Two different speaker loads, one amp?

[Bassmankr]

I'm using a Sansui AU-517 amp which has the typical speaker set switching function, (all off/A/B/A+B). On the back of the amp at the speaker wire connectors is a warning that when using 2 sets of speakers, both must be 8 ohms. I just picked up a set of LSR32's at the tent sale and they are listed at 4 ohms. I also have a set of Sony's that are 8 ohms. I would like to have both sets hooked up to the amp to check my mixes but I don't want to damage anything. Any suggestions? By the way I love the LSR32's, even though they are not setup in the room yet I can hear great imaging. I've tried out some options and it seems in this room, speakers set to horizontal with vents/tweeters to the inside works best. Maybe when they get moved to a larger space I'll retry vertical.

[Zilch]

Your amp is likely rated for a 4-Ohm load. It's O.K. to hook up a 4-Ohm pair and an 8-Ohm pair, so long as you do not play the two pair simultaneously (which is bad sonic practice, anyway.) "A+B" connects both pair in parallel, resulting in a 2.67-Ohm load, too low....

[Don Mascali]

When the impedance gets too low your output transistors see it as a short. You'll hear the dreaded "zzzzzzzzzit" sound of a transistor in thermal runaway and then the magic smoke comes out.

[Bassmankr]

"It's O.K. to hook up a 4-Ohm pair and an 8-Ohm pair, so long as you do not play the two pair simultaneously"Thanks for the info, looks like I'll desolder the "A+B" option from the knob as a safety just incase someone decides to start turning knobs.

[fumi]

if using the tube amp 40W to connect L100 & 4311 (use the jumper),
will also damage the amp or not??
sorry to silly question,
many thanks!!

[fumi]

like as follow pic, i am using the jumper connect with 4311 & L100 connected with the 40W tube amp!

[doyall]

I would like to have both sets hooked up to the amp to check my mixes but I don't want to damage anything. Any suggestions?

Maybe try a speaker selector box that equalizes the load. I have seen some advertised that claim to equalize at 5 ohms.

[Paul C.]

Maybe try a speaker selector box that equalizes the load. I have seen some advertised that claim to equalize at 5 ohms.

No, don't. They put resistors in series with some of the speakers and that serously screws up the crossover function.

Just don't run both the 4 ohm and 8 ohm at the same time at high power settings. You can run at low power settings with no problem. It is amperage that kills the output transistors, and as long as the power is kept down, so is amperage. If you crank it up, you might have problems.

I would not desolder anything from the speaker switches. The wiring on those is quite complex and you may screw something up. Just don't run both sets of speakers at high levels.

SOME amps, like older Onkyos, in the A+B position put both pairs of speakers in series. Unless the A set and B set of speakers are identical this causes some real problems.

[fumi]

thanks comment