The Spitfire - a neon bulb discharge distortion pedal

[Ksander]

I wanted to build a Poor Man's Plasma Drive. On youtube, I found a video where a transformer is used to create a high voltage signal, and a neon bulb is used for clipping (https://youtu.be/BmYvxnKo2pA?feature=shared). After some initial problems with an earlier version (addressed in another topic), I now built a something that works well; simply by merging what is essentially a ruby amp with the transformer and output part of the circuit in the youtube video.

This is the schematic:


And here is a video:
https://drive.google.com/file/d/1WfuV0QkqX87_904sY_iq4_hL-qDceiFZ/view?usp=sharing

In the video, I play a guitar with a P90 in bridge position through a Laney miniature amp. It is recorded with my phone.

Comments and suggestions are welcome!

[duck_arse]

DA (the other), 42 pages already.
https://www.diystompboxes.com/smfforum/index.php?topic=94608.0

also, some bloke named Mayer has one.
https://www.diystompboxes.com/smfforum/index.php?topic=36350.0

I'm wondering if that 386 might like some protection from any inductive kickback the transfomer might generate. diode clamps to supplies, maybe?

[merlinb]

A ground lift is never required on a transformer output (leave it floating)

[Ksander]

DA (the other), 42 pages already.
https://www.diystompboxes.com/smfforum/index.php?topic=94608.0

also, some bloke named Mayer has one.
https://www.diystompboxes.com/smfforum/index.php?topic=36350.0

That's disappointing... I found the name quite apt, considering the fireworks produces by the neon light. I'll see if something else comes to mind.

I'm wondering if that 386 might like some protection from any inductive kickback the transfomer might generate. diode clamps to supplies, maybe?

That sounds interesting - how would that work, exactly?

[duck_arse]

firespirit? flamefront? nasty discharge?

flyback diodes - well I don't know if they are actually needed, someone competent needs to answer that. but they would look like a diode Anode to ground, Kathode to C6 (-) leg, and another diode Anode to C6 (-) leg, Kathode to supply + 9V. then any spikes from the Tx can't go lower than 0V or higher than +9V.


edit: obviously, those catch diodes would need to go, instead, on the (+) lead of C6, because the other side will swing below ground/0V.

[Ksander]

A ground lift is never required on a transformer output (leave it floating)

I didn't know that, but I needed it also to have the ground connected when the effect is bypassed. Maybe then I should wire it using a 4pdt stomp switch.

[merlinb]

I didn't know that, but I needed it also to have the ground connected when the effect is bypassed. Maybe then I should wire it using a 4pdt stomp switch.

You can still do that with a 3pdt stomp switch; in active mode, ground connects your status LED. In bypass mode, ground connects to the output jack.

[amptramp]

You should let us know whether ambient light affects the firing voltage (and sound) of the neon light.  In some uses, it pays to have a constant amount of light aimed at the neon bulb to keep the firing voltage down to certain limits.  It also suggests that if you have the neon light visible on the outside of the box under stage lighting, you may get hum modulation from the reduced firing voltage when the AC-powered light is at its peak compared to when it is dark.

I have a ground fault interrupter outlet in an upstairs bathroom with a neon light indicator.  When the bathroom light is on, the neon light is on continuously.  When the light is off at night, the neon light flickers due to the randomness of ionization.

There have been some organs built with neon divider stages from the top oscillators.  It was always found useful to have a lamp on the circuit to stabilize the firing voltage.  You could do the same with a LED behind the neon bulb.

[Ksander]

I don't notice any difference between playing in the dark or with the lights on, but I have not yet made measurements. I'm also a bit scared of shocking myself 

[PRR]

ambient light affects the firing voltage

True; but I suspect the worst-case variation is a couple dB. Poor for pitch, minor for amplitude. Just lean-in when playing in the dark.

> a bit scared of shocking myself 

For any public setting, you should rig a plastic peanut-butter or cheez-balls jar over it.

Frankly I doubt a mere LM386 and transformer on music can kill a healthy human. (Your cows will stop coming to your shows.)

[Ksander]

ambient light affects the firing voltage

For any public setting, you should rig a plastic peanut-butter or cheez-balls jar over it.

the bulb itself is placed in a small glass jar, isolated from the enclosure by a (3d printed) plastic spacer. The wires also have an additional layer of heat shrink.

[merlinb]

I'm also a bit scared of shocking myself 

On the output you'll never feel anything through that 1Meg divider. The driver is flea power so nothing dangerous even if you grabbed the transformer leads.