Curing Audio Buzzing ?

championc · 10-09-2014 11:18pm #1

Hi all,

I'm stuck and need advice please.

I am attempting to install a CarPC (running Ride Runner) on an old Atom Thin Client PC (Dell FX160), with an SSD. I took out the factory Bimmer HU and got a mini 12v AMP on eBay, which has a 3.5mm and RCA inputs and the speakers are connected into the clips

.
I have removed the PSU from the PC and connected 12v straight onto the motherboard connection.
image?p=953&i=6

If I connect earphones to the PC or if I connect my Android phone to the Amp Input, in both instances, everything is squeaky clean. However, if I interconnect the PC to the Amp over 3.5mm, with the keyswitch on but the engine off, I get a gentle tumping sound about once every two seconds. With the engine running, the buzzing then starts up. Music generally starts to drown it out but I issue will be if I use the car but decide not to have any audio running.

Both devices are running off the same power source, which was a tap off the Cigarette Lighter. So really, the noise only comes when both devices are interconnected. I have a Ground Loop isolator which helped slightly but I'm at a loss to understand the source of the noise, particularly when the ignition is on but with the engine not running.

Eric Cartman · 14-09-2014 8:57pm

no. 1 - get yourself a propper car power supply from mp3car.com or similar, a car alternator puts out about 14 volts and can fluctuate a little, there are special regulated 12v power supplies that could stop your motherboard getting fried.

secondly, what you need is a ground loop isolator
http://www.ebay.ie/itm/Ground-Loop-Isolator-Hum-Filter-DJ-PA-Laptop-Car-Audio-01187-/191321894447?pt=UK_Sound_Vision_Cables_Leads_Connectors&hash=item2c8bac6e2f

two pieces of audio equipment with the same power supply that isnt cleaned can start using the ground terminal of the audio cable as their electrical ground because of lower resistance. This device stops that happening.

championc · 14-09-2014 10:08pm

Eric Cartman wrote: »

no. 1 - get yourself a propper car power supply from mp3car.com or similar, a car alternator puts out about 14 volts and can fluctuate a little, there are special regulated 12v power supplies that could stop your motherboard getting fried.

secondly, what you need is a ground loop isolator
http://www.ebay.ie/itm/Ground-Loop-Isolator-Hum-Filter-DJ-PA-Laptop-Car-Audio-01187-/191321894447?pt=UK_Sound_Vision_Cables_Leads_Connectors&hash=item2c8bac6e2f

two pieces of audio equipment with the same power supply that isnt cleaned can start using the ground terminal of the audio cable as their electrical ground because of lower resistance. This device stops that happening.

Many thanks for the reply

Unfortunately I have both (sort of). I have a DC-DC step down converter which gives me a steady 12v input for the PC like this

I then have a Ground Loop Isolator like this
lrgBumper%20Ground%20Loop%20Isolator2.jpg

The one thing I have noted is that the buzzing is the same with or without the ground loop isolator connected. Any thoughts ?

Eric Cartman · 14-09-2014 10:39pm

get an ipod or some similar mp3 player that you have a car charger for (you could even borrow one) , connect the car charger and try play music through the amp with it connected. This will tell you if the amp is trying to ground through the audio jack or if the cable may not be grounding correctly, you wont hear the hum unless the charger is plugged in.

If you get the hum while this is connected , its an issue with the amp. At that point try get a big brand (kenwood, pioneer, alpine, clarion, rockford fosgate, etc...) car amplifier off donedeal.

if the hum doesnt come through with this setup then it may be a poorly designed soundcard in the car pc. A USB soundcard should be under 15 euro off ebay and would probably solve it.

some amps on donedeal : http://cars.donedeal.ie/caraccessories-for-sale/various-car-amps-2-and-4-channel/7332151

championc · 14-09-2014 11:42pm

Thanks again.

Sound is clear when the earphone port of my android phone is connected to the amp. It then gets buzzing when my phone is connected to a car charger.

Eric Cartman · 15-09-2014 12:15pm

championc wrote: »

Thanks again.

Sound is clear when the earphone port of my android phone is connected to the amp. It then gets buzzing when my phone is connected to a car charger.

Amp isnt grounding properly , drill a small hole in the metal casing of the amp and connect another ground wire to that hole, see if it stops. Personally id reccomend getting a big brand 4 channel amp though,

championc · 15-09-2014 9:35pm

Eric Cartman wrote: »

Amp isnt grounding properly , drill a small hole in the metal casing of the amp and connect another ground wire to that hole, see if it stops. Personally id reccomend getting a big brand 4 channel amp though,

Oh god, give me patience !!

I connected a length of good quality multistrand copper hi-fi speaker wire to the cars' frame. I then connected a hoop type connector on the other end, took a screw out of the amp, passed the screw through the connector and re-screwed it back into the amp body. On the Amp power connector, I then disconnected the -12v connection.

Arrrrrgh, the noise. I disconnected the new "earth" and reconnected the old one and bliss once again (with the engine off).

I'm so stumped, I really don't know where to turn next

TherapyBoy · 15-09-2014 10:35pm

If you're getting interference;

You have an earthing problem
Or
Your amplifier is picking up signal noise from somewhere.

If you are getting clean sound when using headphones from PC & when MP3 player is plugged into your amp then best guess would be your PC is picking up signal noise from the car somewhere & transmitting it to the amplifier. Or possibly it's being picked up in the wiring between the PC & amplifier. Is the wiring shielded & insulated properly? Is there any wiring crossing, interference can be transferred through insulation when wiring is run across each other or even close to each other.

Diagnosing unwanted signal noise in a car audio system can be very tricky & fixing the problem can be hit or miss. Start at one end & work through the system, eliminating each component as the problem as you go. There is generally no easy do-this-and-your-problem-is-solved solution, but I think the problem is from the PC, its internal wiring/layout etc is just not designed for use in a car & is picking up signal noise from somewhere.

Just best guess though! :pac:

championc · 15-09-2014 10:54pm

Hi @TherapyBoy,

Can you please re-advise based on my last posting. I have simply tested the Amp ONLY - standalone !!

So in short, the car body is providing massive electrical interference (certainly seems to pick up interference from the fuel pump priming) but yet the earth of the cigar lighter appears "clean".

But when the engine runs, both are horrendous - mainly alternator whine

TherapyBoy · 16-09-2014 2:14am

Then the problem is either in the amplifier or in the wiring to the amplifier.

Firstly, wiring. What way is the amplifier wired? Where are the 12v live & switch running from? What type of wire are you using, where did you get it? Are the wires lying across each other or other wiring in the car anywhere? Are the input cables to the amplifier lying near or crossing any other wiring?

Second, your amplifier. I see you got the amp from eBay, is it designed for use in a car in the manner you wish to use it? A proper high-power automotive amplifier with dedicated seperate power/switch/earth inputs designed for use in a car by a known brand like JBL would probably be a better option.

championc · 16-09-2014 9:12am

TherapyBoy wrote: »

Firstly, wiring. What way is the amplifier wired? Where are the 12v live & switch running from? What type of wire are you using, where did you get it? Are the wires lying across each other or other wiring in the car anywhere? Are the input cables to the amplifier lying near or crossing any other wiring?

The amp is tapped off the cigarette lighter socket since that cable is quite a heavy duty cable (for both the - and the + 12v). I have used 3g 0.75mm2 electrical cable from a standard electrical kettle lead. All the wires are in a mish mash in the front console, so all wires are on top of each other ............ however, this is the setup when everything is clear with the engine off

TherapyBoy wrote: »

Second, your amplifier. I see you got the amp from eBay, is it designed for use in a car in the manner you wish to use it? A proper high-power automotive amplifier with dedicated seperate power/switch/earth inputs designed for use in a car by a known brand like JBL would probably be a better option.

The amp I bought is for a car / caravan. I can only assume it's somewhat OK based on the connectors it's made with. I'm using the 3.5mm input and using the speakers as output - simple as that.

So with the Amp connected to nothing, I suppose my goal is to get rid of alternator noise initially and if I can do this, maybe I'll solve everything else.

TherapyBoy · 16-09-2014 9:37am

If the engine is off you won't get interference from the alternator.

The power system that came with the amp, did it have a 3 pin plug with a transformer on it? I've never seen an automotive amplifier with a power input like that, it looks more like a small PA amp or something.

I suspect the interference is being picked up through your wiring (the power side, not 3.5mm input or speakers). Disconnect & rewire it more carefully, try coming directly from a live at the fusebox (and put a separate fuse on it) and earth directly to the body of the car. There should be earth straps to the car body near the fusebox. Keep the wiring as short as possible & keep it away from other wiring. Use proper automotive cable, the bit you're using borrowed from the kettle might not be suitable.

If after this you're still having problem your amp is unsuitable/faulty. The next step would be to replace it. If you replace it & you're still having problems then you will need to bring the car to a car audio specialist.

What sort of radio is in the car? If it has an aux input or you could replace it with a radio that does, you won't need the amp at all!

championc · 16-09-2014 8:43pm

Thanks again,

The radio is long gone. Let me clarify things a bit more. When a NON-powered device (like my droid mobile) is connected to the amp (via a 3.5mm plug), sound is still more or less clear. This issue only occurrs when I connect a powered device (like starting to charge my droid mobile).

The amp is completely DC like the very top photo. Obviously the general intention is to power it off an AC transformer but in this case, I'm powering it straight from DC. However, you'll see plenty of these listed on eBay when searching for "car audio amp".

So basically, the problem is ONLY when I connect the audio of two powered devices together, and the problem is there too whether or not I insert a Ground Loop Isolator in the middle

TherapyBoy · 16-09-2014 9:04pm

The problem is in the wiring or the amplifier itself. Clean up the wiring as much as possible & see if that helps. If not, replace the amplifier.

If it's possible to put a radio back into the car this would be the easiest, safest & tidiest option. You can get Pioneer cd/tuners with aux 3.5mm or RCA inputs for under €150 including fitting. Amplifier in any aftermarket headunit will be far superior & more powerful than the one you have.

championc · 16-09-2014 9:31pm

The plan was to install a CarPC. I started it over a year ago and of course at this stage, a tablet would possibly do most of what I wanted the PC to do. Once I get the noise sorted, everything is complete. So close and yet so far

whizbang · 20-09-2014 10:59pm

Find an old pc modem card and remove the transformer from it.

Wire one channel of the amp input to any side of the transformer, and one channel of audio source to the other side of the transformer.
power it all up, and listen..

The trafo generally will have poor audio quality, lack of bass etc, and will die easily with too much signal, but useful for testing.

I stuck 2 of these onto, and wired them in between the 3 jack sockets from an old audio card.

whizbang · 20-09-2014 11:05pm

Quick pic of a transformer.

Another issue you will find, those pc's will always make noise that's very hard to remove. The power supply will affect it, but its not easy to find a PSU that keeps quiet.

Try also various value load resistors across the PC audio outputs. If you have a 5k pot, start with max and slowly reduce it while listening. There will be a reduction in audio level, and noise, but you might just find a sweet spot.

Most digital audio circuits are designed to work with a certain type of load, this is why it sounds good with headphones. Audio transformers are a similar type of load.

championc · 20-09-2014 11:42pm

whizbang wrote: »

Quick pic of a transformer.

Another issue you will find, those pc's will always make noise that's very hard to remove. The power supply will affect it, but its not easy to find a PSU that keeps quiet.

Try also various value load resistors across the PC audio outputs. If you have a 5k pot, start with max and slowly reduce it while listening. There will be a reduction in audio level, and noise, but you might just find a sweet spot.

Most digital audio circuits are designed to work with a certain type of load, this is why it sounds good with headphones. Audio transformers are a similar type of load.

The pc is an old Thin Client and had a transformer giving + and - 12v to a 4 pin atv connector on the motherboard. So the transformer is gone and the 4 pin atx is connected directly to the car electrics.

championc · 26-10-2014 10:34pm

Hi all

I'm still struggling to solve this problem. I really need help.

My problem is really simple. WITH THE ENGINE OFF - I have a mini 12v amp connected directly to a NEW connection from the car battery. When I connect my phones' earphone 3.5mm plug to the amp, the sound is perfect - crystal clear. However, the minute I connect my car charger to my phone, I get the following sound. I have tried a ground Loop Isolator between my phone and the mini amp and it makes absolutely no difference.

https://www.youtube.com/watch?v=WIQz4cQHLAg

whizbang · 27-10-2014 10:40pm

can you post a pic of the Isolator you tried.

There are basically 2 ttypes: Transformer based, Electronic based. But there are some completely fraululent ones out there also.

However it may also be your phone.

championc · 31-10-2014 1:17am

Problem SOLVED !!!

I got a loan of an Identical Bumper Ground Loop Isolator from a friend in work and Bingo, everything was perfect. So I basically had a defective unit

Curing Audio Buzzing ?

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