Autoformer vs Speaker impedance Curve

You may want to ask McIntosh or a big McIntosh dealer like Audio Classics about the function of their autoformers.

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? 

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?

With either an autoformer or output transformer the operation is similar, so we don’t have to separate them.

Transformers **transform** impedance. To do this, it goes both ways- if a lower impedance as you suggest above is on the 8 ohm tap, a lower impedance is thus also seen by the output devices.


This is exactly the same as if there were no output transformer at all- think about it- if an amp has no output transformer, it too will see a varying load.

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.

Now there is the issue of the varying load, and a lot depends on what the designer of that load expects. You might want to read the article at this link:
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php

ESLs have an impedance curve that typically varies by about 10:1 over their range. Yet it works better for them if the amp can make constant power rather than constant voltage. A lot of box speakers don’t behave this way- for them, constant voltage over the range is more important, this in order to control the normal resonance and resulting impedance peak usually in the bass region near the speaker’s cutoff. To accomplish the latter, enough loop negative feedback applied will cause any amplifier, tube or solid state, output transformer or not, to behave as a voltage source and the resulting output will be constant voltage. This is why this comment:

Large impedance swings and severe phase angles do exactly what you’d expect; they produce dips and humps in response. McIntosh is about the only solid state manufacturer to use output coupling transformers. If you’re driving benign, modestly reactive loads, all is peachy. But you throw some significantly reactive speakers at it, not so much.

- is only partially true- if the amp is acting a voltage source, the above statement is false. Specifically in the case of MacIntosh, the statement is false; Mac led the way in the late 1950s towards developing the idea that speakers be ’voltage driven’ (IOW act like a voltage source) and I don’t think they’ve backed away from that, since most of the industry has followed their lead.

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.

A major factor contributing to this, and what is probably the most major factor in many cases, is not the output transformer itself, but the interaction of the output impedance of a tube amp with the speaker impedance variations that you are referring to. In contrast to nearly all solid state amps, most tube amps have output impedances that are a significant fraction of speaker impedance, usually somewhere between a large fraction of an ohm and several ohms. That in turn causes the voltage divider effect to have significant effects on tonality, to the extent that the speaker’s impedance varies as a function of frequency.

In the case of McIntosh solid state amps which use autoformers that particular effect is essentially negligible with most speakers, because as a consequence of being solid state their output impedance is much smaller than the output impedance of most tube amps. (Although that certainly does not mean that an amplifier having low output impedance is necessarily the best match for a given speaker, in terms of tonality). For example the MC302 has a specified damping factor of "greater than 40," which for the 8 ohm tap theoretically corresponds to an output impedance of less than 8/40 = 0.2 ohms.

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

While as I’ve said the effects you appear to be asking about are usually not due to output transformers themselves, autoformers do have significant advantages relative to output transformers in typical applications. One is that autoformers don’t have to be designed to handle significant amounts of DC, while the output transformers in tube amps must be able to do that. Another is that in typical applications an autoformer just has to provide a small transformation ratio between input and output voltage, current, and impedance, while the output transformer of a tube amp usually has to provide a much larger ratio. Those differences mean that a well designed autoformer will tend to have fewer sonic side-effects than a comparably well designed output transformer.

Regards,
-- Al

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. 

73max OP
Autoformer vs Speaker impedance Curve

Just don’t get sucked into the McIntosh propaganda, or others hype here.

They (autoformers) allow an amp to work with a speaker that it normally wouldn’t be a good match for.
Better to rather spend the money and get the RIGHT AMP instead of putting a "soft comfort cushion" (autoformer) between the amp and speaker.

Your B&W 802D3 deserve better than this, get the right amp for them.

https://www.stereophile.com/images/616BW802fig1.jpg
" B&W 802D3 The magnitude drops to 3 ohms between 100 and 130Hz, and again between 670 and 770Hz; and while the electrical phase angle is low in the lower region, it becomes increasingly inductive above 600Hz, reaching +46° at 1kHz, where the magnitude is 4 ohms. There is also a combination of 4 ohms and –64° at 69Hz, implying that this speaker does require an amplifier that is not upset by a low effective impedance."

This statement "There is also a combination of 4 ohms and –64° at 69Hz" means the amp could see an EPDR load of down to 2ohms!!!!!!! And it stays at 3ohms for the rest of the bass and upper bass!!!


Cheers George

@73max

Your B&W 802 D3 will be better off driven by a pair of Classe Delta CAM-300 monoblock amps or the CAM-600 monoblock amps. I’ve heard these B&W 802 D3 paired with the Classe Delta CAM-300 & CAM-600 monoblock amps before as well as the Mac MC601 monoblock amps in the same setup and same listening room environment.
They sounded best driven by either the Classe Delta CAM-300 or CAM-600 monoblock amps. These Classe Delta series amps have been discontinued last year and can be had at discounted prices if you can find a used pairs.
The Classe CAM-600 originally retail for the same price as the Mac MC601 ($14k/pair) and the CAM-300 originally retail for $11k/pair). 

These B&W 800 series D3 speakers pair really well with Classe Delta series amplifiers. They sounded great together.
I’m currently using the Classe Delta CAM-600 monoblock amps to drive my B&W 800 D3 front speakers in my dedicated home theater room. They sounded spectacular together.
I’m also using the Classe CAM-300 monoblock amp (single) to power the matching B&W HTML1 D3 center channel speaker. Classe and B&W have great synergy together.

08-17-2018 11:41am@73max

Your B&W 802 D3 will be better off driven by a pair of Classe Delta CAM-300 monoblock amps or the CAM-600 monoblock amps.

+1 This is what I meant by the right amp  73max OP

Cheers george

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.

Thanks guys for this discussion. Informative and educational.

My confusion stems from the fact that some posts imply that autoformers help

Very simple Max.

Yes they do "help" with amps that can't drive those loads.
Best is to get the right amp that will drive them.
Not to put a band-aid on ones that can't.

Cheers George 

When considering an amp for my Magnepan 3.7 I contacted the factory and a large dealer and both said the autoformer would not make a good match with the Maggie's and that I would need at least 500 watts to even consider a Mc. 

johnto

For an amp that doesn’t drive the Maggie’s to well because it can’t handle a 3-4ohm load, an Autoformer would work, because it’s one of the only speakers that presents a very benign 3-4 ohm impedance load. That 8ohm peak in the graph is bought back down to around 4ohms because of the "dotted" -phase angle dipping down at the similar frequency.
But your right you need big wattage as well for them, as they are also inefficient, these one 83db

https://www.stereophile.com/images/archivesart/magfig1.jpg

Cheers George

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

Does this mean Macs are voltage paradigm amps?

Yes. Which paradigm an amp fits into is determined by its output impedance. (And btw, that categorization is along a continuum, rather than being a purely black and white distinction. Especially in the case of tube amps, which vary widely in their output impedances).

If the output impedance of an amp is a tiny fraction of an ohm, or is at least a very small fraction of the impedance of the speaker at any frequency, it will behave as a voltage source. Which means that for a given input signal to the amp, it will output a voltage which essentially has no variation as a function of the impedance of the speaker at whatever frequencies may be present, as long as the amp is operated within the limits of its maximum voltage, current, power, and thermal capabilities.

And in the case of McIntosh solid state amps having autoformers, the combination of their solid state output stages, the autoformers, and what I’m pretty certain is the liberal application of feedback is most of their designs, results in a very low output impedance. The MC302 I referred to earlier being an example.

Tube amps, on the other hand, will just about invariably have relatively high output impedances, usually somewhere between a large fraction of an ohm and several ohms, as I mentioned earlier. That will bring just about all tube amps much closer to the power paradigm end of the spectrum.

Regarding your questions 2 and 3, it follows from Ohm’s Law (I = E/R) and the definition of power (P = E x I, for a resistive load), where I is current, E is voltage, and R is resistance, that if a constant voltage is maintained into a varying load (as it would be by a voltage paradigm amp) more current and hence more power will be delivered into low impedances than into high impedances (assuming at least that all of the impedances are mostly resistive). It also follows that a power paradigm amp will come much closer than a voltage paradigm amp to maintaining constant power into those varying impedances, for a given input voltage to the amp, rather than maintaining constant voltage.

It may help to clarify some of this, btw, if you take a look at the Wikipedia writeup on voltage dividers that I referred to earlier. In the first figure on that page, consider Z1 to represent the output impedance of the amp, and Z2 to represent the impedance of the speaker. And consider Vin to be the voltage the amp is "trying" to put out, meaning the voltage it would supply without a speaker or other load being connected, and Vout to be the voltage seen by the speaker.

None of this necessarily means, however, that frequency response flatness (which you appeared to be referring to when you mentioned "linearity") will be compromised if additional power is or is not supplied into impedance dips. Depending on the design of the speaker its efficiency (SPL out vs. watts in) may or may not vary in a manner that is consistent with its impedance curve. As Ralph (Atmasphere) has said in a number of past threads, a tonal imbalance is especially likely to result when the paradigms to which the speaker and the amp conform are not the same.

Regards,
-- Al

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.

Atmasphere, regarding your link:

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

That has to do with the intentions of the speaker designer. In a general fashion, another way to answer this is that most speakers with highly reactive loads are Voltage Paradigm devices and so the answer would be 'yes'.

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?

Linearity usually refers to distortion... to the latter question, the sound pressure should stay constant, while the power input fluctuates.

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?

If the amp is on a speaker that is designed using Power rules, the output will vary only a little since the designer isn't expecting the amp to throttle its output power back on higher impedances. A good example of this phenomena is an electrostatic loudspeaker, whose impedance is based on a capacitor rather than the impedance of a driver in a box. The idea here is that distortion is kept down, with a preference for lower distortion rather than perfectly flat frequency response, since **the latter doesn't exist** despite what speaker or amp is used.

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!

Mac amplifiers have always been voltage source amplifiers since the 1950s. It does not conflict with the use of an autoformer; such use is not the defining aspect. Most transformer coupled amps are voltage sources too. The taps are used to optimize the interface between the output devices and the speaker to minimize distortion. To make a power paradigm amp you have two pathways- either no feedback at all, or current feedback and voltage feedback of equal amounts. Since all forms of loop feedback are known to add higher ordered harmonic distortions as well as intermodulations, zero feedback is preferred, if adequate means are employed to otherwise suppress distortion in the amplifier. In this way the result can be considerably less colored, despite likely not having perfectly linear frequency response, due to the way the ear perceives distortion. 

Put another way, the ear hears tiny amounts of higher ordered harmonics with striking ease. So if an amp has 0.001THD, but all the distortion it has is the 5th harmonic and above, it will sound bright and harsh. **That** is a coloration, and not a particularly pleasant one. This is why tubes vs transistors has been such an on-going debate and why tubes are still around.

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 

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

This statement ignores just how much loop feedback is needed to fully compensate for this sort of thing. We all know what too much feedback has the reputation to sound like.
And also ignores if there is no global feedback just local feedback which many good amps use, as well as some amps that don't use feedback.

Like I said before  73max OP  your better off using an amp that is right for the job, and not spending money on autoformers, better spending it on the right amp instead which your B&W 802D3 deserve.
 
Cheers George  

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

 ...such as?

...such as?

With this kind of impedance and phase angle load graph,
https://www.stereophile.com/images/616BW802fig1.jpg

I would look at good quality amps with big power supplies (that means heavy), that can "almost" double their wattage from 8 to 4 to 2 ohms, this is usually reserved for amps with BJT (bi-polar) output transistors.
EG: Krell, Gryphon, D'Agostino, Parasound Halo JC1's, and many others 

The 802 D3's are efficient, at tested 91db, so a even 100w amp at 8ohms is fine, so long as it "almost" doubles to 4ohms (200w) and 2ohms (400w)  

Cheers George 

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. 

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.

Seeing you have a thing for Classe, this is what i’d like to see on them, it will control them with an iron fist, and if you need colourations try different preamps, they all sound different.

Find a used Classé Omega power amplifier, no fans, this below from the test bench is what "current (wattage doubling)" is all about and wattage. Not that you need that much wattage, a 100 at 8ohms would do.
.
" The Classé Omega proved a powerhouse on these tests (fig.8), generating
506W into 8 ohms
985.4W into 4 ohms
1886W into 2 ohms
and an astonishing 3425W into 1 ohm!!!!!"

It’s RCA input at 129kohm is fine for all preamps .
But it’s XLR input is only 8.4kohm so the preamp need to be very low output impedance (solid state) if the xlr is used.


https://www.stereophile.com/solidpoweramps/97/index.html

Cheers George

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…

This would be nice, if you could up the ante a bit more.
https://www.stereophile.com/content/mark-levinson-no534-power-amplifier

If??? if you look at Class-D, something I'm not warmed to yet. I did hear one that made me take notice once, and that was the Belcanto M600 monoblocks, these "could" do the 802 D3's justice.

Cheers George    

With your B&W 802 D3, you will be better off keeping your Classe CA-2300 or upgrade to Classe CAM-300 monoblock amps or the CAM-600 monoblock amps rather than getting the Mac MC601. 

Try and have a listen to the Classe CAM-600 monoblock amps on your B&W 802 D3. The Classe CAM-600 is a step up from and is in different league than your Classe CA-2300 or the CAM-300. Not only the CAM 600 have twice as much power than the CA-2300 or the CAM-300 but the CAM-600 sounded and perform better, quieter, more musical and better separation and better image focus much more dynamics better slams larger wider deeper soubdstsge better image depths and better overall more refined sounding than the CA-2300. The CAM 600 can also do subtlety better than the CA-2300. The music has more presence with the CAM 600. The CA-2300 is great but the CAM 600 does everything more and better. 
They will sound really good on your B&W 802 D3. 

I'm myself using the Classe CAM-600 monoblock amps driving the B&W 800 D3 in my dedicated home theater room with the Classe SSP 800 as my AV preamp surround processor. I use this setup strictly for home theater (bluray & 4k UHD disc playbacks from my Oppo 205). 
I didn't find the fan annoying at all. It was hardly audible even when it's on when no music or sound is playing. Depending on how far back your listening position is from the amp(s). You might want to check and see if the fan filter needs to get cleaned. 

As you might already know that all Classe Delta series gears, which include the CA-2300, CAM-300, CAM-600, CA-5300, CP 800, SSP 800, CA-D200, have been discontinued last year and nowaday can be had at discounts. The CAM-600 originally retail for $14k/pair and you can find a used one for probably less than $10k/pair. 

Or alternatively, the Classe Omega monoblock amps are even better sounding amps than the CAM 600 and all other Delta series amps but the Omega series gears are older than the CAM 600. I think the Omega monobloclosed amps were discontinued like 10 yrs ago. They were first introduced around 2001/2002 I think. If you can find a used Omega monoblock amps in mint excellent condition and make sure all the caps are still good or have been replaced with Classe original ones I think you should not be hesitant to grab them. They are excellent amps. 

In regards to class D amps, as suggested earlier by Georgehifi, Bel Canto, Theta, NAD Master Series, Classe Sigma series amps all make excellent sounding class D amps. They aren't my favorite amps. I'm more of class A or AB or valves kind of guy. Actually I had listened to the Classe Sigma Mono Amps monoblock amps (class D design) paired with the B&W 802 D3 before at a local dealer here and I thought they sounded great together but I prefer the analog class A/AB amps from Classe such as the CAM 600, CAM 300, CA-2300 or the Classe Omega series amps. But the Classe Sigma series amps are very good considering they are class D designs. 
Classe uses its own proprietary design in designing its class D amps with the Sigma series amps. 

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? 

I personally have never heard Pass XA-160.8 or any Pass amps on the B&W. 
I have heard Pass amps on different speakers such as Focal, Magico etc But not on B&W. 

73max OP14 posts08-27-2018 3:48amAny thoughts on Pass Labs XA-160.8 with 802D3s?

While great amps and very nice sounding, it's bit of 6 of one 1/2 dozen of the other for your speakers though, they are Mosfet and when done in complimentary n and p channel push pull, can't really supply the current like BJT's (bi-polars) can, there are a one or two Mosfet amps that are push pull, but they only use an N channel for both top and bottom which may do the job (much higher current), but I can't remember what is was.    This if you read will give you the gist, of not being able to do your speakers justice "maybe" not worth the chance in my opinion.
https://www.stereophile.com/content/pass-labs-xa160-monoblock-power-amplifier-measurements

Cheers George

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. 

73max OP

Just look at amp reviews on Stereophile and in the bench tests you see they test them into 8 4 and some times 2ohms if they can handle it. Doubling the watts from 8 to 4 to 2ohms is good current, but no amp can double exactly without losses, so instead of 2 x the wattage 1.8 is fine.

Look at the watts they get of of it EG
at 8ohms (eg 100w),
4ohms should be at least say 1.8 x higher (180w)
2ohms at least 1.8 x higher again ( 324w)

This is the sort of amp you should look for, one that almost doubles it’s wattage for each halving of ohms, with those loads that your speaker gives to get 100% of of them.

Your Classe ones look good, maybe yours just has noisy fan bearings or your filters are blocked?

Cheers George

I I agree with Georgehifi. Your noisy fan on your Classe CA-2300 was probably caused by dirty filters on the fan. You might want to check your filter. Cause the fans on all my Classe CAM-600, CAM-300 & two CA-2300 amps that I have in my dedicated HT room are silent and barely barely audible. My dedicated HT room is very well treated and get dead quiet when there’s nothing being played, and while it’s true that I have a very large dedicated HT room.

Which Classe Omega amp is it that you saw for sale? Was it the Omega stereo amp, Omega monoblock amps or the Omega Omnicron monoblock amps, which are lower end series of the regular Omega monoblock amps.
The Omega stereo amps are even older than the Omega monoblocks or the Omega Omnicron monoblocks.
I believed that the Omega stereo amps were first introduced in the late 90’s, whereas the Omega monoblock amps and the Omega Omnicron monoblock amps came out in early 2000s if my memory served me well maybe between 2001 to 2004 I think and remained in production until late 2000s around 2008 or 2009 or maybe even 2010.
Make sure you get the one from late production around 2008 or 2009. You can ask the seller for its serial # of the amp and once you have it, I would suggest you contact Classe give them the serial # of that Omega amp and ask them what year it was being manufactured.

Omega Mono Refrence purchased new in 2004

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

@73max

You might want to clean the fan filter.

In regards to the Classe Omega Reference monoblock amps that are for sale and were purchased new in 2004. There’s no way to confirm that unless you get the serial # from the seller and contact Classe and give them the serial # and ask them what year the amps were manufactured. The Classe Omega amps are still the best sounding amps that Classe made and are superior sonically to any Classe Delta series amps.
These Omega series amps are pure class A deigns whereas the Delta series amps such as your CA-2300 are class AB designs. Those Omega series gears were very expensive more expensive than the Delta series gears.m
The Omega Reference monoblock amps original retail price was around $30k or $35k for the pair when they were still in productions.
Sometime certain Classe dealers still are able to get V stocks of these Omega series amps brand new directly from Classe.
My local Classe dealer here had a pair of these new Omega Reference monoblock amps v stock brand new form Classe 2 yrs ago.

This statement ignores just how much loop feedback is needed to fully compensate for this sort of thing. We all know what too much feedback has the reputation to sound like.

20 db is plenty. The problem area with feedback is **moderate amounts** between about 4 db up to about 15 or so. Over that and the feedback is usually sufficient to make almost any amplifier act like a voltage source.

IOW George, the quote above was completely misleading. If you doubt me, read Nelson Pass' article on distortion and feedback:
https://www.passlabs.com/press/audio-distortion-and-feedback
Any of the amps that you recommend run 20 to 30 db of feedback! In this case you're trying to play both ends- when all the amps in question run large amounts of feedback.

Consider your bubble popped.

Any of the amps that you recommend run 20 to 30 db of feedback!

Bubble still up, your having illusions, or didn’t do your homework.
Two of the amps are "local" and not sound destroying "global" feedback, and are designed to be low output impedance with resorting to global feedback, and have huge reputation for stunning bass and speaker control especially hard to drive ones like these B&W 802d3’s.

I repeat 73max OP, don’t get autoformers for your 802d3’s, unless you have an amp already that’s not right for them and want to use them as an interim band-aid fix, till you get the right amp to do the job, then autoformers are not cheap around $700, better to just put it towards getting the right amp!

Cheers George

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. 

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

Will be fine if only used a few hours a week. Unless he was a nutter who left them on all day many times a week.

Also, where does one find the level of feed back and global vs local for a given amp???

Unless stated in the topology description, or by the owner in interviews. The only way to tell is to look at the circuit diagram, which can be impossible to get unless your in the know. Or you could email the manufacturer and ask.

Cheers George

Trust your ears....there are too many variables and competing criteria in the design to try to follow. Also, recommendations from someone who designs and builds amplifiers for a living (Atmasphere) is much more credible than someone who reads specs and just spits out what they’ve read. Name starts with a "g".

@73max The amount of feedback is usually given in the spec sheet.

Bubble still up, your having illusions, or didn’t do your homework.

Really?? Your prior statement which I quoted suggested that you don't understand how feedback works. And here you are doubling down.

We make zero feedback amplifiers because of some of the problems that Nelson also points out in the article I linked. In other threads, @georgehifi , you are adamant that Nelson is the guru, but in this case you don't seem to want to acknowledge him. You can't have if both ways.

Here's a little primer on how it works with feedback- you can use little or none (which means you have to rely on other means to suppress distortion). If you use a moderate amount of feedback, Bad Things happen- its use will be a degradation. But if you use a lot of feedback (20db or more) then it use is far less audible (it can start to compensate for the distortion it introduces) and so can be pretty effective. Of course, this is the tip of the iceberg; I don't like feedback because even in high amounts it makes the amp brighter than real life (so its a coloration).  Since we make tube amps, I also want soft clipping, and feedback pretty well means that soft clipping isn't going to happen.

Here is another excellent article on some of the nuances of feedback design in an amplifier:
http://www.normankoren.com/Audio/FeedbackFidelity.html
When you are done with Part 1, read Part 2 as well. All the math and proofs are presented.

73max OP

Don’t listen to those that have anything to gain with their own product by promoting Autoformers, as they are biased and blinded because of it.

Just do the experiment for yourself, you have a great amp already (the Classe), borrow beg or steal some Autoformers and put them on your Classe and see what happens to the sound.
You will realize in first 30sec they are not good for amps that can do the job correctly without them. But that they are a band-aid fix for amps that are not correct for the job at hand, and you’d be better off just getting the right amp instead.

Also the fan noise you say you have. As I said before you make sure the filter is clean and you "could" have noisy bearings in the fan they are just like desktop computer tower fans which get nosier with age.
Another thing is to make sure the wall behind the amp if close has a sound deadening pad on it as the noise can reflect of this back into the room.

Cheers George

+1 @georgehifi
Your Classe CA-2300 amp is a perfect choice for your B&W 802 D3. If you want to upgrade, you can get the Classe CAM-300 monoblock amps or the CAM-600 monoblock amps. Just clean the fan filter.

In most ideal scenario, autoformers won't be perfect choice for your B&W 802 D3. Classe amps will be better choices for your B&W 802 D3.
I've heard the B&W 802 D3 driven by Mac MC601 monoblock amps and have compared them with the Classe CAM-300 & CAM-600 monoblock amps in the same setup, and the B&W 802 D3 sounded best driven by the Classe monoblock amps. I've also heard the B&W 802 D3 driven by your Classe CA-2300 stereo amp and it was even better than they were driven by the Mac MC601 monoblock amps. 

The Classe Omega Reference monoblock amps are phenomenal and indeed superior to all Classe Delta series amps including the CAM-600 monoblocks, which is the flagship in the Delta series amplifier line.
If you still want to purchase those Omega monoblock amps from 2004 I can only say go ahead but you will need to send them back to Classe in Canada to get them looked at, to see if the caps or anything that need replaced or serviced.

@73max  Just for the record, I've nothing to gain if you buy a Mac with an autoformer in it :) 

However, you if you can find a set of ZEROs (which, so far as I know, are the only outboard autoformers available for this task), I think its a very good idea to give them a shot if you feel like it.

One thing George is ignoring here is that in a Mac, the autoformers are inside the feedback loop, which makes a difference on how the amp behaves. As others have suggested, audition is the arbitrator.

One thing George is ignoring here is that in a Mac, the autoformers are inside the feedback loop

One thing Ralph is ignoring here, is if the solid state Mac was deigned and built correctly, it wouldn’t need autoformers, inside or outside the feedback loop!
Ask him directly if he honestly believes the sound will improve with autoformer on better solid state amps, like Classe’s, Krell’s, Halo’s, Gryphon’s ect ect ect, driving speakers like 73max has, in the B&W 802D3’s! then do the comparison yourself.

As I said before, put them on your Classe CA-2300 and see what they do to it’s sound, (I’ve done it on a few good ss amps and it’s not pretty) and one of the amps was a Classe DR25!, it’s the only sensible advice given so far from the pro autoformer side.

Cheers George