mpro71vette

Hey Guys,

I just got a new stereo put in and I have whistling in the speakers. It gets louder when I go faster. I have an HEI distributor, could that do it? How do I fix it?

resdoggie

I think they sell noise filters for your alternator that may or may not work.

mpro71vette

Thanks, do you know what kind or where I can get one? Does it go on the alternator or stereo?

Richard454

First you need to tell us what kind of radio.

And if it's just installed a radio or if you have added an amp.

You need to determine where the noise coming from-rather than buy as bunch of filters.

Alternator- the pitch is goes higher with the RPM.

HEI is possible will change pitch as well with RPM- with the cheaply made China ones..

The Alternator noise will come through the power wires- where as the HEI will come through the air - as the HEI will act as it's own little radio station.

Disconnect the plug on the Alternator and see if the noise is still there- then we can determine how to filter/fix the noise.

Richard

mpro71vette

Thanks, its an alpine stereo and I do have an amp, this was installed by a professional. The pitch goes higher as I go faster. At a stop I don't hear it. The sound comes out of the speakers in back. It sound like its the alternator? What kind of filter for that? Does the filter go on the alternator or stereo?

ddawson

Is the amp only for the rear speakers? Do you also have front speakers driven by the radio?

Assuming the amp is connected to the battery what happens to the sound if you remove the RCA connection to the radio?

mpro71vette

AMP is for the rear speakers, front speakers to the radio. The original radio used the front speakers and they didn't make a high pitch sound. The sound is definitely coming from the rear speakers. AMP is connected to the battery.

havesometo

The first thing I would try is take a piece of wire ground it to the back of the radio and to the amp ground. A lot of times that will get rid of it.

SwampeastMike

All components used in the sound path of a stereo system should share a common route to ground lest you get "ground loops". Such isn't as likely in a traditional car (the steel body itself [usually] acts as that "common route") but it become critical with our glass bodies

Richard454

Years ago I use to teach those "professionals!!!" A real professional would not have let the car leave the shop with engine noise...

These could be a couple sources of you noise-

As 'ddawson" said you need to unplug the RCA jacks-

At the Radio - if you disconnect the RCA's - no music but still get noise-
1) you might have a cheap set of RCA cables and the noise is being induced by a power wire near it.
2) The AMP (if other than Alpine) doesn't have a good ground- or you might see if grounding the chassis of the amp helps.

If the noise goes away- most likely-

1) You could have a ground loop through the pre-amp of the Radio to the Amp-this would solve that-

https://www.amazon.com/PAC-SNI-1-Noi...r/dp/B000K50HJ


What the ground loop Isolator does? uses a little transformer (since audio is AC current) and separates or 'floats" it from the car's 12V system.

2) Could be a cheap set of RCA's- get a good set that's shielded and just run them from the Radio to the AMP and see if that solves it-if not use the isolator.

3) Bad ground on the radio- unplug the antenna and see if that makes a difference. Find a good ground.


4) IF the amp is an off brand- it might not have an isolation circuit on the pre-amp in the input stage- a ground loop Isolator will solve this.

Hope this helps-

Richard

mpro71vette

Thanks, I will try all suggestions when I have time. Your link didn't work, what were you linking to? I have a Rockford fosgate amp and Alpine radio with kenwood speakers. I think he said he used the battery. I am thinking now it could be a grounding problem. They have a lifetime guarantee on installation so maybe I'll let them sort it out.

Richard454

All good stuff- I use to work for Kenwood.



Here you go-

https://www.amazon.com/PAC-SNI-1-Noi.../dp/B000K50HJE

mpro71vette

What if they used regular speaker wire and not RCA wire?

Richard454

I really don't know what they would have used the speaker wires from the Radio to the Amp- as the radio has a pre-amp out (AKA as low-level) and the Amp has the inputs. Using the speaker level input on the Amp is there to accommodate a radio (factory one more likely) which doesn't have the pre-outs.

MOST believe taking a clean un-amplified signal and letting the amp "amplify" the sound is the best way.

Makes sense- rather than taking amplified speaker level signal(AKA high level) - then dropping the signal back down and re-amplifing it -will bring in distortion and possible noise- as the speaker wires are un-shielded.

The design of RCA cable is to "shield" the signal wire with the braided wire- Also look at a Big Blocks sparkplug wires- same idea-but was used to keep sparkplug noise from the AM radio.

mpro71vette

Thanks Richard, I really appreciate al the information you have given me!

mrvette

Through the decades I have done tons of tunes in cars, from econo boxes through hotrods.....quite honestly I don't care anymore about car toons but here are a few thoughts....

Number one is to take the power off the battery, DIRECTLY for the positive and negative leads of the preamp/tuner/control head....run nice heavy wires, and put a large, say 1000 mfd cap across the power leads into the head end....maybe add a .1 mfd cap to that, internal cap construction reasons....
also to maybe put a relay in the power + lead, controlled by the ignition switch......

the power amp itself should not pick up much in the way of alternator whine.....but the same cap on the + lead to main chassis ground of the ENGINE should help it out, if necessary......

a typical alternator puts out maybe 700 mv of ripple under normal operation....that's almost a volt and under heavy use it can go high as 1+ volts.....you maybe have to add some inductance (choke coil and caps to the head end +- supply referring to above caps....but doubtful.....

the battery is a very good solid 'sink' to the ripple from the alt, and so much better source for head ends.....

mpro71vette

Thanks for the info. I just got back from the place were it was installed and they redid grounds, but I'm not sure it was the battery. Either way it didn't work, it was a little better but still had it. I'm bringing it back Saturday and having them put in heavier wire. I'll mention what everyone is saying here. The interference has to be going through the amp because you can hear it through the speakers. Theres a lot of info here, I'm not sure which one to take. Oh yea, he did say there was a filter on the head end.

7T1vette

Most modern radio head units DO NOT use chassis ground for the 'negative' side of the speaker connections. The speakers are supposed to "float". C3 speakers were 'grounded' on the negative side.

You might look into this as a possible source of your problem. May need to think about how to 'isolate' the speakers. I'm thinking that this is done with the speaker wiring, rather than with the speaker mounts. So it might be an easy change. Or you might have to remove a 'jumper' wire from the metal speaker frame to the (-) terminal on the speaker.

mpro71vette

Thanks, I'll bring that up to them. The amp and speakers are mounted in a box in the back.

7T1vette

If your noise turns out to be just 'ignition buzz', you may need to run + power and - ground directly to the battery to eliminate it.