Sound system farting - advise?

Question

Hi folks,
My sound sytem connected to this repeatedly makes long farting noises. It is the best that I can describe it.
I suspect a local radio ham or similar, so I fitted an RFI filter.
(Oh, Radio Frequency Interference" thing.)
It still farts. In bursts of 30 secs or so.
Charming !
Any ideas ?
Bob.

Answer 1

It is unlikely this can be caused by RF. Usually, this type of problem, known to radio technicians with the much more polite name of "motor-boating", is caused by positive feedback giving rise to low-frequency oscillations. Again, the most likely cause for this is too high impedance in the filter section of the power supply.

Power supply filters have usually one, at most two, large-valued electrolytic capacitors used to reduce ac ripple to acceptable low values. As I can surmise by your description of the problem, it is probably due to an intermittent broken contact in one of the filter capacitors. If there's only a single capacitor, the unfiltered ac ripple could indeed cause a noise such as you describe.

Although printed circuits can crack easily, causing a broken track, it is possible also for a capacitor to have or develop an internal broken connection.

Hope this will help.

Answer 2

Don't let it have beans or fizzy pop.

Answer 3

open all the windows........! grab a towel and just keep wafting....