I have a '91 300E. I installed a top SONY ES CD head unit with a 10 CD changer in the trunk.

In addition, I have 4-channel 400 watt Blue Thunder amp. in the trunk too. The amp. has a direct power link to the battery. The amp. is linked only to the two rear and the two door speakers. The front one's go only on the headunit.

The MB has the delux speaker option. The stock amp in the rear (is that the only one?) has been bypassed.

I have two problems:

1. Varying engine whine out of only the rear speakers--HELP;

2. If playing the sterio high for more than 1 hour, the amp overheats and shuts off. My thinking is that the ohm level is too low on the front speakers and that over works the amp. Do these door speakers have an amp built-in the door unit? How can I fix this????!!

Neither the whine nor amp shut-off is cool or impressive to the ladies. PLEASE HELP ME!! My sanity is at stake!

Esquire
HELP

Ok first the whine. Take the ground wire from your amp and make the shortest connection to the car's sheet metal that you can. Don't just go find a bolt somewhere and tie the wire under it. Go out and get a self tapping screw and a crimp on ring terminal. Sand the paint off the area where you are going to ground the amp and then drill a hole for the screw and secure it all. Be careful as to what is on the other side of that hole!!!

As for the shutting down of the amp. You obviously have too much of a load on it. I am betting that you have the + from both speakers (front and rear) to the + terminal of the amp and the same setup for the - terminals (parallel wiring). This causes a lower resistance and higher current requirement for the amp. You have two choices. Either go + from amp to + from one speaker and then - from that speaker to + from other speaker and then from - of that speaker to - of the amp (series wiring), or only connect one set of speakers.

Thanks for the engine whine tip --- I'll check that.

The amp. is a four channel amp. and each set of speakers (front and rear) is connected to their own output terminal on the amp. There is no doubling up of speakers to the amp. --- which is what I think you were suggesting. If that's correct -- the problem remains!

I had the same problem last week.

I had to change the suppressor - kinda like a filter diod which is placed under the front mat. It filters out the "aeroplane" sound on take-off.

And the reason for the amp cutting off? It is not able to handle the excess power coming out, thus overheating ... if this was fine previously, it means that you might want to take your amp to the nearest dealer to run an internal check as something has worn inside it. It might take about 1 week to get the results.

Grounding won't solve the problem.

Sorry.

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... Kerry

126 tailed by a 203, 129 leading the pack.

Newer cars bring about interesting challenges with regards to electronics...one of them is the electromagnetic radiation emitted by all of the vehicle components.

You've already determined that the amp is the source of the "whine"...are you sure? Disconnect the head unit from the amp and see if the noise is still there...if it goes away, the problem is the head unit and not the amp.

I read that your amp is mounted in the trunk. Are there any MB electrical modules in close proximity? You may need to "shield" the unit, so that the radiated emissions are blocked. Keep all power cable runs away from large factory wiring harnesses.

Short ground wires is a good tip. The best method however, is to have all audio components share the same ground point to prevent "ground loops", a very common noise source.

I assume that your power lead harnesses from the amps are not laying parallel with speaker cables throughout the length of the cable runs. If they must meet at some point, right angles are best. By the same token, keep the speaker cables AWAY from any of the factory harnesses as well, running them at right angles as well.

Noise suppressors are fine, but should only be a last resort (kinda like aux fan switch bypass circuits when you can't figure out how to keep your engine temps down).

As far as your load problem, you are correct in determining that the ohm load is putting your amp in "protection mode". The other possible problem is that the power lead to the amp is not large enough. If too small, the amp cannot draw sufficient current, so it shuts down. In extreme conditions, a fire could result!

If your power leads are fairly warm after the amps shut down, then you need to bump up to thicker wire, which dissipates heat more effectively. For a 400-watt amp, I wouldn't get anything less than 4-gauge wiring...thick and hard to bend, but safe.

The ground wire should be about as robust (6 or 8-gauge). It's no secret that sound-off competitors use zero-gauge wiring for all of their power supplies (zero-gauge is what arc welding equipment comes with)!

I am also assuming that your power lead is fused?

The OEM "deluxe" system does indeed have power amps, and you should be running line level, not speaker level signals...that is probably why your amps are shutting down...if the full output was capable, your speakers would be laying smoldering on your lap.

You should bypass the internal (speaker) amps and connect the speaker leads directly to the speaker terminals. That way, the amp sees a "balanced" load, and isn't trying to send 4-ohms to one set, and some undetermined load to another.

Hope this helps...

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