[DerAlte]

Which HU?

Quite likely the gains are set too high at the amp. Re-tune your system with the HU volume set at ~ 40% OR set amp gain mid-way and see at what HU volume do you get decent output. When the amp gain is correctly set, you shouldn't be able to hear the noise.

[CrackedHead]

@DerAlte - the HU is a pioneer 7950UB. I tried with the gains turned all the way down and at 50 % - but I can still hear noise if I turn the HU volume high enough.

(noise is only audible when there's no music playing)

[navin]

Originally Posted by DerAlte

Usually there are 2 sources of 'buzz' from a speaker

Originally Posted by tsk13

The buzz is from Rear speakers. Front speakers are running from HU and rear from Amplifier. The wiring for sub is JBL and rest it's either Chinese or the ones supplied with speaker.

Tsk is it a buzz or a hiss? Is it continous or only when the speaker is playing loud?

[DerAlte]

Originally Posted by CrackedHead

... but I can still hear noise if I turn the HU volume high enough. ...

Of course you will hear the hiss when you turn up the HU volume with no music playing. Noise is omnipresent (in your case the source is quite likely HU grounding, wither inside or outside), and when you turn up the volume the noise voltage is more (the % still stays the same, but the amp does not care about %, only the voltage of a signal). Also, probably you listen to music pretty loud (volume kept high) for you to have observed the noise during silence.

Are you able to notice the noise when you mute the HU (even if the gain is set high on the amp)?

Gain tuning is about getting that point right at which the HU is giving sufficient signal to the amp so that the noise will be an insignificant voltage, hence inaudible. HUs which put out a higher voltage at Pre-out, like 4V or more, are less likely to face this problem than the ones that put out 2V.

[sudharma]

Originally Posted by DerAlte

Of course you will hear the hiss when you turn up the HU volume with no music playing. Noise is omnipresent (in your case the source is quite likely HU grounding, wither inside or outside), and when you turn up the volume the noise voltage is more (the % still stays the same, but the amp does not care about %, only the voltage of a signal). Also, probably you listen to music pretty loud (volume kept high) for you to have observed the noise during silence.

Are you able to notice the noise when you mute the HU (even if the gain is set high on the amp)?

Gain tuning is about getting that point right at which the HU is giving sufficient signal to the amp so that the noise will be an insignificant voltage, hence inaudible. HUs which put out a higher voltage at Pre-out, like 4V or more, are less likely to face this problem than the ones that put out 2V.

Recently I replaced my old Pioneer KEH-P6025 stereo player with a Pioneer DEH-8650MP unit. With KEH-6025 the rear speakers were driven by Sony X-Plode Amp. the sound quality was fine. After replacing the HU with the 8650 unit and connecting the RCA out put of the HU to the AMP as done before It was noticed that when the Engine is running a very loud Motor Boating noise coming from the rear speakers. When the engine is "Switched Off" the noise stops and the sound quality is very good. Alls fine if I connect the rear speakers to the Rear Speaker connection of the HU. So I am now using the unit without the AMP. How to rectify this. Also the front panel won't "Open" or "Close". Every thing else works ok. For the time being I have hot wired the front panel ejector motor to open and close the panel.

Any suggestion to rectiify these problems is much appreciated.

[navin]

Lets get this straight.
1. 6025 + Xplod amp is fine
2. 8650 HU also is fine
3. 8650 + Xplod amp gives motorboating sound.

Is the 8650 new? Can you get it checked? Have you connected all power cables including ground and remote?

[sudharma]

Originally Posted by navin

Lets get this straight.
1. 6025 + Xplod amp is fine
2. 8650 HU also is fine
3. 8650 + Xplod amp gives motorboating sound.

Is the 8650 new? Can you get it checked? Have you connected all power cables including ground and remote?

The 8650 is not new. All cables were connected.
When the rear speakers are connected to the 8650 directly alls fine. No motor boating.
Remote is connected to the Xplode otherwise it won't powerup.
The motor boating starts only when you start the engine, otherwise all fine. I even grounded RCA cables individually without any effect.

[navin]

Originally Posted by sudharma

The motor boating starts only when you start the engine, otherwise all fine. I even grounded RCA cables individually without any effect.

somehow the 8650 is letting the ignition noise thorugh. get it checked.