Q for audio geeks

Hoping maybe there are a few audio geeks in the community, so here goes.

I recently replaced the OEM stereo head unit in my car, and the replacement (purchased from Crutchfield) has a low-level hiss as soon as I turn the unit on. The hiss doesn’t seem to get louder as I turn up the stereo, and while it’s audible when the car is running/moving, it’s harder to notice (i.e. not super-loud).

According to the results of my bing-fu searching, a likely culprit is ground loop, but before I pull the head unit out of the dash again, I figured I’d see if any of my esteemed gadget geeks had a second opinion.

FWIW, I did ground the unit to a screw that screws into the metal frame of the dash, but it’s possible that it isn’t making good enough contact, as the dash frame itself appears to be painted. The rest of the wiring harness connections are made with crimp connections, not soldered, so that could also be a potential point of resistance/noise.

Would love some feedback on this (pun intended). :slight_smile:

I have similar issues with one of my classic cars and I still can’t figure it out, and I’ve done most of the things you can imagine to find the issues with no success. funny thing after I changed the Main battery the hiss got lower go figure :wall:

it might be your spark plugs, and or spark plug wires… some have a resistor that helps weed out the noise others do not… check into that as well.
here what I will try when I have time and I recommend you check into this solution.
also you might want to solder one of the ground in your RCA output to the chassis of your radio, this worked for me in the passed.

I would recommend you supply your audio from a second small battery like one of these motorcycle ones: https://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=motorcycle+battery&rh=i%3Aaps%2Ck%3Amotorcycle+battery&ajr=0

coupled with one of these isolator relays: https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Daps&field-keywords=isolator+relay will allow your alternator to charge the batter and keep the main isolated from the second batter along with it’s problems… again I haven’t had the chance to try this but I see no reason why it wouldn’t work.


@ Jay Jay - Thanks for the response.

I’m certain it’s not the spark plugs, because I get the hiss regardless of whether the engine is running or not. I’ve experienced issues with spark noise before, and it usually changes with engine speed as well, which is not the case here.

Appreciate the other suggestions. Will report back if I figure it out and get it resolved.

Need a bit more info. Does your new radio power the speakers directly, or does it then go to an amp?
Just so you know, there are some vehicles that have their own small amp tucked away. For instance in my truck, there is an amp tucked away above the glove box. When you look at the radio it looks like normal speaker wire connections, so without a bit of digging you would never know there was an amp in there.

I would suggest to start by eliminating all the unknowns. Try running the head on your bench first to ensure it’s working fine first.

Pretty sure there’s an outboard amp. The factory system had the Infinity branding, so I’m fairly sure that uses an outboard amp. From what I can gather, the amp is under the passenger seat. The head unit shipped with a wiring harness adapter that is intended to make the unit work with the OEM (Infinity) amp. With the exception of the hiss, audio quality is quite good, and plenty loud. Just need to knock out the hiss.

Given that several things I’ve read point to ground being a potential problem, I think my next test will be to run the unit without the antenna connected, since it may be providing a second ground (in addition to the wire I connected to the metal dash frame).

Thanks for the feedback!

@ devhammer - tinnitus?

Heh…I do have a touch of that going on, sadly, but the hissing in question is definitely an artifact of the new head unit. It goes away when I power off the head unit. As well, my kids can hear it, too, and they’ve got fresher ears. :slight_smile:

@ devhammer - that’s how the voices started for me, too. First, it was just a faint hissing noise in the car when I was alone during the drive to/from work. Then I started hearing it in the shower and eventually I learned to understand that it wasn’t a hiss. It was actually voices. Now they never shut up. Fixing your radio will only make them talk louder. Send $100K to my offshore bank and I’ll let you know the secret cure. :wink: