Do you know whether it ever worked quietly on a wall wart? It may simply be that the ac supply option was an afterthought and they never provided adequate filtering and regulation. I assume that the wall wart is supposed to be a DC-output type and not an AC output one? Which type did you use? Is it the OEM unit? As James said, it can also be some funky RF behavior. One receiver I designed (it was a direct-conversion type) would develop audio oscillations if the headphone lead was too long or placed too close to the antenna. It turned out that the local oscillator was being radiated via the headphone lead and this produced a feedback loop since variations in the self-reception of the local oscillator caused audible signals by the nature of how a direct-conversion receiver works. The fix was to add a ferrite internally to the cable running up to the headphone jack. Something similar could be happening with the external power lead (although I highly doubt that this is a direct-conversion receiver because it is almost certainly FM). If you can, try a regulated DC supply. If that helps, then you might consider a regulated wall-wart (like a switching type - as long as it doesn't radiate at 49MHz!). You can also try adding a large electrolytic cap to the output of the wall wart (provided it outputs DC) but you have to be somewhat careful because having a large capacitance on the output of rectifiers reduces the conduction angle (duty cycle) of the diode conduction, raising the RMS to average current ratio in both the transformer and the diodes. They can overheat if the cap is way over-sized. Sean On Sun, May 13, 2018 at 4:47 PM, James Cameron wrote: > Perhaps RF is arriving via the wall wart lead. Try running the wall > wart lead through a ferrite toroid several times as close as possible to > the receiver? > > Is the frequency of the hum the same as power line frequency at your > location? If so, perhaps AC line frequency is affecting the audio > ampifier; use a regulated DC supply with capacitors closer to the > receiver, or replace the capacitors in the audio amplifier. > > -- > James Cameron > http://quozl.netrek.org/ > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .