Got myself a '98 ES300 last week- It's got 7 speakers, an amp and head unit that's all intertwined. Metra makes a Toyota adapter that is the solution to using an aftermarket head unit with the existing speakers & amp. I bought one and spliced it together with my Empeg adapter, everything matched fine. It takes every wire and puts it together in a single harness, so it has RCAs for LR/LL FR/FL.

It fits and I can turn the Empeg on, but i get tons of garbage sound with the music. I think it's a ground loop..

So, I ran the Empeg its own ground to a bolt on the frame (scratched off the paint, too) instead of using the adapter's ground. No difference.. so I ran the empeg its own power from the battery, no difference. Grr. So I unplug the Empeg RCAs from the adapter, and got a RCA-> headphone converter. Plugged headphones into the Empeg and it sounds fine! no noise. fscking weird...
So, using the adapter for power but not the adapter's RCAs I can hear it fine (through headphones). But, if i plug it back into the adapter for the amp, i still get a lot of crap sound with the music. I put the stock head unit back in and it sounds fine., no sound artifacts at all.

Anyone have a clue? Maybe I have bad RCAs or wires on the audio part of the adapter? i'm stumped, i tried the obvious.. and the leads on my empeg harness are getting shorter by the day!

Yeah, the headphone thing is normal/expected behavior with a ground loop.

First, read this.

Then try plugging the empeg RCAs directly into the amplifier, with all power, RCA, and ground wires from that other head unit completely disconnected from everything.

Then try going through all the steps here, and also go through all the steps in all the articles sub-linked from that page.

A couple of my Empeg installs have have had ground loops that were notoriously difficult to remove.

To help diagnose the problem, try grounding your RCA cables where they go into the amp (aligator clips, wire & tape...whatever...it's just temporary). In every case I've had so far, the loop was between the empeg and the amp. If the noise goes away when you do that, you know that the empeg is not grounded properly. Make sure you double check the sled harness connector to make sure you're getting a good connection (some had dodgy crimps). I'd resolder that pin just to be sure.

I assume the neg of a RCA is its outer metal ring, correct?

Hope I can find this thing.it's elusive thus far and I only get 2 hours of daylight after work a night, heh

thanks for the info

hm, ok. gonna have to remove the passenger seat to get to the amp while it's still hooked up. I'll try JBjorgan's advice to test. I'm afraid that the audio wires will be in a harness like they are on this end, so is it sensible to solder a needle or paperclip onto a wire and jam that into the back of the ground pin's socket, for testing?

i'm trying my hardest to make sure each step is properly tested. I don't want to miss whatever it is

I'm not really electrically inclined (software guy) so bare with me here: To check this with a multimeter does the + of the multimeter go to the + of the device and the - to somewhere on its ground wire or ground point (of the device) to test? what do i look for? a deviation from 12v ?

Sorry to have so many questions, hope that's readable

Tony,

I respectfully disagree. Why would it be called a ground loop when the shields (at ground potential in a single ended installation) aren't involved? That's not really the point here anyway though.

Basically as I understand it generally (as an electrical engineer) for a normal unbalanced situation:

- The signals from the head unit to the amp are signal ended and referenced to it's ground at the head unit end.
- The amp simply amplifies the voltage it sees between the centre pin of the RCA and the shield. It's merely amplifies the "difference" in potential but right at the input to the amplifier.
- If the ground of the amp is not very good OR the ground of the head unit isn't very good, the ground reference point of either the amp or head unit (or both) end will move, particularly with voltage fluctuations (stuff like alternator, switching loads such brake lamps, indicators etc).
- If the ground reference point moves at either end, that's when the noise gets in, since the ground has moved with respect to the centre signal wire.
- If the grounds are bad, the amplifier's and/or head unit's supply return current will travel via the grounds of the audio cable. This current will change according voltage fluctuations. Any resistance will then cause potential differences when current flows. And again the potential difference is what is amplified.
- The supply currents for the amp and head unit are unlikely to be flowing on the audio level signal lines of the RCA cables.

Grounding the shields should effectively achieve nothing since the should already connected to ground. What it does do though is provides another current path for the supply currents to take which can help with the problem.

Well, that's my take on it. Feel free to debunk it. I don't mind being corrected.

I took the glove box apart and I can see the wiring harness that goes into the amp. Can I do this test at the head unit rca adapter end? i'd have to rip the damn wire out and put another in if i test it at the amp. its tiny

thanks for any input

One thing worth trying early is running new ground wires to the amp and HU.


/strip away any dirt paint etc before attaching the ring terminal - shiny metal is what you want. afterwards,put on rust protection on top


While you're at it,check the grounding of the battery (negative terminal) and the alternator (commonly grounded to the mount on the engine block, so also check the car body to engine block grounding strap. Beefieer ones doesn't hurt; clean the attachment points)

I did that test, and it certainly helps but it doesn't make the problem go away. Would I be better to run a wire to the negative post on the battery, or try to find better grounding? also, having this wire on the sled made an improvement too. not entirely, but it did help

any input would be appreciated. the lexus forum people suck, they never post a solution. tons of people with ground loops and no "this worked for me" after everyone helps them.. makes you wonder if there are thousands of people driving around with what they consider an ignorable hum...