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Advanced Member
Username: Chad

Post Number: 890
Registered: 11-2004

Posted on Friday, June 02, 2006 - 9:44 am:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

We all know that it's ideal to connect the radio straight to the battery but I would wager a guess that the majority of mobile operators do not do this out of the convenience of having the radio activate with the ignition switch. I'm one of those people, sometimes when I get out of the car you'd swear it's on fire or I have an ejector seat :-)

During the early days of car audio when digital tuners came out car radios had 3 wires, red, yellow, black. The red went to the ignition, yellow to constant power to retain memory and black to ground. The yellow wire usually had a smaller fuse (.5A) and was just to keep the presets alive. The red wire was the larger current draw, powering the amplifier and the rest of the unit.

The newer units have switched around. The yellow wire is the big current draw and the red simply tells the unit to turn on. In most cases now (Alpine is one) they strongly suggest attaching the constant power source to the battery with a dedicated fuse. Many units now have higher power then before and include DC/DC conversion to get this to happen, they also use DC/DC conversion because they use Bi-polar power supplies for the preamp circuitry.

After reviewing the schematic of the Magnum 257 it became obvious that much of the radio is constantly powered (even when "off") and adding a control circuit would be easy as cake. I think the addition of this to Magnum's microprocessor controlled radios would be a wonderful asset to those who like the convenience of having the radio activate with the automobile. This would also retain presets/settings and urge people to do a more "proper" radio install giving the radio clean power. I used an external relay in my truck that would sometimes sit during the weekdays to sort of do this, but had to re-program the radio when I got in Saturday morning. If I put a 257 in my car (when they arrive) I will certainly put an internal relay controlled by the ignition in series with the power switch to achieve this goal.

Is this a decent idea for Magnum or am I dreaming?

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Username: Tech808

Post Number: 10200
Registered: 8-2002

Posted on Tuesday, June 06, 2006 - 5:38 pm:   Edit Post Delete Post    Move Post (Moderator/Admin Only)


I just got off the phone with Sam Lewis and he suggested and recommended that No One should connect a Magnum Radio directly to the Ignition switch.

On a drained ignition he say's it can cause an arc to occur inside the radio that can cause damage to the CPU.

While this is rare it has happened in the past and is just not worth the chance of blowing your radio up.

He highly suggest's that all Magnum Radio's be connected DIRECTLY to the vehicle's battery which will also give you a battery back up for the radio.

Hope this help's,

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Advanced Member
Username: Chad

Post Number: 925
Registered: 11-2004

Posted on Thursday, June 15, 2006 - 10:12 pm:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

Sam is very correct. Even with the switch off on the radio, if power is applied to the radio it will remember things as long as there is power applied +approx3 days :-) A small relay in series with the power switch circuitry would allow the radio to have constant power to the MPU but remotely turn the radio on via the ignition. The relay will act as the power switch and the radio would be hooked up as Sam suggested. (the PROPER WAY) Then only thing coming from the ignition circuit would be the relay coil. If ignition power really wated to be kept iolated then an OptoIsolator could be used in conjunction with a Darlington transistor to achieve the same thing. The ignition line would simply turn on an LED. To hook it up conventonally a switch could be added to the rear of the radio to bypass this feature or the remote and power can simply be tied together.


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