no_clue

I upgrade my head unit, and now all speakers create hissing sound. ( it is low level hissing BETWEEN songs )

Hissing noise is constant regardless the speed I drive, or volume I adjust from the head unit. *** To be honest, I can only hear it at night or when car is NOT moving***

Bring the car to Tweeters, VA (professional Auto shop) and Bestbuy, VA, tech guy all said that's normal!!!!

Crutchfield also replace another brand new head unit, because I complain about it.

I put my old Becker in and there is no hissing at all...needless to say, Amp is working fine, as well as all speakers.

Well... what do you guys think? What's the lease expensive alternative? Noise filter? New Amp? New Speakers? (please bare in mind, I usually have volume set at the lowest. I don't blast music... I usually listen to nice'n'easy )


Does anyone know the schematic diagram of 97 E-class Bose amp?

battlecat714

are these stock speakers?

no_clue

Everything stock~ "except" new head unit.

MagicO309D

What model/year car? Do you have Bose or HK system? More information is needed to help.

battlecat714

I'm probably sure you already know that a good HU unit should be accompanied by good aftermarket speakers...for best sound quality

no_clue

97 E420 Stock Bose set up.
The point is..... these pro said it is "normal"?!

MagicO309D

Now we may be on to something! I believe that Bose uses much lower line-input voltages in their Spec. than than normal practice. 500mv instead of 1v peak to peak. This was true during Bose's early years and it could still be true for your '97 too. The net effect would be to boost the noise floor of your headunit's output (as well as overdriving the Bose amps at higher volume levels). Is there a line-out gain adjustment on your headunit? If so, try reducing it as much as possible. If not, maybe your local shop can install a simple voltage divider in-line with each line-out output of your headunit.

If this is not possible, they may suggest replacing the Bose amp with one matched to your new headunit.

If you reach this stage, listen to your system for a while to see how you like it. If you think the sound is "off" a bit, post again and I can offer some additional pointers.

no_clue

I think you know what you are talking about
I did noticed I can only turn my new head unit volume to around 5 before feeling discomfortably loud for my taste
(Max is 66)

I installed my own head unit, because Blaupunkt Key West MP36 is direct plug and play. (no hardware adaptor needed, the schematic is identical even the "speed sensing volume" can be actived and adjusted)

There is no "line-out" control of any kind in the menu, except Bass, Treble, Middle, X-bass.
If I turned all the selection back down, I can still hear some hissing when at night or car is not moving.

I like to do all the "improvement" myself. (I am cheap) But what's the easiest way to do? I am not very comfortable to get into my trunk, yet.

I know how to remove Bose Amp, but the wires....... they just scare me.


BTW, do you know the schematic diagram of the connector?

MagicO309D

I don't have any wiring diagrams but since your system basically works, you should be able to work off of the diagram that came with your headunit, at least for the headunit output connections. Since it appears that Bose hasn't changed their specs for so long, I'm now wondering if anyone makes a Bose attenuation adaptor with built-in voltage dividers that would simply plug in-line with your headunit's output connector. Have you contacted Blaupunkt or done a Google search yet? A big outfit like Crutchfield may also be able to help.

If so, the Bose amp and speakers, let alone those used for MB, are really quite good so it would be worth trying to preserve them if you can. Otherwise, I'd leave the amp conversion to a good shop, not a big-box retailer!

no_clue

PROBLEM SOLVED.

New After-Market HU push too much output when cross w/ Bose amp, it creat noise.

I got a PAC OEM-2, Hi-Low Level Convertor, and now everything is perfect!!!!!!!!!!!!!!!!!!!!!!!

No hissing.... even I put my head next to the speakers!!!