Autoformer vs Speaker impedance Curve

I would like to know how to measure that. 30% is hard to imagine.

+1

73max OP 
Guess that explains the bloated bass when I run 802D3s on my tube amp.

From Stereophile:

" 802 D3's 8, because the bass was entirely devoid of bloat or emphasis or resonance. Despite this, there was no lack of authority when that was called for, and the speaker's reproduction of deep bass was formidable."

This was achieved with Parasound Halo solid state, and Theta Dreadnought, also solid state. 
The big MacIntosh 303 with output transformer was kindly referred as being leaning towards the power, which to me "kindly" says "bloat" (remember MacIntosh are huge advertisers in Stereophile.)   

 
Also this is said about the design of the 802's bass alignment.

"the 802 D3's low-frequency alignment is free from underdamped boom."

  And this is the load the 802's present to the amp. especially in the bass

The magnitude drops to 3 ohms between 100 and 130Hz, and again between 670 and 770Hz.
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 last paragraph will represent a EPDR load close to 2ohms to the amp.

As I said before with what you have without resorting to buying anything else, go with the bi-amping, your Classe on the bottom for control of the the bass and whatever the the tube amp you have on the mids/highs.

Cheers George
 
  

73max OP
bloated bass when I run 802D3s on my tube amp
60 Watt push pull, KT88, “some” local negative feedback

Without global feedback to keep the output impedance low, you probably have quite high output impedance giving you very mediocre damping factor, and no control over the bass hence your term "bloated" compared to the control the Classe has over the bass.

You could always bi-amp with the tubes on the mids/highs and the Classe on the bass, but you’ll need a passive volume control on the input of louder of the two amps to reduce and set it so it’s the same gain as the other amp.

Then use your master volume control on the main pre or dac to vary the whole (both amps) volume.

Cheers George

ramtubes
Second, modern SS amps already have good current capability and low output impedance. They "don’t need any help"

And I’ll add to that, they will also make that amp sound worse if used, as I’ve proved to myself with 3 or 4 amps that were very capable without the autoformers, they made the amps sound like they were cushioned, like looking through opaque glass instead of clear glass.

They are for amps "that need help", but I say save your money and get the right amp instead, or change the speaker to one that the amp in question is happy with.

Cheers George

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

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

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

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

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

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

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    

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

...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 

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  

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

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 

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

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