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HIGH VOLTAGE STEREO MUSICAL ARCS

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LAN_403

Signification

Mon Jan 25 2016, 04:48PM

Registered Member #54278 Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367

I am in the process of designing a high voltage (STEREO) musical arc system. I am still in the early stages of this design, but have noticed a few members doing very similar and larger designs.

I am considering first a pair of identical flybacks. First, I will look for the best driving signal for the flyback(s). The finished circuit will consist of two identical circuits which can be independently driven with stereo audio signals. The plan was to first find a good input drive as a flyback primary. I will use an old circuit I built years ago consisting of a pair of 555's. The first 555 is in the standard astable mode (simple oscillator), with a pot controlling the output frequency (jumpered caps can alter the primary frequency range). the output of this 555 will drive the 2nd 555 which is configured in the triggered monostable mode (one-shot or pulse generator), with a pot controlling the (low) pulse width of this pulse. Again, jumpered caps can control the pulse width range extremes if the pot pegs out before you get there.

Now, each falling edge of the oscillator waveform (1st 555) will trigger the pulse width (low time)--or duration of the one-shot output of the 2nd 555. As you can see, summarily, I now have a pulse-generator whose FREQUENCY is controlled by the first pot, I also have --INDEPENDENT-- control the pulse DURATION via the second pot.

Of course, ranges and restrictions must be kept in mind. For example, the one-shot pulse output (main drive signal) is triggered by the "negative-going" edges of the oscillator output waveform of the first 555. NOW, the one-shot should NEVER be re-triggered before it has had time to complete it's cycle (i.e. output pulse goes from high to low back to high). Put another way, the period of the driving oscillator must be longer than the width of the output pulse. If things are not in range with the pots, a capacitor jumper can be moved, thus changing the scale via capacitance value--I have this feature, independently, on each 555! General restrictions like the >50% duty cycle of the oscillator, and the >10ns trigger pulse requirement of the one-shot are not a problem here.

With a pair of prepared flybacks--one primary coil and the HV secondary wire pair-- (building two!), I plan on driving the flyback with at least 12VDC to ground via a power FET controlled by the 555 output pulse (watch the 555 Vcc range!). I plan to now put the flyback through it's paces by varying the driving pulse frequency and width with the oscillator--(I may have to include a safety feature to prevent hitting an over-current sweet-spot: just thought of that!). It would be nice to get a powerful spark at a high enough frequency, that the music does not squeal like a pig! After I settle on a drive waveform and if I can get away with a sufficiently low modulation percentage, I may be able to use a single 555 (per channel) and modulate the audio carrier via pin 5 coupling (the "control voltage" pin) on the 555.

Although, I have never made an audio modulated HV arc, I have, many times, music/voice modulated (mono) the 555 via it's own control pin (pin 5)--I have to say, the sound quality was amazing! Even when compared to a --linear-- ramp (the 555 is exponential) which I built as a separate circuit. If it's only for your listening pleasure, you can't tell the difference--so just couple to pin 5 of the 555.

When I have built the stereo pair, I will have TWO HV flyback secondarys sitting in the air.
Any suggestions on a connection scheme--remember, I have TWO separate signals in the flyback pair and don't want to distort one with another. I was thinking of, maybe connecting the two "secondary grounds" together (can you phase these things?) making a HV ISOLATED COMMON. The musical arcs then could sing together when arcing to this common HV ground. OR--I could just make two separate HV circuits.
I have no idea what kind of frequency and duty cycle these flybacks use even in their home domain! Can anybody help here?

...Helpful hint--hopefully: If you have used these 555 timers a bit, you may have noticed that if you turn a pot to it's limit, that the 555 output "crashes" (sticks high or low) and can sometimes cause serious damage, depending on how and what is being driven. I solve this problem by simply placing a small R "limiting" resistor in series with the pot (well rheostat really) to limit this "zone".
The DUAL 555, the 556, is two 100% 555's in one 14-pin IC (The 555 is 8-pin), however the QUAD 555, the 558 (16-pin), IIRC shares a common "Control Voltage" input.

NEXT STEP:
I have used ignition coils (iggies) for many years too--they seem MUCH more powerful. I got at least a 6" to 8" white loud spark out of a pair of iggies connected in inverse parallel with the two HV connections as the outputs--I used a disposable camera cap as the energy source. Any ideas on using iggies in this application?

AND IF THINGS WORK OUT:
...Aren't there ways of coloring each arc...like...for "Dueling Banjos"

hen918

Mon Jan 25 2016, 06:36PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

Flyback transformers (LOPTs) can be very powerful, trying to get that much power out of an ignition transformer and you will end up with a lot of smoke. They are designed for very short duty cycles.
I would advise using some (or one) fiddy's flybacks and not running them in flyback mode (so input and output current are more or less in phase).

I know fiddy's flybacks will be happy from 5kHz to 100kHz, not sure about standard TV flybacks.
Play about with the duty cycle, I've used flybacks, mostly with Mazzilli drivers, with pure sine so I can't comment.

basically without the core spacers, it's just a high voltage ferrite cored transformer.

dexter

Mon Jan 25 2016, 08:48PM

Registered Member #42796 Joined: Mon Jan 13 2014, 06:34PM
Location:
Posts: 195

monitor flybacks are a good choice because are designed for 50-75kHz operation

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