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Discussion Starter · #1 ·
Fairly recently the truck started experiencing irritating static on the radio. It is present across the dial and at all volumes. I am certain it is coming from the engine as it increases when the load on the engine increases and decreases as the load on the engine goes down. In other words, while accelerating to get on the highway the static is loud but when backing off the throttle to slow down for a slowpoke in the left lane ;) the static almost disappears.

The truck is a '69 Chevy. The wiring is all stock and does include all the original grounding straps. I have added an HEI but that's been there all along and well before this static problem started.

Any obvious things I can check? The old coil had a static suppression condensor on it, can I add one somehow with this HEI system? The plug wires are 5-6 years old but in good shape and the truck runs fine following a tune up, cap, rotor, plugs this past Spring. The static problem was not evident immediately following the tune up. It makes no sense and is probably coincidental, but the problem started when I began installing the air conditioning but the static problems started long before I ever hooked up the electrical connections to the new ac system.
 

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is this like a whine? it speeds up with engine speed ??? if so the alt brushs are where I'd look
 

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If it's coming into the radio through the power line (12 volt) try filtering it. Easier that chasing it around. You can get a small choke from an audio store or someplace like Radio Shack. A choke looks like 1/2 of a transformer. Installs next to the radio. They are not that expensive.
68KMENO is probably right, I'm just too lazy to chase it around.
 

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Discussion Starter · #4 ·
No, no whine at all. It does not speed up or slow down, the "speed" of the sound is constant, the only thing that varies is the volume of the sound.

The alternator was completely rebuilt (by me) when I rebuild the engine. It only has about 12k on it. I can check it but I plan to add a larger alternator soon to help with the ac system I installed so the solution will be to simply install a whole new unit.

Any other thoughts? It's a cheap radio and many of the wiring connections were hacked in by the previous owner. I've rewired the speaker connections myself but I've never looked at the power connections too closely. I don't believe it was wired in using the original radio's power wire which I may just fix this weekend.

What is this choke thing you mentioned? Is it a device I need to splice into the existing radio power circuit? There's a Radio Shack on my way home so getting one would be easy.
 

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It goes in series with the power line by cutting the power line and installing the choke. Here’s a radio tech site that discusses it. May be other information if you look around on it. Not sure I’d install capacitors near the battery like they mention in there somewhere. Batteries leak.
Another link shows a picture of a true noise suppressor with both a choke and a capacitor installed together in a module. If the problem is caused by a noisy 12 volt power input, this should filter whatever it is.

http://www.radiotech.org/forum/messageview.cfm?catid=3&threadid=7911
http://www.shoppingfish.com/car-parts/Decks/In-Line-Heavy-Duty-Alternator-Noise-Suppressors-Fo.html
 

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Discussion Starter · #6 ·
Oh, one other tidbit. The volume of the static is constant regardless of the volume setting on the radio! If I care to, I can turn up the volume loud enough to pretty much mask the static. I've never experienced static like this before!

So, using my limited electrical logic, this would seem to indicate the static is INDUCED into the system externally instead of coming down the power circuit, right? The speaker wires have to run to the firewall to run under the carpet to get to the speakers, could the wires be picking up a signal from the distributor/coil which is just on the other side of the firewall? Wouldn't the firewall itself act as sufficient shielding?
Due to the ac install, the amp meter got moved even farther away from the radio so I don't think that could be doing it. If this is the case, the suggested choke on the power circuit might not do the trick I would guess.

And yet another little tidbit, I just went out to poke around at the power circuit. Everything seemed in order but I noticed the coax for the antenna lead was hanging down to the floor. It is way too long for the current installation so I tucked the excess up above the glove box. Much of the static has now gone away! It's still there though. Radio on, volume at zero it can clearly be heard. It is equal in both speakers. Disconnecting one speaker does nothing, the other continues to buzz. It now sounds like a geiger counter buzz.

Wiggling the speaker wires at their connections seemed to make it go away briefly (I could be hearing things) but I was never able to make it go away for good.

I'm more baffled than ever now but I think a good look at the coax antenna lead is in order this weekend.
 

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The noise is being amplified so it’s audible. That can’t occur if it’s noise being induced into the speaker lines. The car isn’t near something like a powerful antenna so noise can’t be induced though the box. The three possible sources are:
1, Induced down the power line.
2, Coming through the radio’s antenna
3, The radio itself has a problem.
Does it occur when the car is off? The 12 volt DC is real clean when the car and accessories aren’t running.
 

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geiger counter sound .... thats Ing wires leaking signal.... moveing antena wire making effect less.. leads me to the same thing tonight in dark open hood (look for light show) :D
 

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Run out of things to try or look at, maybe try this.
Use a spare battery.
Connect the ground lead to the dash.
Connect the radio power lead to the spare battery positive, disconnecting it from the car wiring. The spare battery provides a clean DC voltage to the radio. A battery charger won't work. It's too dirty.
 

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Hey Guys,

I've installed stereos for years so please don't think I'm trying to put anyone down. If you had said you added an amp, I'd have a better diagnosis for you. However, very minute chance of it being an alternater problem. It will not be a positive connection problem, if you have power, there's no problem there. The only other possibilities I can think of are poor ground of the radio - you'll need to find a good clean ground and use a gauge wire of some size(nothing smaller than 14 gauge), you have bad spark plug wires - I know it sounds dumb but that's a lot of electricity and creates quite a disturbance field, or you have an exposed speaker wire - this is the least likely, usually if this is the case the speaker won't work. Might try to make sure the speakers are mounted well also. Best of luck.
 

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Additionally, I bet this sound doesn't happen when the car is not running. If this is true, it's either a ground or spark plug wires. If it makes the sound without the car running, could be the connection of the car's antennae. Make sure it's not touching anything.

Please don't hook up a separate battery with the stereo still mounted! Done that, ended up being a smokey mess.
 

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Originally posted by Chevelle Daddy:
[QBPlease don't hook up a separate battery with the stereo still mounted! Done that, ended up being a smokey mess. [/QB]
Yeah, there was some hesitation typing that out but re-read what I wrote. I said to disconnect the radio from the car wiring. No connection it's strictly in bench test mode.
BTW
Your input is appriciated. Wish more experienced input to electrical problems would come by once in awhile.
 
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