We know that Class AB amplifiers can demodulate AM RF signals applied to the speaker terminals, but I suspect that Class D amplifiers would not suffer in the same way - they have an output filter with a capacitor directly across the speaker wires.
We know that Class AB amplifiers can demodulate AM RF signals applied to the speaker terminals, but I suspect that Class D amplifiers would not suffer in the same way - they have an output filter with a capacitor directly across the speaker wires.
Worth saying that, for the large part, a properly implemented amplifier not subject to unusual RF interference is in the category of "not a worry". We don't worry about acoustic interference in the form of tiny tiny noises from ordinary acoustic sources. None of us have silent listening rooms. There is always a little but of leakage from outside. Any residual interference in our audio gear might well be the cause tiny intermodulation products, but generally at levels well below audibility.you should worry about RF interference, it’s just that the amplifier is what you should be looking at
So less ~30V/m in an uncontrolled environment for the general public
Certainly, I wouldn't be happy too if we had to rewrite half the language, and especially technical terms, every generation. So, yes, assuming he knew about the other meaning, he should have called it differently. But otherwise, he's right about this certain, well, confusion.Words have meanings. People who stick to them are easier to understand than those who invent their own.
What are we looking at?No universal answer here. Better class D amps have the output filter inside the FB. And e.g. NC400 is prone to frequencies near 2 x Fosc and demodulates/intermodulates it into audio band. There are no simple answers, guys. You need to investigate everything, thoroughly.
View attachment 113724
We won't hear 100 MHz, but RF can enter audio circuits via cables and get demodulated. It can result in offset shifts in opamps, for example. See fig. 11 in this app note: https://www.ti.com/lit/an/snoa497b/snoa497b.pdf
Don't believe me? Hold a GSM cell phone near an old transistor radio and call the phone. You'll hear a "burr, burr, burr" sound just before the phone rings. You can also toggle airplane mode. As the phone reconnects to the cell network, you'll hear the interference as well. That said, a cell phone transmits at up to 2 W RF power (+33 dBm). Much higher than the -60 dBm Amir measured.
Wifi is a common source of interference as well. The SSID broadcast will create tons of spurs at multiples of 30 Hz that my APx 525 will happily pick up from any circuit sitting on my lab bench. A metal chassis works wonders for keeping that RF out, though.
RF usually enters audio circuits via the input, not the output as the output has much lower impedance. Not thereby said that RF cannot enter through the output of an audio amp. I recall various HAM radio books explaining how to address RF entry with ferrite rods and/or cores.
Modern consumer electronics are supposed to be somewhat RF tolerant (at least if they're marked with the CE or FCC logos). They're also supposed to "play nice" and not emit or conduct RF out of the chassis.
That said, I find it exceptionally unlikely that a different speaker cable would somehow prevent RF entry, though. That part is snake oil.
Tom
Two Speaker wires going to two speakers act act like a dipole antenna.
https://upload.wikimedia.org/wikipe...ceiving_antenna_animation_6_800x394x150ms.gif
(amirs test only used one speaker wire?)
How long this wires are and the speakers apart diktats the antenna tuning
https://www.everythingrf.com/rf-calculators/dipole-antenna-length-calculator
Maybe 20-200Mhz seems reasonable.
thats what i'm showingSpeaker outputs are seperated so no.
Why do you think so?Think of 2 mono blocks, theres a very high impedance between the 2 speaker outs
As shown in my schematic. If its a full bridge amplifier there is no speaker cable going to ground.And each speaker cable has 2 wires usualy one to ground,
Yes it could be 100 wires close together, it dose not matter for this.First, your making a dipole (2 pole) with 4 wires
Whats the impedance between the the positive speaker out of your left monoblock and the positive speaker out of your right monoblock?
What's the impedance from left the speaker to right speaker at 100MHz? We have no idea! probably not 70Ohms.
Assuming 70Ohms anyways we would get ~20dBV RF at the amplifier's output.
A dipole has 2 wires, or its not a dipole!