power amp thru cigarette lighter

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steph280

Member - Posts: 4

Joined: April 27, 2004

Location: United States

Posted: April 29, 2004 at 4:00 PM / IP Logged

A couple of us have retrofitted a Toyota navigation unit to Toyota vehicles. Everything works except the voice output which requires some type of amplifier/speaker setup. We have tried using a small amplifier powering an indash speaker, and also a radioshack speaker that has its own small amplifier. The problem occurrs when we power these amplifiers through a cigarette lighter adaptor (12v to 9v). The speaker outputs lots of noise and high pitch sound when the engine is started. With the radio shack unit, it works perfect if we skip the cigarette lighter and use a 9v alkaline battery.

Are there some type of feedback which causes these noise, or is it a ground issue? Could we eliminate the noise if we power the amp via the same ACC power/ground as the navigation head unit?

Thanks in advance for help.

Stephen

Teken

Gold - Posts: 1,492

Joined: August 04, 2002

Location: Aruba

Posted: April 29, 2004 at 4:14 PM / IP Logged

Noise is either induced or amplified. You should start by powering the unit and grounding it from a clean source of reference.

Whether you follow the route you suggest from the ACC from the ignition.

If the noise is still there after that, it could be possible that the noise is being induced.

Using the 9 volt battery, you noted that the noise is not there. That still does not tell you, or isolate the actual cause, whether it be induced or amplified.

But based on what you have written it could be a combination of the two. As the Radio Shack unit could simply be of low quality and the T.H.D & S/N ratio may both be high and low amplifying the noise, or inducing it.

Try your first suggestion, with a clean ground and power supply from the ACC.

Regards

EVIL Teken . . .

steph280

Member - Posts: 4

Joined: April 27, 2004

Location: United States

Posted: May 03, 2004 at 11:22 AM / IP Logged

Well he issue is not the amp or the power source. Other people have tried different amp and powering directly from the ACC power going into the head unit, and I have tried hooking up different 12v device (reverse camera), samething. The camera just gets some static on the screen, no image.

It sounds like this nav head unit is particular about where it gets power from. Could there be a special ground point where all the devices must connect to?

Thanks again for the help.

Stephen

Teken

Gold - Posts: 1,492

Joined: August 04, 2002

Location: Aruba

Posted: May 03, 2004 at 3:31 PM / IP Logged

Matters not where the ground comes from, so long as it is a low resistive ground plane.

If you have not done so already, insure that the ground plane is attached to the chassis frame, and not any tubular mountings.

Next make sure you varify the ground plane with a DMM. Following the basic ground principles of proper wire diameter, and the shortest length possible.

Finishing up with installing the ground point with a star washer and dieletric grease compound.

You will of course want to keep all the ground points away from any high voltage / current power leads, which will cause inductive noise.

Regards

EVIL Teken . . .

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power amp thru cigarette lighter

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