Expert: Cleggsan - 7/2/2010

Question
Hi there! I've just installed two 8 ohm omni speakers (OSD-OS790) in my garden. They're powered by an NAD T763 receiver. Rather than run them stereo, I've hooked them up mono, using a KEF CiTR-SM stereo-mono transformer. I'm coming off the B speaker portion of the receiver, to the transformer, then from that comes the single pair of wires. The two speakers are wired parallel. Total wire run (14 gauge) is 100 ft.

Problem is the amp shut down last night, so I've got a resistance problem of some sort. I was driving both my A speakers and the outdoor B speakers - not excessively loud or anything.

Receiver says it likes 4 ohm speakers; I assume my two 8 ohm speakers in series are 4 ohms. But running mono, and with that little transformer, I have no idea what sort of load i'm putting on the amp. Help me wire this correctly!

Also, I'd like to put two more matching speakers, still mono, in the garden. Tell me how to do that, please.

Chris

Answer
I hope you have not damaged the amplifier.  This transformer, the KEF CiTR-SM, is to be used in constant voltage installations.  

In your case you have jumpered the two channel outputs of the NAD amp together and it has placed an ac low impedance loading on each amp output - which will cause it to overload.  

You may have wiped out the final stage amplification; hopefully not.

But this receiver is a 5.1 unit with 6 power amps built in which are configurable into a stereo mode. This complicates the matter.

You are much better off by just connecting the speaker to one amp and not use the transformer.  You can put the NAD in mono mode, surely.

But, conclusion is, the transformer is not a viable use for this amplifier.

Sorry.