Richard Corfield (M0RJC)
Daddy modification
We initially replaced the speaker with a bulb which worked quite well showing signal power as varying brightness, but with the speaker in we found the bulb lit in absence of music or even radio circuit connected. looking on the oscilloscope we found a 450kHz signal and lots of harmonics. I wonder if it's from switching supplies in the house perhaps with the speaker coil resonating. The "speaker" has added circuitry, presumably to protect it from damage.
It's hard to add in bypass capacitors and filters on that circuit board with limited space. The passive components take two units of space and must be aligned horizontally or vertically.
Daddy modification
We initially replaced the speaker with a bulb which worked quite well showing signal power as varying brightness, but with the speaker in we found the bulb lit in absence of music or even radio circuit connected. looking on the oscilloscope we found a 450kHz signal and lots of harmonics. I wonder if it's from switching supplies in the house perhaps with the speaker coil resonating. The "speaker" has added circuitry, presumably to protect it from damage.
It's hard to add in bypass capacitors and filters on that circuit board with limited space. The passive components take two units of space and must be aligned horizontally or vertically.