Musical interrupter problems

[RoamingD]

Hello everyone, this is my first post here and on a forum actually, in the last 2 months I managed to build a SSTC based on Kaizer Power electronics SSTC III
https://kaizerpowerelectronics.dk/tesla-coils/kaizer-sstc-iii/ and got some amazing results with the internal interrupter as you can see in my avatar picture  but I am having problems with this musical interrupter that I also took the inspiration from Mads website https://kaizerpowerelectronics.dk/tesla-coils/musical-sstcdrsstc-interrupter/, the output goes trough a coaxial cable whose outer shielding is connected to earth to prevent interferences.


So basically I designed and etched my own pcb based around that schematic but I got mixed results, the problem is that the 3.5mm jack that is connected to Audio- is constantly at 1.92 volts and Audio+ is at 0.9volts, I experimented with using different voltages from 7-14v to power the interrupter but the problem is still there, i even tried to put a 10kohm pot between pin 5 pin 1 and gnd of the ua741 op amp

This voltage results in my audio source (old phone) to brick itself and start rebooting, I know the circuit works because just briefly it played Darude Sandstorm before shutting down my phone :'(
Does anyone have suggestions on how can I solve this problem or other ways to play music on my tesla coil

[Mads Barnkob]

The simplest improvement would be to add a optical isolated interface and use fiber line between the interrupter and Tesla coil driver. The cable connection and sensitive electronics likes a smartphone, is simply not a great match.

If you want to keep the cable, add a "sacrificial" amplifier in-between your phone and audio interrupter. The older the better

[RoamingD]

Hmm, thank you so much for your fast response, I'm a huge fan of you and I am very honoured 
I think I will implement just like you said, an old amplifier or one of those dirt cheap lm386 modules
But budgetwise I will have to stick with the coax cable for now... I will have fiber optic in my next build, hopefully a DRSSTC

[davekni]

This voltage results in my audio source (old phone) to brick itself and start rebooting, I know the circuit works because just briefly it played Darude Sandstorm before shutting down my phone :'(

Possible, but I'd be surprised if the DC voltage is true cause of phone shutting down.  More likely electrostatic or magnetic coupling from coil back to phone.  You could test this to see for sure.  Try again with only interrupter circuit powered and coil unpowered.  If phone still shuts down, then DC theory is likely correct.  In that case, I'd just add capacitors in series with both wires from phone audio output to interrupter input.

If phone reboots only with coil powered, then interference is more likely.  As Mads said, fiber optic coupling is best solution.  Can be done at reasonably low cost if you are willing to glue fiber ends to LEDs and photo-transistors.  I did this for LED end only in my fiber-coupled scope probe project:
https://highvoltageforum.net/index.php?topic=1263.msg9259#msg9259
Same technique can be used for 5mm packaged photo-transistors.  LEDs and photo-transistors and 1mm-core plastic fiber are all available on EBay.  Fiber usually comes with TosLink ends, which can be cut off.
Another option to try if you have suitable transformers laying around:  Transformer-couple phone audio output to interrupter input.

Good luck!

[RoamingD]

I am so thankful for your ideas to solve my problem, I took both of  your suggestion and I added a mylar capacitor on Audio- and I managed to find a gem in my box of dissasembled crt tv's, a AN5265 audio amplifier chip which I used along other old components to build this ugly thing but atleast it works flawlessly in this scenario.

I managed to get these "crazy" (for me they are, but compared to other's results...I have a long way until then) arcs from my SSTC

[Mads Barnkob]

You are doing great!

Long sparks or beautiful Tesla coils are not something that comes out of the first project. It is more important to learn how it works, why it works and how you can use that knowledge in a new and improved Tesla coil

Just check out my first audio SSTC from 2009. Filmed with the cutting edge in compact camera filming technology at the time. I think it was Canon Ixus 40, massive 640x480 pixels at 30 fps

[RoamingD]

To be honest, I watched your video of that tesla coil playing Fur Elise almost every day since I started building this coil ) I was obsessed to get this coil working and playing music just like yours.

This tesla coil is the second one I've built, this is the first one, a very compact CW 12V Irf530 Slayer Exciter whose resonant freq. is about 3Mhz
This is the circuit that I designed (its in Romanian, sry) and I recommend with all my heart over those 5 dollar kits, as it is even cheaper and by building this you actually learn in a safe way about tesla coils



Again, thank you for all of your support, I wont spam this thread anymore