McIntosh autoformers vs direct-coupled output

Broockies, the Expressions are 13A’s, one up from the Impression 11A’s.

Expressions are great speakers, they would definitely need some decent power to drive though.  Not necessarily in watts, they need a solid power supply with enough headroom to reach the 0.7 Ohms at 20khz.  

Thanks to all!  Ziggy: what are M.L. 11A's?  I'm looking at a pair of
Expressions (powered bass).

Actually, The Triton Ones aren't tipped up in the treble.  If they were, I wouldn't be listening to them and I wouldn't have bought the Triton Refs for my main rig.  The Parasound just wasn't for me.

George, I think he was referring to option 3 from your original post.

Ah yes, same reply.

Cheers George

No stereo5, always provide your opinions as I will. I have read those with ears I trust, here on A’gon, state that the GE’s tweeters are somewhat tipped up, like some home theater speakers. This could explain why the Parasound, which is neutral in its presentation, sounded thin with the GE’s, while the laid back and less resolving Macs tamed the tweeter and brought you the sound you wanted?

There is no arguing that at least some of the Mac’s have fantastic resale value.

1: Full range CLS/CLX, 
2: Two ways with passive bass driver. 
3: Or two way with active bass diver? 

George, I think he was referring to option 3 from your original post.

@jetter...…………………..

So, because I found the Parasound Halo to be thin and lifeless I shouldn’t say anything? I had the Parasound Halo Integrated paired with Golden Ear Triton Ones, Sony HAPZ1ES Music Server, Cambridge Audio CXC Transport, Magnum Dynalab MD102 Tuner and found the sound to be thin, lifeless and very uninvolving. That is how I heard it and that is how I called it. I switched to a McIntosh MA6600 Integrated, MCD301 SACD player and MR85 tuner with the same speakers, same Sony music server and the same cables.  It was a night and day difference for the better. I switched to the Mac equipment in September 2017 and listen to this system every day and still love it as much now as I did then, actually more now.  It was the Mac MA6600 that made the BIG difference, I bought the other 2 Mac pieces to match the amp.

Don’t anyone here ever tell me not to describe the sound of equipment I have owned weather you agree or not!

M.L. #3 -

There is no such Martin Logan speaker that I know, but seeing your saying it has it own active bass, the amp you are to use will just see the ESL panel loading only of 40ohms-0.9ohms, if an ML.
I would go with the direct coupled Mac IF it is stable into these wild capacitive loads, and doesn’t act like a tone control (stays flat throughout the FR) I can think of far better amps for your needs.

Cheers George

Viridian, the X was Acoustats first speaker and it used the direct drive amps that clio mentions. They continued to use that amp in various models for two years but people wanted to use their own amps so Acoustat developed a two transformer interface which made the speakers reasonabley easy for most amps to drive. By the time my speakers, the model 2+2 came along the direct drive amps were no longer made. 
About 20 years ago I decided I could improve the performance of the speakers by doing several things. The first was designing an adjustable high voltage supply to the diaphragm. This allowed me to push the voltage right up to the point where the speakers started arching then back off just a little. Doing this gave me another 1000 volts. Acoustat had to design the speaker to tolerate the most humid environments. Up here in New England we are pretty dry and I run A/C in the house. Next I tossed the two transformers and their crossover and got one very big 1 to 100 transformer which favored high frequency response. Since I use sub woofers bass response did not matter to me. The overall result was a speaker that was 6db more efficient, more dynamic and I think more detailed. I also can not saturate these transformers without making my ears bleed. It is actually not the panels that limit headroom, it is the transformers. ESLs have a reputation for being fragile with limited headroom. That is not the case with properly designed ones at all. Sanders explains this nicely in his white papers and I like his speakers a lot. I just wish he would do a line source version. 

@broockies, 

It all ends up what sound signature you like listening to.  Two similarly measured amps can sound different with the same speakers.

As George mentioned, the ML panels go below 1ohm in the higher frequencies.  From my experience, the amount of power needed to bring out the full potential of the panels is related to the size of the panel itself.  What could easily drive my older Source MLs speakers, sounded anemic with the 11As.  

With MLs if you want a crisper sound signature go with direct coupled.  If you want warmer sound with more rolled off highs then go with autoformer.  If going directly coupled, my recommendation would to make sure the amp is rated down to at least 2ohm.  Otherwise, go with autoformer to make sure you provide enough stable power to the speaker.

I do believe that matching preamp and amp is the way to go.  Only reason I mentioned alternatives is that a used McIntosh amps sell far higher on the used market than far newer competitive brands.

Viridian:
"Don't all opinions mask subjective bias"?
Of course! Sorry. I might have simply asked for factual technical info to
help me determine a direction.
Georgehifi: M.L. #3 - powered woofer.
To all: I accept the notion(s) that there are better amp choices
available, but I have a limited budget and have a DeWick re-built C-37
which offers the low-level sound shaping I require.  Unless there there is a compelling cost/performance disparity, I'd prefer to continue with a
Mac amp. Now, given my answer to George, what Mac amp - Auto,
or direct, and what power - would be the most suitable, least
compromising pick? 
Most appreciative of your input - all of you!
Bo

stereo5, you have repeatedly described the parasound halo series as thin and lifeless. I am not sure what your other components were that you paired it with, but I disagree with your subjective evaluation and think you do a disservice to others who may be seeking opinions on what amps to purchase who might pass on these very good amps.

I have ML 11As and picked up a McIntosh MC452.  I spent a lot of time trying to figure out why I couldn’t get some instruments to sound natural, especially violins and pianos.  I found and bought an older MC7106 6 channel directly coupled amp for my center and future surrounds.  I tried bridging two channels and connected the 11As.  The MC7106 brought a more crisper sound to the instruments, it wasn’t perfect since the sound felt a bit thinner probably due to not having enough current.  Nevertheless the instruments were less muddled than the MC452.

Let’s just say I spent a lot of money working around the MC452 not realizing that it was the primary reason I wasn’t happy with the sound.  It’s a great amp, just didn’t fit my preference paired with the 11As.  

What I learned through demoing a bunch of amps is that ML panels naturally roll off highs and are a tad warm.  Match it with a Mcintosh ss amp with autoformers which is also warm, just doesn’t makes good match, for me at least.  It’s all a matter of personal preference, it may work for some.

I liked Luxman the most, especially the 900 series separates, but budget constraint ended with with the 509X.  Others amps work great as well.  Constellation amps, even their entry level line, seem to resonate as well with ML owners, though I never got a chance to demo then myself.

Is this just another of those opinions masking subjective bias, or is there technical substance here?

First you need to say the model ML you have, what type of music, if you have ML’s
1: Full range CLS/CLX,
2: Two ways with passive bass driver.
3: Or two way with active bass diver?

There are far better amps than Macs, for the same money to drive ML’s models in general with. As ML's impedance can be as high as 40ohms and drop to very low 0.9ohm, this is not Mac territory in my opinion. 

Cheers George

stereo5,
I had a similar experience. I put an ancient Mac 2105 up against a Pass 250.5, (I owned both) in my system using 4 different speakers that I own, and the Pass 250.5 sounded thin and electronic (not natural) compared to the Mac. My buddy thought that it was obvious as well. 

With much respect for the technical discussion, I'd like to get back to the focused point of my inquiry:  Mac Autoformer amps vs Mac Direct Coupled.
I'm contemplating acquiring a pair of Martin Logans, and I'm hearing
 that these bi-polars prefer Direct-Coupled, that the Autoformers
have some difficulty in the mid-base region - just about the low end
of the M.L.'s panel's low end. 
Is this just another of those opinions masking subjective bias, or is there techical substance here?
Any help on this issue will be greatly appreciated!
Bo

@audioman581...………….

I owned a Parasound Halo prior to purchasing a McIntosh.  The Parasound sounded thin and lifeless compared to the McIntosh.

The Acoustat direct drive amps are transformerless with solid state input and tube output. They put 5000V on the panels. I use them on my Acoustat Model 2 in place of the magnetic (transformer) interface.

I have Zero’s between my Atma-Sphere’s and Quad 57s and have a Music Reference OTL with built in autoformer (although the soon to be released MR OTL won’t have one). No ill effects using either. Actually building an autoformer volume control as we speak to replace my Beveridge direct coupled preamp so I’ll have plenty more wire in the signal path.

Weren’t the amps in the Acoustat X output transformerless?

Yes but also deadly as they supplied the HT to the ESL’s stators via the speaker cables, instead of the esl voltage step up 1:50 audio transformer (attached).
https://ibb.co/wcVZGSV

Imagine if you have a normal ESL and the amp gives out 20v for music then the 1:50 stepup makes this 20v 50 x higher 1000v!!!!! and this is what travels on the speaker wire in direct drive ESL's like the Acoustat X 

Cheers George

Well, you should see the monster transformer I have on my Acoustats and they for certain do not have that problem, at least when going in the opposite direction on ESLs. One also needs to keep in mind that a wire is a tube full of ping pong balls. You shove one in one end and another pops out the other end. This happens at the speed of light. By comparison music barely moves.  

That is exactly the purpose of the output transformer. To drop the output impedance normally of high impedance tubes to an impedance low enough to drive loudspeakers. SS outputs have low impedance to begin with and do not normally need a transformer. Mac uses the transformer to isolate it's output section from the load which I believe they feel enhances stability which enhances sound. They certainly do have a signature sound and it is not bad it is just not the most detailed, dynamic sound out there.

Pair of Kanta 2's with the mc452.

+1 with kosst, I'm driving a pair of Kanta 2's and have never heard of this? Would something like a Pass Lab amp drive them more appropriately?

It is extraordinarily hard to blow a Mac amp. The transformers protect the amp from impedance irregularities and back EMF. Mac amps have this sort of floating smoothness for lack of a better term that many find attractive. On the speakers I use they are not as detailed or dynamic as a direct coupled class A amp but if reliability is your greatest concern Mac is the best.

I admit that I'm a fan but not a fanatic when it comes to Mac gear. That said, after having owned autoformer coupled pieces and non autoformer coupled, I feel autoformers coupled sounds fuller and more natural.

Now prepare to hear from the Mac Autoformer haters. Where are you georgehifi?

i don't know too much about equipment but i think with the mcintosh autoformers the power is the same into 2,4 and 8 ohms. with a direct-coupled amp the power is different in those 3 different ohms.