Matching a coil to ... an OP-amp?

[0pss]

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
 

[CaptDon]

Any clues or online links to the circuitry used in the original design? The display on the screen just looks like the audio frequency fed into the video input? Not sure if video modulation provides a real function in the feedback circuit or if it just 'Looks cool' and the only real feedback obtained by the coil is the proximity to the huge magnetic field generated by the horizontal yoke winding at the N.T.S.C. or P.A.L. sweep frequency? The horizontal magnetic field when sensed externally to the actual monitor is very strong and it is very easy to then filter out the low frequencies of power line interference as well as the much lower vertical sweep frequency. The amplified and then rectified sense voltage coming from the coil may drive a very simple Voltage Controlled Amplifier such as found in / on synthesizers.