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Old 31-03-2008, 10:34   #1
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Jensen marine stereo

Just installed a Jensen MCD-5112 AM/FM/CD on the weekend. Everything went according to the installation instructions (Yes! I did read the freakin' instructions ).

Problem arrose when I turned up the volume (about half way) the speakers cut out. Display on the unit shows it's still working. Second indication that maybe something is wrong is the heat sink on the back of the unit (probably to cool the onboard amplifier) gets very very hot. The only way to get the speakers working again is to turn the unit off for a few seconds then back on.

I am thinking that maybe the old speaker wiring on the boat has/developed too high a resistance for the new speakers (50 Watt 4 Ohm Audiovox). Driving up the volume is requiring more power than the unit can handle with the increased resistance in the old wiring.

I e-mailed ASAElectronics the maker of Jensen marine audio equipment but only got back their FAQ's on the unit which don't address this situation.

Any ideas as to what's going on? I might rig up some temporary wiring with home based speaker wire and see if that makes a difference.
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Old 31-03-2008, 11:06   #2
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What is the output of the radio (Ω) in relation to the speakers. Some speakers are only rated at 8Ω whereas, the radio might be 15Ω.

Another problem could be the speaker's coil may have built up a little corrosion and gets stuck when the volume is accelerated.

I'll bet Alan W. would have good info on this one.
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Old 31-03-2008, 11:48   #3
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Hi Del

Speaker impedence (4-8Ω). It's a 200 Watt total (4x50W channels).

The speakers are brand new as well (guess I shoulda said that) so corrosion shouldn't be an issue. I'm going to run some temporary speaker wire (new) tonight to see if that clears it up. If so I'll be pulling new wire and new crip on connectors all round.

Could it also be to protect the speakers if there's too much noise in the signal to the speakers? I found on a few radio stations with poorer signal that it cuts out at lower volume levels. Also when playing a CD (which should have a near perfect signal w/no noise) it cuts out at an even lower volume level. Damn I didn't know they made stereos this smart. Last time I tinkered with a car/boat stereo it was an 8-Track!
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Old 31-03-2008, 12:36   #4
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Yup...head units have become a lot more complex since the time of 8 tracks and way better.

The speakers cutting out when you turn the volume up is more indicative of a partial short (like one strand of wire crossing over to the other speaker terminal) or too low an impedance speaker causing the amp to put out too many watts causing the circuit breaker to open. A too high of an impedance will only make the speakers sound too low of a volume or not make any sound at all.

Take the speaker out of that questionable run of wire and then use two short length leads of wire to connect the head unit to the speakers. Generally, car type/12 volt head units use 4 ohm speakers. See with certainty if your speakers are 4 ohms or 8 ohms by placing an ohm meter across the speaker terminals. Also check for a 4ohm/8ohm switch on the back of the head unit so the amp is set for the correct impedance. Some amps automatically sense the impedance and adjust and others don't.

Check your run of wire for shorts or high impedance by connecting the speaker back up and see if the resistance is very close to that of the speakers resistance....there should only be a little more resistance with the speaker connected back up to the run of wire in question.

If that does not work then it is was probably not functioning in the first place.
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Old 31-03-2008, 12:55   #5
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Best guess is a short in the speaker wire OR at the terminals of the speaker. Check for any thin, stray wire strands at the speaker terminals!! Home speaker wire to replace is fine. Use 16 gauge. STOP trying to play the radio!!!
Check for continuity in the speaker wires before pulling everything out with a multimeter or continuity tester.
Other thought is that you may have a bad or intermittent ground wire connection. Check the connections and termination!
"Ohms" of the speakers and radio are of NO importance.
BOTH speakers must be connected before you attempt to play theradio through them again.
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Old 31-03-2008, 12:58   #6
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Thanks David

Plenty of things to check. The vendor just sent me an e-mail and suggested I run a second ground (larger) from the mounting stud on the back of the unit to the DC ground. I'll give that a try to see if it makes any difference. I'll run your checks also to see if there's a short somewhere. You got me thinking too that the two aft speakers (and the two forward speakers) share a common ground wire. There was a switch on the dash to disconnect them using this ground so the ground split to the individual speakers from there. Do you think the shared ground between the aft speakers causes this?

Rick
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Old 31-03-2008, 13:21   #7
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Unlike cars, the vendor probably does not know that the negative wire on boats is the same gauge as the positive and that negative wire on boats is not running through a potentially bad negative ground through a metal auto body.

I'm not certain if you meant a common negative for the 12VDC or the speaker terminals...so here is my long drawn out explanation for both.

You cannot share a common negative between the left and right speaker terminals on modern head units ...they will sense this and shut down when you do this. The reason is that an audio signal is an AC source and there is no phase synchronization between the right and left channels with audio signals...therefore connecting the negative terminals together between the right and left channels would cause problems. I have learned this the hard way. The pos and neg terminals of speakers is only for keeping the speakers in phase with each other..so that none is 180 degrees out of phase with the other. Speakers that are 180 degrees out of phase with each other cause full or partial phase cancellation...basically making them sound like crap, especially at lower frequencies.

You can put two speakers in series or parallel on the same left channel or right channel. Be careful if you do this because speakers in parallel or series will either halve or double your impedance. In series will double it.

I have found that if you want different volumes in different areas of the boat then you have to fuss with the Fade feature...for 4-way sound systems. If you want more speakers than four then you should probably buy an external amplifier and use the pre-amp out directly to the amp..and then of course wire all the speakers to the external amp. An alternative to fussing with the Fade is to build your own speaker controller with stereo 8 ohm L-pads (potentiometers meant for this)..but this of course might be more than it is worth and where do you fit this on a boat?

As far as the 12VDC goes, you can share that ground with any other 12 volt ground on the boat as long as it is ultimately going back to the same battery. Take your ohm meter and put it across the chassis ground and the negative 12VDC terminal. If there is zero resistance then there is no difference electrically between the chassis ground terminal and the 12 volt negative terminal on the head unit. Therefore what the dealer said to do of running a second wire from your chassis ground all the way back to the battery would make no difference from an electrical standpoint...unless your negative wire is under-gaged.
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Old 05-04-2008, 11:37   #8
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Thumbs up Project Update

I pulled all new wires to each speaker (90' total). Hooked it all back up and WOHOO!! Ask Knottygirlz, it ROCKS! Now I can really disturb the marina denizens!

Thanks for all the tips & hints fella's!
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Old 05-04-2008, 15:06   #9
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I hope you used a good heavy gauge wire. If you have very long runs, use a good heavy gauge. Like maybe 2.5mm or even heavier still if you can pull it. Ensure you have a good solid wire feed for the power as well. You will most likely have two power feeds. One is ACC backup memory(this remains connected to battery at all times to store channel settings), the other is the main feed. (Although sometimes that can be reversed, as in the ACC also is the main supply) Which ever one is used for the main supply, ensure it is a good sizing. All this above equates to good solid bass thump.
You are lucky. There are usually no "cutouts" in Car audio anymore. The cutting out was actually the output device overheating and shutting down. It must have been a partial short, because a dead short would have killed the output device.
So how good does it sound?? I have never been a fan of Audiovox. But then, maybe what I see here of that stuff is the cheap knock off's. Plus every one has a different taste to what they want to hear. Because of my Carrer, I perhaps "Listen differently".
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Old 05-04-2008, 16:05   #10
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Hey Wheels

Heaviest guage speaker wire I could find was 16ga. Seems to be ok. The units wiring harnass has probably 18ga coming out of it. Boat. Longest run was probably only 25' around the back end of the boat. I looked for heavier wire but couldn't find any. I got all the power feeds lined up properly all run to terminal strips with double crimped ring terminals. All in all I probably have <$200 in the whole rig including 4 new speakers and new antenna. Sounds pretty good, certainly a lot better than what was in it before. The unit also has a wired remote that I mounted in the dash. I'll grab a pic tomorrow. I'm no audiophile but I had AC/DC Live thumpin' pretty good, the neighbors had to yell to each other over the ruckus I was causin'!
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Old 05-04-2008, 17:35   #11
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Ah...acka dacka as they are known here in their country of origin. Does your stereo volume control have 11 on it ? We have a lane named after them here in Melbourne (ac/dc lane) but the signs keep getting knocked off. ("stolen" in aussie, not "a cheap copy") When ripples start coming from the boat in time with the bass you know you have got the volume about right !! ; )
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Old 07-04-2008, 17:54   #12
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I always figured I would be able to tell I got my stereo loud enough when the DNR gives me a ticket for illegal fishing with a subwoofer.
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Old 20-05-2008, 16:45   #13
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Quote:
Originally Posted by Alan Wheeler View Post
I have never been a fan of Audiovox.
Well neither am I anymore. The unit packed it in! Good thing I bought a warranty eh? PITA to have to pull it out and replace the damn thing plus eat the shipping charges.
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