Issue with hiss through amp

[ashren315]

In my install I have a 3 way front stage set up. I will give you the rundown of the install.

Kept stock HU.

HU runs to 3Sixty.3 through high level input.

Focal Tweets and 4" midrange from the Power ES line run off of old school (1999) Fosgate 600a4

Old school Fosgate 6.5" midbass in kicks from their FNQ line of comps and one old school Fosgate 12" DVC sub running off an old school Fosgate 800a4. I have one set of channels bridged for the sub and the other two run the midbass.

The problem I'm having is with the two channels that run the midbass. Unless I cut the low pass filter on on those two channels, I get a static like hiss sound coming through the midbass speakers, once you flip the switch to turn it on, it clears up. The two channels I have bridged to the sub do not exhibit this issue.

Any ideas what would cause this?

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[LosIsATool 5,000+ posts]

So it's only coming through a narrow passband?

What car? My **** Ford has a bad noise floor at low to no volume

 

[ashren315]

2013 Chevy Spark and it's only through the midbass and only when the filter is turned off.

 

[shredder1 10+ year member]

That's weird... I remember a local guy that had a RF800.4 and ran it bridged on a set of channels then later had the same problem in another install... I'm not an amp technician but it turns out that he damaged something running it bridged in the first install... it was at like 2.66 ohm... anyways the fix was not too bad... $75 from a tech in Tucson... Probably not YOUR problem but it does sound the same.

 

[ashren315]

I'm running the bridge to an 8ohm sub (4ohm DVC) so it shouldn't have damaged anything and it's not doing it through those channels. I have the filter turned off on those channels and just letting the 3Sixty.3 handle the filtering.

 

[shredder1 10+ year member]

I'm running the bridge to an 8ohm sub (4ohm DVC) so it shouldn't have damaged anything and it's not doing it through those channels. I have the filter turned off on those channels and just letting the 3Sixty.3 handle the filtering.

Just a question... are you the only owner of the amp?.. was it new?..

 

[LosIsATool 5,000+ posts]

I'm running the bridge to an 8ohm sub (4ohm DVC) so it shouldn't have damaged anything and it's not doing it through those channels. I have the filter turned off on those channels and just letting the 3Sixty.3 handle the filtering.

Go into the DSP and move that channel around. See if the noise follows it. Just be careful with the crossover points

 

[ashren315]

Just a question... are you the only owner of the amp?.. was it new?..

Yes. I purchased these amps new many many years ago.

I think I might have figured out were it's coming from. I think it's in the rca inputs on those two channels. If I move the cables around, I can get it to go away. Just pulled the amp to open it up for a look.

 

[ashren315]

Looks to be the RCA inputs. Just took the amp apart and that one is loose on the backside of the board. About to solder it and put it back together an test it out.

 

[shredder1 10+ year member]

Looks to be the RCA inputs. Just took the amp apart and that one is loose on the backside of the board. About to solder it and put it back together an test it out.

You're a braver man than I am... Rockford stuff can be tricky...

 

[ashren315]

Ok. Either I'm terrible at soldering (entirely possible) or that was not the issue. It is still puzzling that if you move the cable at the input around, you can find a spot where it goes away. I just remembered another interesting thing that's happening with it. If you crank the car while it has the static sound, you also get engine whine through those channels only. Absolutely nothing but clean sound comes through the channels I have bridged for the sub. I've tried switching RCA cables around. I've tried different settings with channels on the DSP. Another interesting thing about it. I just hooked up the midbass speakers to it tonight as the kick panels are not covered yet but I just wanted to hear what they sounded like before I covered them and even before I went into the DSP to open those channels up, it was doing it. That leads me to believe it's not coming from the DSP and solely from those two amp channels.

 

[ashren315]

Well, I can't figure it out. It's definitely in those two channels only. I guess I'm just going to have to find someone who knows more about them than I do to see if they can repair it.

 

[shredder1 10+ year member]

Well, I can't figure it out. It's definitely in those two channels only. I guess I'm just going to have to find someone who knows more about them than I do to see if they can repair it.

Almost every 800.4 Rockford I've seen that's been in more than 1 install and run in 3 channel mode in both installs has exhibited that exact same problem... it might not be the amp, but I've seen it before... NOT LOL!

 

[ashren315]

This is the first time I've run it in 3 channel mode. I haven't tried disconnecting the sub and leaving the 2 midbass drivers hooked up to see what that does.

If it is a problem with it being used in 3 channel mode I guess I will have to buy new amps since I want both amps in the install to match. My only other option is that I do have some old 800a2 amps. I could use one of those but I would lose the ability to adjust any settings between the right and left midbass drivers. On the bright side, it would be give me way more power to the sub and the two midbass drivers.

 

[shredder1 10+ year member]

Nothing is certain in this case... I'm only making observations here... Someone may find the magic fix yet!