# High noise floor "HISS" using LOC



## sienna1 (Sep 4, 2009)

I'm experiencing a noticeable "hiss" at lower volume levels with my OEM head-unit and after-market amplifier/speakers. My set-up includes 09 Corolla NON-JBL head-unit feeding an AudioControl LC6i which sends it's out-put to an Alpine PDX-5 amplifier. The amp powers Alpine's S 6.5 coaxial at the front, Alpine's S 6x9 coaxial in the rear with 2 JL 10W1's subs. I have to decrease the gains on the LC6i to minimum on the front and rear in order to keep the "HISS" to an acceptable level. Having to do this, defeats the basic fundimentals of proper gain adjustment. I replaced an MTX reQ-5 with the LC6i to see if that would cure my delima but found that because of the higher output voltage of the LC6i, that the gains of the AudioControl had to be set at the min to mask the "HISS". Unlike the LOC, increasing the amp's gains has little affect on the level of "HISS" audible. Has anyone experienced this high noise floor after using LOC's on a OEM head-units? I'm going to reconnect the head-unit directly to the speakers to see if the "HISS" is as noticeable as with the current set-up. I can't recall if this problem was present but because of the lower amplification and with the OEM speakers it was not audible. I have no alternator whine with the current set-up.


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## Oliver (Jun 25, 2007)

Sounds like an issue with the audio control 

someone may have been to hard on it


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## papacueball (Jun 26, 2008)

Maybe you could try grounding the LOC and HU to the same point? Or maybe run the LOC ground directly to the battery?


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## 60ndown (Feb 8, 2007)

try different combinations of levels on loc/amps/hu. (start with your hu @ 3/4)

and ground everything.

audio control make good stuff.


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## VP Electricity (Apr 11, 2009)

That hiss isn't too uncommon with Audio Control LCs in my experience - but there are many complaints about PDX amps hissing too A dealer I know has decided that it's the amps - that some hiss and some don't - and a forum member's experience here seems to bear this out (search for PDX Hiss). 

The LC is designed and intended for high-power OE amps - deck power is low voltage enough that if you don't need summing (and you don't), there's no real reason for it to be in your system. 

I would try an iPod on the PDX and see if it hisses. 

I would also consider losing the LC and running the speaker level into the RCAs on the PDX. It takes balanced inputs all day according to the E90 BMW people... and that HU doesn't put out that much voltage.


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## sienna1 (Sep 4, 2009)

The LC6i shares the same ground and pwr as the amp. I've tried a common ground between the head-unit and LC with no change in the amount of hiss. Both the MTX reQ-5 and the AudioControl are new units and as I had stated, they both have the same hiss but it's higher on the LC6i because it has a higher output gain section (9V vs 4.5V). It would almost seem as though the hiss is being produced by the head-unit or is a by-product of the conversion which becomes more audible when the LC's are used to provide the RCA outputs.


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## VP Electricity (Apr 11, 2009)

I think that what's causing you to hear the hiss - which is present in all audio signals, but usually too low to be audible - is that there is attenuation on the input of the LC that you don't need, given that it's for 400W and you have 12W. 

But none of this matters if you have a bad - i.e., hissy - PDX, so test that first, because it's easy.


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## VP Electricity (Apr 11, 2009)

Are you sure you grabbed speaker outputs from the HU? Is there any chance your non-JBL system had an external amp?


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## sienna1 (Sep 4, 2009)

VP Electricity said:


> I think that what's causing you to hear the hiss - which is present in all audio signals, but usually too low to be audible - is that there is attenuation on the input of the LC that you don't need, given that it's for 400W and you have 12W.
> 
> But none of this matters if you have a bad - i.e., hissy - PDX, so test that first, because it's easy.


I tend to agree with your statement. I reconnected the head-unit directly to the speakers and the hiss is present. I guess the combination of non-OEM speakers (more detail and higher frequency response) along with higher amplification extenuates the floor noise. I've checked the PDX and it's fine, no noise. The hiss is barely noticeable at volume "1" but is not noticeable once the volume is increased (can hear it on some really quiet music passages). I guess I'll have to live with it. I have the OEM SAT receiver and OEM Blue-tooth module and I also like the look and ease of use of the OEM head-unit (large buttons with no "BLING"). Keeping the gains on the LC6i and the PDX set low still provide an acceptably level of floor noise. I did find that the LC6i provides a more detailed and musical signal than the reQ-5. My future plans is to upgrade the front speakers (FOCAL???? components????) for a more musical and rounded sound (SQ over SPL).


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## silverdiesel2574 (Feb 22, 2008)

Im going this this right now but alittle bit different.
Im running W505 to AudioControl DQXS to Alpine PDX 4.150 front, 2.150 rear and 1.1000 subwoofer.
The amount of noise in my system was awful loud. As soon as you raise the volume you cant notice but at 0 or 1 the noise was super loud. Re wired the truck 2 times. Had a buddy that owns a shop help me for 2 days.
We see that the rear output of the DQXS is peaking out at times, so we changed out the DQXS this one does it too. So I swapped in the unit from my toyota its working fine.

2- BAD units from AudioControl one after the other and 2 different sources of purchase.
I'm calling audiocontrol and monday to see WTF is going on.
And yes the PDX are hissy for some reason. That was another problem. We kept swapping PDX for PDX until jose swapped in a ARC audio and an old Linear Power and no more noise..
We then bench tested the amps thru a jacobs accuvolt and the PDX's had noise. Thats with gains at half. The other 2 amps at full gains no noise at all. So now I'm rethinking my amp set-up. I got most of the noise out but what a PITA. I might switch to the new leviathan 6ch from ZED audio so I can get rid of the audiocontrol.


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## Gary Mac (May 12, 2009)

Were you guys using the pre-factory amp wires or the post factory amp wires for your systems? I am having the same problems.


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## sienna1 (Sep 4, 2009)

Speaker output from the OEM head-unit (no external factory amplifier)


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## Aaron'z 2.5RS/WRX (Oct 24, 2007)

Is there a reason for using the LOC, other than stealth? 

It won't ever be as good as an actual HU doing the work, not in my experience..


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## sienna1 (Sep 4, 2009)

Aaron'z 2.5RS/WRX said:


> Is there a reason for using the LOC, other than stealth?
> 
> It won't ever be as good as an actual HU doing the work, not in my experience..


I prefer the look and simplicity of the OEM head-unit. With the exception of a few (EXPENSIVE) after-market units, I find that most of them have too many small buttons and too much "BLING" (features I would never use) cluttering the face of the unit. I also don't like having to open the face of the head-unit to gain access to the CD's (the norm on many units). I've read articles comparing many OEM units to after-market that show very little difference in performance/sound quality, again....... the more expensive head-unit were the exception. With my car being parked on the driveway, it keep the chances of prying eyes to a minimum. In my set-up, the PDX-5 only has the ability to accept a 4V max input signal....... which would be border line for my OEM head-unit's output. With the LOC, I get the benefits of the amplifier/speaker upgrades without the advertising. The LOC also provides a remote turn-on signal which my OEM unit lacks. No need to mess with separate switches or turn-on/turn-off thumps.


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## Gary Mac (May 12, 2009)

any aftermarket HU I have used has always had better SQ, imo.... But when the heating, cooling, navi and HFL are intergrating into the factory HU, there is no other choice.


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## VP Electricity (Apr 11, 2009)

Using preamp signals - balanced or common-grounded - I have gotten similar performance to aftermarket in terms of noise floor and SQ. WIth speaker-level, it varies somewhat. 

I would expect a passive LOC to sound like ass. They usually have poor audio performance. I avoid them whenever I can...


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## sienna1 (Sep 4, 2009)

VP Electricity said:


> Using preamp signals - balanced or common-grounded - I have gotten similar performance to aftermarket in terms of noise floor and SQ. With speaker-level, it varies somewhat.
> 
> I would expect a passive LOC to sound like ass. They usually have poor audio performance. I avoid them whenever I can...


SQ is not an issue in my case except for a less than ideal noise floor. Both MTX reQ-5 and AudioControl LC6i LOC's seem to accentuate the noise floor that I've confirmed is coming from the head-unit. The extremely low hiss would usually not be noticed except when you become aware of it, then.... it seems to be bigger that it really is. While setting gains on the LOC and amplifier, you become more aware of low volume noise issues as opposed to just listening to music.


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## don_chuwish (Oct 29, 2009)

Wow, not sure how I missed this thread in previous searches, but it sounds like exactly the same hiss I've been trying to kill. The OP's '09 Corolla and my '07 Prius probably share a bit of stock HU genetics.
As in this thread, VP Electricity has been very helpful (via PMs). I have some 4ohm resistors on the way to try an experiment he suggested. Should arrive tomorrow.
I'm not completely stuck on keeping the stock HU but I don't see anything on the market right now that makes me eager to spend money on (even if I had it!).

- D


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## sienna1 (Sep 4, 2009)

don_chuwish said:


> Wow, not sure how I missed this thread in previous searches, but it sounds like exactly the same hiss I've been trying to kill. The OP's '09 Corolla and my '07 Prius probably share a bit of stock HU genetics.
> As in this thread, VP Electricity has been very helpful (via PMs). I have some 4ohm resistors on the way to try an experiment he suggested. Should arrive tomorrow.
> I'm not completely stuck on keeping the stock HU but I don't see anything on the market right now that makes me eager to spend money on (even if I had it!).
> 
> - D


I eventually changed my head-unit to a Pioneer AVH-P3100 (no more "hiss"). The OEM head-unit has an inherently high noise floor (confirmed even when set-up returned to factory configuration). Therefore, I don't think anything will cure this side-effect.


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## don_chuwish (Oct 29, 2009)

How depressing! Yes, if I re-attach a stock tweeter (direct to HU) as a test I can hear it hiss too, but just barely. I have to hold it up to my ear to catch it. One more cheap experiment with the resistor will tell me how futile it all is.
Happy with the AVH-P3100?

- D


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## sienna1 (Sep 4, 2009)

I've found that the level of "hiss" is different between head-units. The 3100 is great. The only negative, it only has 4 pre-outs (the new AVH-P3200 now has 6) but I've remedied that with a dual amp balancer (hard to find, not as common anymore). I also have the PAC steering wheel control, easier to access regularly used buttons (still find myself reaching for that volume knob). Tried everything to keep the OEM head-unit because of the ease of use but finally gave up in search of better SQ.


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