Hi all:

I just installed a sony cdx-7705x cd/mp3 head unit in my 1998 e320. The oem stereo unit was a Becker 1692. The player works fine except for a nagging hissing sound present at every cd/mp3 song from beginning to end.

It's a consistent hissing sound during silent moments when the unit's playing cd/mp3 discs. I've tried to tone down all the sound properties, but i'm still getting the hissing noises. The noise is prevalent even if i turned down the volume knob to the lowest level possible.

I've connected the usual blk ground, red pwr, yellow ignition, and blue amp lead wires to the corresponding wires from the factory harness. The only wire that was different was the orange illumination wire from sony's unit. I connected this orange wire to the illumination wire from the factory wiring harness.

I'm fresh out of ideas on how to attack this problem.

Also, does anyone have a technical support number from Sony's car audio division?

Thanks very much,

Mars

I am beginning to suspect that this might be just a grounding issue, since the hissing noise is at a consistent loudness level regardless of stereo volume level.

Can anyone confirm my suspicions?


okay, feedback:

Redid the ground connection but the hissing sound still persists. I'm beginning to think that this might just be a limitation on the sony head unit.

I suspect your OEM amps.
How are you feeding them the signal?
RCA's or speaker wires.

If it was a grounding issue then the
pitch would varry according to engine speed.

Does it do it all the time?
Meaning: how is the FM/AM?

Blue normally is the remote turn on for the
amps,but sometimes it can also be for the
antenna trigger.

Yellow is for the clock and memory, yellow goes
to a constant 12 volt source.
Red goes to the ignition.

Louis.

Thank you for the help, Louis. The oem Becker 1692 unit powers the speakers internally, so there's no external amps. I wired the 8 speaker wires from the sony unit to the factory stereo harness directly (the harness has 8 speaker wires as well).

The hissing is very consistent, and it does not vary with engine speed. I'm beginning to wonder if this is due to the limitation of the sony's internal amp.

Maruzo.

This is a brand new radio/cd player with higher
power then the OEM head unit, so it should have
no problem driving the speakers.

Does it do it only while playing cd's/mp3's?
Or is the radio affected too.
If it only does it in cd mode then there is
an internal problem with the unit and you
need to bring it back.

Firstly hook the red wire to the ignition switch,
then hook the yellow wire somewhere where
it will get constant power(usually cigarette lighter
or the likes).
Undo the blue wire since you don't have any amps
it should not be connected to anything,unless you
are using it to trigger the power antenna.(but there
should be a wire for that)

Also on the mb's the ground wire is brown.
But I would look for a better ground(a screw
in the chassis).



Louis.

Hi Louis:

The sony unit has a blue antenna wire, a blue amp wire, and an orange illumination wire. I was under the impression that I should connect sony's blue amp lead wire to the antenna turn on wire in to oem harness.

It was the only way my sony unit would give out sound.

The hissing is present when i play cd/mp3, turn on the tuner, and even when i switched to aux input. It's a constant low volume hissing noise. I can't hear it when i turn up the volume. The music would drone out the hissing.

It's almost like the sound a tape player makes when you're playing a tape without activating the dolby settings.

I'll try disconnecting the amp lead wire and see what happens.

I have a strong suspicion that you have an amp in the trunk. We had exactly the same issue with our C280. The hiss was due to the mismatch from the new radio and the amp. You can apparently buy a couple of line level converter modules, and adjust this and that, but here is what I did:

http://www.luddite.net/c280/radio.htm

First thing to do is look for the amp, or at least for the fuse in the fuse box for it. A good sign to me that you have an amp is that you got *no* sound without the blue (remote) wire connected.

-Tad

Hi Nazrat:

Thank you so much for the article. It was a very good read. I'm not sure i'm electronically savvy enough to handle the work you described.

Btw, what year is your C280? Is your oem head unit a Becker 1692? Does your car also come with cd changer wires already in the left rear trunk space?

I've found that when I adjusted the mid db adjustment on the sony unit down from +4 to 0, majority of the hissing went away. This feature was available on the Sony CDX-R3300, but not on the CDX-7705X. I've reconnected the wires again between the sony unit and the oem wire harness, and the hissing seems to have decreased a bit.

I get excellent volume even at 1/4 of the volume level. Playing a club mix tune at 1/3 level was almost like being at the center of a nite club with full volume blaring at me.

You might be right, I suppose the effects of double-amplification is causing the hissing as well as the abnormal and excessive amounts of volume from this unit.

If I just connect the 8 speaker wires from the sony unit directly to the speaker wire inputs that goes into the factory amp, will that solve the hissing problems?

Your article points out the necessity of wiring resistors between the sony speaker output wires to the factory speaker wires. What will happen if I skip this step? Will I incure amp damage to the sony unit immediately?

The work on this resistor mod will probably fry my brain before i accidentally fry the entire car. LOL

I'm also thinking about an alternative: Putting the becker 1692 back and just replace the old oem 6 disc changer. Scott from La Jolla Stereo was kind enough to point me in the right direction. With the replacement of the oem changer to an alpine 634 CDC mp3 changer, I should have the functionality of the oem hu with an added cd and mp3 features.

Which head unit did you install on your c280?

From your earlier posts, I gather that the trunk CD changer is dead, so probably not connected to the new Sony at all? But what isn't clear is whether there is an external amplifier involved here as well? Could you clear us up on this point. If the Becker 1692 had leads into an external amp, then they would have been low-level inputs, and the wiring to the speakers would go from the external amp directly. Is there a chance you have connected the low-level inputs to the external amp to the (high level) speaker leads from the Sony? That will do really interesting things to your amp, if there is one!

__________________
1986 560SL
2002 Toyota Camry
1993 Lexus

Sure you are. If you can solder, or have a friend who can, this is really easy. You connect the radio to the resistors to the speakers and back to the radio.

It is a 1995. It did not come with the CD Changer, but that was an option.

Yup, that sounds like what we had with the stock amp in place. If your head unit has pre-amp outputs, you can run those to the stock amp. You won't have any more hiss, but you won't get much volume either.

Yes, but if your radio's internal amp won't handle the 2ohm load (and I haven't seen one that will) - the amp in the radio will live a short life.

See above.

We chose a Clarion that has mp3 capability. My wife loves being able to have all of the CDs that she normally listens to on one CD(rom).

-Tad

Hi Don:

I'll open up the trunk mats and see if i can find this elusive oem amp. I'm beginning to believe it does exist. Will report back as soon as i get my hands on it.

Here's a diagram of the becker connections:


I connected the 8 speaker wires from sony's harness directly to the 8 speaker connections on the becker harness. The sound came in when I connected sony's amp lead to the becker's antenna lead. Not sure at all if i've connected low-level inputs to high level leads.

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here's the bottom of the diagram:

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Hi Tad:

Thanks for the help! It will take me some time to divulge all the information you've graciously contributed. I'm now armed to the hilt with advanced means to tackle this "hissing" enemy. :p

Speaking of tackling one's enemies, has anyone seen The Last Samurai? I stayed til 2am last night to finish the movie. It's pretty good!


Anyway, i'd like to study up on your method of wiring the resistors in parallel to remove the hissing. Sounds like fun.


No seriously. Should I connect aftermarket's speaker wire to one end of the 2 resistors, and then connect the other end of these 2 resistors to the factory speaker leads from the oem harness? If that's the general idea, how should I connect these 2 resistors side by side?

Thanks again, Tad. I'll report back when I've gathered enough nerve to go thru with this exercise.

Mars

I've taken some picture of the factory amp residing above the left rear panel. It has more wires than i care to decipher. There's a 20amp fuse connected to the amp, and about 13~14 twisted wires going into the amp connector. But the connector itself has 20 pins.

Anyway, just thought i'd post it so everyone can see what it looks like. I'm still not too sure how to go about running resistors in parallel to create same volume for both front and rear sets of speakers, and to bring the speaker ohm readings to within aftermarket's amp's acceptable levels.

So if anyone figures out a way to run wires directly from the aftermarket hu's lines to the amp connectors, please kindly share your thoughts. Even though i might have to bring the hu's wires from the dash all the way to the back of the car, it might just be worth it to avoid causing any permanent damage to the speaker/ amps/ whatnots.

I did the same thing on a 1990 560sel by running the aftermarket hu's speaker wires directly into the rear factory amp's connectors. The sound was perfect. No hissing whatsoever. I'm wondering if i can do the same thing on this newer bose amp.

Any ideas?

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Update:

Installed a PAC OEM-2 Universal Interface High-Low input filter and removed the hissing completely.