Tube Amp for Martin Logan Speakers

I do not manufacture amps that may or may not need the Zero in circuit, so there are no ulterior motives for me to hide or protect.
I just don't like to see blanket statements like the Zero will improve all amplifiers regardless of topology.
They have their place in that they make an amp that has trouble to drive certain loads with relative ease, able to do so.
But it is not the definitive answer, it is a bandaid fix, changing the amp/s or speakers is the way to go in these cases.

Here is another point made from Dick Osher's review of the Zero Autoformer that was conveniently left out of the link to the excerpt of the review.

"T-Rex 300B SET, a DIY design project in the works (still unpublished) using Plitron output transformers with only 8-ohm taps, and the Lowther DX4 BassZilla - a 97dB.
At his point, it became clear that although bass lines still benefited from the ZERO, overall the T-Rex - BassZilla interface sounded better with the ZERO out of the way."
"Small, but noticeable errors of commission crept in. Soundstage transparency diminished, which reduced the music's intimacy. Microdynamics now sounded slightly over damped, releasing some of the music's tension. The midrange, which for me paints a window onto the music's soul, became slightly cloudier. On balance, I would rather give up 20% of bass definition for a 10% increase in midrange clarity.":

As you can read the 300B set amp (and others eg OTL's) not known for good drive current, was improved in the bass area with the Zero, but the midrange diminished by 10%
The same 10% detriment will happen to the midrange using a Zero with a good solid state amp or powerful tube amp that have no problem in delivering good bass without the Zero.
The word Dick Olsher used "cloudy" in reference to the midrange is also what I heard in my system with the Zero's attached to a good SS amp that could drive the speakers with no problems, and as well as the bass tightness and drive diminished just as much with it in.

Cheers George

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

Hi Bruce the Quad are not too bad
http://www.stereophile.com/images/66Quadfig01.jpg
when you look at the ML Monolith'
http://www.martinloganowners.com/forum/showthread.php?6301-Impedance-curver-graph&p=69831&viewfull=1#post69831

Cheers George

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