AUX Problem.

[Frank]

This is one of those 'for information' sort of posts.

If you've ever plugged in your MP3 player/iPod/tablet, etc. into the Aux socket and wondered why the sound is a lot quieter than when using the CD or radio, then you are not alone. It's a problem that is found on BMW, Mercedes, Range Rover and many, many other cars. You also find it with the Connects2 adapter, which taps into the CD changer feed.

Here's the dull stuff - Aux is the abbreviation for Auxiliary Line In and that's what the car audio manufacturers put in. Trouble is, in the car, you haven't got a Line Out to feed into it (unless you've dragged your home HiFi into the car), what you have are headphone outlets/sockets, which are not the same. There is an impedance mismatch (just means the headphone line doesn't provide enough power to do the job) and that's why it's quiet, compared to the built-in CD, etc.

Just to complicate things further, not every device suffers from this problem and some can give pretty good performance when using their headphone sockets and, oddly, this seems unrelated to the price. However, if you have this problem then, obviously, you can turn the device volume right up and the car audio volume up to compensate (great fun when you forget and switch to the CD player!) but that will result in distortion and hiss.

The solution is an active (requires power) preamp between the device headphone out and the audio Aux or, better still, a passive preamp that requires no power at all and just plugs in between the two. Quite why car companies like the above didn't shell out an extra £3 in parts and had one built into their £1,000+ audio systems from the start, is anyone's guess. Bizarre.

 

[Frank]

Just an update on this one - all sorted. (no idea why this problem is all over the Net as it's pretty easy to solve.)

Usually, you have Line Level > Amp > Speaker Level and would only use a pre amp for something like a mic, i.e. Mic > Mic Pre-Amp > Line Level > Amp > Speaker Level, but finding the right pre-amp looked to be tricky for this.

There's a company in America (I never buy outside the UK) that does a passive preamp for exactly this ICE problem, but with the postage is over £31. HiFi companies make preamps, but all are well over £100!

The answer is to use one of the many purpose made headphone speakers for this. By definition, they have an amp to power the speaker, but because the speaker is pretty small, then so is the amp and so can be turned into a preamp for the Aux input. You just replace the speaker with a panel 3.5 mm stereo socket (making sure you take off from the stereo connections on the amp) and you're done - you might have to, depending on which speaker you use, trim the gain to ensure you don't over signal the Aux feed. They even supply a charging lead to plug into the device micro/miniUSB, so that you can charge this up at the same time as you charge the device.

Total cost - £7.

Made one for a mate and it works fine. When the bits arrive I'm going to make one for myself (my tablet headphone output is a bit below par - a MP3 needs to be set at 25 to give the same volume as a CD set at 10!). Worth doing as it means you can leave both your device and car audio settings where you would normally have them, plus you can now hear the stuff far more cleanly/loud/hiss less, etc.

 

[Frank]

[post]346694[/post]Made one for a mate and it works fine. When the bits arrive I'm going to make one for myself (my tablet headphone output is a bit below par - a MP3 needs to be set at 25 to give the same volume as a CD set at 10!). Worth doing as it means you can leave both your device and car audio settings where you would normally have them, plus you can now hear the stuff far more cleanly/loud/hiss less, etc.

I was doing some pics of other things today, so did this as well -

PreAmp

• Frank
• May 21, 2016

Aux In Pre Amp

On the left is the original speaker, which can open up with that bellows design for better bass and on the right is my converted Aux In Pre Amp.

You just remove the speaker and replace with a 3.5mm jack socket and take the left/right signals (which the original merges for mono) and wire it up and the 2 level amp in it does the rest. Volumes from tablets/mp3 players, etc now match or exceed what you get from the built-in CD player and, of course, all without any hiss or distortion at high volume. You notice this clean signal most clearly on things like films, audiobooks or Gregorian chants and stuff, but also on the much louder/bassier stuff.

 

[moondustka]

I need this for my Leon! The volume isn't a problem. What is a problem is the buzzing and hissing and it's very annoying.

Might give this a go

 

[lusid666]

you could build 2 of these, 1 for each side of the stereo signal, should have the same effect and work out a lot cheaper.

http://hackaweek.com/hacks/?p=327

 

[Frank]

[post]352259[/post]
I need this for my Leon! The volume isn't a problem. What is a problem is the buzzing and hissing and it's very annoying.

Hi Ben,

Yeah, most decent ICE systems will be able to bring the volume right up, whatever the input, the problem is that if the input is small then the signal to noise ratio goes through the roof. As it seems like you've found.

[post]352281[/post] you could build 2 of these, 1 for each side of the stereo signal, should have the same effect and work out a lot cheaper.

Cheaper than £7 in total?

You don't need 2 of them, the jack plug input is already in stereo, you just take off from the right pins.

 

[lusid666]

The circuit in it the link is only a single channel amp so you would need 2 and you should be able to buy all the components for £2-£3. It all depends on your electronics skill level as yo weather you could build it or not. I would probably add another resister on the positive power line and run it from the switched live from the car

Just ebayed the parts and the components work out to 11p

 

[Frank]

[post]352286[/post] buy all the components for £2-£3

Good luck with your project. Be sure to post back and let us know how you got on.