#1 mystery whine
Posted: Thu Oct 21, 2021 1:55 pm
not really a project but I struggled to find a better place for it....
for the last couple of weeks I've noticed a whine coming from the stats when the system is idle. The whine is audible in the room but not loud. I say idle because the breeze class d is switched to standby but the pi and the dac are always on.
So I made an effort to trace the whine a week or so back. I switched everything off at the wall socket(not the stats charge) and the whine persisted.
I switched everything off individually(pi, dac and amp) and the whine persisted.
I removed the I/Cs individually and the whine persisted.
I removed the speaker cables and the whine ceased.
so I've no idea which component is causing the whine...yet.
I'm thinking that the amp has residual so switching it off might not yield an immediate result.
today I heard the whine while passing the music room so it was like a red rag to the bull.....and I got the scope out.
as soon as I connected the scope the whine stopped...but the scope still measured a signal between 350hz and 500hz at 5mv. The frequency was stable but varied between the 2 figures at about 1/2 second intervals. A pedant might say that that is not stable...Pah!
I scratched my head!
I disconnected the scope and all was silent for about 2, maybe 3 minutes....and then the whine came back.
I paid close attention while connecting the scope back...and caught the little rascal red handed...as I connected the probe ground to the the black speaker socket there was a brief spark....and the whine disappeared.
The whole system is smps driven: pi, dac and class d amp, so this is the first time the system has seen a real ground...
my only certainty(so far) is that connecting the scope stops the whine.
anybody got anything to suggest?
edit..with the scope switched off but the probe ground connected to the black speaker socket there is silence...
for the last couple of weeks I've noticed a whine coming from the stats when the system is idle. The whine is audible in the room but not loud. I say idle because the breeze class d is switched to standby but the pi and the dac are always on.
So I made an effort to trace the whine a week or so back. I switched everything off at the wall socket(not the stats charge) and the whine persisted.
I switched everything off individually(pi, dac and amp) and the whine persisted.
I removed the I/Cs individually and the whine persisted.
I removed the speaker cables and the whine ceased.
so I've no idea which component is causing the whine...yet.
I'm thinking that the amp has residual so switching it off might not yield an immediate result.
today I heard the whine while passing the music room so it was like a red rag to the bull.....and I got the scope out.
as soon as I connected the scope the whine stopped...but the scope still measured a signal between 350hz and 500hz at 5mv. The frequency was stable but varied between the 2 figures at about 1/2 second intervals. A pedant might say that that is not stable...Pah!
I scratched my head!
I disconnected the scope and all was silent for about 2, maybe 3 minutes....and then the whine came back.
I paid close attention while connecting the scope back...and caught the little rascal red handed...as I connected the probe ground to the the black speaker socket there was a brief spark....and the whine disappeared.
The whole system is smps driven: pi, dac and class d amp, so this is the first time the system has seen a real ground...
my only certainty(so far) is that connecting the scope stops the whine.
anybody got anything to suggest?
edit..with the scope switched off but the probe ground connected to the black speaker socket there is silence...