HELP - Denon 4 OHM Speaker Issue

[Turtle2012]

Hi Folks. First time here. I will apologize in advance for my igorance, but need some help. I have a houseboat that has (10) Alpine 4 OHM 2-way marine speakers. Sound used to be powered by a junky built-in Pioneer boombox - been that way for years. However, it would overheat and then shutdown if I pushed it too hard. I would just wait for it to cool down, and then start over. Last month I replaced it with my vintage Denon DRA-635R receiver amp that I had at home (80W per channel at 8 ohms). It ran for a week, overheated, and then flamed out. Rather than fix it, I bought a replacement Denon DRA-825R on eBay (90W per channel at 8 ohms). It lasted 40 minutes at 25%-30% volume, and then went up in smoke. It didn't even give me the pleasure of blowing a fuse first. So, I have 2 fried amp's now and no music. What the heck?!@ Going backwards and wasting a lot of money doing it. Any recommendations would be very much appreciated. Tkx. Turtle.

 

[Jeff R.]

You need to figure out how all the speakers are wired.....once you do that you can then figure out what your actual OHM load is and determine how best to power it.

 

[markw]

Like Jeff said, more info is needed.

But, in the meantime, here's some basic info for you to ruminate on.

Amps don't like low impedance. The lower the impedance, the harder the amp has to work.

Many don't even like one pair of four ohm speakers to begin with, much less two or more.

How speakers are hooked up can affect the impedance an amp sees. IE. Two four ohm speakers in parallel are two ohms. If they are in series, it sees eight ohms.

Your speakers are possibly wired in some combination of these two, but without knowing, it's hard to tell what.

But, from the way you're smoking receivers, smuptin' tells me the end result is well below four ohms.

If you've got an ohmmeter, we might be able to get an approximate (VERY approximate) idea of what the amp is seeing if you measure the speaker leads going into the receiver, after they are disconnected of course.

But, rather than play with this parallel/series puzzle, perhaps something like this coupled with a modest front end (even automotive) might be your best bet in the long run.

 

[TLS Guy]

Hi Folks. First time here. I will apologize in advance for my igorance, but need some help. I have a houseboat that has (10) Alpine 4 OHM 2-way marine speakers. Sound used to be powered by a junky built-in Pioneer boombox - been that way for years. However, it would overheat and then shutdown if I pushed it too hard. I would just wait for it to cool down, and then start over. Last month I replaced it with my vintage Denon DRA-635R receiver amp that I had at home (80W per channel at 8 ohms). It ran for a week, overheated, and then flamed out. Rather than fix it, I bought a replacement Denon DRA-825R on eBay (90W per channel at 8 ohms). It lasted 40 minutes at 25%-30% volume, and then went up in smoke. It didn't even give me the pleasure of blowing a fuse first. So, I have 2 fried amp's now and no music. What the heck?!@ Going backwards and wasting a lot of money doing it. Any recommendations would be very much appreciated. Tkx. Turtle.

Obviously this system was missed wired from the beginning. I suspect you have two pairs of five speakers, all wired in parallel. If you have two sets of +ve and -ve wires going to the receiver, then that is the way they are wired. That is the only way to wire an odd number of speakers 5+5, in other words five per channel. That would be a load of 0.8 ohm. If that were the case, the result would be what you got.

Can you run wires from each speaker back to the receiver location?

If yes, then a multichannel amp that has been suggested would be a good suggestion.

In a boat I suspect all the wires are hidden and rewiring is not possible. If that is the case you will have to convert to a 70 volt system and use a dual channel PA amp. That will entail placing a transformer at each speaker location to balance out the power and impedance. If that turns out to be the case, then I will tell you how to switch your system to a 70 volt one.

 

[Turtle2012]

Thanks for your replies. I appreciate very much. TLS Guy: The vessel has 5 separate music zones. Each zone has its own volume control. I have only two pairs of speaker wires (L/R) to work with at the amp. All wiring is enclosed in the ceiling/roof. There isn't anything that I can do with it, so a multi-channel amp probably won't be the solution. I do have an ohmeter that I can use to check the impedances, however, based on what I have heard so far, this would probably just confirm that (10) 4 ohm speakers are reducing total impedance to nearly zero, thus leading to an inevitable outcome. The thing that is still a mystery, though, is how the junky Pioneer casette stereo that I replaced managed to survive for years without melting down like the Denons. I have a 250W 12v car stereo amp kicking around. Maybe I should consider this path. Your thoughts?

 

[TLS Guy]

Thanks for your replies. I appreciate very much. TLS Guy: The vessel has 5 separate music zones. Each zone has its own volume control. I have only two pairs of speaker wires (L/R) to work with at the amp. All wiring is enclosed in the ceiling/roof. There isn't anything that I can do with it, so a multi-channel amp probably won't be the solution. I do have an ohmeter that I can use to check the impedances, however, based on what I have heard so far, this would probably just confirm that (10) 4 ohm speakers are reducing total impedance to nearly zero, thus leading to an inevitable outcome. The thing that is still a mystery, though, is how the junky Pioneer casette stereo that I replaced managed to survive for years without melting down like the Denons. I have a 250W 12v car stereo amp kicking around. Maybe I should consider this path. Your thoughts?

That gives us hope. I suspect the volume controls are not impedance matching. You need to remove them for inspection. I suspect replacing them with impedance matching controls correctly wired will solve your problem.

The old Boombox survived likely because it was low powered. However it was going into protection and having to cool down. That is no way to run a rail road. It really had no business surviving as long as it did. So there was obviously an element of dumb luck.

Don't us the car amp, you will blow that too.

 

[Turtle2012]

TLS Guy: That's a pretty decent suggestion. I will check out the zone volume controls and see if there is a story there. One of them has been flakey for a while. I had intended to replace it, and perhaps the others as well. Thank you!

 

[markw]

The thing that is still a mystery, though, is how the junky Pioneer casette stereo that I replaced managed to survive for years without melting down like the Denons. I have a 250W 12v car stereo amp kicking around. Maybe I should consider this path. Your thoughts?

any times , those "junky" stereos, which are specifically designed to work with their own particular speakers, which may be designed to be a lower impedance to maxiize the capability of the central unit.

Speakers designed for the "mainstream" component market generally fall into the 4 to 8 level, which is what component stereos are expecting.

It sounds like you got lucky and had the center unit from a unit that was designed for it's own special lower than standard impedance speakers.

That's just a guess, though.

aybe that car stereo amo might do the trick if it can handle the low impedance and you can work up a workable, high power 12 volt power source for it. I don't know boats so, unless someone else here does, you're on tyour own there.

 

[TLS Guy]

TLS Guy: That's a pretty decent suggestion. I will check out the zone volume controls and see if there is a story there. One of them has been flakey for a while. I had intended to replace it, and perhaps the others as well. Thank you!

This will be your cheapest solution. You will need 5, so that will run you $14.38 each.

Get the rotary controls. Apparently the slider version sticks and breaks.