2. amps-preamps
  3. 137607-103348

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
mechans
2,999 posts
 
You may want to ask McIntosh or a big McIntosh dealer like Audio Classics about the function of their autoformers.
kosst_amojan
2,095 posts
 
An autoformers is just a transformer where the primary and secondary share a terminal. It doesn't make them behave radically different than a normal transformer. Pretty much everything that applies to trasformers is true for autoformers. 
73max OP
23 posts
 
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? 


More to discover