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My 3rd DRSSTC playing "William Tell Overture"

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LAN_403

TheBoozer

Mon Dec 21 2009, 09:00PM

Registered Member #1535 Joined: Wed Jun 11 2008, 11:37PM
Location: Northeastern Pennsylvania - USA
Posts: 117

First light of my latest DRSSTC went better than planned. It's difficult to contain my excitement. I really wanted to share at least this video with everyone here.

There are more, but this one sounds so nice...

This system is running @ 61khz on a pair of CM150DY-12NF

Secondary is 6.5" O.D. PVC. Smaller toroid is 12x3 larger one is 24x6

Coronafix

Mon Dec 21 2009, 10:07PM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

Very nice!! Well done.
What is the sparking at the bottom right corner of the vid at approx. 0:46 ?

Daniel Uhrenholt

Mon Dec 21 2009, 10:42PM

Registered Member #125 Joined: Fri Feb 10 2006, 01:52PM
Location: Aalborg, Denmark
Posts: 155

Nice work, I like it:-)

It sounds like you don't have enough filter cap to hold the bus voltage high at long notes... How big a capacitor do you use here?

I have a video of the exact same number, but I have 5600uF on the bus

Cheers, Daniel

TheBoozer

Tue Dec 22 2009, 02:06AM

Registered Member #1535 Joined: Wed Jun 11 2008, 11:37PM
Location: Northeastern Pennsylvania - USA
Posts: 117

Coronafix: It's actually the OCD light coming on... No biggie. We are good there. :) It's actually set to a mere 500amp...

Daniel, any compliments from you is a high honor. Your work is outstanding!!! This DRSSTC engine was built to be as physically small as possible. So far it stands at under 7 inches or 17.5 centimeters. I'm not sure if I'll leave it with this coil yet or not. The 400vdc bus comes from a 140vac with a doubler. The doubler has 3300ÂµF. The DRSSTC engine has 4800ÂµF. I tested the engine in a similar setup and the bus drops to 375 at the most... By the way, I saw your version the day you put it out. I thought: Wow!!! I gotta have one that does that. That's an awesome tune for these. Here we are today. :) Thanks for the inspiration... Back to your observation:

The first two songs I attempted appeared to have the notes running into each other. I didn't want a waving arc playing music. I wanted one that put out note bursts. I decided to take advantage of the way duty cycle is handled. Duty cycle is based on note frequency. I put a routine in that decays the duty cycle at a constant rate while a note is playing. So high notes decay a lot faster than low frequency ones. It improved the overall arc appearance so I let it as is. I figured it was like a piano. Tap the key and then it decays. It gives it character. High frequency notes play with moderate arc length and then the big bass notes kick in with long arcs. It seems more realistic this way... I haven't tweaked this since I threw it in. I'll get back to that sooner or later...

Daniel Uhrenholt

Wed Dec 23 2009, 04:27PM

Registered Member #125 Joined: Fri Feb 10 2006, 01:52PM
Location: Aalborg, Denmark
Posts: 155

Sorry for the late answer, I had some difficulties coming home to my apartment due to snow here in Denmark yesterday:-)

My interrupter just have a fixed duty cycle that I can change with a potentiometer, so yours is a little more advanced than mine:-)

You say you had problems with the notes running into each other, did the coil make a popping sound? I have this problem with my bigger coil, as it needs a lot more on time than the coil on the video, so I make the bursts in the midi software I use... The coil in the video only has 50us on time, so I can play really high notes with it.

Cheers, Daniel

TheBoozer

Thu Dec 24 2009, 12:05AM

Registered Member #1535 Joined: Wed Jun 11 2008, 11:37PM
Location: Northeastern Pennsylvania - USA
Posts: 117

I'm just glad you haven't abandoned this thread yet. :) I am fortunate so far this year. It only snows on my day off and I didn't need to go anywhere...

Notes running into each other meant the arc doesn't extinguish between notes. There is a really weird pop near the end of my William Tell tune. Probably a software bug. I'll figure that one out sooner or later. No other oddities in any other tunes with any of my coils so far....

I started with a fixed duty cycle. I didn't like being fixed to whatever the highest note could handle. I blew apart many bricks at this stage. I needed something more dynamic. Duty cycled is now derived from 1) Note Frequency 2) Microcontroller frequency & 3) Desired IGBT average ontime in %.

My typical notes range from 50ÂµS to 150ÂµS. This roughly translates to between 3 & 10 rf cycles. Today I took a peek at William Tell decay rates. The longest & low notes might start at 150ÂµS and decay to 100ÂµS. I like having this kind of control. I could translate my formulas if you wanted to see my approach to this...

Today I raised my IGBT ontime from 1.5% to 2.0%. I also raised the OCD from 500a to 625a. Arcs were longer, fatter. It stuck the ground quite often. Hmm.... I think the next test will be 2.5% @ 750a. If it doesn't blow up at that point, I will stop there. I will then try to figure out what kinda of primary to replace this with and then get back to the midi software...

I've had a burning question for months and am dying to know anyone else's answer: How do you deal with chords?

Right now my software only allows me to choose between the highest or lowest of the bunch. In the video I released, I had the software pick out the highest note in the chord. Is there a better approach???

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