Autoformer vs Speaker impedance Curve

Omega Mono Refrence purchased new in 2004

Thanks all!

I’ve looked at Mac’s Autoformer benefit explanations. My takeaway: better matching of amp to speaker impedance. Ie, 4 ohm terminals for 4 ohm speakers, 8 ohm terminals for 8 ohm speakers, etc. The catch is these are “nominal” loads. 

What isn’t addressed is, what happens “electrically and sonically” with Autoformers when 8 ohm speakers, like 802D3s, dip down to 3 ohms or exceed 20 ohms???  

With typical output transformers (common with tube amps)  speakers with wild impedance swings (and phase) present a challenging load to the amp and fidelity can suffer.

Can the same be said of autoformers? Or, are these electrically different enough from transformers as to not present the same issues?

Can any of you electrical engineers or techs explain the relationship between autoformers and large speaker impedance swings? 

Thanks all!

Some questions to clarify all of your thoughts and input are “gelling”. I need to digest this further. 

Very interesting read atmasphere. I had briefly read it once before, but it was much more clear the second time through.

More to follow. 

Thanks George.  I’ve actually read that.

My confusion stems from the fact that some posts imply that autoformers help with a difficult load.   This would seem to imply they would be a good match for the 802D3s.   If, in fact, autoformers function similar to an  output transformer, the opossite would seem to be true.

I suppose it depends  how one defines a  difficult load.  Are these posts just considering the nominal impedance and the sensitivity,  ignoring the importance of impedance curve and phase issues??? Much yet to consider.

Atmasphere, regarding your link:

1. In general do reactive speakers match better with voltage paradigm amps?

2. What happens to linearity with a voltage paradigm amp?  Does the sp increase where the ohms dip (ie watts increase)—with an increase in distortion—and decrease where the ohms increase? 

3.  Same question as above, but with power paradigm amp. What happens to sp where ohms dip or increase...is it the opposite of voltage paradigm amps? (

(I’m sure the above varies with speaker and amp design, negative feed back and such, but just in the most general of terms)

Mac led the way in the late 1950s towards developing the idea that speakers be ’voltage driven’. 

Does this mean Macs are voltage paradigm amps? Doesn’t this conflict with the way autoformers function?  Seems they would be power paradigm, especially given their multiple output taps. A little over my head here, but learning, so please forgive my ignorance!

Even though I addressed this to atmasphere, I welcome and want all input!

Rob

Thanks Al. Very informative!  Will take a look at the Wikipedia reference 

an Autoformer would work, because it’s one of the only speakers that presents a very benign 3-4 ohm impedance load.

This statement ignores the fact that loop feedback compensates for this sort of thing.

Loop feedback compensates for the autoformer

How the designer set up the amplifier with the transformer plays a big role. The reason you do this BTW is to reduce distortion- all amps have higher distortion playing lower impedances, so if you can raise the overall impedance seen by the output devices distortion will be reduced. This is why Mac uses autoformers. 

Autoformers reduce distortion

Since all forms of loop feedback are known to add higher ordered harmonic distortions as well as intermodulations.

Loop feedback causes distortion 

Okay.  Got it:

Autoformers reduce distortion but need to be compensated for with loop feedback which adds higher order harmonic distortion...the worse kind!  🤯

Sorry, couldn’t resist having a bit of fun with this!  🤪

I’m sure the interplay between these forces is well beyond the scope of this discussion  and certainly well beyond my very limited knowledge.

Thanks all for your input!  Much to think about.

Rob 

 your better off using an amp that is right for the job

 ...such as?

Find a used Classé Omega power amplifier

Nice!  Don’t see any on the market and they are 20 years old.  Recap time. I’m terrible with a soldering iron, and sourcing all the caps…

Thanks for the suggestions George. I  probably shouldn’t have take this thread off topic by asking for suggestions. My bad. There are plenty of threads on that topic.  But...

I’m currently running a CA-2300 with my 802D3s (both bought used) and am very  satisfied with the combination. I will say, on very quiet passages, I can hear the air movement from the fan. This has pushed me away from the CA-M600 that was suggested.  But, the upgrade bug has hit.

With the MC611 out, there are lot of used MC601s on the market.

I’ve run the 802D3s with a very nice tube amp, 75 wpc Kt88. Sounds good, but a little loose and bloated in the bass with a very very slight glare in the upper mids. Mathematically, and to my ear, tubes and 802D3 are not the best match.  (Still on the hunt for speakers for my tube rig)

My my concern is  that  Autoformers may have a touch of that (obviously nowhere near as much as tubes...especially with 600 SS wpc!) without the magic of tubes.   

Just to get a feel for the Mac “sound” I listened to a MC452 with 802D3s in a poorly set up big box store. (The 601s we’re hooked up to Maggie’s, and they didn’t seem inclined to move them...they knew I was “window shopping) Seemed warmer, yet slightly less detailed than my 2300. Overall, I preferred my CA-2300, way better staging and presence, but that is likely more to do with the room.  

Way off topic and rambling. Probably just keep the CA-2300. 

Thanks caphill!

I’m definitely a Classé fanboy.  I absolutely love the sound of my 2300 and can only imagine how good your CA-M600s sound. I haven’t ruled them out, but the fan noise has been an issue for me.

I’m in an extremely quiet and smallish room with fairly extensive acoustic treatment so the slightest noise can be heard. Once I que in on the fan noise I fixate on it and notice it even more. I’ll definitely try cleaning the filter. 

A pair recently sold for $6500 and I almost bid on them, but it was a local pickup (not in my area) and I still have my concerns about fan noise. 

Im a little afraid of the class D stuff. No good reason as I haven’t even listened to one. Maybe I will. They seem to be improving rapidly. Manufacturers  must love them, as they seem considerably less expensive to build. They are passing some of that savings on to the consumer…For now. I’m certain as acceptance becomes greater the prices will increase.  

  There are quite a few McIntosh MC 601s on the market due to the new 611 coming out. I haven’t ruled that out either.  I have listened to a Mac 452  with 802D3s and preferred my 2300. However that Mac was in a horribly set up room. I’m still going to try to listen to a 601 with the 802D3s.  I have to admit, I am a sucker for the big blue meters!  I absolutely love the way the macs look. But, sound first! 

I’m still going through all  the other recommended amplifiers on this post. A lot to consider. 

Any thoughts on Pass Labs XA-160.8 with 802D3s? 

Thanks for the link. Doesn’t look like a good match.  There is a Classé Omega for sale for that is tempting, but I just can’t bring myself to part with that kind of coin for a 15 year old amp.  Too close to a recap.  Not sure I could find a local tech willing to hoist these monsters on the bench... never mind sourcing parts.  The hunt continues. 

Thanks again both! Was just listening to “Interstellar” sound track. Can definitely hear the fan on soft passages.  I will clean the fan filter.

Love this forum. The level of knowledge here is amazing!  

Any thoughts on how old is “too old” for higher end SS amps? Still have my eye on the Classé Omega Monos but it’s at least 15 years old (I have the serial numbers and will get exact age).  

Also, where does one find the level of feed back and global vs local for a given amp???  Doesn’t seem like a spec often given by manufacturers. 

Excellent link atmasphere. Great read...I’m on my second time through and taking notes. 

A twist on the original question.  Numbers and graphs aside, what we hear is the ultimate arbiter. 

With a tube audio transformer:

What happens to what we hear when the speaker impedance dips hard at a specific frequency? Will that “frequency” be heard louder or softer?

...and the opposite. What happens to what we hear when the impedance spikes?  Will that frequency be heard louder or softer. 

Same question, but with an Autoformer?

Thanks Al.  Guess that explains the bloated bass when I run 802D3s on my tube amp. 

Thanks atmasphere. Maybe bloated isn’t the correct word. The bass is markedly more pronounced from my tube amp (60 Watt push pull, KT88, “some” local negative feedback) than my SS CA-2300. It’s also seems “looser” or less defined.

Nonetheless, it seems reasonable to my novice brain that if an increase in speaker impedance increases the sound level “heard”,  that the bass should sound louder where the impedance spikes. No?