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

Well, still trying some tests with speakers
& still not a lot of luck. I have contacted the Outlaws and have been doing a few different checks for Steve. I have disconnected all of my Studio v.3's & checked all wiring.

There are no shorts in any in wall wires. I have connected the fronts & the center with different wires to eliminate the in wall wires. I have been running the system at -05 db with the same material for the same period of time and have still encountered the amp dropping channels.

I have not had the circuit breaker trip again but have had the channels drop out at various times when moving around the amp's outputs. I have left the 950 set to 7 channel stereo throughout all of the testing.

With only 2 speakers playing at a time, it takes longer for the 770 to drop out compared to when all 7 channels are playing at -05 db. I played it at 00 db for a few minutes - cuts out very quickly. I have measured the top of the amp with an infrared
heat gun & it gets to about 160 degrees with any 2 channels running, above those respective channels.

It measures that temp. all across the top of the amplifier with all 7 channels playing at -05 db. I don't know if I have to run it with fans or what. The equip. rack it is in is adjacent to another room & open to the back with plenty of room above the amp.

Is there a way to post some pictures of my setup here? Maybe someone will spot something that could be causing this???

This may have been mentioned before, but what's your electrical situation? In other words, how much stuff do you have on the same circuit as the 770? If you've already tripped a power breaker, then this whole thing may be related to your electrical system. Also, just running two channels and getting better results would point towards that sort of problem.

Maybe some of the more technical electrical guys around here can talk a bit more on that...

Jas1: Hopefully your saga of trouble will come to a happy solution soon. You have been great about coming back to this post and keeping us up-to-date. I appreciate it!

As to pictures, you would need to host them elsewhere and reference them from your posting here.

Jason J has a point. There are some power issues that could affect this, even if they are rare. The easiest test is for sufficient voltage under load. Either while your audio gear is operating at the –5db level, or while all your video/audio gear is off but you run a toaster or a 1600/1800 watt hair dryer on high on that circuit, CAREFULLY* measure the supply voltage. The toaster/dryer test will provide a constantly large load, whereas your audio gear will draw a varying amount depending on the moment-by-moment demands of the audio signal. If the circuit measures between 110vac and 120vac under load, it is unlikely that you have significant mains power issues. If it immediately or over time falls to 97vac or something, that would be a definite source of trouble. *Only perform the measurement if you are certain you can do so without causing harm.

I doubt you’ll find a power problem, but who knows until it is checked?


[This message has been edited by bestbang4thebuck (edited April 27, 2004).]

Wow, weird problem. It actually sounds like the voltage is too high if all channels run hot. This is a way long shot, but could the amp be wired for 100V operation and running at 115? I don't even know if Outlaw offers that voltage option, but I do think something is runnin up the B+ lines. I guess it could also be possible that the bias is too high in the output stage, but this seems unlikely as all channels seem to have the problem and all the amp modules would be built and tested seperately. 160 is way hotter than my 755 runs. It is warm to the touch, but 160 is basically untouchable. It really sounds like it is going back to outlaw for return. I will be very curious what the final outcome will be.

The air above my 750 gets up to around 95F when it's been heavily driven for an extended period of time (couple hours) in a space that is more enclosed than I would like. I don't know what the surface temp is, but I don't think it's close to 160 - probably closer to 110 or less.

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gonk -- 950 Review | LFM-1 Review | Pre/Pro Comparison Chart | Saloon Links

Oil Can - you an a&p mech too???

Yes, I got my license in 1974.

Jas1 since you have been doing some voltage testing I would suggest one other. Check the AC voltage at the speaker terminals while playing loud passages or test tones. My speakers are pretty inefficient, dipping to 3.6 Ohms at certain frequencies an I have never had a heating problem even after many hours of loud playing. While playing LOUD I have measured the voltages by placing the meter across the biding posts and setting the meter to capture the highest voltage. This loud playing will ussually give reading peaks about 20 VAC which works out to around 100 watts or 5 amps. Doing this may give you some idea of how much current individual speakers are pulling which may in turn help diagnose the problem. You could also use this method to check at the speakers first and then at the amp to see if the wiring is adding much of a load.

If this process of diagnosing is flawed I am sure someone will post with corrections

It has been a while since I have been back to report on my 770 issues. I have gone over the speaker connections, ran new wires across the floor, used different power sources, measured resistances, voltages, etc., etc., while operating the 770.

We have played a few movies now and the 770 works great for that. Without a constant loud volume, it works great.

I have accepted the fact that this amplifier does not dissipate enough heat to play music at the levels that I have been testing it at without a thermal shut down occurring. I will continue to do some testing as advised by you guys that are offering your help.

I have had a few conversations with the Outlaws and they have been supportive.
But the ball is in my court as they have offered to check it if I want to send it back. I am in Canada & with all the shipping
& duty issues, I don't know if I will.

I suspect that if they do test it they may find it OK for what they are using as a test system. I would like to have someone test it with the same speakers, 2 runs of 14 gauge wire to each, with the same material & volume levels to compare apples to apples. The material I have been using (to stay consistent) is Metallica - Master of Puppets at -05 db.

Even though I have an open back rack, with 8" + clearance above the 770 and at normal room temperature, I am planning to run a vent from the rack to a bathroom fan somewhere in the ceiling, or have a duct to the cold air return installed. That may cure it.

Of course, my visits to my B&M store, who sold me my Paradigms as well as many other pieces of gear over the years and who wanted to sell me Anthem product, see my with my hat in my hand("We told you so"). Would the Anthem stuff thermally shut down? I don't know.
The 950/770 combo is impressive for movies, and I think that they certainly compare to the AVM 20 or the Anthem power amps, (forget the difference in price) after spending hours listening to them in the store.

I suppose for a true apples-to-apples comparison, someone would need to mimic your setup exactly, including the exact music that you’re playing when the 770 overheats.

But for a kind of Red Delicious-to-Gala apple comparison, one might only need to have the same load impedance that your speakers provide driven by a 950/770 combo in the same mode and at similar electrical levels.

My speakers are 6-ohm nominal x 7, driven by a 950/770 combo. In what way could you measure the output level of your 770 that leads to overheating?

The speakers, according to Paradigm, are"compatible with 8 ohms". Pretty vague, I guess. Mine measure between 3.8 - 5.7.

I have moved the wires around to all the channel outputs, ran combinations of fronts only, rears only rears & sides, etc. While it does takes longer to "thermal" with less speakers connected and in various combinations and locations on the outputs of the 770, it still does.

Measuring the output voltage while running? I don't know that I can tell anything from that - not an engineer by any means. The voltage at the receptacle
stays right around 115-117 vac using a meter, at the levels I have been testing at.

Is a controlled load that a tech would use for bench testing the same as actual speaker loads that vary with music?

Is the resistance variance in my speakers enough to cause a problem? Either way, I have had only the ones with the same measured impedance running at once during this anyway.

I've spent a little time thinking of a way that some type of measurement information from you would allow me to know if I'm recreating the about the same level of output as your 770 is experiencing, but haven’t thought of one using measuring devices that aren’t very good at audio frequencies. Perhaps an easy way to drive all channels equally at 60Hz so that the 770’s outputs can be measured accurately with common AC measuring tools. This would require setting all speakers to large or setting the crossover points low enough for all speakers that 60Hz is not routed away from the 7 speakers. If so, you could determine, for example, that at an output of 18 volts AC on all 7 channels, it takes 14 minutes for your 770 to shut down thermally.

My guess is that your speakers that measure about 3.8 ohms DC are probably about 6 ohms at low frequency AC, and the ones that measure about 5.7 ohms DC are probably about 8 ohms at low frequency AC. That would mean that, at 18 volts RMS AC, the 6-ohm speakers would have to sustain a continuous 54 watts and the 8-ohm speakers a continuous 40 watts without damage until the 770 shut down. I don’t know if that would be good for the drivers. Anyone with speaker driver experience want to comment on that idea before we attempt this?

I’ll be away from the computer for a few days, so I check back next week.

As far as a source is concerned, one could use the tone generator in the True RTA program to find a steady 60Hz tone. Even the free/trial version of True RTA has a working tone generator. So if I feed a signal from a PC running True RTA into the 950 in Stereo7 mode and make the proper adjustments, I should be able to get a nearly identical voltage level from each output of the 770.

I’m still not sure about running a continuous 40 or 50 watts into a speaker’s voice coil, even if that speaker is rated to 300 watts.

How long does it take to make an adjustment?

Hi again to anyone that was interested in my problem back then(or now). I have not gone any futher with any testing.
While I have watched a lot more movies using the system, I have not done much more music listening. I have only recently added cables for DVD-A and hope to get back & try some more testing using that format.
I have not tried BB4TB's testing advice butI still think that I will install a fan for the 770.