Under $2 Fix For Alternator Whine In Stereo

DC3

Well-known member
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Dec 9, 2008
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Location
Lubbock Texas
I put a pretty decent stereo in my '73 a few years back. I had some alternator whine noise in the system that I've been trying to solve ever since. I read everything on the web I could find. Re-installed equipment a couple of times. Verified all grounds. Verified the noise was not coming through the antenna lead. Verified the noise was not being picked up by the RCA cables. Rerouted all cables away from other sources. Installed filters on the incoming red and yellow leads to the head unit. I tried most every trick in the stereo noise book but still had the whine. The volume of the stereo, the engine and the road noise masked the sound when cruising so it wasn't a huge deal but I did want to eliminate the noise.

So, I found this at Corvette Central:

yb.dll


Link: http://www.parts123.com/parts123/yb...T5157HSY99645120150x~Z5Z5Z5YES~Z5Z5Z50000050G

Didn't really want to pay the Corvette premium and guessed this was nothing more than a capacitor. I also didn't want to potentially waste $20 experimenting. So I searched the internet again and came across this site:

http://www.avweb.com/news/maint/182896-1.html

In the article, the author talks about using a 0.5 to 50 microfarad capacitor as an alternator filter.

So, I headed for Radio Shack and picked up this 47 microfarad capacitor:

pRS1-11856594w345.jpg


Link: https://www.radioshack.com/product/index.jsp?productId=12424832&numProdsPerPage=60


I actually used the 35 volt version as that's all my local Radio Shack had.

Installed this capacitor across the terminals on the back of the alternator and the whine is gone. Finally.

Note if you try this that these capacitors have a definite positive and negative terminal. You have to get it right or you'll blow the capacitor. You can see in the picture above, the stripe has arrow heads that point to the negative terminal. This negative terminal goes to the ground terminal on the alternator. Keep the leads as short as possible.

To install, I soldered some ring terminals onto the capacitor and encased it all in heat shrink tubing filled with RTV silicone. This particular capacitor is an electrolytic capacitor and is only rated at 185 degrees so it may not last. If not, I'll find one more appropriate for the environment but now I know the fix will work.

Hope this helps someone else.

DC
 
Been doing that fix for decades, better to install at back of the amp, cooler location.....putting a choke and then the cap will certainly kill the whine.....

Old Geek.....:bounce:
 
You probably know that already, the capacitor should be rated at twice the maximum voltage.
While fine under normal use, it may not stand transients (voltage spikes).
 
You probably know that already, the capacitor should be rated at twice the maximum voltage.
While fine under normal use, it may not stand transients (voltage spikes).

With the battery across the alt and heavy enough wiring, the transients are suppressed all to hell and back....I remember years ago taking my scope to the car I wanted the whine out of......the alt wine on my vette don't exist, cause I don't have any tunes in it.....:devil: Magnaflow and top down preclude that.....

I have 700 mv of alt ripple on my vette, at the alt stud....

:smash::eek:
 
You probably know that already, the capacitor should be rated at twice the maximum voltage.
While fine under normal use, it may not stand transients (voltage spikes).

Good to know. Guess I got lucky that Radio Shack only had the 35 Volt cap in stock. I was looking for the 16 volt.

I tried everything on this one including Gene's suggestion of filters at the amp but nothing worked. I even got the whine with the separate amp disconnected from power and ground.

The article I referenced said electrolytic capacitors have a short life and recommended tantalum capacitors. I'll be on the lookout for one in the correct rating but at least for now I have fix that works.

DC
 
You probably know that already, the capacitor should be rated at twice the maximum voltage.
While fine under normal use, it may not stand transients (voltage spikes).

Good to know. Guess I got lucky that Radio Shack only had the 35 Volt cap in stock. I was looking for the 16 volt.

I tried everything on this one including Gene's suggestion of filters at the amp but nothing worked. I even got the whine with the separate amp disconnected from power and ground.

The article I referenced said electrolytic capacitors have a short life and recommended tantalum capacitors. I'll be on the lookout for one in the correct rating but at least for now I have fix that works.

DC

Tant-Mylar caps.....40+ years ago were the hot lick and replaced the old wax/paper crap from decades earlier, and yes made by Sprague we called them 'orange drops' from the candy orange appearance with black letters on side...always came in a 600 volt rating.....

Good old Vacuum Tubes.....:shocking::p:devil:

I dunno they make large crapassity caps from Tant/mylar these daze....

but probably do, after 40 years or better.....
 
The article I referenced said electrolytic capacitors have a short life and recommended tantalum capacitors.
DC

Well, the article was right. Capacitor failed while I was cruising last weekend. I could tell the whine was back when I pulled into the garage before I shut it down. Capacitor must have shorted because my battery was stone cold dead today when I tried to start the car today. Guess I need to ramp up my search for a proper capacitor.

DC
 
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