LM4880 Question

[Blargaman91]

Hi everyone. I have a question - asking for opinion, really - about a lot of hissing that I get from my GameCube. I just built a small amp with a stereo amplifier chip, the LM4880, and it's surprisingly efficient, but it has a hissing problem with my GameCube. At any level of volume, some hissing is audible, but it does change with the volume knob. The hissing is also not present when using other devices to input sound. So, the hissing is coming from the GameCube (kind of strange) and is coming from the AV chip before it hits the pre-amp. I even get a considerable about of noise from an un-modified GameCube that is still in its shell? It must be some kind of interference, but what do most people know to cause that? My wires are scattered about, but from what I can tell, none are so close as to cause such loud hissing (it is bad with headphones). Just any helpful advice would be nice, if someone knows about it.

 

[DuHasst0]

Try shielded cabling for both your inputs and outputs. Also, did you use new components, cause if not you could have one or more that don't like you or your amp. So if ya did, get some more give it a try.

 

[Blargaman91]

Yeah, the components I used were all new, but I don't have any to make another one. Mouser screwed up my order and sent 2 small SMD capacitors instead of 2 reels of 10. Same with all the components. I found the exact same hissing is still there when connecting headphones directly to the GameCube (no amp) with short wires, so that must be some really elusive interference. I don't understand...

 

[DuHasst0]

How do you have it connected? Did you trim your board? If you did l, did you relocate your caps?

 

[Blargaman91]

I have not trimmed the board yet, but I have removed the caps. I put them back on to make sure, and it made no difference. I never had this loud hissing problem with my last 4-5 motherboards, all trimmed OMGWTF. I never did connect headphones directly to the other cubes, though, so maybe they all had that problem and this amp I built is just not good at handling the natural interference.

 

[DuHasst0]

Are you using shielded cable? I want to say that is the issue, but I could be wrong.

Edit: can I get a pic of the amp you built?

 

[Blargaman91]

The whole setup is messy. No shielded wires, except for video (partially).

The amp is not cut out of the board it was built on yet.

But even though my wires are long and unshielded, I can't help but think that doesn't really affect anything because I still get the exact same background noise if I connect a pair of headphones directly to the GameCube with short wires. My amp also has no background noise with other devices, still having these long wires and whatnot.

I'm so confused... I think I may have a damaged AV chip.

 

[DuHasst0]

Check everything with a multimeter and look for any shorts that could removing the caps from the amp it self because of a short. It is kind of a mess but for sure check that circuit dude.

 

[Blargaman91]

Dang, NO shorts whatsoever. I mean, the hissing is definitely coming straight from the GameCube's AV chip, regardless of what's going on with my amp. If I can't identify the source, is there some way to effectively reduce that hissing within the workings of the amp? I imagine there has to be some way.