# Hiss of static with gain up



## don_chuwish (Oct 29, 2009)

This must be a DQ because I don't see a better forum for it.

With great expectations I finally put in the used JL 300/2 I got for my front comps (Boston SL60). Since the 300/2 takes either high or low level inputs at the RCAs and I'm stuck with the stock HU at this point, I went with high level inputs tapped off of the speaker wires. Just clipped one end off a cheap Stinger interconnect, stripped, and made the connections. Even with the gain way down I got a lot of hiss from the tweets, like white or pink noise. I verified it's not from the amp or speaker path, playing a different source (iPod) through it directly produced no hiss.
So I tried a different interconnect, a little better job stripping and connecting the fine wires but still got a hiss, tho quieter and more 'pink' this time for some reason.
So after killing about $30 worth of interconnects I grabbed an $18 Scosche LOC at Walmart as a cheap experiment.
Switched the amp over to low level inputs and made the connections. Turn up the gains on the LOC more than a tiny bit and I get hiss. Gain on the 300/2 has to be kept minimal as well.
When the stock HU was directly feeding the speakers there was no hiss. The amp doesn't cause the hiss, so it must be between the two, correct? But I've tried three different paths and they're all noisy. Kinda sucks to have 150W per channel available but keep it throttled back so much!
Ideas anyone? Any help appreciated!

- D


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## quality_sound (Dec 25, 2005)

My bet is the OEM HU DOES produce hiss but doesn't have enough power to make it audible. Only thing I can think of.


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## sqshoestring (Jun 19, 2007)

quality_sound said:


> My bet is the OEM HU DOES produce hiss but doesn't have enough power to make it audible. Only thing I can think of.


:smart: I agree.



Have to remember you are amplifying the signal much more than before. Garbage in, garbage out.


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## Hernan (Jul 9, 2006)

don_chuwish said:


> This must be a DQ because I don't see a better forum for it.
> 
> With great expectations I finally put in the used JL 300/2 I got for my front comps (Boston SL60). Since the 300/2 takes either high or low level inputs at the RCAs and I'm stuck with the stock HU at this point, I went with high level inputs tapped off of the speaker wires. Just clipped one end off a cheap Stinger interconnect, stripped, and made the connections. Even with the gain way down I got a lot of hiss from the tweets, like white or pink noise. I verified it's not from the amp or speaker path, playing a different source (iPod) through it directly produced no hiss.
> So I tried a different interconnect, a little better job stripping and connecting the fine wires but still got a hiss, tho quieter and more 'pink' this time for some reason.
> ...


I just read the 300/2 specs at the official site.
It has not high level input, just low level.
The input sensitivity swich ranges from 200mv to 2v at high and 800mv to 8V at low.
You need a high to low level converter.


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## don_chuwish (Oct 29, 2009)

quality_sound said:


> My bet is the OEM HU DOES produce hiss but doesn't have enough power to make it audible. Only thing I can think of.


Yeah that thought tickled my brain too, just didn't let it fully form (denial, LOL!). A different HU is in my future, just hoped to put off the spend a bit longer. Thanks for helping me face it!

- D


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## don_chuwish (Oct 29, 2009)

Hernan said:


> I just read the 300/2 specs at the official site.
> It has not high level input, just low level.
> The input sensitivity swich ranges from 200mv to 2v at high and 800mv to 8V at low.
> You need a high to low level converter.


Thanks Hernan, at this point I do have a LOC in place and it helped. But reading the manual, it says:
"The “High” position on the “Input Voltage” switch selects an input sensitivity range between 800mV and 8V.This is useful for certain high-output preamp level signals as well as speaker-level output from source units and small amplifiers.To use speaker-level sources, splice the speaker output wires of the source unit or small amplifier onto a pair of RCA plugs."
JL even sells some pre-cut RCA wires for this purpose JL Audio - RCA to Speaker Wire.
One thing I've noticed is that the hiss is pretty obvious sitting in my garage, but not so much out in the world, even parked. I may turn up the gain just a bit more and see if I can live with it for now. Gotta pace the spend on this project!

- D


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## sqshoestring (Jun 19, 2007)

The newer MTX automatically switch to take speaker level into the RCA.


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## yoshiboy_21 (Dec 11, 2009)

I wouldnt advice on purchasing the JL Audio RCA to speaker wire. Your LOC should be just as good.

The LOC should have a gain setting. Set the gain on the LOC on the lowest level possible. See if the hiss disappears if the your gain is on the lowest level.

At the same time, set the level of your amp somewhere in the middle just to hear if there is signal coming.

If there is an invput voltage setting(I'm not familiar with JL amp settings), switch it to the lowest first. With these, you should have the lowest noise possible with the engine off.

Now if the hiss is a whole lot lower or barely audible when the setting on the LOC is on the lowest level, keep it at that level at the LOC then just adjust your gains on the amp.

Let me know if this helps.


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## don_chuwish (Oct 29, 2009)

Thanks Yoshi. Yeah, already tried my own "RCA to speaker wire" splice job with no luck. No reason to think JL's version has any magical properties.
You're advice is right on with what I went through. The gains on the LOC can barely be cracked open, then same on the amp. Net result though is not much power. When I was using the high level inputs and "RCA to speaker wire" splice job the noise level was unacceptable but the power was great, really brought the speakers to life. Now, not so much!

- D


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## yoshiboy_21 (Dec 11, 2009)

By the way, what kind of car do you have? Do you know if your car has a built in amplifier?

Did you splice the wire behind the head unit or spliced it near the speakers?


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## don_chuwish (Oct 29, 2009)

2007 Prius package #2 - no JBL upgrade so no amp. I spliced about 2 inches from the molex that comes out of the back of the HU. Actually clipped the wires and connected with crimped spade disconnects. Good, solid crimps, promise.

- D


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## yoshiboy_21 (Dec 11, 2009)

Is your amp at the back? 

Try tapping from the rear speaker output. See if it produces the same hiss.

This guy did it that way. http://www.diymobileaudio.com/forum/diyma-build-logs/71700-2007-prius-mild-upgrade.html

You and him have the same amp.

I believed you posted there too.


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## don_chuwish (Oct 29, 2009)

yoshiboy_21 said:


> Is your amp at the back?
> 
> Try tapping from the rear speaker output. See if it produces the same hiss.
> 
> ...


LOL, that guy is me! I have yet to update the build log with this latest work. I only tapped the rear in that case for the sub in back. This is for the front comps, amp is under the passenger seat. Nice part about getting this 300/2 installed is that now I'm using it's preamp to feed the J2 250.1 mono sub amp - no more speaker level input for it.

- D


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## tanakasan (Sep 8, 2007)

don_chuwish said:


> Nice part about getting this 300/2 installed is that now I'm using it's preamp to feed the J2 250.1 mono sub amp


Try temporary disconnect your RCAs to the sub amp...ground loop issues? Recheck amp ground. No paint, good connection to solid steel? Hiss sucks! G/L!

Robert


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## yoshiboy_21 (Dec 11, 2009)

don_chuwish said:


> LOL, that guy is me! I have yet to update the build log with this latest work. I only tapped the rear in that case for the sub in back. This is for the front comps, amp is under the passenger seat. Nice part about getting this 300/2 installed is that now I'm using it's preamp to feed the J2 250.1 mono sub amp - no more speaker level input for it.
> 
> - D


Ooops. My bad. I should have read who posted it. lol


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## yoshiboy_21 (Dec 11, 2009)

The only I'm asking to try to tap at the rear speakers just to see if there is a hiss if you tap from there.


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## don_chuwish (Oct 29, 2009)

tanakasan said:


> Try temporary disconnect your RCAs to the sub amp...ground loop issues? Recheck amp ground. No paint, good connection to solid steel? Hiss sucks! G/L!
> 
> Robert


Thanks for jumping in, from what I can tell it's not ground loop. I've heard that before and this is different - just a steady hiss. But thinking back on it I can't remember if I ever tried it without the sub amp connected. It'd be about the easiest thing to check...... nope, no difference. Thanks tho!

- D


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## don_chuwish (Oct 29, 2009)

An update on this, for reference. I got a very lightly used (looks brand new) AudioControl LC6i off of a fellow Prius owner for $70. He got a new HU after having the LC6i for only a month. I wasn't sure it would fix the hiss so I didn't want to spring for full retail on one. This way I can pretty much break even if I decide to sell it off.
Put it in last night, hardest part was finding a place for it.

At first I tried their documented method of optimizing the level control but with it set that high (almost maxed the pot) the hiss was pretty loud. So then I just started trying to dial away the hiss. If I keep the level control on the LC6i at about 25-30% the hiss fades to something less than other ambient noise (like the fan for the display screen). Then if I crack open the gain on the amp gently until I notice hiss, then back off just a bit I can make it effectively go away. Put your ear to the tweets and you'll hear it tho.

Then listening to some tunes I was unimpressed with the fullness, so I played with things a bit more, making them a little hotter but still an OK level of hiss. End result is that I have to turn up the volume a little more but the hiss is next to insignificant and the sound is good. Also moved the RCAs for my sub amp off the 300/2 pre-amp output and onto the LC6i. Can't be sure if it's any better or not to be honest. Certainly not worse.

So the LC6i didn't magically erase the hiss, I didn't really expect it to, but it did give me better control over it.

- D


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## putergod (Apr 23, 2008)

Try a Matrix after the LC6i, but before the amps. Or an EQS or similar EQ/Line driver combo.
I have a similar issue with an aftermarket system in a GTO. Have two line drivers (Matrix and EQS) all but eliminated it. You could BARELY hear it, and I was able to have good about at resonable volume level with the amp gains at minimum.


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## don_chuwish (Oct 29, 2009)

Wow, thanks for revisiting this. But at this point I think I'm done fiddling until I find a HU worth my money.

- D


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## sienna1 (Sep 4, 2009)

don_chuwish said:


> Wow, thanks for revisiting this. But at this point I think I'm done fiddling until I find a HU worth my money.
> 
> - D


It's your HU. I had the same problem with my 09 Corolla's OEM HU. Began with a MTX Re-Q5, then tried a LC6i with the same result as you have described. Finally solve the problem with the annoying HISS - I changed the head-unit to a AVH-P3100 = NO HISS (even with an Alpine PDX-5 for amplification).


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## don_chuwish (Oct 29, 2009)

Yep, I'm at that conclusion too, just haven't seen an aftermarket HU that makes me happy enough to take my cash. I can wait!

- D


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## ghostmechanic (Mar 2, 2009)

You could just trade the car off on a real car! Then you'd be able to stop too:laugh: I'm just joking. It's good you got it under control & I agree with you about it probably being the head unit. I also agree about buying a new. I've thought about "upgrading" my head unit but I'm less than impressed with anything I see.


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## don_chuwish (Oct 29, 2009)

ghostmechanic said:


> You could just trade the car off on a real car! Then you'd be able to stop too:laugh: I'm just joking.


Oh hardy har har. :laugh: I actually had a great emergency braking situation just the other day and I must say that in my other car there would have been contact, but there wasn't. Just scared the crap out of my wife is all.

- D


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## Hernan (Jul 9, 2006)

This is not by the book recipe but deserves a try:

Isolate your OEM HU from ground. You could just take it from the dash and remove the ground wire. Try it before putting it in the bay. (as a LapHU... ja ja)

This solves the problem at some installs.

If this works, no ground and some isolation from the metal cage and call it a day.

Good luck!


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## ghostmechanic (Mar 2, 2009)

don_chuwish said:


> Oh hardy har har. :laugh:


Glad to know you saw the humor. I'd never really make fun of a man's car. At least not to his face:laugh:

Though there is one question I always wanted to ask a Prius owner... Do they really top out at around 45 MPH? Because I swear any time I encounter a Prius on the highway, that's about the rate they're going & of course there's too much traffic to pass Just curious.


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