Ebow Expose Part II - Ebow Anatomy Inside

[Paul Marossy]

Well, I got my dismantled Ebow in the mail today. Someone else did all the work for me and got all the goop off of it so we could see what's "under the hood". 


The is showing how the PCB sits in the base and how the coils are held by the PCB. The LED is on the right side in the picture.


This is the other side of the PCB with the coils dismantled. The coils are about 1.3" apart from eachother (center to center)


This is a closer view of one of the coils. It is composed of a steel core, the copper windings, a steel ring approx. 1/2" in diameter and a magnet that goes on the bottom. The magnet is farthest away from the strings. The coils are physically identical, but one of them uses wire about the size of a human hair and the other one uses windings that are considerably larger.


Here is a little closer view of the PCB. The is what appears to be an LM386 on it, a 1N914 type diode, two resistors and four capacitors on the board. There are no magnets on the PCB as I thought there were, only the two on the coils. The PCB is 1.5"x.875"


This is showing how the coils fit into the bottom piece.


These are all the plastic parts as they look individually. I looked at the switch assembly. I think my theory about a multi-tapped coil might be right from studying the PCB and how the switch is wired.


Interesting, huh? 

[petemoore]

  Very nice displays Paul !!
  Being the less than extremely adventuresome type who would like to try an Ebow, this is getting closer to where I'd actually try building one!
  So, being the shy type, I'd be as bold to say I'd be scared to try one until I had the layout and wiring where I had complete confidence/understanding, almost a step by step instructional or reference..not that I expect it, but it is getting close..
  Source the magnets/coils etc., building on perfboard from schematic, other things I might not be able to have real easy.
 

[markm]

Interesting, huh? 

To say the least!
WOW! 

[Paul Marossy]

Yeah, as you can see, building an Ebow clone is not for the faint of heart. 

BTW, the PCB might look like it's broke on both ends, but it's actually made so that the hole for the magnets doesn't actually close. Don't know why, but that's what the deal is.

[Paul Marossy]

One thing that has piqued my curiousity is the steel pole piece. The patent says it's a magnetic core of Alnico-5, but it's just a piece of steel. Isn't Alnico-5 a magnet?

[markm]

One thing that has piqued my curiousity is the steel pole piece. The patent says it's a magnetic core of Alnico-5, but it's just a piece of steel. Isn't Alnico-5 a magnet?

To my knowledge it is.
Isn't that the same type of Magnet Leo used?

[petemoore]

Alnico-5 a magnet?
  Alnico-5 is a type of metal alloy, which can be magnetized:
  Alnico-5: Any of several hard, strong alloys of iron, aluminum, nickel, cobalt and sometimes copper, niobium, or tantalum, used to make strong permanent magnets.

[nephsuperman]

alnico is a magnet made of and alloy of aluminum, nickel, and cobalt.  

[Paul Marossy]

alnico is a magnet made of and alloy of aluminum, nickel, and cobalt. 

I know that much. 

So then Alnico-5 doesn't necessarily have to be a magnet then? Interesting. 

[MarcoMike]

Alnico is an alloy of Aluminum nikel and cobalt, yes. but these are not the all the components. the main component is Iron, other metals may be present depending on the alloy (alnico X)
and it should be a permanent magnet, which means it retains its magnetization until it stays below a certain temperature (which is usually high). if yours is not magnetic, then I doubt it is ALNICO.

[MarcoMike]

mh, I wrote the previous post before your last post...
I guess ALNICO may exist as non-magnetic metal, but why woould you do something out of alnico when you don't deserve it as a  permanent magnet?
so, just to clarify my last post: if it was a permanent magnet it is not so easy to delete its magnetization. heating it over its Curie (or someone else) Temperature will allow you to change its magnetization by an external M.field. and I guess at higher temperature it will loose it because of internal thermal agitation.

[mattpocket]

You had to break this to get it apart! Your nuts man! It's great for us guys, but you just broke it! :

[Paul Marossy]

You had to break this to get it apart! Your nuts man! It's great for us guys, but you just broke it!

No I didn't. Someone else dismantled it in his quest to try a make a DIY sustainer system (like a Sustainiac), I just bought it from him for $10 plus shipping in order to satisfy my own curiousity. 

[mattpocket]

Thats cool enough!

Interesting nethertheless.... are you going to build one, Paul?... You seem like the biggest fan of the ebow around here, and you know what it sounds like, so you are a good candidate in my opinion! 

Matt

[Paul Marossy]

are you going to build one, Paul?... You seem like the biggest fan of the ebow around here, and you know what it sounds like, so you are a good candidate in my opinion!

Yeah, I'm going to try making the circuit just for fun. I'm not really the biggest fan, I just find it to be a very interesting circuit. More so after I got a couple of working ones the last couple of weeks. 

[MKB]

Yeah, as you can see, building an Ebow clone is not for the faint of heart. 

BTW, the PCB might look like it's broke on both ends, but it's actually made so that the hole for the magnets doesn't actually close. Don't know why, but that's what the deal is.

Thanks for posting the pics!!  It is very interesting, however they are doing quite a service to guitarists (and keeping themselves in business as well) by making such a strange circuit/device affordable.  Around $80 street price on such a thing is a good price.

The PCB's look like that as they are most likely panelized (many of the boards are supplied in one large panel); the panel is much easier to work with.  After stuffing the panelized boards and soldering them with a wave solder machine, the boards are then broken apart for use.  So they are broken, but were meant to do so.

Is there any other circuitry in the ebow, like up near the octave switch?  I find it hard to believe they can implement all those functions (automatic power on/off, octave switch, LED driver) with a single off the shelf part.  But the newer ones have the power switch and octave select in the same switch.  Maybe the older chrome ones had more circuitry in them. 

FWIW, I had both a chrome one from the seventies and currently have the new one with the blue LED.  The newer ones are WAY better in every way than the chrome ones IMHO.  Only down side to the new ones is that they no longer are supplied with the cool leather belt case.   

[Paul Marossy]

Is there any other circuitry in the ebow, like up near the octave switch?  I find it hard to believe they can implement all those functions (automatic power on/off, octave switch, LED driver) with a single off the shelf part.  But the newer ones have the power switch and octave select in the same switch.  Maybe the older chrome ones had more circuitry in them. 

Nope, it's just the opamp, two resistors, a diode, four capacitors, the input/output coils and the SPDT switch which apparently somehow reverses the current in the output coil for the harmonic effect. That's where my theory of the center-tapped coil comes into play. AFAICT, the schematic here looks pretty close to the Ebow circuit: http://logosfoundation.org/kursus/4047.html - I'll see if I can verify the resistor/cap values on the PCB.

EDIT: I looked carefully at the PCB. There are two tracks leading up to where one of the leads of the output coil connects. I think what the SPDT switch does is reverse the coils while simultaneously allowing the circuit to be powered up. That has to be how it's done, I can't see how else it could be done with a SPDT switch... 

Yeah, it's a panelized PCB, I could tell that right off the bat. 

[Thomas P.]

Is it really non-magnetic or is the effect just really low?

If there are pickup builders in the thread they propably now that in the process of building a single coil the last step would be "reorientating" the magnetic dipoles via  two strong ceramic magnets. So if the magnetization is low (really low) it could be due to age. If that's not the case the dipoles can be randomly orientated by vibration.
To thermally randomize the magnet you have to get over ~800°C which is the curie temperature of alnico

[Paul Marossy]

Is it really non-magnetic or is the effect just really low?

If those pole pieces are magnetic, they are extremely weak magnets as they do not appear to be attracted to steel/iron in the least bit. The 1/2" round ones are pretty strong magnets, though. Not like rare earth magnets, however.

[Mark Hammer]

FYI, Alnico, whether 2, 3, or 5 (common types for pickup polepieces and speaker magnets) is simply an alloy, and is magnetized for the purpose of use in pickups or speakers, etc.  Good thing too, because shipping magnets in any quantity must be a real nuisance.  Its non-magnetic nature in native form means that pickup manufacturers use a magnetizer prior to installing them.  Stew-Mac will sell you Alnico polepieces and has instructions on their website for how to magnetize them, using rare earth magnets.  Since rare earth magnets are ALSO a nuisance (now let's see, did I or did I not have my credit card and ATM card in my pocket when I was leaning over the bench?), manufacturers tend to use electromagnets for "charging" the polepieces.  Unlike rare earth (cobalt samarium) magnets, once those babies are off, they are OFF.

Because the slugs/polepieces have to be magnetized, that means they can be magnetized to varying strengths/gauss-levels.  I would imagine that anything which is intended to use in close proximity to strings, with the express purpose of keeping those strings moving, would be designed to have very modest magnetic "tug".  the use of Alnico is really more for the long term retention of magnetic qualities, I imagine, as well as machineability (prior to magnetization).