Car Stereo - No sound only while engine is running?

[hamerhead]

I've installed a million car stereos but this one has me baffled. Just finished installing 2 speakers and a powered sub in my brother's '51 Ford pickup. Sounded great, until I had him start it up to listen for buzzes. Then, no sound. Everything is still lit up and appears functional, but no sound. Shut off the truck, works fine. Disconnected the sub, same thing. Went direct to the battery (bypassing everything), same thing - as soon as the engine is running, no sound except for a very quiet pop, pop, pop thru the speakers.

This truck is converted to 12 volts, but still uses a generator.

I plugged a flash drive in to see if it was in the radio/antenna or something, but it played like it wasn't getting enough power, kind of sputtery (for lack of a better word).

I've never seen/heard anything like it and hellifIknow what's going on. Any ideas?

[velorush]

Spit-balling here, but (back in the day, a loooong time ago) I used to convert 6v to 12v with great results, BUT, always replaced the generator with an alternator.  

Did you try the stereo while driving down the road?  One of the benefits of an alternator is more consistent wattage output across the RPM range.  That (6v) generator might provide enough wattage at higher RPMs to meet the full power requirements of the system (not just the cool LEDs).  I'm betting a consistent few thousand RPMs might permit the system to work (until you get to a stop sign).

What would prevent your brother from replacing the generator with an alternator?  Would do wonders for recharging the battery and ensuring a much more effective electrical system.  The cool choice (again, back in the day) was modern (ha! late 70's) alternator with built in voltage regulator (I was always a GM guy, but I'm sure Ford had the same thing going) - only one wire to run IIRC.

[hamerhead]

You're onto something there. We never revved the engine, just let it idle. I also learned that when converting from 6 volt to 12 volt, resistors are used so as to not overload the gauges and other electrical stuff. Could have something to do with it as well? I thought we had bypassed all that.

Not sure why he didn't switch the generator for an alternator. Could be he got the truck that way and just left it.

[velorush]

I'm not expert, but I never changed a thing with gauges and such - everything runs better on the higher voltage.

The change to alternator is really pretty easy and I'm sure now there are YouTube videos detailing every step.  I'd say low RPM output was the principal reason for changing cars over to alternators.  They're just way more effective.

A cool experiment would be to try the stereo while driving down the road (for a minute or so at a consistent RPM).  If it still doesn't work, you might try unplugging the amps to the subwoofers - those require a relatively large amount of power. 

[gtrdaddy]

Tim, I think Jeff May be onto something. But also, the popping has my attention. I think something else is possibly going on. When you listen to the popping noises, when you rev the engine, listen to hear if the popping noise modulates to a higher pitch when the engines rpms increase. If it does, it means you have a lifted ground somewhere, and I’d check the grounds on the battery and generator  first, and then work your way back.