I have one of these LG Optimus smartphones (Android) that I use as a podcatcher and to stream audio content. It's a new age Walkman basically for me.
I've been using these (I have several) to stream content to the Talking House I have.
Have a big problem though.
When I plug the phone in to recharge it, there is a very strong hum that is very audible and annoying that makes the AM transmit sound unbearable.
The charge port is a USB mini port, very standard.
I though it might be the wall main power plug causing issue, so I used a USB cable from a nearby computer and experienced the same hum. Clearly it is originating somewhere in the phone in the charging mechanism.
Is there a way to filter or clean this hum up?
It's not the end of the world. Just makes my options for testing audio harder as the phones pickup our wifi signal on both lots and very convenient right now as I begin planning site/spot checks for the system.
The charger has a half-wave rectifier which will cause hum. Some are also of the switching supply type and those too cause hum.
Just tear open the charger and either add a full bridge rectifier and at least a 2200uF electrolytic cap for filtering. If it's a switching type supply, just add more filtering with an electrolytic cap on the output, around 1000uF or so.
RFB
Can ya isolate the audio out thru a 1:1 isolation transformer? Try it, ya mite like it..
1:1 isolation transformer? Those are new to me.
Is there is source of reasonable affordable models? Seeing rather high costs for these and unsure if right thing.
Where would the isolation transformer get put in the chain of things?
http://www.amazon.com/PAC-Ground-Isolator-3-5-Applications/dp/B001EAQTRI/ref=pd_sim_sbs_pc_1
Dual 1:1 600 ohm transformers for both channels. Isolates your audio source to whatever you connect it to. They do wonders..
Thanks @12vman! Awesome low cost device there.
This piece should be mandatory for anyone getting started with Part15.
Similar problem at a public venue where a DVD player had to be patched into a stage amplifier system.
Thing BUZZZZZZZED terribly until I put an isolation transformer on the audio line.
Isolation transformers are great. They do solve a lot of problems when interfacing different types of equipment, especially properly grounded equipment with non-grounded equipment such as a typical DVD player which sports a standard polarized AC plug but without a ground lug compared to the amplifier system which the PA no doubt had a proper 3 prong grounded plug.
RFB
And it didn't help that the DVD and stage amplifier are about 300 feet apart on separate power feeds. This is a prescription for ground loop problems.
Breaking the ground loop with the isolation transformer solved the problem.
"And it didn't help that the DVD and stage amplifier are about 300 feet apart on separate power feeds. This is a prescription for ground loop problems."
Indeed. Better to isolate and solve than to run another 300 foot power cord so that it's all seeing the same AC power source circuit.
However even on the same AC power source circuit, ground loops can still happen with ungrounded gear connecting to grounded gear.
A show host of a program my station airs (Jiggy Jaguar Show) had this issue with his gear running off the same AC supply circuit. He was connecting typical unbalanced audio gear, including the computers, up to a Peavy mixer which used a grounded 3 prong AC plug. Everything was powered via a power strip from the same AC electrical outlet. The mixer and an amplifier for monitoring sported the 3 prong grounded AC plugs, but everything else was just the standard 2 prong polarized non-grounded plugs, and a few other things ran through wall-wart power adapters.
The audio was plagued with not just ground loop hum, but also power supply "buzz" hum from the computer systems and other digital devices powered via those wall wart adapters.
Upon consulting, I advised him to install those 1:1 isolation transformers between everything powered by non-grounded plugs before going into the Peavy mixer.
Problem solved.
RFB
I had some big fubars around here, tryin' to run audio stuff with everything being powered from the same battery.
I had to build a seperate power supply (panels, battery, charge controller) to operate my projection TV system. My head unit and the projector (which is connected to the main shack battery) had big issues thru the HDMI connection and I didn't have any other way to isolate the two. The audio wasn't an issue. I isolated with a isolation transformer but the video was all messed up. It was so bad that it would shut down the DVD player in the head unit! I'm just glad that I didn't fry it..
My head unit..
My projector..
http://www.lg.com/us/projectors/lg-HX350T-led-projector
A lot of money to fry over a ground loop..
No edit function.. Dangit..
I tried both on the same supply and had issues. I was forced to build the second supply to power the head unit seperatly from the projector.
The head unit operates @ 12 v.d.c. and the projector operates on 19.5 v.d.c. I had to boost the 12 volts up to 24 and regulate that down to the 19.5 volts. The head unit isn't as hungury as the projector so the secondary system didn't need to be as big..
"No edit function.. Dangit.."
See there admin/mods? As I noted in another thread, the edit function is a must have and something that should not be considered a problem to justify having it removed.
Please consider putting the edit function back so that we can add/clarify/correct our posts without having to begin new posts when all that is doing is adding to the thread pages needlessly.
RFB