I am using the WT 32 Bluegiga bluetooth module to stream music using the A2DP profile. Shown here https://www.sparkfun.com/products/8952
What I observe is that when there is no bluetooth link, or when the iPhone is connected but in idle state, the audio jack seems to always have a buzzing noise in the background, which is loud enough to be an annoyance especially when I feed it into a power amp for speakers. When music starts playing, the noise reduces to very low levels as the music plays with great quality.
I've tried to seek a software solution to this, but the noise seems to be unaffected by changes in internal gain of the WT32.
Does anyone have any suggestions as to how to resolve this problem??? Thanks!!
Perhaps the audio outputs go high-impedance when its not streaming music? Try connecting 1k resistors from left to gnd and from right to gnd. This ought to reduce hum pick-up substantially.
Alternatively to confirm/deny this guess, if you can touch the audio signal (perhaps via a metal probe) you should be able to make the hum much worse - if this hum goes away on playing music then the device must be driving the audio signals at low-impedance only while the music plays.
If making contact with the signal makes no difference to the behaviour then the hum isn't being picked up in this fashion and is coming from some other part of the circuit - less easy to fix I fear.