I have an RN-52 bluetooth audio module - https://cdn.sparkfun.com/datasheets/Wireless/Bluetooth/rn-52-ds-1.1r.pdf
I am using it with this amplifier - https://images-na.ssl-images-amazon.com/images/I/B10A-G24SrS.pdf
I am using these speakers - https://www.amazon.com/dp/B01IN8YI4Y/ref=sxbs_sxwds-stppvp_1?pf_rd_m=ATVPDKIKX0DER&pf_rd_p=d45777d6-4c64-4117-8332-1659db52e64f&pd_rd_wg=AALON&pf_rd_r=6Z3DA4J7GSR0E1KRMZNE&pf_rd_s=desktop-sx-bottom-slot&pf_rd_t=301&pd_rd_i=B01IN8YI4Y&pd_rd_w=zkxrm&pf_rd_i=8+ohm+speakers+15+watts&pd_rd_r=4a779bab-7431-4589-b841-82d4479e7677&ie=UTF8&qid=1540677652&sr=1
I am experiencing a hum in the left channel, I am using a ground loop isolator, and the right channel is clear. I have made sure it isn't the speaker by switching the speakers that I was using for each channel.
On the RN-52 my soldering connections seem solid, one thing I am not sure about is (you can see on the RN-52 datasheet), one of the ground wire connections is very close to the L+ connection on the module. The solder I am using for these two connections is very close to touching, and possibly touching, but I don't think that it is. I have used flux to try and lightly wear down the side that has the larger amount of solder (the ground wire connection) to try and make sure that it is not touching the L+ connection.
I also tried re-soldering the L- connection on the RN-52 (to see if it was the - connection and not the + connection) because I wasn't sure if there was enough solder. Also the soldering points on the RN-52 are very small, so it isn't really possible for me to see, even with my magnifying glass, if everything is perfect - I am just kind of going by the result that I get when I test it.
Wire connections (I know it is not the best picture, but you can see on the two connections furthest to the right, they seem pretty close together with the solder):
Some questions I have, with the hum - is it possible to narrow down whether it is the L+ or L- connection? Is it possible that only the + connection could cause this, or only the - connection could cause this? Could it be something with the amplifier? Could it be the 3.5mm wire I made to connect the RN-52 to the amplifier? Could the + connection very slightly touching the GND connection on the module cause a hum? Also, I am not using speaker wire, it is just electrical wire, but the fact that one channel works regardless of the speaker (and the wires) I think means it isn't the problem.
Any help would be great, thanks.
I unplugged the RN-52 from the amplifier, so it was just the amplifier and the speakers turned on, and the buzzing goes away - so that concretely narrows the problem down to the RN-52 or the 3.5mm wire I made to output from the RN-52 to the amplifier.
Something that is interesting though...if I unplug the power to the RN-52 but keep the 3.5mm cord plugged into the amplifier, and then turn on the amplifier, so it is only the amplifier and the speakers powered, the buzz returns.
This makes me think that the problem is with my 3.5mm cord, and how it is interacting with the 3.5mm input on the amplifier (there is also an RCA input on the amplifier, but I used an adapter to try and use that and the buzzing continues, so this further narrows it down to my custom-made 3.5mm cord?). Could this be it? Or could the problem still lie with the soldering connections, even though the RN-52 isn't powered when I hear the buzzing?
Also, I am using two 12-volt plugs (one for the amplifier, and one for the RN-52, not super efficient i know, it at least makes the DIY soldering situation a little less messy). Both of the power cords are plugged into the same powerstrip, I read that the problem could stem from the wall jack, or a powerstrip and that there are "filtering" power strips which can eliminate a hum like this, but I also am already using a ground loop isolator, so I was wondering if that is all a "filtering" power strip does.
Another bit of information that might help narrow down the problem. When I use this equalizer on my mac, https://bitgapp.com/eqmac/ and set the output to the bluetooth speaker, it reduces the hum significantly - how is it doing this? Could this be a firmware issue with the RN-52? Why is software on my computer reducing the hum? Also, the wire for the L+ connection on the RN-52 is a little unwound before it hits the soldering point, I know cleaning this up would help (eliminating the area of uncovered wire, and resoldering) but I was wondering if adding solder to the unwound part of the wire would make it better at conducting, and possibly eliminate the hum?
In the amplifier document above, it says:
"When you connect the difference input, two jumpers need to remove." I am using the 3.5mm jack right now, and there was still a hum with it, and I am in the process of rewiring the RN-52 to try and clean things up, but I am wondering. If I use the (RCA) "difference input," as they call it, and remove the jumpers, would it help with the humming maybe? Or do the jumpers have nothing to do with the humming?