Team-BHP - Honda Accord - Hissing Noise in Stock HU after adding an amp

Today I got a small upgrade for the music system in my Accord. I went to B&T and got it installed.

Stock headunit
Alpine Type R 6.5" Compos in the Front and 6x9s in the Back
Focal Solid 4 amp running of speaker level inputs

Now the Problem
At lower volumes, or in between songs there is a hissing noise. It is reasonably noticeable at lower volumes. Of course when the volume is raised you cant hear it at all, and it is inaudible when the system is off.

Now B&T thinks its coming from the HU but he is also trying to figure out what it is.

At first he told me a processor might help but later said if its from the HU the processor probably wont help.

Do you guys have any other suggestions? Help will be really appreciated since I have to figure out what is the next step to take.

And no im not going around B&Ts back, he suggested I put up a thread here :p

Akshay the problem could be with the hi to low converter.

2 things I would recommend.
1. Try changing Hi/low converter. I have faced problem coz of these in the past and I changed couple of them and rectified the problem.

2. I not sure if you using the high level input or rca input to the amp. I suggest you run the rca from one side of the car and power cables from the otherside to avoid the floor noise if that's the problem.

Quote:

Originally Posted by Invinsible (Post 2120124)

High level inputs are being used to run the amp.

Also this seems to be a very common problem with Honda/Acuras where ICE has been upgraded keeping the stock HU. Apparently one solution is to get the signal from the HU before the stock amp. Any idea how that would be done? Would that mean opening the HU and all?

1. Which source is giving this problem - CDs, FM, Aux-in? Or is the noise present from all sources?
2. Does your HU have Dolby (would have the symbol on the front plate)?
3. Does your HU have a mechanism for setting volume of individual source?

The problem is in the HU, and is most likely due to high gain inside the HU for the audio signal - as B&T said, an external processor will not make a difference unless it has a Dolby compander.

If nothing else works, the only solution is to change the resistor values in the LoC - reduce the signal going to the amp and turning up amp gain a little bit to compensate.

I would suggest you first flatten your eq bass treble loudness everything. Try different sources to see where it is most prominent.
Also try which pair of speakers its coming from. Only front then only back or all four. If you can get yourself a track that is blank. I.E. Does not have any sound and confirm with that for the presence of the sound. You can do this by using sound recorder on your comp and setting it to mic-in with nothing in the mic input or muting it. You could also ask B&T to try the amp somewhere else or try playing from an ipod into the amp. That's just to be sure the amp is not the culprit. And try moving the power wires away if possible.

Quote:

Originally Posted by DerAlte (Post 2120232)

1. Which source is giving this problem - CDs, FM, Aux-in? Or is the noise present from all sources?
2. Does your HU have Dolby (would have the symbol on the front plate)?
3. Does your HU have a mechanism for setting volume of individual source?
1 - All sources. 2 - Nope, only says premium audio system. 3 - Nope

The problem is in the HU, and is most likely due to high gain inside the HU for the audio signal - as B&T said, an external processor will not make a difference unless it has a Dolby compander.

If nothing else works, the only solution is to change the resistor values in the LoC - reduce the signal going to the amp and turning up amp gain a little bit to compensate.
But no LOC is being used now. The amp is running on High level inputs. Do you think using an LOC will help?

Answered above in bold.

Quote:

Originally Posted by valhallen.282 (Post 2120276)

The noise is present with the eq flat too. It is coming from all speakers. And I am sure of the sound since it can be heard clearly at low volumes and in between tracks. So its not a ground issue, or a wiring issue.

This is a problem with all Honda/Acura HUs. On the net some have suggested taking a pre out from the main circuit board will help.

Quote:

Originally Posted by valhallen.282 (Post 2120334)

Try a separate high low converter then. That seems to be the only other solution. Does it come even if the speakers are not connected through the amp?

Not tried that, but from other reports on the net it does come with aftermarket speakers even without an amp.

Ajay is also speaking to someone. Hopefully we will be able to come up with a solution for it.

Quote:

Originally Posted by akshay1234 (Post 2120083)

I can try that. But will using a line out converter or a processor help in any way?

Quote:

Originally Posted by akshay1234 (Post 2119573)

Focal Solid 4 amp running of speaker level inputs

Try a line level connector (and line level inputs) - some speaker level inputs are prone to a little hiss.

Quote:

Originally Posted by akshay1234 (Post 2120322)

This is a problem with all Honda/Acura HUs. On the net some have suggested taking a pre out from the main circuit board will help.

You need to reasonably skilled with a soldering iron to do that.

Quote:

Originally Posted by jkdas (Post 2120345)

Try disconnecting each speaker input on amp and see.I used to face this and I found if was from RCA. I troubleshooted by taking each RCA pin off from amp.

JK, right now there are no RCA connectors. The OEM HU's speaker level outputs are connected to the speaker level inputs on the amp.

Quote:

Originally Posted by navin (Post 2120373)

Try a line level connector (and line level inputs) - some speaker level inputs are prone to a little hiss.

You need to reasonably skilled with a soldering iron to do that.

JK, right now there are no RCA connectors. The OEM HU's speaker level outputs are connected to the speaker level inputs on the amp.

Yah Navin and hence I asked him to take out each speaker level input out and try (unscrew each).