Is it common for the 770 to cut out? I have only started to use my 950/770 recently, maybe 3 or 4 hours of use since I hooked them up, both new. I have it connected to 2 Paradigm Studio 100's, a 570 center, and 4 ADP Studio surrounds. It seems that it was running warm at nominal levels, then when I played less then 5 minutes of louder levels, it cut out. I let it sit for a few minutes,and then it cut out again after maybe 2 minutes of loud playing. I had to reset the switch in the back both times. I have it in a rack with about 8" of clearance above it. Does it need a fan on it all the time? I am shocked that it will not handle this level, as it wasn't loud enough to distort. Does this problem occur for anyone else?

I have a 950/770 combo and have never had an overheating problem. All of the speakers I drive with the 770 are 6-ohm nominal impedance.

I would think that 8 inches above the 770 would be plenty. This assumes that there is also sufficient room to allow air to enter underneath the 770, that the air entering the 770 has not been pre-heated by other equipment, and that your rack is an ‘open’ environment that doesn’t partially trap heat in. I know some people with closed racks that use a fan or two to intake and/or exhaust air from the rack and others with fans on their power amps that are in an environment where they are not ‘free to breathe on their own,’ regardless of brand.

Seeing 770 overheat problems reported here is pretty rare. After a thermal shut down, how hot does the warmest part of the top of the 770 feel to you? Is the heat pretty even across the top, or mostly coming from just one channel’s heat sink? If just one channel seems to be the culprit, try switching that channel to another location a few channels over, both input and speaker, and see if the ‘hot channel’ moves to the new location. If you do have a single hot channel that follows a particular speaker connection no matter which amplifier channel is used, I would wonder if that speaker were still presenting a proper impedance.

Outlaw tech support once told me that the channel labeling on the back of the 770 was just for convenience and that I could use the channels in any order I wished. Perhaps I’m eccentric, but because my center, left main and right main will have a higher continuous output than the other four channels, I separate these ‘hottest’ channels by connecting in this order across the back: right main, right side-surround, right back-surround, center, left back-surround, left side-surround, left main.

Regardless of what you find out, if the problem is in the 770 and it needs replacement, I’ve found Outlaw customer and tech support to be great.

I had a similar problem when I installed in-wall speaker wire. It drove me mad until I figured out what I had done. This was twelve-gage wire, but had very fine strands. When I re-inspected my in-wall terminations I found that there were maybe one or two fine strands that were touching. Surprisingly if I ran the system at low volume all was well, but if I turned up the volume it would shutdown. Check you connections carefully, and you may find your problem. Here is an old adage from A&P Mechanic’s School: If you have worked on a system that functioned correctly before you worked on it, and you now have a problem. Go back and inspect what you have done. Chances are very good that something you did, or didn’t do has caused the problem. We all make mistakes. The good mechanic finds, and corrects theirs before they become someone else’s.

Thank you for the input. I have all speakers connected to the 770 with 2 runs of 14 gauge wire each, with fine strands and definitely a concern of a strand or two crossed over(which is also suggested to check for in the troubleshooting part of the 770 manual).Your experience sure sounds familiar, Oil Can.

I thought that I was very careful in the connections, plus I also checked them all for resistance at the amp end of each respective speaker and they all seemed OK. However, I am certainly going to disconnect them all and check very close. The hottest part of the amp is above the center channel area. The rack is ajoining another room, which is open in the back & not very hot.

The speakers & all of the in wall wiring was put in during construction, none of this system has been used before as we only recently moved in. I may very well have a shorting problem with one wire somewhere, as I have also really not heard of this amp having this problem, as bestbang4thebuck stated. Would you try connectors for termination? I have always been comfortable with inserting speaker wires directly into the binding posts, but maybe connectors would reduce the risk of strands contacting each other. Sure hope that this isn't the amp. Thanks again for the help.

[This message has been edited by Jas1 (edited April 13, 2004).]

[This message has been edited by Jas1 (edited April 13, 2004).]

If you have a good DMM, just check the resistance. The DC resistance should be around 6 to 8 ohms. If there is a wire short it may show. It's also possible it won;t because there may be a small dielectric between the short that arcs over when the amp is driving harder. Still worth a quick check if you have the DMM. [Of course disconnect and measure at the amp]

I disconnected all of the speakers and checked all the wires and again measured the resistance. The fronts are 3.8 ohms each, the 4 surrounds are 5.7 ohms each, and the center is 4.8 ohms.

I reconnected and set up the configuration so that the fronts are on the outsides, the center in the middle & the rears & sides connected to the other 4 locations. I played the 950/770 for about 5 minutes at about -05 db and it cut out.

I reset it again and then played for about 20 more minutes when everything cut out except the RH side speaker. I did a tone test and only the RH side speaker, and of course the sub, tested at all. I left it turned down, shut off the 770 for a few minutes & turned it on and retested.

The fronts would then sound with the tone function, but no center, and no RH or LH rear, and no LH side. I let it play at low volume for 20 more minutes and then did another test - all speakers then tested OK. The amp was hot to the touch and had an even temperature across the top.
I have not contacting the Outlaws yet, but I guess that I will have to.

[This message has been edited by Jas1 (edited April 21, 2004).]

I'm sorry that you're having such difficulty.

The readings you mention are about right for measuring the DC resistance of loudspeakers made to have a 4 to 8 ohm nominal impedance for audio signals.

The only other thing I can think to suggest, and this may be tedious, is to run one speaker at a time with the exact same material for the same amount of time at the same volume level to see if driving a particular speaker causes much more heat than any other. Because your speakers do not appear to have identical impedance, I would expect there to be some variance from one speaker to the next, but if a particular one causes the cut-out when no others do, I would tend to suspect something about that speaker. If 2 or 3 of your speakers, one at a time, cause cutout, I would tend to suspect the amp.

In any case, if your amp was recently purchased and proves to be defective in some way, Outlaw is likely to exchange it for another one. Especially if you are still within the first 30-days, I recommend that you contact Outlaw immediately.

I'd try one more thing I think. I'd see if it cuts out with the volume all the way down. Then, if it does, I'd disconnect the inputs from the amp & see if it still gets hot. One possibility might be the preamp is dumping a high freq oscillation (>20KHz) and that is heating the amp up. It sounds like it really is thermally shutting down. I believe each channel is thermally protected seperately. It would make sense the two outermost physically channels in the amp chassis would be the coolest & least like to shut off. The transformers are about the only shared component in the amp, so its pretty odd that all channels are shutting off. Could your line AC voltage be really high?

One more thing you could try if you have some extra wire. Run the wires to the speakers with the extra instead of the in wall. Maybe some weird load caused by the wires is causing the amp to go unstable & oscillate at a high freq, which would make it get hot.
good luck

Make certain that there is no DC or excessive high frequencies (above the audioband) coming into the amp. Beings you are able to measure resistance, I am assuming that you can also measure DC voltage coming into the amp and coming out of it. The ultrasonic measurement may be more difficult.

Paul

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the 1derful1

I have the same combo. I run 5 electostats (martin logans) off 770. The longest/loudest I have used is at -4db (very loud) watched 2 movies. The amp was warm, I could touch back of the amp and not get burned. My speaker impedence varies from 5 ohm to 2 ohm.
I think its something in the amp, you may want to try with different set of speakers..

Just my 3 cents