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Storm860triple
12-20-2003, 01:44 PM
I have an NAD Monitor 7000 reciever. I've had it since I bought it new in 1990. For the last 6 years I have had it powering a set of Bose AM5 series II speakers off one set of channels, and a set of Advent Legacy's off the other two channels.

About three months ago, My housemate bought a new DVD player. So now this new DVD player is our "new CD player" as well. It is a Phillips DVD737.

Shortly after getting this DVD player, and hooking it up, the power amplifier portin of my NAD reciever shorted out and blew. I had it repaired w/OE components and it worked great again.

I changed the configuration of my system to this; I bought some cheap-o RCA "splitters" and plugged then in to the "pre outs" on the back of my reciever. One side of the splitter went to back to the recievers "main in" so I could still use the recivers power amplifier to power four spleakers. The other set of RCA's went to an external amp, which drives another set of speakers. SOOO, The recivers Power amplifier was is driving the Advent Legacy's, and a pair of pretty big, cheap-o Pioneer's. The aux amp is driving the Bose AM5's. Got that?

Last night I had a party. I was playing music moderately loud; 1/3 to 1/2 on the volume knob. Half way through the party, the power amplifiers in my NAD reciever blew again!! GRRRRR! So I lost power to the Advents, and the Pioneers, but the Bose's continued to play on (fortunately).

SO my question is, WHY IS THIS HAPPENING??? Does it have something to do with the DVD player?? Somehting else?? This is BS. I need to figure out why this is happening so it doesn't happen again. Thanks for reading and input.

trollgirl
12-21-2003, 08:20 AM
I've never thought too highly of driving multiple sets of speakers with a given amp or receiver. Even if NAD says you can, and there are two sets of speaker connections, proceed with extreme caution. My Yamaha CR-1020 has capability for A, B, and C speakers, but they wisely set up the selector so that you can't use more than two pairs of speakers at a time. Do you really need the Pioneers??

Laz

Geoffcin
12-21-2003, 08:51 AM
OK, I'm pretty sure it's not your DVD player, although that might be enabling this to happen because it has a larger output gain than the other components you have hooked up. This is why you blew the amp only 1/3 volume. It just simply plays louder at that setting.

Your setup sounds funky and there's probably an impedance dip when you hook up the two sets of speakers. Advents weren't very efficient speakers, and it takes a LOT of power to make them play loud. It sounds to me you had a party going, and were trying to rock the place.

I'm kinda disappointed with your receiver though. It should be better protected. My Pioneer is overload protected in so many ways it's been impossible for me to blow it. I've driven it to overheating, overloading, and no permanent damage so far.

Bryan
12-22-2003, 06:03 AM
You truly do have a strange setup. I'm with Geoffcin here and would say the speaker impedence (ohms) was at fault. Connecting the dvd player to the amp was not the cause of the failure. Now, I would say you will likely need to get a new receiver and do not connect all three types of speakers to it unless it has A, B, and C speaker capabilities.

piece-it pete
12-22-2003, 08:07 AM
Bummer about your amp.

Even though it's an older model you might let Denon know of your trouble - they may offer you a discount.

Pete

Storm860triple
12-23-2003, 10:20 AM
Thanks folks. A couple points:

Trollgirl, Goeffcin, and Bryan. I don't belive impedance is the problem. The reciever has two completely separate SETS of outputs, and amps to power them. I have run four speakers for YEARS with no problems until I hooked up this DVD player (I have also run the reciever w/other DVD players w/no problems). Actually I have had the reciever driving four speakers (one per channel) for 95% of the 13 years I've owned it.

Please keep in mind,
1. The reciever is only "driving" the four speakers it was designed to; the Pioneers and the Advents. The Bose are being driven by a separate amp by splitting the pre amp signal. I could see how possibly splitting the pre amp signal could be drawing too much current through the pre amp protion of the reciever, and blowing that, but that's not what blew.
2. The same thing happend just a couple months ago, when I had just four speakers hooked up in a conventional fashion.

Geoffcin, The NAD reciver does have good protection, and has used that protection several times in the past. Though is WAS a party, the volume was never that high either volume knob wise or db wise. The party was "rocking" w/o excessive noise (great people at that party). I had intented to crank it for the duration of the night, but never needed to, based on the mood of the party. I have played the reciever at parties before, w/4 speakers hooked up LOUD for 5-6 hours striaght and no prblems. MUCH louder than at this most recent event.

When it blew, it wasnt' even that warm. Not nearly as hot as I have gotten it before (like at the 5-6 hour event mentioned above).

I think it has something to do with the DVD player, but I don't know what. One other thing about this DVD. Ever since my housemate bought it, it (or my system) does this weird thing I've never noticed before. When there is a rapid transition from quite music to powerful, like a little intro and then heavy bass, either punch or bass guitar, as soon as that transition occurs there is massive distortion of that bass for about 1/2 second. After that, it's fine, like it takes a second for *something* to saturate with power -like it wasn't ready to work, then it sees the load, adjusts and is fine. The last time my amp blew (a couple months ago), it blew when this phenomena occured; transition-distortion-blown amp. This time, I didn't hear when it happend due to the people talking and the fact that music continued on the Bose through the other amp.

Sorry for the essay, but I just wanted everyone to fully understand what is up. Thanks again for the reading and replies!
-Tom

Bryan
12-23-2003, 12:18 PM
If the dvd player was the culprit then the Bose speakers would experience the distortion as well. This does not appear to be the case as: 1. The Bose speakers continued to play fine and 2. They are driven by a separate amp. My math may be a little rusty here, but the Pioneers would be drawing a load of four ohms per channel and the Advents four ohms per channel (assuming you have both Pioneers hooked up to one channel and both Advents hooked up to one channel).

Ohm's law is:

V (Voltage) = I (Current) x R (Resistance)

Though your speakers may read 6 - 8 ohms each the combined effect is they are drawing a load of 3 - 4 ohms.

If you can, try hooking up either a cd player or different dvd player. My guess is you will experience the same brief distortion as the player is a source, much like a tuner, and all the amplifier is doing is amplifying the signal it is given. Nothing more, nothing less. The facts lead me to believe the amp is the culprit due to the ohm load rather than the new dvd player. You are zeroing in on that as the cause because that is the lastest thing that was added and are more inclined to blame it as being the culprit. Your are listening for a change and have found a problem, which is not all that surprising as we want to see the effects of something new added to our systems.

Storm860triple
12-23-2003, 05:57 PM
Bryan, thanks for responding again. I need to respond to a couple things though, either for clarification for you, or so you can then correct me;

If the dvd player was the culprit then the Bose speakers would experience the distortion as well. This does not appear to be the case as: 1. The Bose speakers continued to play fine and 2. They are driven by a separate amp.....You are zeroing in on that as the cause because that is the lastest thing that was added and are more inclined to blame it as being the culprit. Your are listening for a change and have found a problem, which is not all that surprising as we want to see the effects of something new added to our systems.
The Bose do distort when this happens. All the speakers do simultainiously. I hear what you're saying about listening critically when you install a new component, but you're going to have to trust me; I would have DEFINITELY heard this if it EVER did it before. It's very obvious and I wouldn't have missed it. You wouldn't either. Plus, adding that extra amp isn't the first thing I've added/changed in the last 13 years I've owned the reciever, so "extra" critical listening has certainly occured before. This part of my respons back to you I'm SURE about. The next part, I'm not totally...


My math may be a little rusty here, but the Pioneers would be drawing a load of four ohms per channel and the Advents four ohms per channel (assuming you have both Pioneers hooked up to one channel and both Advents hooked up to one channel).

Ohm's law is:

V (Voltage) = I (Current) x R (Resistance)

Though your speakers may read 6 - 8 ohms each the combined effect is they are drawing a load of 3 - 4 ohms.
O.K. First of all, the Advents, Pioneers, and the Bose are all rated at 8 ohms. My reciever has four seperate channels and four seperate outputs; front rt, front left, rear right, and rear left. So, IMO, if I hook up four speakers, there is an ~8 ohm load on each portion of the amp. Right? Even if I'm not seeing this correctly, why did the reciever successfully run four speakers for the better part of 13 years (under ALL conditions!) w/no problems??


If you can, try hooking up either a cd player or different dvd player.
This is a great idea, and I'll try it, but I have to get the amp portion of my reciever repaired (again) first. :(

RGA
12-23-2003, 09:43 PM
One addition to the ohms.

Even thougha speaker is rated at 8ohms it may very well have a minimum impedence of 2-3 ohms. I am not familiar with your speakers but, if both of these speakers say had a minimum impedence of 2-3 ohms then you are presenting a load of 1 ohm to that receiver and at loud volumes you could be in serious trouble of blowing the amp's fuse(if it doesn't have a fuse then a protection circuit) and if neither then the amplifier. Receivers generally are pretty gutless though some at least have a 4 ohm tap but I was present when the Top opf the line Pioneer Elite Receiver blew playing a speaker with a minimum 1.2ohm impedence...and the receiver was rated to handle 4ohms.

With two sets of speakers, presumably, the amp has even more difficulty because both will have impedence dips at different frequencies. In complex passages at louder volumes the amp no longer just has to produce instantaneous extra power but possibly extended power to an impedence beyond the amps capability.

This should cause the amp to clip which could blow a tweeter and at least severe distortion.

If you hear distortion espeially in the high frequencies you're playing it too loud and it's that simple. The fact that the DVD player may suck is something else again. Tweeters don't like distortion or being overpowered(and it hates if you do both).

The amp blowing may simply have another problem altogether, a failed Capacitor etc. 13 years old it is conceivable that things need replacing. Receivers are the most compromised amplifiers to start with with shorter lifes than separates or integrated's.

Still I should think a NAD would last a solid 20 years. But a lot of use will drive that down. It may be that you've been overtaxing that amp for 13 years where most other amps from a Denon or Sony would fall apart after 6 months - in which case the NAD can be considered a brute.

I seriously doubt the DVD player could cause these problems.

FunnyName
01-14-2004, 04:02 PM
...
SO my question is, WHY IS THIS HAPPENING??? Does it have something to do with the DVD player?? Somehting else?? This is BS. I need to figure out why this is happening so it doesn't happen again. Thanks for reading and input.

Just a quick question (it might be stupid and completely irrelevant but...) , what is your power source? Is All your equipment connected to the same power outlet? Maybe it's just another electronic device connected to the same circuit causing inconsitencies and making it tough for your amp?

Good luck in finding a solution.

FunnyName

Storm860triple
01-14-2004, 06:15 PM
Just a quick question (it might be stupid and completely irrelevant but...) , what is your power source? Is All your equipment connected to the same power outlet? Maybe it's just another electronic device connected to the same circuit causing inconsitencies and making it tough for your amp?

Good luck in finding a solution.

FunnyName
All the equipment, the Reciever, the DVD, TV, Satalite box, are all powered by a power strip that is obviously plugged into one outlet. Interesting thought, but I don't know how to test/check this.

I've kind of given up. For the time being, I'm just going to continue to use the reciever as a Preamp, and run two Soundstream Refference 300sx car amps, bridged per side(one amp for the left channel and one for the right. I will run two speakers off of each bridged amp in parallel, giving me 4 ohm loads per amp, which will be a breeze for these things.

To RGA, I never did understand what in the world you were talking about with regard to the ohms. The speakers are 8 ohms each. The ohms don't change through out the playing of music. Also, I didn't have the speakers wired in parallel off one channel; they each were wired to one channel, so the load on heach channel should have been 8 ohms.

Further there was never any tweeter distortion as you mentioned in your post. Not sudible anyway. And as I said in an earlier post, I have run the reciever in the same configuration for years, AND for one party many years ago at a much higher level for about 4 hours straight. Thanks for your everyone's input though.

-Tom

Pat D
01-14-2004, 09:40 PM
I've kind of given up. For the time being, I'm just going to continue to use the reciever as a Preamp, and run two Soundstream Refference 300sx car amps, bridged per side(one amp for the left channel and one for the right. I will run two speakers off of each bridged amp in parallel, giving me 4 ohm loads per amp, which will be a breeze for these things.

To RGA, I never did understand what in the world you were talking about with regard to the ohms. The speakers are 8 ohms each. The ohms don't change through out the playing of music. Also, I didn't have the speakers wired in parallel off one channel; they each were wired to one channel, so the load on heach channel should have been 8 ohms.

Further there was never any tweeter distortion as you mentioned in your post. Not sudible anyway. And as I said in an earlier post, I have run the reciever in the same configuration for years, AND for one party many years ago at a much higher level for about 4 hours straight. Thanks for your everyone's input though.

-Tom
RGA's point is quite sensible. The impedance of most speakers varies considerably with frequency. Moreover, the impedance of many speakers gets well below the rated impedance in some frequency ranges. Manufacturer's ratings for the impedance of a speaker are often unreliable, and good reviewer's measure the impedance vs. frequency curve of a speaker. Voltage sensitivity ratings are often equally unreliable. So, you don't in fact know the impedance your speakers are offering to the amplifier unless it has been measured.

As to why you should have problem with DVDs, perhaps they have a good deal of deep bass content and your speakers have a relatively low impedance in the bass. Driving two pairs of speakers from the same amplifier can offer a difficult load, often well below 4 ohms at some frequencies.

Storm860triple
01-15-2004, 11:43 AM
Well I guess I just learned something about speakers. Just for yuk-yuk's I'm going to bring my DVOM home and ohm the speakers, both at idle and while playing and see what readings I get. I'll report back.

THat still doesn't explain why I played the same set up for 6+years and then suddenly blew the amp(s) twice in three months. I'm going to stick with teh car amps until I get that figured out. It's too expensive otherwise.