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A+B bi-wiring impedance quiery

B

bargain

Guest
First of all, hi all, this is an awesome forum, I've been reading away for a few hours :)

My setup:

Sony STR-V555ES (it has A+B front speakers...)
B&W DM604s2 nominal impedence 8ohm
B&W DM600s3 nominal impedence 8ohm
B&W LCR600s3 nominal impedence 8ohm
B&W ASW675

My question:

Now, the amp has 2 impedence options. 4ohm and 8ohm. I'm not sure which one to use....

here's why.

From the v555es manual...
To enjoy multi channel surround, connect front, centre, and rear speakers with a nominal impedance of 8 ohms or higher and set the speaker IMPEDANCE SELECTOR to "8ohms." Check the instruction manual supplied with your speakers if you're not sure of thie impedance.

You may connect a pair of speakers with a nominal impedance between 4 and 8 ohms to all of the speaker terminals. However, even if one speaker within this range is connected, set the IMPEDANCE SELECTOR to "4ohms."

Notes
-Be sure to turn off the power when changing the IMPEDANCE SELECTOR.
-Be sure to connect front speakers with a nominal impedance of 8 ohms or higher if you want to select both sets (A+B) of front speakers. In this case, set the IMPEDANCE SELECTOR to "4ohms." Do not set the SPEAKER selector to A+B if you connect speakers with a nominal impedance of 4 to 8 ohms to either Front A or B jacks.

Now, I've used the A+B jacks to bi-wire the 604s.
So it does seem fine... the speakers are 8ohm, the jacks require 8ohm if they, (A+B), are both to be switched on...

but now do I have to set the amp to 4ohm??? it sortof seems that way... but I'm not using 2 sets of speakers, which is what the manual was assuming i think.

So which impedance is more appropriate?

cheers for any feedback :D
 
B

bargain

Guest
thanks for the quick reply

well that's what i'm hoping... and I know it's almost certainly the case... but I just don't want to be wrong, despite how unlikely. what sort of damage can be done etc :/

does anyone have a more conclusive answer to my dilemna?
 

vizslaraner

Standard Member
I must confess to having no knowledge of the 555, but generally, when I see A+B mentioned it usually has something to do with speaker placement.

Am I right in assuming that you have a selector switch allowing A, B, A+B positions? If so, it means is that you could, for example, have one set of speakers in one room (A) and another set in a second room (B) and switch between the two. Alternatively, you could have both sets in one room working together (A+B). However, if you do this one would need to ensure the impedance is 8Ω plus because the amplifier power output module "sees" the speakers connected in parallel, which is effectively a 4Ω load if the speakers are rated at 8.

I would suggest the easiest answer to your dilemma is to forget A+B and connect your speakers to either A or B. Then select accordingly. Alternatively, If you really would prefer to bi-wire using A+B on one set of speakers, use the 8Ω setting. This is exactly what EJ2 says, albeit without reasoning behind why.

David
 

alexs2

Distinguished Member
bargain said:
thanks for the quick reply

well that's what i'm hoping... and I know it's almost certainly the case... but I just don't want to be wrong, despite how unlikely. what sort of damage can be done etc :/

does anyone have a more conclusive answer to my dilemna?

What eviljohn's said about biwiring a single pair of front speakers using the A+B front terminals is entirely correct.
The warnings given in your manual apply to using two sets of front speakers,in which case the overall impedance seen by the amplifier will drop to 4 ohms or less.

The result will be that your amplifier is likely to at best overheat,and at worst suffer damage to the output stage.....as both of us have said though,it would apply to connection 2 sets of speakers to the A+B terminals,using speakers of less than 8ohm impedance,as detailed in your manual.

It is worth pointing out that whilst most B&W speakers(yours included) are rated as 8ohm speakers,they usually dip to somewhat less in the bass regions....used as eviljohn has suggested,you should have no problems,but 2 sets would almost certainly produce trouble.
 
B

bargain

Guest
cheers guys, that's pretty much what I was after :) You've enstilled that little bit of confidence I needed :D heh

I just needed to see if anyone disagreed with eviljohn as his answer was exactly what I wanted to hear :)

thanks again
 

eviljohn2

Prominent Member
It's good to know I'm not going crazy in my old age. :laugh:

Go ahead with it in fact I used to do it before deciding it was a waste of effort.

On a different note, you might like to try setting your amplifier to the 4ohm setting and see how you get on with that. All it does is drop the internal power supply voltage and may help generate more juice in the lower end for your speakers. :)
 

alexs2

Distinguished Member
eviljohn2 said:
It's good to know I'm not going crazy in my old age. :laugh:

Go ahead with it in fact I used to do it before deciding it was a waste of effort.

On a different note, you might like to try setting your amplifier to the 4ohm setting and see how you get on with that. All it does is drop the internal power supply voltage and may help generate more juice in the lower end for your speakers. :)

May simply be that we're both mad,john.....

It works with some speakers,and not with others,so it's certainly worth a try,and nothing is lost if it doesnt work.
 

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