2. speakers
  3. 182859-520

Sensitivity 86 v 90

I am considering an upgrade from speakers with a sensitivity rating of 90 db, 4 ohms, to larger speakers rated at 86db, 8 ohms nominal.  Same brand, PMC. My tube integrated amp is 80-112 watts triode/ultralinear, and it’s fine for my 90 db speakers.  Although, it is sometimes at around 4 o’clock on the volume control, approaching the max at 6.  I am aware of the “amp power must double for each 3db increase in volume” rule of thumb, but really have no practical experience with this.  I do like having 90 db efficiency, always assumed that meant a less powerful amp would suffice. 

   My question is, would the decreased efficiency be a concern? 

128x128lloydc
yogiboy's avatar
yogiboy
5,753 posts
 

" but (as I understand it) the gain from the phono preamp can be increased by switching the driver 12AU7 tubes for 12AX7’s, if necessary."

Did the manufacturer of that preamp tell you that? If not you should find out if you can swap to a higher gain tube!

atmasphere's avatar
atmasphere
11,938 posts
 

phono preamp is a Rogers PA-2.  Cartridge is Lyra Kleos, .5 mv output version. I agree with the suggestions that the phono output is probably too low.   I can increase it by changing the driver tubes from 12au7 to 12av7 or 12ax7; I will try that. 

@lloydc 

While a higher gain 12Axx tube can drop into the same socket without damage to the tube or the circuit, that's not the same as saying it will sound right. The various 12Axx tubes have different operating points; if the circuit is to bring out the best in them it will be optimized for a particular type.

bigkidz
3,404 posts
 

Ok my recent experience driving 83 db speakers.  Repaired a class A single ended triode amp 28wpc.  To our disbelief, it drop the crap out of those speakers.  So there is much theory about this subject, some times it doesn't always add up.  Go figure. Happy listening.

Post removed 
lloydc's avatar
lloydc OP
755 posts
 

I went ahead and bought the less sensitive speakers (PMC 25.26 @ 87db, replacing PMC FB1i Signature @ 90db sensitivity) and if anything, they seem to produce more volume at a given setting.  I can only speculate as to why, but now I’m certain that speaker sensitivity has very little predictive value, given my level of (mis)understanding of these things. I suppose there are just too many variables involved.

@ atmasphere

Roger says the circuit is designed to use any 12a_7 in that spot.  I don’t know how he does it.  Apparently the 12au7 is the quietist (and lowest gain) and perhaps, the best sounding, but 12au7, 12ax7, and 12at7 all work fine in that spot.

 

More to discover