@suprarx7nut, I agree for the potential of the potentiometer to be too late in terms of the hiss but I am feeling determined to try it, at least to give me a bit more volume adjustability at the HU before being too loud.
To clear up a few things, my HU isn't an "android HU" it's got Android Auto and Carplay (features provided by Google and Apple). I chose NOT to use an Android based HU because I questioned the quality of their amplification and general circuitry as well as reliability and system lag. That said, I'd be embarrassed to say the major brand of the HU I got...it's basically the cheapest HU you can get with Android Auto capabilities and the next deck up is double the cost so it represents a fantastic value for what it is. Definitely not without its faults. For example, why ON EARTH do you include an antenna turn on lead but turn on the antenna ANY time the HU is powered on for any reason at all, including to display the backup camera even when the deck was otherwise off! Yes, it will fire up the antenna when I put it in reverse with the HU off...
The preamps are rated at 2V on my HU. I actually reached out to a local car stereo expert to get some clarification on the hiss I'm experiencing and he's shared some interesting things. I mentioned using some of the potentiometers he makes and sells and he all but ignored that part (which leads me to trust his advice somewhat since he wasn't trying to make an easy sale). He says the hiss is the noise floor of the HU and if it had a hotter signal from the RCAs, the amp wouldn't have to listen to the noise (and amplify it). I think he's crudely explaining signal to noise ratio but he didn't use the term. He claims the factory radio can send voltages to the factory amp up to 16volts by amplifying the 12v system...Not sure I buy this. To me, it seems more likely that the factory radio is sending out a low signal which is why the gain seems to be so high on the factory amp. He's claiming I should try passing the high level speaker leads to the factory amp and this will get rid of the hiss but I'm not sure I'm buying that.
As for the volume too high, I do think it's mostly because this is a cheaper HU so it's volume control is a bit basic and doesn't have much resolution for variability. I do think the potentiometers WILL help in that regard. If it reduced the hiss, that would be icing on the cake. I think the potentiometers will fit behind the AC controls in that dead space, I don't plan on installing them for constant tinkering, hoping to set and forget if I can.
I'm not sure my hiss is even the same that others have experienced. I really can't even hear mine if the cabin fan is turned on and blowing or the vehicle is on the freeway. It has to be at a dead stop and quiet to notice the hiss.
Some of that shop's advice scares me.
1. High-level signals are VASTLY different than the low-level RCAs. When setting up amps with a multimeter you can set the gain by the output AC voltage of a test signal. Typical values are on the order of 17-35V. I very much doubt the factory amp is setup to accept that as an input voltage without damaging something. Maybe the headunit's internal amp is puny enough to barely produce a voltage worth worrying about, but that seems like a dangerous gamble.
2. Noise floor in my mind just means the ground loop is different. You can't remedy that with anythign short of internal circuit modification of the head unit or amp. There are band-aids, but they are all just band-aids. The only "correct" fix is removal of the factory amp, IMO.
3. Antenna turn on lead: yeah, that's a sign of a really cheap manufacturer reusing parts from other products or failing to implement software plans.
I'm no car audio expert though, so maybe the shop is right. :dunno:
I think my next steps are to test the RCA shield ground to chassis ground with my multimeter and maybe add fused ground wires on the RCA grounds to the HU chassis bolts? Might be worth a try to see if I can get rid of the whine to be able to use the PAC LC-1 devices to solve the original problem!
