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Discussion Starter · #1 ·
Hi everybody, just updated my car audio system and I am having a hell of a time getting rid of a static white noise hiss coming from the speakers. I have a Mazda CX-5 Touring(non Bose) and the equipment is as follows:
Factory head unit
PAC aoem-maz2 interface
Audio Control D.4.800 Amp
Hertz DSK 165.3 front
Hertz DCX 165.3 rear
JL Audio powerwedge+ 10"

So this is been going on for a while and I've tried 3 different amps, switched to the PAC interface instead of using speaker level inputs, the sound just won't go away. I'm just at my wits end. Seriously I'm the point of just returning all of this or selling it for what I can and just putting the stock system back in.

It is a static White Noise hiss that is always on even when there is no source. It's most audible coming from the tweeters but if I really listen for it I can hear it coming from the 6.5 in the front as well so it's coming from all channels.
  • Signal muted through DSP it's still there.
  • Unplug RCAs and it's still there

This leads me to believe that it has to be something from the amp onwards. However, considering the hiss is always there even when muted BUT it does get louder as the volume gets turned up. Does that mean it could still be something with the car itself and not the amp/speakers?

I've tried re grounding the amp several times in several locations. The install was done at Best Buy(I know not the best) but the guy is one of the regional trainers and has been doing installs for 25+ years and really knows his stuff. He's been helping me work through this but he's at a loss as well so I'm just trying to figure out if there are other troubleshooting tips or ideas that I can try to use the nail this down.

Any help would be greatly appreciated!
 

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Discussion Starter · #3 ·
How high are the gains turned up on your amp?
Typically, hiss is caused by the gains being too high...
They're really really low. I have them turned down as low as I can to try and minimize the hiss and it's greatly impacted sound quality.
 

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Have you used a muting plug?
Basically it’s an rca with the wire chopped off and the jacket and tip wires twisted together.
Also, can you wire a test speaker that is full range and also 4 ohms to the amplifier directly but outside of the car.
last, can you attach the amps power and ground to another car while the amp is still in the Miata?
You can use small power/grounds as you don’t want to actually crank it or even play anything. Just listen for the hiss.
 

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I would toss that Pac unit and go back to speaker level inputs, and then run an iphone thru the amp to eliminate the Headunit as the cause of the noise.
 
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If you unplug the RCAS and the hiss is still there then it is 100% the noise floor of the amplifier nothing else it could be. This is why you want high signal to noise and gains turned all the way down. The only way you can keep your gains turned down all the way is with high voltage on the RCA's...

Try turning down the gains ALL the way.. not just as low as you can go and still get it as loud as you want it... If it works then you need to look into options to boost your RCA voltage.. line driver.. or best option just a new line out converter for a better RCA source to begin with.

I went through this same problem and trust me i know how you feel i was ready to rip everything out of my car i wont put up with it after spending that much money... its fixable you just have to verify what it is before you throw more money at it but i am almost certain thats your problem.. PAC probably puts out low voltage like 2v or something so your gains are way too high...
 

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Also.. let us know what amps you've tried.. my guess is they all have high input sensitivity..

Like a JL Audio amp on Low input mode. it goes 2V(gain all the way down counter clockwise) up to 0.2v (gain all the way up clockwise) - it takes 2v RMS to get the amp to full power or clipping point (probably loud AF)

But a Rockford Fosgate amp or the Audiocontrol amp you have goes like this...
8v RMS (gain all the way down) up to 0.2VRMS (gain all the way up)


As you can tell if you only have 2V rms from your source and your amp needs 8v RMS at minimum gain to reach full power then you need way more voltage or you will have to turn your gain wayyy upp and in turn get the dreaded humm/hiss...

Also some amps like JL and some alpine have a "low level input" mode and a "high level input" mode which gives you the best of both worlds... high voltage input for high voltage sources but a switch to go to low mode for situations exactly like this where you just need the gain turned down but if you turn it down then it doesn't get loud enough...



And just to clarify.. I love Audiocontrol and Rockford amps.. but you need at least 5v RMS to get them right IMO.. Audiocontrol DSP's put out 5 or 10v RMS (switchable via a jumper internally) so im sure their amps are made to work well with their DSPs and the higher voltage differential inputs also allows for high level speaker lines to go straight into the amp so thats another reason manufacturers are doing this....

I think JL made the best solution but they are not cheap.. its something nobody cares or thinks about until it happens to them kind of thing.
 

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If you unplug the RCAS and the hiss is still there then it is 100% the noise floor of the amplifier nothing else it could be.
This. Have experienced it with the same amps
 

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Discussion Starter · #9 ·
This. Have experienced it with the same amps
This. Have experienced it with the same amps
Couple things I don't understand.
1 - if the issue is strictly the amp noise floor
If you unplug the RCAS and the hiss is still there then it is 100% the noise floor of the amplifier nothing else it could be. This is why you want high signal to noise and gains turned all the way down. The only way you can keep your gains turned down all the way is with high voltage on the RCA's...

Try turning down the gains ALL the way.. not just as low as you can go and still get it as loud as you want it... If it works then you need to look into options to boost your RCA voltage.. line driver.. or best option just a new line out converter for a better RCA source to begin with.

I went through this same problem and trust me i know how you feel i was ready to rip everything out of my car i wont put up with it after spending that much money... its fixable you just have to verify what it is before you throw more money at it but i am almost certain thats your problem.. PAC probably puts out low voltage like 2v or something so your gains are way too high...
Ok I think I'm following you on most of what you're saying but can you help clarify a few?
  • A typical amp will usually have a gain of something like 5v-0.15v but this has nothing like that since it's all digital. There are 2 settings in the DSP software for each channel, input gain(range from -20db - 12db) and output level(range from -48db - 0db). The input gain in the DSP software runs from -20db-12db. I've currently got the input gain set at about -6db and the output level set a touch over 3/4ish(-9db)of the way up. Is this the issue? Are these settings too high?
  • I think the amp does have a high S/N right? Specs are: Signal to Noise: 102 dBA, Ref 200 W @ 2 Ohm THD+N: < 0.1%

If those setting are my issue and I'm understanding you correctly I need to get a strong line driver to put between the PAC and amp, something like 10v or so. Then I'll be able to crank the input way up and amp gain way down which will drop the noise floor low enough to kill this hissing sound?
 

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If it stays when unplugging rca's it has NOTHING to do with whats before the amplifier. Lower the output gain and that will most likely lower the noise, but then... less volume. This is just how a lot of not-so-great amps are.
 

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Discussion Starter · #11 ·
If it stays when unplugging rca's it has NOTHING to do with whats before the amplifier. Lower the output gain and that will most likely lower the noise, but then... less volume. This is just how a lot of not-so-great amps are.
Isn't audio control one of the better amp brands available? Particularly these D series amps w/ DSP?

Yes, if I drop the gains the noise does go away. Same if I mute the output.
No signal + low gain = NO noise
No signal + higher gain = YES noise
Signal + low gain = NO noise BUT low volume

So if I can turn the gain down to the point it kills the noise(and the volume), but then add a line driver to jack up the input voltage, will that give me my volume back?
 

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You may just need to raise input gain then
 

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Nearly every amplifier with DSP has a higher noise level than an amplifier without a DSP. Why? Because no matter the voltage of the signal into the amplifier, the preamp has to attenuate it to fit the ADC, which usually has a max input voltage of 1 - 1.4 VRMS. The preamp that does this needs to be really quiet or else. It's helpful to know whether the input sensitivity control on the amplifier reduces the level of the analog signal before the ADC or the digital input level in the DSP.

If, with nothing plugged into the amp, the noise is reduced when you turn the gain down, then it's the amp. No doubt about it. If this amplifier only drives tweeters, then turn the gain down and then retune. You can boost high frequencies in the DSP quite a bit without trouble becasue the level of high frequency in most music is like -20dB.
 

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Discussion Starter · #14 ·
Also.. let us know what amps you've tried.. my guess is they all have high input sensitivity..

Like a JL Audio amp on Low input mode. it goes 2V(gain all the way down counter clockwise) up to 0.2v (gain all the way up clockwise) - it takes 2v RMS to get the amp to full power or clipping point (probably loud AF)

But a Rockford Fosgate amp or the Audiocontrol amp you have goes like this...
8v RMS (gain all the way down) up to 0.2VRMS (gain all the way up)


As you can tell if you only have 2V rms from your source and your amp needs 8v RMS at minimum gain to reach full power then you need way more voltage or you will have to turn your gain wayyy upp and in turn get the dreaded humm/hiss...

Also some amps like JL and some alpine have a "low level input" mode and a "high level input" mode which gives you the best of both worlds... high voltage input for high voltage sources but a switch to go to low mode for situations exactly like this where you just need the gain turned down but if you turn it down then it doesn't get loud enough...



And just to clarify.. I love Audiocontrol and Rockford amps.. but you need at least 5v RMS to get them right IMO.. Audiocontrol DSP's put out 5 or 10v RMS (switchable via a jumper internally) so im sure their amps are made to work well with their DSPs and the higher voltage differential inputs also allows for high level speaker lines to go straight into the amp so thats another reason manufacturers are doing this....

I think JL made the best solution but they are not cheap.. its something nobody cares or thinks about until it happens to them kind of thing.
Amps were:
D4S
Nearly every amplifier with DSP has a higher noise level than an amplifier without a DSP. Why? Because no matter the voltage of the signal into the amplifier, the preamp has to attenuate it to fit the ADC, which usually has a max input voltage of 1 - 1.4 VRMS. The preamp that does this needs to be really quiet or else. It's helpful to know whether the input sensitivity control on the amplifier reduces the level of the analog signal before the ADC or the digital input level in the DSP.

If, with nothing plugged into the amp, the noise is reduced when you turn the gain down, then it's the amp. No doubt about it. If this amplifier only drives tweeters, then turn the gain down and then retune. You can boost high frequencies in the DSP quite a bit without trouble becasue the level of high frequency in most music is like -20dB.
Okay it definitely sounds like it is amp noise, no question.

So if I get a line driver capable of pushing the input voltage closer to the 8v max of the amp, that should allow me to reduce the gain enough to kill the noise but still keep my volume levels? Is that correct?
 

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Couple things I don't understand.
1 - if the issue is strictly the amp noise floor

Ok I think I'm following you on most of what you're saying but can you help clarify a few?
  • A typical amp will usually have a gain of something like 5v-0.15v but this has nothing like that since it's all digital. There are 2 settings in the DSP software for each channel, input gain(range from -20db - 12db) and output level(range from -48db - 0db). The input gain in the DSP software runs from -20db-12db. I've currently got the input gain set at about -6db and the output level set a touch over 3/4ish(-9db)of the way up. Is this the issue? Are these settings too high?
  • I think the amp does have a high S/N right? Specs are: Signal to Noise: 102 dBA, Ref 200 W @ 2 Ohm THD+N: < 0.1%

If those setting are my issue and I'm understanding you correctly I need to get a strong line driver to put between the PAC and amp, something like 10v or so. Then I'll be able to crank the input way up and amp gain way down which will drop the noise floor low enough to kill this hissing sound?
OK well the numbers you gave us of your gain settings indicate your gain is turned up quite high that is your problem. And it doesn’t really matter if your gain is set digitally or on a potentiometer manually it still affects the noise floor. You indicated by turning it down the noise went away that’s what I figured would happen…

Audio control is an interesting company… I have a lot of respect for their products and especially home audio but I have a few reservations about their car audio products. Mainly their lack of a usable signal to noise number on their spec sheets and lack of paramtetric EQ on their DSP.

Don’t get me wrong their amps are good, and perform well. But their signal to noise is referenced at full power output. That is essentially useless. Reputable manufacturers will reference it to the CEA standard at 1 watt into 4 ohms and even then I’m not sure if there is a set input voltage required because I know Rockford tricked the CEA test with the t400x4ad… (one of my favorite mini amps they sound really good BTW but you need decent voltage to keep the gains low) but the owners manual states 90db signal to noise at 1watt @ 4 ohm (CEA spec) and then I’ve seen hifitest.de AND Pasmag test the T400x4ad at closer to 75db signal to noise so yeah… somehow they bull$hitted the CEA test.


I emailed audio control about a year ago because I was interested in buying their amplifiers for my car I emailed them and asked them if they could give me a signal to noise number referenced to one watt into four ohms… They ignored my email twice. It doesn’t mean they are bad amps it’s just a marketing decision that I do not agree with. a lot of company's do it to inflate their signal to noise numbers.


So yes with a Line Driver it can solve your issue. It will allow you to keep your gain turned all the way down or close to.

You do need to check with maybe a RCA to headphone adapter coming out of the PAC unit that there is no noise coming from it… and then yeah basically if turning the gain down in your settings lowered the noise then a line driver should work.


Now comes the extremely frustrating part… trying to find a line driver with a low noise floor that will not add to the problem… I’m not sure I can help you there I decided to buy a helix DSP with 8V RMS output on the RCAS for this exact problem… my previous DSPs with 2.2v (about 8vpp) RMS output were not enough I tried Several. Even the Dayton with like 3.5v was not enough for me I still had gain noise. My minidsp 8x12v2 with 4.5v RMS was barely enough for my t400x4ad amps…I could keep my gains low with no audible noise. but the helix makes everything so easy I can use any amp I want with no need to try and balance all these variables…


I hear the ARC dsp is also 8v RMS output.. Helix DSPs are all 6v RMS or 8v RMS. Both are sufficient…


Your problem is there are a lot of crappy line drivers… I’m not sure how to help you but someone else might know of a decent one
 

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Ok
Couple things I don't understand.
1 - if the issue is strictly the amp noise floor

Ok I think I'm following you on most of what you're saying but can you help clarify a few?
  • A typical amp will usually have a gain of something like 5v-0.15v but this has nothing like that since it's all digital. There are 2 settings in the DSP software for each channel, input gain(range from -20db - 12db) and output level(range from -48db - 0db). The input gain in the DSP software runs from -20db-12db. I've currently got the input gain set at about -6db and the output level set a touch over 3/4ish(-9db)of the way up. Is this the issue? Are these settings too high?
  • I think the amp does have a high S/N right? Specs are: Signal to Noise: 102 dBA, Ref 200 W @ 2 Ohm THD+N: < 0.1%

If those setting are my issue and I'm understanding you correctly I need to get a strong line driver to put between the PAC and amp, something like 10v or so. Then I'll be able to crank the input way up and amp gain way down which will drop the noise floor low enough to kill this hissing sound?
You need to raise the input gain first. You mentioned it ranges from -20 to -12 then say you set it to -6. -6 is not between -12 and -20

Raise the input and lower the output gain.

is there channel level also or is that the output gain?
 

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Discussion Starter · #17 ·
Ok


You need to raise the input gain first. You mentioned it ranges from -20 to -12 then say you set it to -6. -6 is not between -12 and -20

Raise the input and lower the output gain.

is there channel level also or is that the output gain?
Sorry it's -20 - +12 for input and I have it set about -6.

I ordered a line driver from audiopipe. Looks like it's got decent reviews and can put out 10v. Hoping if I kick it up to 6-8v in I can drop the output enough to kill that noise. Fingers crossed.
 

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Discussion Starter · #18 ·
Sorry it's -20 - +12 for input and I have it set about -6.

I ordered a line driver from audiopipe. Looks like it's got decent reviews and can put out 10v. Hoping if I kick it up to 6-8v in I can drop the output enough to kill that noise. Fingers crossed.
Oh,
Ok


You need to raise the input gain first. You mentioned it ranges from -20 to -12 then say you set it to -6. -6 is not between -12 and -20

Raise the input and lower the output gain.

is there channel level also or is that the output gain?
It's marked as "Level" on the output side of the dsp software. You can assign different values per channel.
 

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Set the input to 0 and output to 0

then set yoir amplifier gain I have an audiocontrol amp and setting the gains is super easy with the built in clip led. I verified their clip led against a smd dd1 and it’s accurate .

The audiopipe you are going to add can also cause hiss and noise so that’s probably not the fix.

what made you chose the input and Output gains that you chose instead of using 0 and 0. Just because?

It’s yoir dsp gains causing the hiss 100%. Even a helix dsp can hiss turning the gains up.

I have a helix and it’s input is 0 and I won’t go past 0 for channel gain.
My audiocontrol lc6-1200 the gains are at half way ( that’s where the clip light comes on) I have no hiss! I would go insane with my sensitive ears.
 
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The input gain should never be negative unless you have enough voltage to clip the inputs of the amp.

Add those 6db back to the input and subtract 6db from the output gain and your noise floor drops considerably.
 
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