Why did my receiver overheat (from an electrical point of view)?

gurot1

I was testing out the sound of the different speakers I have lying around (a pair of csi5's, an LSiM706c and a 705). I had them hooked up to my NAD 7600. Initially I had all 4 speakers playing for a couple of minutes, then I listened to different, mismatched pairs using the A and B speaker selector switches (I know, not ideal as I would be hearing the sound of two different speakers, not just one) Then I decided to listen power down the receiver and disconnect the speaker cables at the two csi5's. On had been connected to A speakers and the other to B speakers. I did not disconnect the wires at the back of the receiver. I then put in a DVD and had speaker output A driving the 706 and speaker output B driving the 705. After about 20 minutes of decent but not so loud listening, the receiver went into thermal protection mode. It did work again after about 15 minutes of being turned off.

I knew I was asking for trouble when I was hooking up multiple speakers and then disconnecting them, but how does this whole thing work electronically. I have heard before, that hooking up just three speakers to an amp that is set up to output to two pairs can be an issue. So is this a variation of that? I was just wondering what was happening electronically to cause the overheating, whereas in the past I've had action movies going for a few hours and the receiver barely warmed up.

Thanks

BTW, my better half could hear a huge difference between my LSiM706 and the csi5's...she described it as a night and day difference. I noticed a difference, but not as significant as her...might be time to get my ears/hearing checked out!

Nightfall

You are running a center channel speaker on a 2 channel receiver?

All the hooking and unhooking terminal A, terminal B, it's all confusing. So you disconnected a center channel speaker but left the wire connected to the terminals on the receiver? Is it possible the wires were touching on the speaker end?

Without more clarification you somehow had everything hooked up in a way that lowered the impedance the receiver was seeing to a lower value than it is capable of driving.

We have no way of knowing if the A/B switch wires in series or parallel.

gurot1

lol. It's a stereo receiver and can output to two pairs of speakers (pair A and pair , with each pair having a left and right speaker. I disconnected two centre speakers (although the weren't being used as centre channels at the time because they were just connected to the stereo amp, not the HT receiver (I know confusing as I have 2 receivers). You are correct in that I left the wires connected to the terminals on the receiver. I made sure the speakers weren't touching on the speaker end; however, maybe they ended up moving and touching once the music was on (stranger things have happened while connecting and disconnecting gear!). Would the banana plug ends of the disconnected speaker wire lying on the carpet cause an issue?

gurot1

took a quick look at the NAD 7600 manual, it says that if two pairs of speakers are connected to it, to set a switch in the back for speaker impedence to 4 ohm which reduces helps protect the receiver, vs having the switch at the 8 ohm impedence level which I have it set at. I wonder if this is still important when only driving one speaker on outputs A and one on outputs B. I am not sure how the A/B switch is wired in regards to serial or parallel.

Dennis Gardner

It is wired parallel making 2-8 ohm loads reduce to 4 ohms per side/pair. The issue is when you run them both at the same time A+B. You shouldn't have an issue at all while running only 2 speakers as long as they are 1 left and 1 right regardless of A or B.

With that said, I could be wrong, though as NAD does some odd things with their setups. There may be a chance that your receiver sees 4 ohms evn though only 1 set is being powered at a time. Who knows?

ZLTFUL

Had the wires been touching, the receiver would have went into protect mode instantly, not after

about 20 minutes of decent but not so loud listening

@Dennis Gardner is on the right track.
Running 2 8 ohm loads at the same time is going to present a 4 ohm load to the receiver which will in turn cause it to run hotter.
And as the device ages, the thermal protection circuitry will age and it's tolerances lower over time causing it to either fail to protect at all or prematurely go into protect mode. Think of the poly switches on old SDAs. Same idea.

Not having the switch on the receiver set to 4 ohm also compounded the problem as it "fooled" the receiver into "thinking" it had a normal 8 ohm load.

Easy Runnin

Aren't the LSiMs 4 ohm speakers? So wouldn't running a pair of 4 ohms and a pair of 8 ohms present a load somewhere below 4 ohms?

txcoastal1

Easy Runnin wrote: »

Aren't the LSiMs 4 ohm speakers? So wouldn't running a pair of 4 ohms and a pair of 8 ohms present a load somewhere below 4 ohms?

LSiM are 8ohm

ZLTFUL

LSi=4ohm
LSiM=8ohm

(Nominal loads of course...the LSis tended to dip significantly...especially the 9s and 15s...the LSiMs tend to be a bit less rangy with impedance)

gurot1

I was being lazy and didnt disconnect the speaker wires from receiver. Laziness usually bites you in the behind!

gurot1

Lol, that's how it started. Was testing the speakers a pair at a time using the a/b switch to flip back and forth. It was supposed to be five minutes and then off to bed...and then we decided to hear what it would sound like with just the lsim speakers and I didnt bother reconfiguring the wires as the back of the receiver so that the speakers were on the same pair of posts. We thought we would listen to one minute and then that would be it...turned into longer listening session...the joys of sleep deprivation with babies...you end up forgetting details...like checking your wiring!

pitdogg2

gurot1 wrote: »

I was being lazy and didnt disconnect the speaker wires from receiver. Laziness usually bites you in the behind!

In this case its a good way to let the magic smoke out......

gurot1

Lol.. in high school my tech teacher used to say that electronics work on magic smoke, if poof, the magic smoke comes out of the electronics, they stop working. Lol it didn't get to that state the other night luckily. Lesson learned...go to sleep rather than tinker around with the system when exhausted!