Car stereo buzz problem

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Kookie
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Car stereo buzz problem

Post by Kookie » Sat May 10, 2003 12:13 pm

I installed a car stereo with a tape player and a front audio (CD player) input. I have a portable CD player I would like to use in that audio input. I put in a power jack for the CD player under the dash so I wouldn't tie up the cigarette lighter. The power jack is 12V running to the CD players power adapter. The CD player takes 4.5V. If I run it this way I get a whining buzz over the audio. If I use the batteries in the CD player it works fine - no buzz at all. Where could this buzz be coming from? Its not the ignition because it happens with the car not running. The buzz gets worse when the CD player spins the disk. One thing I noticed is that everything gets the same ground. Could it be a ground loop problem? Or the power adapter?

chessman
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Re: Car stereo buzz problem

Post by chessman » Sat May 10, 2003 12:26 pm

Are you trying to plug the AC adapter into the car?

toejam
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Re: Car stereo buzz problem

Post by toejam » Sat May 10, 2003 2:59 pm

I would try hooking a 50 mf cap across the cd player in series with a a half amp fuse. The cd player was designed to operate with batterys and probabally did not include filter caps. My guess is you have a little switching power convertor that needs more filtering.

gadgeteer
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Re: Car stereo buzz problem

Post by gadgeteer » Sat May 10, 2003 11:02 pm

Filters are a good idea, but a new power supply might be simpler. Current draw on the CD player should be quite low, lending itself to a linear regulator. These can be bought for $7 - $15; they contain some way of selecting the output voltage, usually a slide switch. There is a way to choose the correct plug and polarity. I believe Radio Shack has such an adapter, with a selection of "ADAPTAPLUGS" (someone actually got PAID to come up with THAT word).<p>www.radioshack.com-300mA, $14.99
www.radioshack.com-1 Amp, $21.99<p>You should be able to find them at WallyWorld and Target and numerous department or automotive stores...<p>You probably know the problem with switching regulators; they use very little power (because they switch between hard ON, with little voltage drop {hence little heat dissipation}, and hard OFF with no current flow {hence ZERO heat dissipation}; inductor/capacitor filters smoothe out that several-thousand-times-per-second-on/off sqaure-wave, into DC. A control circuit adjusts the duty cycle, IE the time ON vs time OFF, so that the filter output is regulated DC.) BUT all that "square-waving" is filthy with harmonics and noise.<p>If you use a LINEAR regulator, it has NO frequency, it's like turning on your water facet to a constant low level; a sensor measures the output and adjusts the "facet" to maintain a constant voltage (or in "FACET" terms, maintain a constant PRESSURE).<p>Your linear supply drops 14 - 4.5 volts, or 9.5 volts for your CD;if it draws 100mA, then P = VI, so power wasted in HEAT is 9.5volts x 0.1amps, or .95 watts. That is a little heat, about ¼ of what a nightlight bulb makes. But NO noise at all...<p>Select the voltage, then fill the gaps in the switch with HOTGLUE (try to keep the hotglue on the SURFACE and away from the internal CONTACTS) --- this will insure that an accidental nudge won't explode your CD player...<p>[ May 10, 2003: Message edited by: gadgeteer ]</p>

Kookie
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Re: Car stereo buzz problem

Post by Kookie » Sun May 11, 2003 1:05 am

gadgeteer, hehe, that's kind of funny, your suggestion, because that's just about what I'm using. I got a radshak 273-1857.<p>http://www.radioshack.com/product.asp?catalog%5F name=CTLG&category%5Fname=CTLG%5F004%5F018%5F000%5F000&product%5Fid=273%2D1857<p>I modded it up a bit. Instead of it's intended use of plugging it into the cigarette lighter, I popped it out of it's box, and soldered some leads to the circuit board for the 12V input. Ran that to a plug that jacks into the dash. The jack leads tap off the 12V lead going to the radio. That's the way it's set up now, at least to try it out. I intended to hide that whole adapter under the dash with the 4.5V leads to the jack on the dash. Then I'd have no bulky adapter sticking out of the ashtray, and instead two neatly bundled cables running between the radio, dash, and CD player. <p>Regardless of how I'm hooking it up, I would think it should have worked without this crazy buzzing sound. I'm wondering now if that adapter is just hokey. Hell, I'm thinking about trying out a simpler home made voltage regulator out of a 7805 or something. I can try that cap idea too, but I would think this $14 adapter thing should have worked good. ....crap.<p>What I've noticed here is that the whining buzz seams to correlate to the motor inside the CD player. When I turn it on, it's an even buzz. When I have it play a track, the buzz is almost like I can hear it search out the track on the disk. The other thing I noticed is that the audio ground is the same as the DC ground. I would think that would be isolated in a way. Not sure.<p>Anyway, this is still quite mysterious to me here.<p>[ May 11, 2003: Message edited by: Kookie ]</p>

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haklesup
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Re: Car stereo buzz problem

Post by haklesup » Mon May 12, 2003 11:00 am

Buzzing is one of the most common problems in car sterio installations. especially when connecting a head unit to an amplifier, in your case it is a CD and the amplifier is the head unit. <p>In any case, it sounds like ground loop noise. You can either make absolutly sure that the CD power supply (car lighter plug) and the radio (head unit) share a comman point ground. They probably don't since many cars simply use the chassis as ground or use a ground loop isolator.<p>Messing with the ground wires dosen't always help but ground loop isolators almost always do. It is basically a 1:1 transformer and you can get them in lots of places. Most have RCA type phono plugs but you can replace them with 1/8" phono sterio plugs if you need to. You don't need much wattage for that wire.

Kookie
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Re: Car stereo buzz problem

Post by Kookie » Tue May 13, 2003 9:52 am

Ooo, alright, yes, I'll try that. That sounds resonable. Radsak has one: 270-0054. This makes sense to me. Hopefully this will work because this is driving me crazy here and I have a deadline to get this done now. Thank you :D

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jollyrgr
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Re: Car stereo buzz problem

Post by jollyrgr » Tue May 13, 2003 4:27 pm

I may be wrong but I think it has to do with the power cord. It appears to use a switching regulator. My cell phone charger has an adapter like this and wipes out AM, FM, and Cassette when plugged in. At first I thought it was the cell phone's charging circuit. But then I found that the charger made all the noise by itself, just more so with a load. The fact that you have the CD player connected to the radio directly does not help. <p>Check for buzz with the audio jack unplugged from the CD player itself. If the buzz is still there you may need a different adapter (linear instead of switching). If the buzz goes away, a isolation transformer will more than likely help.<p>The 7805 is quick and easy. Add a single series power diode to drop the 5 volts to around 4.4 volts. <p>Another thing; did you try shielding the regulator circuit or is it in a simple plastic box? Just for grins, have you tried powering the regulator circuit with a different battery? In other words connect the regulator circuit to a 12 volt battery other than the one in the car and see if the same problem occurs. If it does, shielding the regulator may help. You mentioned that you connected the regulator to the same power lead as the radio. This potentially could cause problems as well. Noise from the input of the regulator could be leaking back into the car radio. Try connecting the regulator to the lighter circuit (temporarily at least) and see if this helps.<p>These types of problems can drive you nuts. But keep at it, you will eventually solve the problem.<p>[ May 13, 2003: Message edited by: Jolly Roger ]</p>
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Kookie
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Re: Car stereo buzz problem

Post by Kookie » Fri May 16, 2003 3:05 pm

Hey I just want to thank you guys, especially haklesup for the isolator idea. Works great! Problem solved. I even used the PS I built for my other problem posted under "blinking LED stops blinking". Now every thing is all under the dash and works great. Thanks again. :D

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