Aftermarket amp & sub strange problem (not found in forums)

[Droo]

So I installed my new Alpine MRV-M500 amp and SWT-12S4 sub alongside Bose system with RNS-D. I used this diagram to tap into the stock loom (right at the original amp). I used 6 for the ground and 9,10 for signal of line level (RCA) and 25 for remote. Everything seemed normal, sound is great, no loud popping I red about before, but there's another issue, there's signal distortion whenever turn signals, power windows etc. are used (the sub "pulses" to turn signal ticks). My amp has high level input, tried to connect that way but the issue prevails. Also I noticed a strange behaviour when even with no ground on line cables (6 disconnected) there's still signal coming to amp and sub is still playing. I know Bose is using "floating ground" and all but why the problem is still there even when using high level output of the original amp? What else can cause this? Maybe my ground is bad for the new amp? I used a spot under the rear seats that I noticed while routing power cable. I tried googling and searching for this problem and solution but all I find is when there's loud popping issues.

[noldevin]

Where is your power coming from? Needs to be a fused line, ideally 4-gauge or thicker, straight from the battery to the amp. Make sure to keep your power lines away from the signal lines (ideally, on complete opposite sides of the car).

It could definitely also be a bad ground, you should be grounding the amp away from any other power or grounds to avoid feedback. Good practice is to use a loop style connector on the end of your ground wire so you can put it like a washer on one of the bolts that touches grounded body or framework. I used one of the bolts in the trunk, I'll check which one later when I'm not at work.

How did you mount your amp? I had an amp that liked to short through the mounting screws, so make sure you haven't mounted it directly to any grounded metal. You can use a wood board in between or mount it somewhere else.

From your description, it almost sounds like you have RCAs connected to the head unit as well as speaker-level inputs at the same time? You should only be using one or the other, never both. You say you tapped the stock loom at the factory amp, did you tap it BEFORE the amp or AFTER? this is important, as before the amp you have a low-level signal and after is speaker-level.

[Droo]

I have a proper separate 10mm2 (I think it's a 4 gauge in american) fused wire from the battery ran through left side of the car ( I think all the wires, including signal lines, to the original amp run on the right side since it's mounted on the right side in the boot), the ground wire has a loop on its end, I'm not using high and low level inputs at the same time. The new amp is mounted on the plastic tray under the boot floor that hides spare tire (avant) but the screws might be just a bit long and touch metal, I'll check that. RCA's/speaker wires do not run to the dash, I spliced them at the Bose amp connector in the boot. Now that I think I might have done a mistake by "coiling up" excess RCA lines together with remote wire and they might get inducted?.. Also I'll try a different ground spot, I'm now using "designated" spot that's shared with something else.

Edit: to make things clear I tapped RCA's to low level/pre amp (6,9,10 on the diagram I linked) and separate wires (not the same RCA's) for the high level (16 to 19) and did NOT have both connected to the amp simultaneously. After testing with high level I went back to low level as I felt it made a better sound in general performance.

Where is your power coming from? Needs to be a fused line, ideally 4-gauge or thicker, straight from the battery to the amp. Make sure to keep your power lines away from the signal lines (ideally, on complete opposite sides of the car).

It could definitely also be a bad ground, you should be grounding the amp away from any other power or grounds to avoid feedback. Good practice is to use a loop style connector on the end of your ground wire so you can put it like a washer on one of the bolts that touches grounded body or framework. I used one of the bolts in the trunk, I'll check which one later when I'm not at work.

How did you mount your amp? I had an amp that liked to short through the mounting screws, so make sure you haven't mounted it directly to any grounded metal. You can use a wood board in between or mount it somewhere else.

From your description, it almost sounds like you have RCAs connected to the head unit as well as speaker-level inputs at the same time? You should only be using one or the other, never both. You say you tapped the stock loom at the factory amp, did you tap it BEFORE the amp or AFTER? this is important, as before the amp you have a low-level signal and after is speaker-level.

[noldevin]

Ok glad you cleared that up. I would first try moving the ground off the shared ground post, you could be getting some feedback from the vehicle's systems. The remote wire shouldn't be enough to cause any kind of induction but you never know. I would try to use the shortest signal cables possible so they are not coiled up. On a previous audio build I had a lot of alternator whine coming through the speakers. I was able to drastically reduce the whine by grounding the "can" (outer metal part) of the RCA cables with a small piece of wire. The rest of it went away when I improved my amp's ground wire connection.

I do find it odd that you are getting noticeable interference on the subwoofer, usually electrical interference is high pitched. Are you not running a crossover? You should have a low-pass filter on any sub, i typically like the low pass set between 60 and 80hz which should filter out most or all interference. This will also help prevent high frequency sounds from the music from heating up the coils on the sub.

From the user manual for your amp - MRV-M500 ..........................60 amp fuse, 4AWG/21mm2
Sounds like you need a thicker power line as well. The amp is getting choked for power with half the recommended gauge wire.

[Fast4esT]

Remote wire should t have any effect on RCAs, most people run remote wire right along side them.
Are your ground and power wires the same gauge? Guessing they are.
Might be a good idea to run rca from the radio to the amp, then reuse factory door wiring.

[Droo]

Ok, I'm currently sitting in my car, regrounded the new amp, unscrewed mounting screws,uncoiled RCA's and with no luck. But I noticed that on full volume I can hear radio playing on different source (cd/tv)... Even with everything related to new sub/amp disconnected! Also the turn signal is heard in the original sub, maybe I just didn't notice since it's a lot less powerful than my new sub? Any ideas why this is happening now?..

[noldevin]

Again, your power line and probably ground line are too small for the current amp you're using, that can cause pretty strange things to happen.
However, if you can hear radio playing while you're set to cd/tv, that to me sounds like a problem with the head unit. That just simply shouldn't be possible.

[diagnosticator]

Ok, I'm currently sitting in my car, regrounded the new amp, unscrewed mounting screws,uncoiled RCA's and with no luck. But I noticed that on full volume I can hear radio playing on different source (cd/tv)... Even with everything related to new sub/amp disconnected! Also the turn signal is heard in the original sub, maybe I just didn't notice since it's a lot less powerful than my new sub? Any ideas why this is happening now?..

All the odd symptoms you described, are consistent with EMI getting into the low level audio signal. The amp itself is shielded against EMI internally, so the typical way EMI is able to get into the HU/Amp, is via unshielded low level audio signal wiring. Google "EMI filtering for car audio" or similar search terms.

[Gin+]

You could connect a separate source to the amp like an iPod/MP3 player to help isolate the issue.