Reviving this topic because I have been doing some experimentation with magnetic pickup concepts for violin.

One of the problems is that comparatively few of the popular violin strings would be likely to contain enough steel to be able to provide a decent amount of signal.  My solution to that was to try stringing my electric violin with cut down electric guitar strings. 

I had seen some speculation in assorted discussions around the net that there would be problems with that.  Allegedly they would be the wrong tension and mess up the neck, or they would be very hard on the bow hair.

I ended up trying Ernie Ball strings (not my first choice, but it is what the local music store had in single electric guitar strings).  I had planned on using flat-wound strings, since violin strings usually seem to be flat wound.  But they didn't have them in stock in gauges I needed, so I went with round-wounds.  The music store owner advised that round wounds would "rip up" the bow hair, but I decided to give it a try anyway and at least get an idea what the worst case scenario was like.

I've lost one bow hair in the first month of using the round wound strings.  That is typical for me.  No measurable bending or warp to the neck of my electric violin. 

So my tentative early conclusion is that the dangers of using electric guitar strings on a violin may be somewhat over-rated. 

The gauges I am using are:

G- .028 (wound)

D- .024 (wound)

A- .013 (plain)

E- .009 (plain)

Those involved some guesswork on my part, going maybe a bit lighter on the E and G string, since those will be physically closer to the pickup coil of a single coil type pickup.  But overall, the set seems to have been a good guess, in that it plays comfortably and the un-amplified volume of the strings seems fairly even. 

They do definitely work with just a standard electric guitar pickup taped to the top of the electric violin near the end of the fingerboard.  But the problem I've run into so far is that standard electric guitar pickups I happen to have onhand are considerably wider than what is needed, and (other than looking rather inelegant) could interfere with normal bowing techniques.  I think it is going to take a custom wound pickup to give the concept a fair try.  I'm no stranger to winding pickups, it is just a bit of work since it takes thousands of winds done with very fine (AWG 42, usually) wire that is really easy to break.  That stuff is copper wire thinner than a baby's hair, and it is pretty fragile to work with.

Back to strings, the data I have so far from my experiments is probably only of any great interest to those interested in using magnetic pickups on a violin.  The possibility that electric guitar strings can be used does open up some options there.  They might also be of some interest for fiddlers who like steel core strings on acoustic instruments and who might be inclined to experiment.  It also gets me to wondering what the synthetic core silver wrapped guitar strings that I prefer on my acoustic guitars might sound like on a violin.  Guitar strings of similar materials to violin strings, and made by makers that are at least very reputable on quality for guitar strings are available at a fraction of what a similar set of violin strings lists for.  But that would be for later experiments.

Now that I've found out that using guitar strings on a violin will not automatically destroy the neck or the bow, anyway.

Yeah, I expect that the roundwounds will wear the fingerboard quicker.  But it's the carbon/plastic fingerboard on my 80$ electric, and it already has some early signs of wear.  I expect it will need replaced within this year anyway, and a student grade ebony fingerboard isn't all that expensive.  Even a bit better than student grade isn't that expensive. 

On plucked strings (guitar or bass guitar), round wound strings are usually a bit brighter sounding.  There are a number of guitar string manufacturers that make flatwounds, though, if the rounds end up being too bright, go through fingerboards too fast, or maybe just make too much "string talk" from moving fingers.

I don't see anyone being very likely to try this to put a magnetic pickup on an expensive and nice sounding acoustic anyway, though.   The weight of a magnetic pickup will be considerably more than the negligible little bit a piezo element weighs, and it would likely throw off the balance on an acoustic instrument more than most acoustic players would find acceptable. 

I don't have a sound sample, but I'll see if I can toggle something together to give some idea what a magnetic pickup sounds like, compared to a piezo one.  So far as I have been able to tell, it sounds even less like an acoustic violin (to my ears) than a piezo does.  But it has a cool sort of sound all it's own that I think can be usable in some musical contexts.  I am not worried about getting it to sound like an acoustic violin.  I have a perfectly good acoustic violin for that, which can do a better job of sounding like an acoustic than any electric I've ever heard, when I want that sound.  LOL