All Of Those Ebow Schematics You've Seen ARE WRONG! (Part I)

[@user-ellievator]

Holy impedance batman! I've been looking at diy ebow tutorials for at least 8 years and this is one of the biggest breakthroughs I've seen. Maybe it's just because I'm drunk, but I biased the heck out my transistor. Time to get out the breadboard.

[@VegasCyclingFreak]

When we DIY an Ebow there’s certain compromises we have to make because we don’t have the same components available to us. These “clones” work to some degree, but none of these DIY Ebows are likely to totally nail the performance of the real one. There’s a lot of variables…

[@J.C...]

Metal marshmallow has a working version he's selling parts kits for.

[@VegasCyclingFreak]

NOTE: I made a mistake in the video at 13:53 regarding the wire gage on the coils. I was looking at a chart that showed AWG sizes , and I didn't do the conversion from metric to AWG. The correct wire gages would be: Input Coil 34/35 AWG and the Output Coil 44 AWG. I also suspect the inductance that I measured - seems too low. Might really be more like something between 10mH and 100mH. For the purposes of simulation it doesn't seem to matter much but it certainly would if you're trying to build one. I have corrected the info shown on the PDF in the video.

[@duncanmcneill7088]

I suspect that you’ve got the coils the wrong way round - I would expect the output (driver) coil to use the thicker wire as it has to tolerate the current that the 386 puts out. The sense coil would use the thinner wire as there’s very little current induced in it.

[@VegasCyclingFreak]

@@duncanmcneill7088 I was able to determine which coil was which by the bits of epoxy left over from the individual that originally dissected it before I got my hands on it. It was pretty obvious which one came from which side.

[@mudsh4rk]

There have been at least two distinct versions of the eBow, and I'm pretty sure the "harmonic mode" was added in the mid to late 90s (it definitely wasn't a feature on the eBows I saw in shops and ads and my guitar teacher's house when I first started playing back in 1991, but it started showing up in ads a few years later and the one I bought in the late 90s has it). It's possible that the differences between the board you have and the common internet schematic are because it was traced from an earlier version without harmonic mode. If it as drawn 20 or more years ago (which seems likely, I don't know the source but it has been around for a long time), there would have been more without harmonic mode than with floating around. On top of that, the person who drew the old schematic would have probably used the cheapest ebow they could find used, or an old or broken one they already owned, which makes it even MORE likely that it predated the harmonic mode. Plus the old internet schematic doesn't include the harmonic mode switch at all...

[@VegasCyclingFreak]

The internet schematic doesn’t have a feedback loop. That is required to get a consistent frequency of the oscillator. Won’t properly couple to the string otherwise.

[@artantme]

Wow, thanks, i'll definitely give this a try. Any suggestions on getting similar coils apart from winding them? Maybe arduino sonic sensor speakers?

[@VegasCyclingFreak]

Apparently there are some kind of buzzers that you can use for the coils but I don't know what they are used in or any of the specs. This guy in Russia made a working circuit using them and also 3D printed the casing - kzbin.info/www/bejne/one2l4qvqKupq7s The ebow is designed so that when you place it over the string it will cause the string to vibrate. Most of these DIY ebows that I've seen won't do anything until YOU pluck the string. That technically works, but it's not the same as what the ebow is actually doing. You don't get a circuit that functions exactly the same as the ebow.

[@artantme]

@@VegasCyclingFreakThank you! I'll research. I'm actually from Russia too. Seems that InfiniToneGS was some kind of DIY version of Ebow made by now closed company of local enthusiasts here. The guy in the video is actually fixing the DIY version made by them. But i'll try contacting him, i update if have some more info.

[@VegasCyclingFreak]

@@artantme Thanks for the background info on that. The video makes more sense knowing that. 🙂

[@J.C...]

Metal marshmallow has one you can build. Or buy from him. No more $100 ebows!

[@VegasCyclingFreak]

Interesting… thanks for the info

[@GeorgeTsiros]

I would have guessed it feeds a coil with a very, very fast pulse waveform. Like, that's what a _bow_ does: the string is pulled aside by the bow strings, until it reaches some maximum displacement at which point it snaps free. It's like you're pinching it with your fingers, moving it just a tiny bit away and releasing it, only it's done like thousands of times a second.

[@VegasCyclingFreak]

That's what I thought when I first started on this journey, but that's not how it actually works. It's based on the principle of feedback sustain.

[@GeorgeTsiros]

@@VegasCyclingFreak I should have expected that it wasn't as straightforward as my first ever guess on the matter.

[@atanquerel]

looking at your website, you showed a 130kOhm resistor not a 13kOhm as you had in your LTSpice diagram

[@VegasCyclingFreak]

Later on in this series, with the help of some knowledgeable people at the DIYstompboxes.com forum, it was determined that it had to be a 130K and not a 13K. I was not able to measure that resistor in my dissected ebow because it was broken in half and visually looking at it was no help either.