I did a troubleshoot for a guy this morning who has this receiver, Polk rt1000p towers, m series rears, and cs center.

At the receiver and at most of the speakers, they meter about 4-5 ohms and seem to work. The problem is his Yamaha has recently started to shut off. I told him I thought it was the load on the receiver (being not the 6-8 ohm range) and it had just finally started to get unhappy and quit on him.

Looking at all the Polk manuals, they all basically said "works with 8 ohm speaker output" or something to that effect.....but no real impedance rating on the speaker itself....another strange thing, I thought.

He will probably buy new speakers and re-purpose the old, but I wanted to pick brains first.

Thanks!

Sadly a lot of the newer amps and receivers with their digital power supplies get pretty grumpy with 4 ohm loads these days! Not like the good old days, when you could just about arc-weld!

Even a speaker labeled as 4 ohms can dip down below 4 ohms, depending on the program material being played, which of course will trigger protection. 8>)

You have successfully measured the resistance of the voice coil, not the impedance of the speaker.

Polk RT1000P are 8ohm speakers. The receiver is shutting off from either a) heat or b) a short on the output stage, either a shorted voice coil or wire touching at the back of the speaker or amp.

An multimeter on an 8ohm speaker will very often read 5-6 ohms resistance.

And only the woofer voice coil at that. Other drivers have a capacitor in series with them so do not show up in an ohmmeter reading. Ohmmeters apply DC and impedance involves AC and the motion of the speaker. And 4 ohm speakers usually measure around 3 - 4 ohms.

All speakers have impedances higher than the resistance you'll measure with an ohmmeter.* The one exception I have seen was a really stooopid design with a bass low-pass filter that was "designed" by ear with no attention paid to its impedance (small series coil, huge capacitor to ground on its input). It smoked a few amps. This was around 1978.

One loose strand of wire touching the paint can short out a Yamaha amp. Check the volume at which the amp shuts off; remove speakers one at a time and suss out whether one particular speaker or speaker wire makes it die. Note that the problem could be at the speaker end. Also find out if anyone moved the receiver between the time it did not shut off and the time it started to shut off.



*I keep repeating "with an ohmmeter" because it is possible to actually measure the real impedance, but not with an ohmmeter, and I want to stress that while an ohmmeter can help you diagnose some problems, its actual information is limited in scope.

Let me add one other note....The customer had said he had heard a noise/something goofy from the rear left speaker and disconnected it (prev to my visit).

I took down that speaker, looked good on the meter, toned out with a toner. I hooked it back up to the receiver with different wiring and the yamaha shut down almost immediately.

With that out of the equation I said he should run just the fronts in two channel for a while and see what happens. (Without a completely blown speaker to point at as the issue, I was at a bit of a loss.) Within an hour or so the amp shut down again. :(

As others have mentioned, that's not likely the problem. But, FWIW, most Yamahas, including the '663, have an option in the advanced setup menu to change the minimum speaker impedance from 8 ohms to 6.

To access this menu: with unit in standby, press MAIN ZONE ON/OFF while holding TONE CONTROL on front panel. Use PROGRAM & TONE CONTROL to navigate.

It suddenly hit me that you might have a short between a speaker wire's hot conductor and ground... say it's scraping over a steel edge on a j-box. Since the amp is likely connected to a dish, which should be grounded, the hot lead hitting the j-box would be a short on that channel; disconnecting the speaker might move the wire enough, temporarily, to lose contact. Disconnect both ends of the speaker wires; inspect any places where they go over edges; set up a tone test that would make a test telephone squawk if the speaker wire grounds to a conduit...

Do they have a cat or puppy? They like to chew on wires.

If you have a toner and assuming the wires were run in-wall, remove the wires from the receiver, connect one lead to the positive wire and the other to a grounded device- if nothing happens, connect the lead to the negative speaker wire. If you hear anything, you have a short. If you don't have a toner, use a multi-meter, set to Ohms.

You could also use a short piece of speaker wire to connect each speaker to the receiver- you may need to connect all of them, though. One speaker connected to a flaky amp may not cause the problem to appear. You could also measure DC voltage at the speaker terminals- if you read more than a couple of milli-Volts, it may have leaky outputs.

Tom, we have an impedance meter if you need to borrow it (haven't seen it in a couple of years!). I agree with the other assessments that it's either a short in the wiring between the receiver and the speakers or a short in the voice coil. Install banana plugs (at a minimum) on all the wire connections and possible dig a little deeper into the speaker. Good luck! This is one of those "I think I got it" moments where it might take a few return visits unless you put every effort into fixing it onsite.

You all missed the info that the left rear speaker "made a goofy noise", which to me indicates an issue in that amp. Noisy transistor, leaky capacitor, etc. This is the most likely reason for shutdown.

1. Check wiring for shorts at both ends, even a single strand could do it.

2. Use an impedance meter to look for differences between the two rear speakers at different frequencies.

If the above two don't yield an issue, it's the amp.

Tom's right that the goofy sound is by itself an indication of a problem inside the amp. However, "use an impedance meter" is usually a pretty expensive step for a CI as it involves buying an impedance meter. If the impedance of a speaker is causing an amp to shut down, it should not matter which channel it's connected to.