Hoping to get the help from all those car stereo wizards to eliminate a stereo whine/buzz I'm having with my 1972.
I pulled the (aftermarket) radio to check the grounds and routing, but found the whine went away when I unplugged the oxygen sensor plug from the AEM A/F gauge I installed a while ago. This gauge has 2 plugs, 1 for the sensor, and 1 that powers the gauge. Power and ground for the sensor come from the gauge, but with only the sensor cable disconnected the buzz goes away, lights are still on the gauge. This leads me to think it's not the grounding of the gauge, but the sensor itself.
the gauge gets power from the radio power wire (yellow) and is tied into the same ground as the radio as well. (I thought this would help with any ground loop issues)

I'd like to keep the gauge functioning, but cant tell how I can get rid of the buzz. My general understanding is to ground the device causing the buzz, but I can't re-ground the sensor itself, can i?

 

You need to isolate the power sources- I'd run your constant hot and the ground for radio directly to the battery. The battery is excellent filter.


If that doesn't solve the problem- try running the switched ignition wire directly to the battery too- just for a test- as the radio will stay on all the time.

If you are still getting noise- with all the radio's power sources to the battery- disconnect the antenna.

Let us know what happens.

Richard

 

Thanks for your response Richard!

I finally got around to trying to remedy this buzzing noise I have in my vette.

I ran a power wire directly to the battery for the constant power for the radio (unfortunately didn't resolve my issue)
Ran ground wire directly back to battery from radio (unfortunately didn't resolve my issue)
Ran power wire directly back to battery for A/F gauge (unfortunately didn't resolve my issue)
Ran ground wire for gauge directly back to battery for A/F gauge (unfortunately didn't resolve my issue)
Unplugged the antenna (unfortunately didn't resolve my issue)
Plugged the amp trigger wire directly to battery (unfortunately didn't resolve my issue)

I unplugged the amp trigger wire, and this got rid of the buzz, but of course with this doesn't power on the amp so I can't listen to music at all. It is a D class amp, which from what I've read can cause interference, but never really had much issue before the A/F gauge install. The D type is suppose to be low heat, and since i have the amp in the jack compartment, I'm a little worried about switching to an A/B class which are supposed to be less efficient and hotter.
Amp ground directly to battery.

Is there anything else i can do remedy this issue?
Am i looking at noise suppressors at this point?
If so, would i put the noise suppressor on the A/F gauge, or the amp?

 

Do all of your speakers run out of that amp?

Anytime I've had this issue, it was when I had a powered music source feeding the amp. For example, charging my phone, while using the headphone jack to the aux input of the stereo.

Try this:

Play music from your phone (on the phone's battery only, not charging), into your amp. Maybe you need a 1/8 to RCA splitter to do this. Keep the wires short, and make sure that the ground of the amp direct to the battery is the only ground.

If that solves the problem, work backwards. Perhaps you don't need the radio head unit. Or you could figure out a Bluetooth solution to prevent a web of ground loop antennas from causing interference.

EDIT: Download podcasts to your phone (or USB stick, if your amp can read them directly), and ditch the radio.

 

Interesting. I also have a Class D amp mounted in the jack compartment. I went through a similar noise issue as you but mine was a whine rather than a buzz and varied with engine rpm. I put noise filters on both the switched and battery wires to the head unit. Both made the whine less noticeable but didn't eliminate it. Based on some info on this site in an old thread, I sourced and installed a capacitor directly across the alternator. That solved the problem but I couldn't keep the capacitors from frying. Apparently engine heat was a problem with the ones I was using. Wondering now if my issue was noise coming in on the amp trigger wire. I never bothered to disconnect it to see. My amp was connected directly to the battery so I doubt the noise was coming in on the main power to the amp. I'm in the process of installing a new engine and transmission along with various wiring upgrades including a new alternator and a small accessory fuse block connected directly to the battery for the stereo and other sensitive equipment. If I continue to have the problem when I get things up and running, I'm going to try installing another capacitor across the alternator. I found this filter on Eckler's site that may fit the bill: https://www.ecklerscorvette.com/corv...1963-1982.html Now wondering if installing a noise filter on the trigger wire would help.

DC

 

To be fair to Eckler's, their price is not much more than you'd pay buying the capacitor directly from an electronics distributor. Cornell Dubilier 4700 uF, 25V, part DCM472U025AA2B.

If you are willing to experiment with the trigger wire (all it does is energize a relay coil, or solid state relay, to turn the amp on, right?), you might try hooking a 9V battery to it, with the negative terminal connected to the car's negative battery terminal.

 

Hey Mongoose-

Yep - you covered all the noise points of entry- almost!!

IF you ONLY have the noise with the sensor connected-and have taken the steps to isolate the power sources-

I'm thinking the A/F gauge sensor wire is acting like an antenna. The sensor actually produces an oscillating waveform at idle that makes voltage transitions from about 0.1 v to 0.9v

Did you run RCA cables to the AMP? Or are you running speaker level wires back to amp? Then using a low level adapter- or some amps actually have a speaker level in.

If so- how close is the O2sensor wire to the radio or RCA cables? Try moving those around.

Let me know what you find-

Richard

 

If this is the case, I wonder if shielding both that wire and the trigger wire to the amp would help? Maybe use one of the aluminized heat sleeves for the O2 wire and ground one or both ends. Does the stereo industry make some type of shielding to slip over vulnerable wires?

DC

 

I would try putting some shielding around the O2 sensor wire and connecting that to chassis ground. Let the shielding 'capture' the stray signals and ground them out before reaching the radio. Someone should make some metallized fabric shielding or wrap for wiring. To test the theory out, you could just wrap the wire with aluminum foil and run a clip-lead from the foil to ground. If the noise goes away, you just need to find some better shielding than aluminum foil.

 

...Yeah, that's what I'm thinking. Another thing to note is the cable that goes to the O2 sensor is really long. i have it coiled up under the dash, and I know coiling up cable creates a magnetic field as well. Not sure how big of a magnetic field when the coil is made with coated wires, or if that has even caused an issue with others in the past.
The O2 sensor goes into the exhaust bung on the exhaust collector, which is aluminized steel. So would this create an antenna the whole length of the exhaust?

I am using RCA cables that go to the amp. Since the A/F gauge is also in the dash with the radio, they do get close. So Maybe I can do something there, but I can't imagine moving it that much further away.

 

A figure 8 tied in the middle instead of a coil will help negate the magnetic field.

DC

 

Do you mind showing a picture how you wired that capacitor?

Even when I unplug the A/F gauge O2 sensor plug, I still have a little buzz that's noticeable at low levels. My main, much louder buzz comes when the O2 sensor is plugged in, but maybe this would help with the buzz that occurs even with the O2 unplugged.

 

Have any of you ever used something like this to shield vulnerable wires?

I would think the shielding material would need to be more conductive than aluminum (foil), no?

 

Why didn't I think of that!
Great idea! thanks

 

I'll give this aluminum foil trick a go.
Have you tried this before yourself? Is the aluminum foil conductive enough?
I'd prefer to give this a try before purchasing that expensive EMI shielding product above.

 

Back in the day- aluminum foil-didn't really work- a copper mesh was much better. Used to keep EMF out of the the tape head in the old cassette players. Mustangs were the big offenders.
Depending how you ground the shielded wire- it often acted like a receiver and amplified the noise.

I'd look at some twisted pair RCA cables- the cables are carrying really low voltage levels (less than a volt) -
The signal is amplified many times by the amplifier- so avoiding it getting in AND cancelling the noise with the twisted wires be the most effective way to stop it.

AND uncoiling the O2 sensor wire would also help.

Look at something like this

Richard

 

I'll be honest, i'm not familiar with twisted pair RCA cables and how/why that helps. I know the phone company uses twisted pair for phone line connections (before IP phones came around). Does twisting the wires somehow cancel out the interference?
I would think the amount of voltage would be dependent on the output signal from stereo head unit. Any chance you could provide some background on these cables and your experience with their intended purpose?

I purchased these a while back, but never installed them. Notice the extra ground wire on the cable; I would think that wire is connected to the shielding layer of the cable. I have a later model Pioneer head unit, and I've read numerous posts about grounding the RCA jacks on the Pioneer head units to the chassis of the stereo. I don't know if this is still a Pioneer design issue. Maybe these would still help with that much lower level buzz when the O2 sensor is unplugged.

Are you saying using these could make things worse depending on how they are grounded?

 

What is lost by 'testing' the theory with aluminum foil? 10 minutes to wrap the O2 cable and run a 'patch' to ground. No brainer. If it reduces the noise, good shielding will likely do the trick.

Get rid of any 'looped' cable. You can try the 'figure 8' approach; I've never heard of that one, but who knows? Easy to test that theory, too. Maybe the best place for shielding would be on the RCA cables....

 

Yes- you can use those RCA cables. Ground to the radio's chassis and to the amp's chassis. Those should solve your problem- or at least minimize it a bunch.
You can also try turning down the "gain" or "input sensitivity" on the amp.

The twisted paircabling is a type of wiring in which two conductors of a single circuit are twisted together for the purposes of improving electromagnetic compatibility Compared to a single conductor or an untwisted balance pair, a twisted pair reduces electromagnetic radiation from the pair and crosstalk between neighboring pairs and improves rejection of external electromagnetic interference It was invented by Alexander Graham Bell.

Look at any computer cat cable or even BMW speaker wiring -





It was done by stage hands back in the day for long mic/audio cables and it was thought to decrease EMF...The thought was using the "right-hand" rule...Using your right hand around the cable, with thumb pointing in the direction of current flow, your fingers will point in the direction (around) of the magnetic field.In the figure "8"- having one magnetic field in one direction, the other side will be in the opposite direction- and supposedly cancel out...

 

Sorry, but I don't have a pic. I took the last failed capacitor out. I had connected it directly from the power lead on the alternator to the ground.

DC