Guitar Sustainer device - which magnet would be best?

[peskywinnets]

Hi there,

I'm wanting to build a guitar sustainer....this device uses a driver to keep the string vibrating (essentially a guitar pickup in reverse)...ie you feed the guitar's normal pickup output signal into the driver coil & it 'stimulates' the string via magnetism.

There's plenty of threads on the internet about building these...but most follow the same doctrine...

signal in ->preamp ->poweramp ->driver.

the driver (by & large) is normally a coil of about 100 turns of enamelled wire, wrapped waround a magentic core of some type (steel, laminated steel etc), with a magnet then attached to the bottom of the core.

So why don't I just follow everyone else?

Well, most need fitting 'into' the guita I'm trying to get my particular driver to be very low profile so it can sureface mount ...ideally the whole unit should be less than 8mm tall (about 1/3"). This is a tough one becuase the top & bottom plates made of acrylic will be about 1.5mm each, so that only leaves about 5mm to fit a coil with a magnet attached to it's core beneath!

Two options...

1. Use very thin rare earth magnets...these can be sourced at about 0.6mm thickness - the problem with this method is, often these magnet are too powerful & have to much quiescent 'hold' on the guitars string(s) which changes the tone - not acceptable.

or...

2. I was wondering if it'd be possible to actually use a permanent magnet as the core. This would save having a magnet on the base....which would rescue back some vital 'height' space. I have two main concerns with this attack .....what type of magent would be best (I'm thinking a ceramic, but they seem hard to source in the dimensions I seek.. which is aboout 5mm diameter and 6mm length. The onther thing that worries me, is that there'll obviously be an alternating current flowing through the coil....wouldn't that demagnetise the permanent magnet if I used it as a core in the coil?

grateful for your thoughts?!

 

[IRstuff]

The properties required for making an efficient actuator are not the properties that make a good permanent magnet.

TTFN

FAQ731-376

 

[dgallup]

I really don't see the need for the permanent magnet at all. What is it's function? You're wasting a lot of height on those 1.5 mm top & bottom acrylic plates too. Why do you need them?

 

[peskywinnets]

You'd think the whole system wouldn't need magnets woiuldn't you (after all that's what the coil working with a ferrite core is), but for some reason you do!

Believe me I and others have spent ages mucking about in our spare time trying different permutations....and this system needs a magnet! I think the magnet - for want of a bbetter word - biases the magnet field (think of it as like a DC offset in an electronic circuit)...then as the AC signal goes through the coil the magnetic fild accts above the coil more efficiently. A bad explanation, but it's better with a magnet.

Why the acrylic? Well, I need a way of holding six of these little coils in exactly the right position below the guitar strings......think of a rectanglar bit of acrylic, but with circular ends (for aesthetics)....there'll be six holes drilled in that at exactly the right spacing for the guitar strings, the coil's 'core' (about 5mm diameter) will jut out a bit above these coils' & therefore slot into these six holes. Therefore the acylic is very much needed.

 

[dgallup]

I think you can eliminate the magnet by adding a DC bias current through the coils. It should do the same thing as biasing the field with a magnet. It will increase your power consumption & heat dissipation however. I see the need to bias it so you only work on one side of zero. The attractive force will be the absolute value of the field. A zero crossing would cause a lot of distortion.

I think the acrylic could be much thinner based on your explanation. I frequently use bobbins with 0.5 mm flanges for bigger coils than what you are talking about.

 

[peskywinnets]

Agreed about DC...but this will be battery powered, so it's not really an option. So, I need to use a magnet...like I say, everyone uses steel for there core & attaches a magnet to the bottom of that. But in order to gain some space back, i'd just like to go straight with a magnetic core...whcih is where I came in - which one would be best?

re the acrylic. I'm not using a bobbins...the wire will be wrapped straight onto the magnetic rod (ie the core of the coil)....as the wire is wrapped onto the coil, there'll be some plactic 'reinforcements at both ends, so the wire doesn't splay out. Also varnish will be applied during the winding process to ensure that once those 'holding' plastic bits are removed, the windings all hold togather 9(the varnish also acts as a vital 'potting' element to stop the coil windings vibrating). So since this is all bobbinless, the acrylic I speak of in this instannce is more akin to the top surface as seen on a normal guitar pickup, (ie for the six individual coil magnetic 'cores' to poke up through. These top & bottom bits of acylic will pull together to keep these bobbinless cokils in place & stable.

 

[IRstuff]

The acrylic is just for show though. You can clearly enamel or laquer the coils in place. You could mold acylic around the coils to make the physical structure more robust, but there's absolutely no need for bottom/top plates.

Alternately, why not rout out some of the body and inset the sustainer into the body?

TTFN

FAQ731-376

 

[peskywinnets]

The acrylic most definitely isn't for show...how else am I going to hold six small coils vertically in place below each string?!! Yes, I guess I could mould the coil into some form of mouldable material...but I have no moulding equoipment (nor experience). I have a hobby CNC machine, so I can cut acrylic sheet to suit.

re routing the body...that's exactly what I'm trying to avoid! (this is why the solution has to be so short in stature, so it can slide between the guitar body & the strings 9total clearance is 8mm ...or a 1/3")

At least goi ng this way, if I want/choose/need to sell my guitar in the future, the next owner won't have to suffer the change in aesthetics I would have inflicted on it with routing (also the sustainer would ave to be sold with the guitar...therefore I lose my sustainer!). Guitarists are (in the main) very precious about their instrument(s)...a router & guitar should never meet!

 

[EdStainless]

Go with a rare earth magnet, make it thinner, you should be able to go to 0.4mm, and it does not need to be the same diameter as the core, it can be smaller in order to reduce the field. You can grind these on wet SiC paper. Use Duct tape to remove the magnetic fines.
If you mount these into an acrylic block you can mill the pocket from the back and leave a 1mm thick front cover. This will give you 7mm to work with. You don't need a back cover, it will be against the body.

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