Quote:
Originally Posted by kmarei
well i can't argue about what the article you quoted says, because the first line said "Unplug the RCA cables from the amplifier/s"
if you disagree with that, there's not much i can do to help.
the inputs can pick up noise, but you have already decided they will.
i said unplug the rcas from the amp, so the amp is not connected to anything.
if the hiss goes away, then the hiss was coming from the headunit.
if the hiss remains, then you know it's from the amp, at which point shorting the plugs would not be of any benefit, since a properly functioning amp should not pick up noise from it's inputs anyway.
i've used the Xd600/6 and it did not pick up noise nor have a noticable hiss on the outputs
i don't need to google something i already know, and have successfully used many times, nor do i need to name drop. 
i just had an issue with you trying to over-complicate things
in suggesting an oscilloscope was required to set the gains.
Most JL audio amps i've seen have already done the work for you
and they tell you how many volts should be present at the outputs to achieve max gain. so you don't need to watch the signal on an oscilloscope to make sure it's not clipping.
with troubleshooting any noise, you start removing things one at a time till you find the culprit. |
Oh, Jesus Christ. I think JL used to recommend the o-scope method on their site. They now recommend THIS method (apparently many people did not have o-scopes - imagine):
http://mobile.jlaudio.com/support_pages.php?page_id=143
I asked if he used an o-scope. I didn't TELL him to use an o-scope.
I will agree that you can't plug shorting plugs into an amplifier's RCA inputs WITHOUT unplugging the RCA cable from that RCA input FIRST. But in the words of Inigo Montoya, "I don't think that means what you think it means."
To the OP: The technique described for gain setting is intended to make sure you develop max clean power out of your amplifier. Depending on what speakers you have, you may not ever want to develop 75W PC out of your amplifier. What I suggest you do is play the system with a good CD, onme with a decent loudness (no Rickie Lee Jones), turn the volume all the way down on the head unit, then turn it up slowly and count the clicks. The volume controls on the BMW HUs have between 47 and 54 clicks (seems to vary with firmware). The last 5 clicks are usually distorted, so that gives you 43 to 49 clicks of usable volume.
So turn the volume up slowly and count the clicks. If you get to a loudness that is way too high for you to ever use while still in the 20s or low 30s in your click count, your amp gains can be safely lowered without you losing any of the usable volume from the system - and your hiss will improve.
It is possible that the amp is the problem. However, until you try lowering the gains, you don't know.