Hi everyone,
I am trying to build an Instrument, a "CRTelecaster" inspired by the band "Electronicos Fantasticos":
They way I figured this works is there is some user-input controlling a function generator, the output being displayed on the screen. A coil is held against the glass of the screen and is inductively coupled the the coils controlling the electron beam inside. The Signal picked up by the coil is then amplified and played on a speaker.
I got most of the stuff working, made a touch sensitive PCB Fingerboard, use an ESP32 for function generation and designed my first variable gain Amplifier to amplify the outgoing audio signal like so:
using a LM358 (since I did not want to bother with symmetrical supply) as a non-inverting amp and a 20k potentiometer and a 20k resistor as R1. And this works great, when I tested it amplifying music coming from a headphone jack (low frequencies are rattling a bit, but still pretty clear)
BUT, when plugging in the coil and trying to pick up the fields emitted by the CRT, it is super noisy!
- the coil is just a random length of wire with a random ammount of turns at this point
- obviously it is picking up some Stuff like AC, and other radiowaves
- but it is still extremely noisy when put in a metal case
- I noticed the noise- characteristics change when I soldered a resistor in line with the coil (not sure if it got "better" tho)
Do I need to somehow match my coil to my amplifier?
So if anyone could recommend some terms to look up or maybe even has an Idea how to get rid of most of the noise other than using a bandpass, that is very much appreciated!
Thank you