Autoformer vs Speaker impedance Curve

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

I design and manufacture audio transformers for all Music Reference amplifiers. I also make OTL amplifiers with and without autotransformers which actually extend the frequency response in the high end. 

Here are a few things to note. An autotranformer is not like a standard output transformer in that there is no need for HV insulation and the winding scheme is totally different. Where we interleave sections in an output transformer we can mulitfilar wind in a autoformer which reduces the leakage reactance markedly.. 

Also, in a 2 to 1 (4 to 1 impedance ratio) autoformer half the current is direct and half is transformed. So they are smaller and lower loss. 

As to McIntosh, their use is very clever and wise. If you note they drive the autoformer typically at the 2 ohm tap. This allows them to use lower rail voltages and stay out of the second breakdown region that all bipolar transistors suffer from. 

This is just a glance, if you want more just ask. As many of you know I have been doing this since 1980 and I find the art of transformers facsinating. Every design brings new challenges.