MIDI Music Note Control for DRSSTC

[Alex_1996]

Hello everyone. It's a pleasure to be back here

After my last DRSSTC build I have been experimenting with music and MIDI files to play on the coil. To clarify that I use an analog interrupter, which, with a potentiometer I control the ton (20uS - 220uS) and with another one, I control the BPS (0-800Hz). I have the following doubt:

I have often seen in forums and other publications that you have to be careful with the ton when playing notes from MIDI files. I never paid too much attention to this because I always thought that I control the ton from my interrupter knob.

I use FLStudio to play MIDI files and to compose melodies. In that sense, it behaves like any other program that processes MIDI files. In FLStudio I can control the duration of the notes in time and the volume of the notes. For example, I can make a note last for 1 second, 4 seconds, 8 seconds... And I can make it sound louder or softer inside the program (under the Control -> Velocity parameter).

I always set the volume of the notes of the MIDI files to maximum within the program and then control the ton from the potentiometer of my interrupter. Is this correct for playing MIDI music or should I set something inside the program? This doubt has appeared because I have read in some sites that some guys control the ton of the notes from the program itself and don't use the potentiometer of their interrupter at all (or so I think).

I would like you to explain me a little more what happens with the ton, volume and duration of the notes in the MIDI files. I also know that you should not play MIDIs at very high octaves to preserve the coil.

Thank you very much. Attached is a screenshot of the program and of a note.

[Benjamin Lockhart]

If you play all the notes at a fixed on-time (maybe 100us), the really high pitch notes will end up with a really high duty cycle causing some part of the coil to overheat (depending on how overbuilt your coil is).

In general 10% or 12% duty cycle seems to be a good limit for most DRSSTCs.

For example, a note at 1kHz has a period of 1ms, and with an on-time of 100us, that's 10% duty cycle while that note is playing. If you played a 500Hz note at the same time as 1kHz (if your interrupter is capable of polyphony), that would be 15%duty cycle.

To get around this, you can either set the on-time of the high pitch midi notes lower, which is a lot of work to program. (or just don't play super high notes unless they are super short)
Or use an interrupter that scales back the on-time on the high notes automatically.

I prefer to implement this a a hard duty cycle limit in the interrupter where if the on time of all the notes currently being played exceeds the duty limit, then it reduces the on-times of all notes.

I'm actually working on an all analog interrupter right now that has duty cycle limiting, a phaser effect, burst mode, and a direct guitar input. I'll make a post about it once it's complete, but I'm very happy with it so far.

[Alex_1996]

Hello! Thank you very much for your quick response

My interrupter is an analog basic interrupter. I usually set the ton stable at about 100uS and with that I get good results: the discharges are getting to the ground.

Thanks to what you have explained to me now I understand better the dynamics of the notes in the MIDI files. As long as you are within a stable duty cycle there should be no problem with the notes.

I'm very interested in the analog interrupter you suggest. I look forward to seeing the results soon.

Here is a link to a video of my coil playing Journey's Separate Ways.

Best regards and thank you very much!

https://youtube.com/shorts/9W9ElQRZqgU?si=HvsaKL5Kci2scwTX

[Benjamin Lockhart]

If your analog interrupter uses a 555 timer to set the on-time you could easily implement my duty cycle limiter circuit.


I've also added a note holdoff timer that prevents the next pulse from happening until 55us after the previous pulse ends. This gives time for the DRSSTC primary current to ring down, because if you have a startup oscillator, turning the coil on while there is still primary current flowing could cause hard switching.

I've tested this circuit extensively for a couple months now and it works well.

[Alex_1996]

Thank you very much

I will try this design you experimented with and let you know the results.

Best regards

[Benjamin Lockhart]

I'm interested to see what you come up with!