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Autoformer vs Speaker impedance Curve

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)



73max
73max OP
23 posts
 
Any thoughts on Pass Labs XA-160.8 with 802D3s? 
caphill
496 posts
 
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. 
georgehifi's avatar
georgehifi
4,966 posts
 
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
73max OP
23 posts
 
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. 
georgehifi's avatar
georgehifi
4,966 posts
 
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
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