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crackling and noise after installing amp.

defecat0r

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Hey boys, got some pretty big problems with my new setup, i'll quicky run down what i had, what i've got now, and what i've done, and maybe somebody will pick me up on what i've done wrong.

My setup; a Pioneer 4850MP mp3 cd head deck, Sony Xplode speakers running off the head deck, and a 12" sony sub running off a (Jaycar) Response 2x150W bridged amp. (not using the front speakers as they're crappy stocks)

Obviously the sony xplode speakers are rubbish, so i've been looking at upgrading them for a while. I managed to pick up a Kicker 4x75W amp on the cheap second hand, and i've just grabbed some Kicker KS 6x9's for $165 today.

I'm mounting the amp under the passenger seat of my VN, i've run power from the battery (no fuse for that yet), the remote (to turn it on) from the headunit's "remote", so it turns on when i turn the head unit on, and i've drilled an earth into the bracket thing that the seat screws into. That takes care of the power.

I've bought an RCA lead from Jaycar and chopped it in half. I've soldered the + and - of each RCA (-ve being the outer wire) to the + and - of each speaker (Front-L, Front-R, Rear-L and Rear-R) on the rear of the headunit. No problems there. I've then run the (now) two RCA leads through the center console to the RCA input on the amp.

Then i ran some new speaker wire from the -L and +L and -R and +R on the amp through to the back to the speaker enclosures.

I powered it up for the first time and got a fair bit of static and noise, with the volume right down on the head unit, and the gain on the amp set at anything above 0 i can hear noise. as i turn it up, it sometimes seems okish, then crackles randomly. If i crank the volume right up, it cuts out altogether and i can just hear the sub going. The amp still has power, but i have to turn the headunit off then on again to get anything out of it.
The louder i crank it the worse the static gets.

SO! i've tried the left and the right speaker individually, same difference,
I've put the old sony xplodes back in, same thing,
I've tried putting the FRONT RCA lead instead of the REAR into the amp, no difference,
As it's a 4x amp, i've tried 'amp1' AND amp2', with the same results,
I've whipped out my amp used for the sub and hooked IT up, same results!

I'm sure all my soldering was fine behind the head unit, iv'e got big thick power cables for the +ve and ground powering the amp, and i've tried different speakers, (and obviously different wires, having run left and right individually) I've had the Filters (crossovers) turned to off on both amps. I'm really at a loss as to what to try now.

What could cause static'y noise, randomly loud distortion, and the sound to the speakers cutting out completely when the volume is cranked? Could there be a setting on my head unit i might need to change?

Welcoming any opinions, observations or advice.

Thanks fellas :)
 

defecat0r

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ok, update!

I just went for a drive, with the head unit on, but the volume on zero, i'm hearing a tone that changes EXACTLY with RPM, the tone follows it even with the little RPM variations when i change gear. So it's picking up some sort of feedback from the alternator? what could cause this? a bad earth?
 

Ra1d

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did u run your rca cables besides your power lead by any chance? make sure that your rca leads are well insulated, especially where you've modified them, and also check all your connections for interference. failing that you could also try a noise filter, you can pick them up from any car audio turnout
 

garfa

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mate where is the ground point? it will probbaly be in a rather bad place creating excess resistance. also how long is the ground lead?
also try a seperate source, a ghetto blaster with RCA output connected to the amp will confirm it if the amp wiring.
 

Phreddy

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I believe a good percentage of your problem stems from the fact that you've run the speaker outputs directly to the line level inputs (RCA sockets) of the amp. (if I've interpreted what I'm reading correctly - that you spliced the RCA cables directly to the head unit speaker outputs...)

The speaker outputs are what is known as a "high level" signal source, whereas your amp inputs expect "low level" signals. As a result of this, the tiniest bit of alternator (or other electrical) noise is being fed to the high impedance inputs of your amplifier, and are hence being amplified. Normally speakers are a low enough impedance that any induced noise is not of sufficient power level to be audible, but when it's piped directly to an amp input then things go awry. The other problem is that the negative speaker output is NOT ground - the amplifiers inside your head unit work in what's called a "bridged" configuration. While one terminal of the speaker is driven positive with respect to ground, the other terminal is being driven negative. There is NO firm ground connection between a normal head unit output and the speaker it's connecting to. In fact, what you might be doing when you connect the RCA cables to the amp is shorting the speaker negative output to ground, which could end up damaging the amplifiers in the head unit.

Certainly check all your earth and power connections as well, but I'd strongly recommend that you get yourself a couple of "LOCs" (line output converters) - also known as "high-to-low converters". These go between the speaker outputs and the amp RCAs, and will solve both the problems I've pointed out above.

Best of luck, let us know how you go.

Cheerz!
 

defecat0r

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Thanks for the replies boys, I've been trying lots of different setups but i don't think i'm getting any closer to finding the problem :(

Yea Ra1d, i was running my power next to the RCA, so i got a good heavy wire and ran it directly from the battery, around the side of the car. No change tho, so that's not it.

There are two raised bracket things on the floor of the car that the passenger seat's rails bolt on to. I drilled into the side of one of those for my ground, the cable is only about 30cm long. I had my doubts about this ground myself, so with the stereo going, i had another cable coming out of the ground and touched it to various other grounded points on the car, but yet again, no success. I've also taken the dash back out, and tried connecting the ground from the amp to the ground of the head unit. no success. At the moment, i've got the ground coming from somewhere else temorarily and the power from around outside the car, straight from the battery.

Great idea with connecting a ghetto blaster garfa, but i've had some issues with it. I grabbed out a ghetto blaster and connected it in, but i got some fairy bad humming as soon as i plugged it in, but if i ground the outside of the RCA to the car, it goes away and sounds fine as best i can tell (can't turn the volume up or down through the RCA on the ghetto blaster).
I also tried plugging audio from the xbox, but it get's really bad humming (can't hear any legitimate sound from the xbox) so i just unplugged it. So i'm not sure if that's all normal or not seeing as the power souce and ground from these things is seperate?

I've also put my little TV in the car and plugged the RCA into the tv's input. The sound SEEMS to be ok, but it's only got a crappy little speaker in it so can't be 100% sure.

Anyway, what i've just noticed now, is that if i plug the RCA from my head unit into 'amp1' on my kicker amp, the LED on top that illuminates the model number of the amp (not the power led) dims, but if i plug it in to 'amp2' it stays fully illuminated. When i crank the volume past 23 when plugged into 'amp1' it cuts out(and i have to turn the head unit off then on again to get any sound), but if the RCA is plugged into 'amp2' i can turn it all the way to 62(no speakers plugged in obviously). This made me think that maybe this $60 bargain amp wasn't such a bargain.

So then i plugged in my Jarcar Response amp, i can hear a bit of noise when the volume is down low, but i hear that's normal for jaycar amps? But once again, when i turn the volume past about 30 it cuts out!

So now i'm at a complete loss as to what's wrong. Any suggestions as to what i should try now?

Oh and ra1d, when you say my RCA leads should be well insulated, how do you mean? i've taped them up so there's no chance of electrical contact, but as far as interference goes, no amount of rubber insulation will effect that right?
 

defecat0r

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I believe a good percentage of your problem ...

hey Phreddy, thanks for the informative post :)

Just trying to get my head around this high and low level, so the speaker outputs on the head unit will be a low impedance, and the RCA inputs on the amp are high impedence? or have i got it the wrong way round. I think this might be explaining why my head unit is cutting out when i go past a certain volume.

Yes, i have spliced the RCA cables directly to the head unit speaker outputs. My amp has inputs labled "hi level input", so should my speaker outputs be connected to this?

ampinputs.jpg

How is this SUPPOSED to be done? The head unit has dual RCA out, but this is soley for subs right? What does a proffessional do, do they run from the speaker outputs on the head unit through a LOC to the RCA inputs on the amp, or from speaker outputs to "high level input" if the amp has one? What is the proferred setup for a pro?

thanks again man :)
 

defecat0r

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alright! so i chopped the floppy drive power plug off a power supply, with a bit of dremel work it fits into the high level input on the amp. I've jimmied up one speaker to the rca cables coming from the head unit, and it SEEMS to be working fine! So i'm thinking now i can just chop the RCA plugs off these cables, get down to jaycar and get some proper plugs and solder them up, but i'll wait and see if i'm doing the right thing before i mutilate these cables any more :p
Is that the way to go Phreddy? or would these Line Output Converters be the preferred alternative?
 

Phreddy

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A-HA!! If your amp has hi level inputs, they're the ones to hook the speaker outputs directly to. However, I reckon you'll get much better sound quality if you run from the RCA outputs on your deck - the signals are "cleaner" if you know what I mean. The RCA outputs on your head unit shouldn't be purely for a sub - I guess it depends on how the unit has been set up. (some high end head units can allow configuration of the RCA outs - have a look in the manual if you have it) and given that you've run the RCA cables back already that shouldn't be too difficult.

Disconnect the cables from the speaker outputs, and solder some RCA plugs onto these shielded cables. If you have the facility to run RCA outputs, that's DEFINITELY what I recommend. You mentioned "dual RCA outputs" - does that mean there are only two RCA sockets, or four? It might be that only the rear or front channels are running through the RCAs if there's only two. If there are four sockets, then all four channels are fed out low level. If you only have the two sockets, I guess at a pinch you could use a LOC for the channels that aren't fed to the low level outs - that would at least get all four channels running through the amp properly.

You got it right - your speakers are a low impedance load, therefore will "sink" more current. Oh, by the way - when we're talking about "impedance", bear in mind that low impedance = high level, and vice versa. Given that power is voltage multiplied by current, that's where your "watts" comes from. Amp inputs are a high impedance load, and are not designed to accept large input currents, the current for the load comes from within the amplifier circuitry. Conversely, they are more sensitive to slight voltage variations, which is what "noise" is. Just remember, low impedance = high level, and high impedance = low level.

I think that the "cut out" that's happening after a certain volume setting is in fact the head unit protecting itself - as I mentioned in my last post, the negative speaker output is NOT gorund, but when you connect the cables to your amp then you are indeed shorting this output TO ground. This will either damage the head unit output chips, or in most cases (as I believe to be happening here) the internal protection will kick in.

I don't want to blow my own trumpet as being a "pro", but I have a pretty good idea of what I'm doing - and I defintely would use low level feeds from the RCA outputs if they're available. (the factory Blaupunkt unit in my VZ didn't have RCA outputs, so I designed a circuit that would give them to me, rather than using the LOC method - that's how much I dislike using those things!) ;)

All the best Mate, fell free to ask any other questions you might have. Cheerz!
 

Phreddy

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Hmmm , our posts seem to have crossed over each other.....

You certainly could do it that way, but as I said it's better sound-wise to run the RCA outs from your deck. Up to you though, whatever floats yer boat! :thumbsup:
 
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