I wouldn’t suggest placing the phone near your amp while connected to speakers either, although I know what you’re talking about from accidentally having done that once on one here. At the time I was attempting to use the phone as a hotspot in a basement.
Amps and speakers aren’t supposed to make those sounds.
Tiny Ferrite cores on output transistor pins can help too, haven’t tried on smaller transistors.
Amps and speakers aren’t supposed to make those sounds.
Tiny Ferrite cores on output transistor pins can help too, haven’t tried on smaller transistors.
Except when the hum is 1uV at the input and it is amplified; then that 20uV at the speaker IS the hum.
Unless I misread your post.
Edit I was responding to post # 40
Jan
Unless I misread your post.
Edit I was responding to post # 40
Jan
Yes, all mains peaks are clipped these days because of all those rectifiers that start to conduct at the mains peak, in all those myriads of consumer equipment in our homes.
Jan
Hum?
Only to the sensitive measurement equipment.
That 20 uV would be 0.1 nW at the 4 ohm loudspeakers. 100 dB below what SPL 1 W would produce.
Ferrite beads are very effective, and I have a bag full of. Their effect was evaluated with BJT CFP output stage, which is prone to severe oscillation with modern BJTs. Ferrite beads at emitters pins would squash oscillation but would also introduce nonlinearity, very well seen as a jagged rising slope of a square wave signal. I use ferrite beads at DC supply inputs of my DIY measurement gear.
That jagged rising slope is not from nonlinear beads, it's an instability.
It makes sense, you squashed the oscillation with the beads but it isn't 100% stable on fast edges yet.
If you put on two beads the jaggies will most probably be gone, but they don't do any harm anyway if the square wave has spectra beyond the audio band.
Jan
Ferrites for this sort of use typically have effect between 10MHz and 500MHz or so, so nothing non-linear in the audio band at least. They have a partly resistive R.F. behaviour (i.e. are lossy at R.F.) making them good at reducing Q and stopping unwanted resonances.
Note there are many types of ferrite materials with different properties, not all suitable for EMI suppression, and DC current level affects properties too. Datasheets are your friend!
Note there are many types of ferrite materials with different properties, not all suitable for EMI suppression, and DC current level affects properties too. Datasheets are your friend!