(because it doesn’t know the words!)
I use a Monoprice 3.5 mm to RCA cable to plug my Galaxy SIII into a simple AuidoSource 100 watt amplifier, which drives a large set of Paradigm speakers. When the phone is plugged in, I’ll often hear a very low hum/buzz from the speakers. This changes with a few things. It’s most noticeable when the amp and/or phone volume is turned up. It goes away (usually temporarily) if things change on the phone, but I’ve found no pattern. That is, sometimes it will go hmmmmmmmFLT if I hit the home or sleep key or change the running app. But then a short while later it will come back. Or it won’t be there in the first place, but starting an app or waking the phone will start it.
How do I figure out why it’s doing that and how do I stop it?
Bonus question: is the sound at all related to the louder hum that happens when I touch the business end of the cord’s 3.5 mm plug? Is that harmful to the amp?
Super Bonus Round question: We want to use the phone as an alarm (this setup is in the bedroom), but we keep getting an “are you sure you want to turn the volume up so high?” warning (and it won’t make sufficient noise unless you click ‘yes’). Any way to disable that?
Is the hum the same pitch, or does the pitch change? What sort of pitch is the hum? DOes the hum have the same pitch as when you touch the end of the 3.5mm plug? (Doing so won’t usually harm the amp, but if the amp is turned up you may risk your speakers.)
There are quite a number of potential sources of interference within a phone - there are multiple switch mode power supplies, and there are also some interesting oddities that than occur in some DAC designs.
The pitch is constant. Tinnier than when I hold the jack directly, but I think that’s a fullness issue, not the pitch.
It’s close to what I remember as sounding like that buzz from a ground loop issue, but it’s been years since I heard it.
The amp is two-prong and when the phone has been plugged in, it’s with a charger that plugs into an ‘outlet’ on the back of the amp. Would either of those negate the possibility that it’s a ground loop buzz? If not, is it as simple as one of these?
Years ago getting rid of a hum was often as simple as rotating a power plug 180 degrees to flip the neutral. Now every damn cord and outlet you find is polarized and you can’t flip most plugs. Once again convenience yields to safety.
Assuming all the plugs are polarized then there is no need to rotate the plugs.
Any ways, does the hum only exists when you have the phone charger plugged in? I’d try both, plugged and unplugged, see if there is a difference.
Another real possibility, as I look at images of your amp, is that it uses a two-prong plug. Since way back in the day, I always have a chassis ground. Either by using separate ground wire to a screw on the chassis to the center screw on the wall-plate. Or, what I prefer to do, is replace the cord with a three-prong cord and take the ground to chassis from there.
Another option might be to take the AC phone charger out of the system and use an external battery to charge your phone at night. A bit more inelegant than the filter but you would then have an external battery which can come in handy. Just charge the external battery during the day.
Haven’t experimented yet, but if the buzz remains after the phone is unplugged, does that point to something other than a ground loop, or is the evidence just that strong that it is? Or is it possible that the issue could persist whether or not it’s plugged in?