kedar

i need help diagnosing a squeal that i have in my speakers. i recently installed arc audio amps in the passenger footwell of my c6. i have a gm-add-24 harness that was once modified by me and again by pentavolvo. i thought this was the problem which is why pentavolvo was gracious enough to modify my old harness. the problem: i get a squeal in the speakers with the gm-add-24 harness connected to the nav (and the nav just loosely sitting near shifter and not bolted in place). however, if i plug an ipod directly into the amp, i get perfect sound with no squeal.

any ideas? could i still have a bad gm-add-24 harness? could the power / ground wire in the passenger footwell and near the car's wiring harness be causing the problem?

some details
head unit: stock c6 nav
speakers: polk audio mm6501 components
amps: arc audio ks125.4 and arc audio ks5001
sub: none yet
power wire: 4 gauge wire through factory grommet and connected to remote location on fuse box in engine bay
ground wire: connected to a bolt in the passenger footwell near glove box (i tried two different bolts, also tried connecting the ground wire to the ground on the engine block using jumper cables, no difference)
distribution block: stinger power / ground distribution block in one unit
interconnects: mid-level stinger
speaker wire: 14 gauge stinger

UPDATE 7.4.11
here is a cliff notes version: ground the rca interconnects to the head unit and add an antenna isolator.

i believe i have eliminated 100% of the whine / squeal / noise from my system. pentavolvo's suggestion to ground the negative side of the RCA's to the head unit eliminated 95% of the problem; however, i still had a high pitch from the speakers that was still perceptible (and annoying). i noticed that this noise went away when the antenna was disconnected from the head unit.

installing an antenna isolator eliminated the remaining 5% of the whine / squeal / noise. the antenna isolator that i purchased from amazon is manufactured by DLC (no part number). the antenna isolator that i received had connections for a standard antenna plug; however, gm changed the size of the antenna plug from a standard plug to a mini plug so i had to use metra 40-gm10 and metra 40-gm20 to complete the connection.


the far left item is metra 40-gm20, the middle item is the DLC antenna isolator, and the right item is metra 40-gm10


here you will see the negative side of the rca interconnects grounded to a screw on the head unit.

i am very satisfied after preliminary testing. as an aside, i tried three different noise filters with varying success. the best noise filter that i tried was PAC SNI1 Noise Isolator. i tried the PAC SNI1 after grounding the RCA's and adding the antenna isolator , but i concluded that the sound quality was the same (if not slightly worse) with the PAC SNI1 so i did not keep it as part of my install.

i hope this helps someone else trying to eliminate noise from their corvette's audio system.

0Andrew6@TheDoubleAA

sounds like some interferance? Could be poor grounding?. . . I had an issue with this before and ended up being bad RCA's

kedar

thanks for the thoughts, i am open to all ideas.

bad ground: i think i eliminated this possibility by using a jumper cable clipped to the ring terminal of the ground wire and then clipping the other end of the jumper cable to the ground bolt on the engine. squealing persists even if amp is grounded directly to engine block.

bad rca cables: this is possible, but the ipod setup uses the same rca cable connected using a male-to-male coupler to a wire that has rca connections going to a 3.5mm plug and then to the ipod. could a bad rca cable have interference when using the stock head unit but no interference when using an ipod?

0Andrew6@TheDoubleAA

possible. WHen running more than one thing off of RCA's theres always a possibility of the interferance. You may have to run a second line out converter

kedar

This may add a new wrinkle: the speakers still squealed when the gm-add-24 harness was plugged into the nav and the wiring harness but without the rca interconnects connected.

pentavolvo

wait so even without the rcas pluged into the gm add24 harness you still get noise... that says amp ground or bad rca's in my opinion

does it only happen with car running?

kedar

pentavolvo - yes, noise without rcs's plugged into the gm-add-24.


all tests are with car running. did not try accessory mode.

kedar

the interconnects that i am currently using are stinger pro 3 series. should i try the stinger hpm 3 series?

as for ground, if everything sounds fine with the ipod then does that rule out a bad ground? i have tried two different bolts in the passenger foot well. i believe both are visible without removing any panels. i am using a bolt that is near the lower left corner of the glove box. if the squeal persists even when grounding to engine block (using jumper cables as described above) then doesn't that also rule out a bad ground?

it is not difficult to remove the console, and i have zero problems removing the connectors from the cigarette lighters (just use a screw driver or a scratch awl to depress the little square to remove the plug). next time i open everything up i would like to try something different. perhaps i should order new rca cables. anything else i should order? all ideas welcome.

could my harness be bad? can i test it with a multimeter?

kedar

here is a pic of the amps in the passenger footwell:



here is a pic of the ground:



the 4 gauge gray wire is obviously the amp ground. the 18 gauge blue wire is the ground for the mild 2 wild. after replacing the stock bose amp with the arc audio amps, the former ground location for the mild 2 wild no longer worked (it was grounded to lower right bolt that holds down the amp).

there is another bolt visible in the picture of the ground. i tried that one and it also worked to ground the amp. squeal in speakers continues if i use the gm-add-24 harness.

pentavolvo

ok imo its deff a ground issue. try with car in accessory just for the hell of it. you are getting a ground loop that you arent getting with the ipod because its not wired into the car. run a ground either to the battery or to the oem ground location under the passenger side seat belt pilar panel. you do not have a good ground where you are. also make sure your rcas arent pinched somewhere

kedar

i have put everything back together (the vette is my dd) and next time i open everything up i will try the gm-add-24 harness connected and with the car in accessory mode. for diagnosing, what will it mean if i get the squeal in accessory mode? will that indicate bad rca's and/or something else? what will it mean if i don't get the squeal in accessory mode but i do get it with engine on? would that indicate a bad ground?

grounding: which is best? a) ground to engine block b) ground to negative battery terminal or c) ground to chassis seat belt bolt in passenger side pillar?

thanks to all for the help.

markcz

The best ground is always at the batery terminal, but then you usually have to run a much longer cable, which isn't always good. The factory ground by the seat belt roller should be fine, but make sure to get good contact.

bass mechanic

check with an ohm meter the speaker wires to ground. disconnect all of the speaker wires from the amp and verify no connection to ground.
if you have an Ipod try connecting a patch cable directly from your ipod to the input of the amp. be sure to lower the volume output of the ipod first.
try playing some music directly from the ipod. if its clean than your problem is probly an impeadance mismatch from the HU to the amp. if that is the case an rca ground loop isolator will solve this issue totally.

i suspect your arc audio amp may have a reference ground for RCA instead of a floating ground. if this is true engine noise will be a battle no matter what you do.

kedar

thank you for the response. few questions (apologies if these are simple or noob questions):

1) how to check speaker wires to ground? multimeter set to ohms and one probe on the amps speaker wire input and another probe on the ground i am using? if so, what should be the output on the multimeter? high resistance or low resistance?
2) how to verify no connection to ground? i understand your directions about disconnecting speaker wires from amp, but then what?
3) i do have an ipod hooked up to amp with a patch cable and i do have clean sound. you recommend plugging the ground loop isolators inline with rca's? gotcha.
4) you really lost me with reference ground versus floating ground. i did some research and still don't understand but it does not really matter. i will try to changing some things around and see if i still have a problem.

my plan:
1) upgrade rca's to Stinger HPM series;
2) if necessary add inline ground loop isolators;
3) if necessary run ground wire through firewall grommet and connect ground wire directly to battery.

pentavolvo

forget all this other stuff u plan on doing first and foremost is get a good ground. run ground to bolt under seat belt pilar panel

kedar

thanks. my amps are in passenger footwell and it may be closer to the negative battery terminal than it is to the bolt under seat belt pillar panel. i will run wire to a new ground.

pentavolvo

i have a feeling that is alot of ur issue... u have good rca's so unless they are routed bad and wrapped around power wires etc its not them

bass mechanic

yes use the ohm setting on your meter and verify its working by touching the probes together, you should read 0 ohms.
then with the speaker wires disconnected from the amp verify that none of them have any readings between your ground connection used for the amp and any of the speaker wires.

i have had this problem before in a 2010 camaro install before. we actually wired the output of the factory HU to the input of the amplifier and unless all the connections on the RCA path were solid we got squealing from the affected channel. a noise filter solved all these issues. its because the HU has a floating ground and the amp had a ground reference to chassis ground.

by using the ipod you have eliminated this as a possible source of the problem.
a ground loop isolator will electrically isolate these different grounds.
however it is important to locate the isolators themselves away from any wireing! you might try next to the tunnel under the carpet. there is a good amount of space there and no wires close by.
the isolators have a transformer inside and they will pick up electrical interference.
some say they degrade the SQ and i disagree. if there is any degradation it's not perceptable and a lot better alternative to the noise you have now.
personally, RCA's are mostly for show. i wouldnt spend a lot of money there. you can take 2 peices of wire and twist them up with a drill and make a great set of twisted pair (noise rejecting) rcas for a couple bucks.
as a matter of fact i have 3 sets running right next to the power wire from the battery and several other wires (actually tied to) and i have 0 engine noise even if i turn the gains all the way up i have no noise!
dont waste your money on expensive RCA cable. as long as its twisted pair it doesnt matter how many layers of shielding it has or how thick they are.
ixos makes some nice stuff if you have a car audio shop that sells it near you.

Spying Beast

Did you have another amp hooked up, a stock Bose amp that may still have power?

kedar

the stock bose amp from the passenger footwell was removed and in its place i installed two Arc Audio mini amps (see pic above).

i have read differing opinions on the issue of where to run the ground. since my amps are in the passenger footwell, it is a shorter run to the negative battery terminal then it is to the body ground in the passenger pillar. should i run my ground wire through the firewall to the negative battery terminal? or is it better to run a slightly longer run of wire to the chassis ground? i am waiting for some more wire from Darvex so am in no particular rush. i just want this done correctly.