Slight hiss in speakers?

[lowkey37]

Hello friends, I just added an external amp and new component/coaxials in the front and rears. Stock amp and nav are still in place so signal is going through jbl amp then to my new 4 channel before it reaches the speakers. The sound is awesome, very detailed and full, in comparison to stock. One problem, there is a slight hiss that I have read about others having! Has anyone figured this out? My installer says if I increase power to speakers, gains can be turned down which would decrease the hiss. Any thoughts from u guys would be appreciated. Specs: 2005 land cruiser w/ nav, Rockford T3 components up front with T1 coax in rear, powered by Memphis mr-480 class D amp. By the way all my stock jbl speakers are for sale!

Mike

 

[N8maher]

Ditch the stock. By having two amps in series you're probably getting way more voltage gain than you need so try bypassing the stocker and see if that cures the hiss. Otherwise you'll be stuck trying to track the source of the hiss which could be the new amp or the head unit. It could also be your source material if you're hearing it between tracks. But if its with the material paused it's likely to just be line noise from over amplification so my suggestion is to start there.

 

[marshotel]

It is likely that the newly installed amp is creating a ground loop, or it is picking up noise from the power source, and that is the source of your hiss.

Use a 'ground loop isolator' at the point where the signal goes into the new amp:
http://www.crutchfield.com/p_127SNI1/PAC-SNI-1.html?tp=2653


Also try a noise filter on the +12v running into the new amp.
http://www.crutchfield.com/p_003S25A/American-International-S-25A.html?tp=2653

This should be a relatively cheap and easy fix. Both filters can be had from crutchfield for ~$30, or from your local Radio Shack. You can install the noise filters yourself where the power and signal go into the new amplifier.

As your installer suggests, you might also want to turn down the gain settings on the new amplifier (usually little potentiometers that you turn with a small flathead screwdriver) to minimize the hiss. Just make sure that after adjusting the gain on the amp you can still adjust the volume to comfortable levels using the knob on the dashboard. You should be using about 75% of the range of the knob on the dash to achieve loud listening levels. i.e.- if you have the knob on the dash unit set to 10% and the music is already too loud, then turn down the gain on the amp.

Ask your installer to make sure that the new amp is hooked up correctly: i.e.- if you are running the speaker-level signal from the stock jbl amp into the new Memphis amp, then you better make sure that the new amp is set-up to handle speaker level inputs, or else you will fry the input stage on the new amp. The facts that you have made it this far and that it sounds good suggest that you are on the right track.

The problem with "bypassing the stock amp" as N8maher suggested is that I think Toyota uses a proprietary signal from the stock head unit to the stock amp on the 2003+ models. If you run the signal directly from the stock head unit to an aftermarket amp, I don't think it's gonna work. I have also heard that the nav system quits working if you remove the stock amp. It is all integrated.

So I would suggest keeping the stock amp in place. If you are running the signal out of the stock amp and into an aftermarket amp, just make sure the aftermarket amp is setup correctly to accept speaker-level inputs. Otherwise you could fry the input section of the new amp. Install ground loop isolator and line noise filter, adjust the gain on the amp and you'll be good to go.

Hope this helps.

 

[ogsuv]

I 2nd the thought about the 2 amps. Amplifying an amplified signal is no good. You will likely never get rid of that noise. If the nav is integrated, leave the factory amp in there but use the input side of the audio rather than the output side to feed the Memphis. Just my $.02

 

[lowkey37]

I didn't think you could maintain nav controls if the stock amp was ditched? Pease correct me if wrong. Has anyone successfully removed the stock mp and maintained nav controls?

 

[marshotel]

If the nav is integrated, leave the factory amp in there but use the input side of the audio rather than the output side to feed the Memphis.

I agree with this, but I was under the impression that the signal from the head unit to the input side of the factory amp on 2003+ models is a 'proprietary signal,' meaning that you have to go through the factory amp first in order to get a signal that the aftermarket amp can use.

I don't think the factory head unit uses the equivalent of line-level RCA outs for each of the channels, which is ideally what you would want to feed the aftermarket amp. -Please let me know if this is incorrect.-

Regardless, plenty of fine aftermarket amps are capable of accepting a speaker-level signal, and as long as everything is setup correctly, you should have no problem using the output of the factory amp to feed your aftermarket unit (i.e.- amplifying an amplified signal).

Use whatever sounds good to you.

I still think the power line filter and ground loop isolator installed at the aftermarket amp will eliminate the hiss. It is easy enough to find out, and if it doesn't work, you can return the parts to Crutchfield and get your $30 back.


In response to lowkey37: I think you need to keep the factory amp in there in order to use the factory nav. Again somebody may have found a workaround for this. -let us know-

Thanks.

 

[lhommec13]

Deleted the factory amp in my 2002 LC and replaced with aftermarket amp and still running factory nav. Can be done, at least in 2002 (and earlier?) model years.

 

[lowkey37]

That's good to hear! I believe 2005 is a little differant. Can anyone confirm?