Autoformers vs speakers with wild impedance curve swings (for instance; MC601 amp paired with B&W 802D3 speakers).
There’s a wealth of information about tube amp audio transformers interaction with speaker impedance, but I can’t find anything regarding Autoformer and speaker impedance/phase curve relationships.
Can any techies enlighten me?
Thanks!
(I tacked a similar post onto the end of a 10 year old thread but thought I might get a few more hits with a new thread. Sorry for the redundancy)
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.
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.
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.
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.
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 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)
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
73maxOP 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.
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.
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.
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.
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!
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
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.
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.
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.
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.
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!!!
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.
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.
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.
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?
You must have a verified phone number and physical address in order to post in the Audiogon Forums. Please return to Audiogon.com and complete this step. If you have any questions please contact Support.
