242 limited s wiring/ Polk pa450um

[MattFX4]

ok, so as some may know I'm in process of installing new stereo but have run in to an issue. Have the jlmx650's in, and the JL m800 amp in and it sounds great, but when I turn volume down I hear a whining hissing sound. Few thoughts I have that may be causing issue.

1. I looked today and I have the amp wired directly to the house battery positive and negative terminals. There is nothing else wired to the negative terminal on the house battery except for my onboard charger, and the jumper wire running to the starting battery. I'm pretty sure I need to move the HU ground over to the house battery ground along with the amp right? Does anyone known which negative wire is the HU ground? There are several connected to start battery.

2. Amp has not need properly tuned yet. I turned the gain up on all channels until I heard music coming from speakers. When I get time I'm going to tune it properly with a voltmeter and test file from JL to their specs. Maybe this is causing the noise?

3. Polk pa450um HU. Could the HU be causing the noise? Is the Polk HU a quality HU? Or is it crap?

 

[Mainah]

I get hissing when using Bluetooth. Polk seems to have used (like many) a not so good Bluetooth chipset in the HU. Don't get me started on Bluetooth chipsets but lets just say some have a quality onboard miniature mofset amp and are really good (not what polk used). Try using the usb or aux in and see if you get the same (resolved it for me).

Tuning will help some as well. You may consider connecting your +12vdc main to the battery switch instead of the post. Won't make a difference with the hissing but just some extra insurance. If you are getting ground loop whinning (not hissing) reground the HU to your amp ground block to ensure the same path to ground.

 

[MattFX4]

Ok plan to tune amp and move power wires to same battery this week sometime. I tried to connect power wire to switch, but the ring terminal I used is too small. Will have to get a larger diameter one and switch it out. Oh, I'm experiencing the noise on Xm, usb, and FM also. I'll look at it more in depth this week.

 

[Derek Fosbury]

I think the tuning will do it for you. I had a similar problem with my last setup in my AR210; the issue was the gain being set too high. I followed the tuning procedure recommended by JL (http://mediacdn.jlaudio.com/media/mfg/9013/media_document/dev_1/gainSetting_07_14.pdf?1404960578), and the issue was corrected.

 

[MattFX4]

Thanks @Derek Fosbury. When I get time I plan to use voltmeter and tune per JL instructions to 17.3 per channel. Hope that will fix the issue.

 

[OperationROL]

81% sure gains are too high.

 

[MattFX4]

I tuned amp today, and still have a few issues.

1. I hear a white noise sound from speakers when volume is very low. Different sound from issue # 3 below. When music is up, it is not noticeable.

2. When volume is all the way down to 0, I still hear music coming from the speakers. It is very faint, but I can hear it.

3. I hear an actual high pitch crackling sound coming from the amp itself when I am down under in the helm compartment. It come's and go's and is not constant. It sounds very similar to the buzzing sound I hear from the speakers from time to time when volume is very low. I made a video of sound below.

http://youtu.be/1pS78YCk-II

 

[Mainah]

That sound from the video is not normal. That sound is the amplification switch in the amp which cycles at a high rate. Assuming all of the input wiring is right and the channel combine switches are set correctly it could be a bad pwm, bad switch transistor, or loose part in the housing (all in the amp). If the input wiring is right I would seek to get a replacement on the amp.

You may want to check for anything touching the rca inputs and outputs on both the amp and head unit. Also check that nothing is touching the metal part of the rca wire connections. My over the internet best guess is that you have a bad amp.

 

[Derek Fosbury]

definitely not normal in my experience. sounds like a bad power supply. would get it checked out. even just show your dealer this video!

 

[MattFX4]

Yeah not sure. Power wires run straight to distribution blocks from battery and in to amp. Rca outputs from head unit and input to amp aren't touching anything. Set gain using JL test tone to 17.3 volts on each channel per JL instructions.

 

[Mainah]

Everthing looks correct. I assume low cuurent setting is for 12vdc and the high for 24vdc for your amp. If so then either the switching power supply for the pwm controllers and main board or one of the switching mofset transitor blocks are making that noise. While the switching is normal hearing it through the chassis of the amp like that is not and may also be the cause of the other issues you have mentioned.

Keep in mind that even with a properly functioning class d amp you may have some "static" from the speakers that will correlate to input, amount of gain, and the quality of the amp components.

 

[MattFX4]

Thanks. Waiting to hear back from Odin at Earmark. It sounds incredible when turned up. Just annoying I'm experiencing the issues mentioned above.

 

[David Analog]

This is really getting off course.
The Low/High Input Voltage is based on the specific output voltage of the source unit. This allows the amplifier input gains to function at the correct sensitivity and in a more linear manner.
The pulse width power supply switches at a frequency ten times higher than what a human can hear.
You should get zero static from a Class D amplifier.
a) Hearing some audio at zero gain is a strong indication that something is very wrong.
b) Certainly amplifier hiss can be present with your ear directly to the speaker at a low gain level. Much more than that is an indication of a problem. a) & b) sound related.

I would be patient and wait for Odin's response. He's steppin' and fetchin' this time year but has always got back to me the same day or within 24 hours. Just follow his advice and it will be right.

 

[MattFX4]

That sound from the video is not normal. That sound is the amplification switch in the amp which cycles at a high rate. Assuming all of the input wiring is right and the channel combine switches are set correctly it could be a bad pwm, bad switch transistor, or loose part in the housing (all in the amp). If the input wiring is right I would seek to get a replacement on the amp.

You may want to check for anything touching the rca inputs and outputs on both the amp and head unit. Also check that nothing is touching the metal part of the rca wire connections. My over the internet best guess is that you have a bad amp.

definitely not normal in my experience. sounds like a bad power supply. would get it checked out. even just show your dealer this video!

Wanted to give you guys an update. Sent amp back to Odin at Earmark and he tested the amp on their bench. Amp made same noise there, so indeed it was a bad amp. Odin said this is the first he had ever seen do this. Just my luck right! Anyways kudos to Odin @Earmark Marine. He sent me a new amp which I installed today and no more noise!