[ujjwaana]

I would be amazed if people say that there wont be hiss/Humm is external AMP is fed with the Speaker line output from the HU, instead of low noise Pre-out.
Controlling noise/hiss/hums are very difficult with power amps than in pre amps, the higher SNR is live example of it.
Powering a premium driver setup like Focal AMP and Infinity speakers is undone if powered from Speaker out of HU.
It is great that significant improvements were made buy proper wiring (which used to be THE critical item when I used to make 3055 based Deck Amp as DIY in school), I still believe some SQ is lost when the Power Amp is fed from Speaker line of HU.

Intermediate driver stage after pre-amp are different design challenge than the final stage Power AMP, where designers don't care about low lever noise/band cut outs, which become significant if same signal is fed to another Amp as Pre.

[Obi-Wan]

I got my ICE updated yesterday in Hyderabad by the renowned ICE installer Mr. Shakir. Everything went smooth with the install, settings etc. However, the front speakers were giving a hissing noise only when the brakes were being applied. When I removed my foot from the brake pedal there was no noise. This only happened with the regular B from the ABC lot and not the handbrake.

So, when we started troubleshooting we were able to narrow down to the RCA cable that connects the HU front speaker ports to the Amp. RCA cables used to connect the Amp were Monster Interlink 101XLNs. The noise became unbearable when we tested with RCA cable that came with the AIV Amp kit. Then Shakir installed a local Ground Loop Isolator near the Amp and the hissing noise has gone away completely. He mentioned that this is an issue with entry level Amplifiers and especially JBL’s. I am happy with the result but I would really appreciate if anyone can help me with the below queries.

1) Why is there a hissing noise only while braking? Is there a bigger underlying issue the installer has missed?
2) Do I need to go for a more expensive RCA cable? But the noise is only during braking and it’s fine during the other times.
3) Do I upgrade to a better amplifier?
4) Will there be any issues in the future if the Ground Loop Isolator is used for a long time?
5) Are there any good quality brands of Ground Loop Isolators available in India?

Below is my ICE setup
Front: Focal 165 AS Components
Rear: Focal 165 AC Coaxials
Amplifier: JBL - GX-A644SI 4 Channel
Subwoofer: Infinity REF 1200S Shallow Mount
RCA: Monster Interlink 101XLN
Amp Kit: AIV 8 Ga (ACS-10)

Sorry about the long post!

[Obi-Wan]

Sorry for posting my query in an old Thread! I would request the moderators to delete my earlier post from this thread. I have raised a query in the right thread.

[venki7744]

Originally Posted by Obi-Wan

I got my ICE updated yesterday in Hyderabad by the renowned ICE installer Mr. Shakir. Everything went smooth with the install, settings etc. However, the front speakers were giving a hissing noise only when the brakes were being applied. When I removed my foot from the brake pedal there was no noise. This only happened with the regular B from the ABC lot and not the handbrake.

IMO ground loop could be caused due to the following:
* Weak Ground Connection - Get a beefier ground cable, find a suitable place where their is enough metal to make a solid contact, peel off the paint around that area (sand it/use wire brush), secure it with a good nut and bolt/rivet nut.
* Amp body touching metal (car body) - The solution is to place the amp in an amp rack made of wood (MDF/Plywood) and screw the amp rack to the body.

Just my .02 cents,
Venki

[Obi-Wan]

Thanks for the reply Venki.

1) But what I do not understand is why isn't there a hissing noise all the time? Why only during braking?

2) Also, the Amp is fixed on a plywood plank. As mentioned by the installer, do entry level amp's do this?

[soumen.blore]

Originally Posted by Obi-Wan

Thanks for the reply Venki.

1) But what I do not understand is why isn't there a hissing noise all the time? Why only during braking?

2) Also, the Amp is fixed on a plywood plank. As mentioned by the installer, do entry level amp's do this?

Do you have a hi lo converter , in my case that stopped the sound.

[Obi-Wan]

I thought a hi lo converter was only used when an amplifier is added to the factory fitted HU. So, I didn't add that because my HU is Alpine IDA X305.

Do I need to add a converter? Please advise.

[venki7744]

Hi Obi-Wan,

Please find my replies inline.

Originally Posted by Obi-Wan

Thanks for the reply Venki.

1) But what I do not understand is why isn't there a hissing noise all the time? Why only during braking?

Venki>> Can you try braking while the RCAs are not connected to the amp. If it still makes sound, it something to do with the amp (may be bad ground) else I think its something to do with your HU or RCAs.

2) Also, the Amp is fixed on a plywood plank. As mentioned by the installer, do entry level amp's do this?
Venki >> I think this is because some of the entry level amps has its ground connected to the amp body.

Cheers,
Venki