treble region is about 1 ohm. Even if doubled, we're still talking about 2 ohms. That's pretty low.

I suppose the only way to know for sure is to try it out and see what happens. But why would I want to drop a ton of bucks on such an uncertain proposition, even with ZEROs.

I gotta tell ya George, ... unless I read a lot of testimonials on A'gon declaring the Ref 150 and one of these ESLs is a match made in heaven, I would be very skeptical. Even if there were a number of approbations, I'd still call ARC and the ESL manufacturers to get a bead from the tech folks.

It kinda raises a different question -- what ARE folks using to drive this ESL speakers? A hydro-electric plant??

Thanks,

Bruce
Robert Deutsch reviewed the ML Montis hybrid for Stereophile and concluded that despite the .5 ohm impedance at 20khz, the speakers could be driven nicely by the McIntosh 275 on their 8 ohm taps and even by the PrimaLuna Prologue Premium integrated amp. He didn't like the matchup with his Audiopax model 88s though.

In spite of the impedance curve, I haven't heard of people having problems driving them and I haven't had that problem myself.