Technical Amplifier strange

[PaulDrage]

Strange, just re-fitted all my old amp and speakers etc in the rear of my uno, when you start the engine the rear speakers are making a whining noise- infact replicating the noise of the fuel pump.

Someone suggested maybe my 2 RCA Cables might be getting interference from the fuel pump.

They do run on the inside of the car down the drivers side, so i suppose they do run near the fuel pump, but there is a floorpan between the pump and the rca cables, so it seems a little odd. (something i can trial and error anyway.)

The other weird thing is that the amp/rear speakers when playing a cd, makes the noise of the cd spinning, and when you press a button on the headunit/stereo the speakers make a small clicking noise - not an inbuilt feature of the stereo im sure! - perhaps one of two things i can think of?
1) stereo needs throwing away. (pioneer)
2) + or - to the headunit/stereo are poor perhaps?

Has anyone ever experience any interference to/from amps?
thanks
Paul

 

[Steely]

Are your rca's/live and remote all running down the same side of the car??

 

[PaulDrage]

The permanent live + and the switched live+ run down the left side, and my rca cables down the right (drivers) side.

Today i tried new rca cables out of the passenger door, and around the outside of the car onto the amp in the boot, but made no difference.

I tried a new earth from battery to amp, to no avail.
I tried a new + from battery to amp, to no avail.
I also tried running a new earth to headunit/stereo from battery.
All of the above i ran the wires over the car/outside the car.
But the rear speakers still whine like the fuel pump.

Feel like bashing my head, very hard against the amp.

It has to be the fuel pump inducing current in the wiring that is possibly disturbing the signals down the RCA cables, just confusing hell out of me, will continue to investigate

 

[Louie Bee]

What is the earth like on the fuel pump?

sounds like a dirty signal somewhere.

may need a Suppression capacitor to get rid of the noise (don’t confuse with a power cap), but I'd look at the earth connection first - at fuel pump and where it meets the chassis.

Perhaps try another earth wire onto the fuel pump

Maybe Alex GS could confirm?

 

[UNO-MK1]

--when you start the engine the rear speakers are making a whining noise- infact replicating the noise of the fuel pump.

Someone suggested maybe my 2 RCA Cables might be getting interference from the fuel pump.--

Low quality RCA cables can be prone to interference compared to a twin or triple shielded cable , but this is rarely the cause of a problem.

Now you said - 'when you start the engine'...
When you START the engine. ?

The electric pump on an EFI car will run for several seconds when you first turn the key to RUN.---we haven't tried to START yet.
The pump will go silent when the fuel rail comes up to pressure.

If there is noise when you do this test (without starting the engine) then the pump is to be focussed on.

Assuming YES You will have to suppress the pump.
The pump is either an electric motor or vibrating diaphragm type and these can emit RF type energy that can radiate to the power cables , or RCA leads ,, or even directly into the amp itself.

Suppression with a capacitor (from your car hifi shop) across the + wire going to the pump should fix that.
Also previous advice to check the grounding of the pump is good to follow.

While you are at it you could get a few extra capacitors , for the electric cooling fan on the radiator , the internal heater fan , and the wiper motor.

They are only a couple of bucks each.

Now , assuming the sound didn't come when the ignition switch is set to RUN , but only is heard when the engine is actually running.,,you might consider looking at the alternator as the noise source.

Does the whine increase in speed with engine speed.??
If YES .,then its the alternator.

Once again , a cap across the + is the answer.
There may already be one there ,,throw it away...
Capacitors break down internally with age.

Other areas to look at is your grounding of the AMP and head unit.

Is the AMP bolted to metal ?
Is the (-) connected via a short cable to the cars body near the amp.?

If either of these answers is YES , then your setting yourself up for ground loop noise. (often its heard as hum)

If yours is set up like this , then use a audio isolation transformer in the RCA lines.
Car hifi shop sells these for about 10 bucks.

gW

 

[Louie Bee]

Sound advice gW!! I see you know your stuff!!

We reckon the fuel pump as it's recently been replaced with a spare..

From me

I must admit I didn't have any sound system in that Uno I broke durring the time I had it.

 

[PaulDrage]

Wow sound advice! (excuse the punn!) how do i add a thanks thing on here?

Well the noise happens with the pump when ignition is on, and the noise does follow the revs of the engine aswell, but, i put this possibly down to the increased flow of fuel thru the pump as the revs increase the pump increases in flow etc etc - so i'll start with some of these supression capacitors accross + of the pump.
The amp is earthed via short cable to a clean bit of metal on boot floor - how else can i earth the amp?
Suppressing the alternator sounds a bit dodgy with a capacitor i mean, will start with fuel pump like i said.
I'm amazed such a small pump can induce this much interference! it's amazing, i suppose its simmilar to starting up a motor bike or a fast running motor near your TV in the house..

 

[PaulDrage]

http://cgi.ebay.co.uk/Legacy-35-Amp-Noise-Suppressor-Clearance-Sale-RRP-18_W0QQitemZ220284789790QQcmdZViewItem?hash=item220284789790&_trkparms=72%3A1301%7C39%3A1%7C66%3A2%7C65%3A12%7C240%3A1318&_trksid=p3286.c0.m14#ebayphotohosting

Would this item, for example, work on the fuel pump? i get the impression it wouldn't be man enough to supply a fuel pump?

Cheers

 

[UNO-MK1]

Over 90% of car hi-fi noise problems are from a 'ground loop'.

Ground loops are caused by resistance in the ground system - whether in wires or in the cars steel body.

We assume that ground is a perfect Zero Volts , but it isn't.
Because of resistance it is likely to be a few millivolts above Zero V.

When we install and AMP , we have to provide a ground wire for the power supply. (direct case connection or wire from (-) on the AMP to the cars body)

Theres is however another ground present in a car hi-fi remote amp setup.
This is the outer (braided) cable in the RCA leads that connect the head to the AMP.

As the AMP now has two grounds , these tiny ground currents in the ground system can circulate in the ground loop and present themselves to the AMPs audio input.
These voltages are very small , but size-able to the AMPs input stages.

As the amp cant tell the difference between ground voltages and signal voltage on the input line , it amplifies them both.

The solution is to break one of the grounds.

If we break the power supply ground the amp wont have enough supply to work -- so we cant do that.

But we can break the Ground on the RCA lead.


This is done with a ground loop isolator.

http://cgi.ebay.com/GROUND-LOOP-ISOLATOR-NOISE-FILTER-SUPPRESSOR-HUM-KILLER_W0QQitemZ370087655938QQihZ024QQcategoryZ50552QQcmdZViewItem

Inside it is nothing more than a 1 to 1 audio transformer.
The audio from the head passes as normal , but the DC connection to ground is broken on one side of the cable to the other.

We should tackle noise from the cars devices as well with suppression techniques while not forgetting the curse of the ground loop.

Some AMPs , external graphics , processors etc , have built into them these isolators , so they don't suffer form ground loop problems.



It is possible to do a simple test to see if ground loop noise is present.
Switch on your noisy device (eg electric fuel pump)
Go to the AMP and with it running , pull off one of your RCA leads - leave that one disconnected.
Slowly slide the second RCA plug out of the AMP audio input socket.

Typically with most RCA plugs , the outer (ground) will disconnect before the inner breaks contact in the socket.

At the moment the outer ceases touching the outer of the RCA socket notice if there is a drop in noise.
If you had music playing softly this should still be heard correctly.

If the noise level has reduced , then 100% for sure, there was a ground loop problem.

*if your RCA plugs or sockets disconnect the inner and outer at the same time..you could try a little sticky tape over the outer of the RCA socket on the amp...so when the plug is pushed onto it , there is no connection to the outer.*

If noise problems persist , then suppression of the suspect devices is your next job.



¨Suppressing the alternator sounds a bit dodgy with a capacitor¨
Capacitors fitted to the + OUTPUT of the alternator was common place when cars only had AM radios.
With the switch to FM , amplitude modulated noise
is not noticed as much so most cars now have no external suppression on the alternator and other devices.

gW

 

[Eklipze3k]

This all sounds very familiar to a problem my brother had in his Mk2 Golf. Out of interest, the ground from your amp, have you got this connected to the chassis or have you run a cable back to battery and connected to the -ve terminal?

IIRC (and my memory is failing me ) sending it back to the battery - rather than earthing to the chassis - sorted it in his case.

 

[UNO-MK1]

-- have you got this connected to the chassis or have you run a cable back to battery and connected to the -ve terminal?

--sending it back to the battery - rather than earthing to the chassis - sorted it in his case.

That is what I asked previously , but I already knew the answer. (short ground wire to the body)

While in some cases returning the negative also to the battery will work , it doesn't always.
If the resistance of the braid in the RCA leads = the resistance of the longer (-) cable then the circulating currents should stop and the noise should be gone.
Its a hit and miss attempt at a fix that one and isn't the most correct way to go.
Isolating the RCA line correctly with the transformer will always work .... assuming thats the problem.

Another down-side is that when you run the (-) back to the battery you have twice the voltage drop in the cables.
That would force you to go to 4G cables as a minimum for these lines.

A drop of a couple of volts in the AMPs power supply will seriously drop the output Watts to the speakers.

gW

 

[Eklipze3k]

Woops, I missed that part of the previous posts

*shuts up now*

 

[PaulDrage]

Thanks anyway eklipze3k, it's always nice when people try to help.

I will try the rca cable trick tomorrow, i actually hadn't realised they had an earth/braded part to them (never really disected one!)

I'll buy a couple of supressors and one of these ground breaking items, i'll let you know how i get on in a couple of days! with any luck no more horrible noise from speakers!

Thanks again!

 

[PaulDrage]

News!

Ok so, i got a three wire capactitor (quite a large looking thing), and wired that so that:
fused + goes to capactitor (red wire)
through capacitor,
Yellow wire + goes into the stereo wiring where it used to be +
Black wire is attached to the metalwork on the stereo (case screw).

This capacitor/noise stopper did nothing that i can see.
Engine noises etc still from speakers when running etc.

Ok today i received a ground loop thing with the 2 sets of rca's on.
I've put this on the amplifier end (havent tried the stereo end yet - limited space),
and it has cured the engine noises coming from the speakers!!
BUT it now causes a noise much like a tazer (zz zz zz zz zz) on, off,on off.
If i remove the new ground loop stopperer/(with rca's on), the noise goes away.

If i disconnect the rca cables from the stereo end, but not the amp end, the noise carrys on (with the new toy fitted).

If i disconnect the new ground loop toy and start the engine i get the old engine noises from speakers, but its dead silent when just sat there.

So i guess the new ground loop isolater is causing the zz zz zz zz, noise, but it's half fixed the fault.
Do you think this could be:
- amp faulty
- faulty/poor ground loop isolater (it was from hong kong on the bay.)

Getting a bit frustrated now!

While i've got your attention, i cant remember is the orange wire on stereo iso loom to after ignition +12v ? if so what is the yellow wire?
or was it orange +12v, and red is after ignition? i cant remember..

Cheers

 

[UNO-MK1]

--
So i guess the new ground loop isolater is causing the zz zz zz zz, noise, but it's half fixed the fault.
Do you think this could be:
- amp faulty
- faulty/poor ground loop isolater--

--While i've got your attention, i cant remember is the orange wire on stereo iso loom to after ignition +12v ? if so what is the yellow wire?
or was it orange +12v, and red is after ignition? i cant remember.--

Cheers

Make sure the AMP isn't making metal to metal contact to the cars body via any mounting screws.
Lift it up and put some carpet or something under it and test it again -- see if that noise goes away.

The ONLY ground can be the (-) wire from the AMP.

Also try it without that power line filter fitted.

The RCA ground loop isolator is dead simple inside , and is most likely working correctly.


Regarding the wiring color codes on car audio looms ---- I don't automatically trust anything that someone has made without thorough testing.

I suggest that you work out for sure what they are - but this might give you some clues.

****Above was taken from a car hi-fi site , use at own risk.***

gW

 

[PaulDrage]

Ah yes, that will explain why my car stereo's memory is lost when switching ignition off - i had it back to front.

AMP deffinately not touching any metal work, I will try it with the in-line capacitor on the stereo off.

Other thing i may try this weekend is running a new earth all the way back to the battery.

Cheers

 

[UNO-MK1]

With it grounded correctly on the (-) wire to the body , and with the body of the amp insulated form the metal , and ONLY the RCA lead connected to the RCA isolator ,(the RCA isolator not connected on the other side) , there should be NO sound from the amp when powered up.

Don't use the power leads suppressor for this test --- leave it out.

Only change one thing at a time and work methodically.
Randomly doing this and that will lead to frustration and likely a poor result.


gW

 

[PaulDrage]

(deleted other text as come to some solution..)

Just tried this:
(smacks head.)
Lifted the amp, maybe 10-20 inches off of the floor/carpet and it's stopped clicking.

So the amp must be picking up current from the wiring / body? it is insulated from other metal work, but it needs to be a long way off of the floor-weird.

Right so, i plugged it all back in, and started engine with amp off of floor (with no isolator or capacitors etc) - still whines like the fuel pump.

So i plugged isolater back in.
Stops the whining.
BUT can't hear anything from the speakers - maybe a tiny tiny bit of noise from the stereo.
It appears either my stereo isn't sending strong enough RCA signals or whatever?

Rather annoying, works fine now with just ignition on and no isolater, but as soon as you start the engine (or the fuel pump primes up), i get the whining.

*frustrated*

 

[UNO-MK1]

---
Rather annoying, works fine now with just ignition on and no isolater, but as soon as you start the engine (or the fuel pump primes up), i get the whining.

The left and right channels are completely separate in the RCA isolator , so if it happened to be defective in some way , you would only loose one channel.

So I doubt that it is faulty.

I would check very thoroughly the (-) wire from the amp to the body.
Remake all the connections - I doubt it is allowing enough current to flow to the amp for the amp to work rite , and the only time it works is when you provide a (-) through the RCA lead.

Something really isn't rite here.

gW

 

[PaulDrage]

Thanks yeah, i think im going to re-wire everything related to the audio circuitry.

And do you think i could use that 3 wired capacitor on the fuel pump?
the one with +12V in and +12V out, and an earth wire/ground wire. (3 wires).

I will post back when i've solved it completely.

cheers