You have constructed an attractive instrument. That is only Part 1 of making a fine instrument. Even a very well made string instrument needs "SET-UP" after construction. "Cheap" instruments are often discarded simply because no one has done that. It usually requires less than an hour of informed action.

As Ken noted, you may need to level the frets. You might find it insightful to read one of his earlier posts on leveling - 
https://fotmd.com/forums/forum/instruments-discuss-specific-features-luthiers-instrument-problems-questions/37078/leveling-of-frets-why
 
Most of the on-line information on leveling is by guitar folks. This video is good in terms of basic technique,
Fret Leveling - The Easy Way // How To

As the video notes, you start by making sure the FRETBOARD itself is straight. Many guitar necks have a metal rod which can be used to adjust the curvature. We don't use such a device. We can usually compensate for a small bit of un-straightness in the stick through leveling. 

We also don't typically use a crosswise arch on our frets.

I'm pretty much in agreement with John, a combination of heat softening of the glue and string tension resulted in separation of the "flat head." I would guess that there is little other structural damage.

You have three clear choices, (1) a very expensive "restoration" (2) a repair to playing condition (3) giving or selling it to someone who would repair or restore it. Don't throw it in the trash, at least give it to Goodwill where it would find a new home.

McSpadden instruments can have a variety of signatures, even if factory assembled. From the shaping or the sound holes, I'd say a kit is a good guess.

It may need new "bridge", spacer, strings, and tuners, but McSpadden can readily supply them. The re-gluing is pretty much a handyman project, not lutherie, and you might want to make it a DYI job. If I was doing the repair, I'd probably keep the discoloration and the story. 

In any case, it is always a good time to get another instrument.

My 6-string conversion of an old Korean dulcimer has a "dropped" A on the middle set and a "raised" D on the base set. Otherwise it has the common, original, DAA tuning. I like it, and it the instrument I usually play.

I'm not at all surprised.

All instruments need to be properly "set up," and this is often left to the retail seller. Amateur builders often don't know how to do the simple adjustments. Many of the string instruments in charity stores are "throwaways" that people got as a gift or as so-called bargains which only need a proper set-up.

I went back to look at the photos of the spacer and fret. Someone obviously messed it up. 

Frankly, if I was dealing with this, I would remove the plastic spacer and throw it away. I would make a new spacer from hardwood or plastic. I would probably then cut a new groove to fit the width and height of the spacer closer to the zero fret. Alternately I would re-cut the spacer hole to square it up, glue in a filler block, and then cut a new slot there to fit my new spacer.

I would also reset the position of the middle string to the middle of the fretboard.

Sorry about misleading you about sloping the grooves. That applies to a nut, not a spacer. 

You don't need or want diamond files for cutting wood or plastic. I use cheap (under $5) "needle" or "jewelers" files like these.

https://www.walmart.com/ip/Hyper-Tough-6-Piece-Needle-File-Set-TR17075C-0-18lbs-New-Condition/49944457?fulfillmentIntent=In-store&filters=%5B%7B%22intent%22%3A%22fulfillmentIntent%22%2C%22values%22%3A%5B%22In-store%22%5D%7D%5D&classType=VARIANT&athbdg=L1600&from=/search

https://www.harborfreight.com/needle-file-set-12-piece-56743.html

Unless, of course, you are using something like stainless steel for your nut.

Some recommend using welder's "Tip Cleaners." They provide a round bottom groove. I've tried them, but I think a ve-bottom is better.

https://www.grainger.com/product/2CYY5?gucid=N:N:PS:Paid:GGL:CSM-2295:6VHHZD:20500801:APZ_1&gclsrc=aw.ds&gad_source=1&gad_campaignid=21369464100&gclid=Cj0KCQjw3OjGBhDYARIsADd-uX7vO8dMz3VBbhcAci8p5LbNQX30CoNKMvqRmH5EiefwGo4KpHnIqeYaAvrLEALw_wcB

To make the slot adjustment, I would use either a triangular needle file or perhaps a welding tip cleaning file. You can do it one string at a time by slacking the string and pulling it to one side while you file while you keep the others tight.

You want to angle the slot so that the high point is on the bridge side to preserve the VSL.

I would NOT "Cut" them with a saw.

John Knopf said "One thing I've noticed is how many of these songs dealt with disasters, death, sickness, loss of dear ones, etc."

Isn't that what a lot of current "pop" music lyrics are about? Only today it is sung in the first person, not the third.

"Today I hoed an acre of beans and split a cord of wood, I'd do the same tomorrow if the good lord said I could," isn't particularly entertaining. 

In addition to ballads, they also sang "play party songs," common hymns, etc.

Many collectors were seeking "old ballads" which "proved" connection to Elizabethan England and seldom notated the other stuff. There was political bias in the collection process.

Excellent suggestion, Ken.

Warren's phone number is on his website https://www.warrenamay.com/contact-us/

When you get the answer, please let us know what he says. I'm sure several of us who do our own maintenance will be interested in why a "bridge" might have different heights for melody and bass.

I would think the bass string might have been set higher to avoid the string buzzing on some of the middle frets. There were no standard "dulcimer string" sets in 2006 and he may not have found a really good size of banjo or guitar would string.

My primary interest in "Jewish Music" is to be inclusive in performances during holiday periods like Christmas/Chanukah and Easter/Passover. I have a number of things like The Dreidal Song in my crank organ collection along with Jingle Bells.

I wasn't surprised to find that there is a book called Union Hymnal for Jewish Worship available as a .PDF at archive.org. This was produced by American "reformed" congregations, and as a result, all lyrics appear to be in English, and some of the tunes are by non-jewish composers like Mozart. 

At a first glance you would be hard pressed to tell from a single page that it wasn't from any American protestant hymnal. They are four-part arrangements.

https://ia801507.us.archive.org/34/items/unionhymnal00cent/unionhymnal00cent.pdf

Hymnary.org has several listing for books with lyrics in Hebrew and Yiddish. One example is
https://hymnary.org/hymnal/CZNS1909

Brown University has a page on Yiddish sheet music with a lot of sheet music.
https://library.brown.edu/cds/sheetmusic/yiddish/

I found that via the Hebrew Union College page on music resources.
https://huc.edu/libraries/free-online-resources/free-online-resources-music-resources/

The resources are there.

The request was for "Jewish worship songs." A lot of the common "Jewish songs" are holiday or folk tunes.

If you are looking for TABs for music for temple or synagogue, some of us here might be able to able to make them from sheet music, but we wouldn't have that or know what to look for.

I think the loudest acoustic dulcimer I have is my Tennessee Music Box (TMB). It is home-built, and I described it in the thread

https://fotmd.com/strumelia/group/42/box-dulcimers

With the 1/2 inch plywood faces it is substantial enough to survive a lot of rough treatment. It might be used as a shield It has a screen door handle on one side so it doesn't need a case

There are very few dulcimers available with proper pickups installed for electric amplification. The piezo types - either built in or attached - will pick up both any bump on the dulcimer or sometimes other sounds not associated with the instrument such as passing trains.

John Knopf built a hybrid TMB about a decade ago. If you are buying, not building your own, at least exchange messages with him.

https://fotmd.com/strumelia/group_discuss/1018/electric-hybrid-tmb

You will occasionally encounter DAA TABs which have 6 1/2 fret notes. Don't avoid an instrument just because it has one.

Your website is informative, not just a sales piece. I like the inclusion of the videos of most of your varieties letting viewers hear them.

You should consider taking your current instrument to the shop and playing both side by side. The important thing is which one suits your ear better.

If a bridge is simply too high, you can lower it by taking it out and sanding or filing the bottom a bit. Do it a little at a time and tune and play it after each reduction.

If you have measured the bridge height and know about how much too high it is, you first pass may be a larger one, then do it a bit by bit.

If you are a "DAA" player, you tune the Bass string down the half note, then use the same "4th fret" on the Bass to get the others. (Relative tuning works similarly for other tunings.)

If you go back to Jean Ritchie's Dulcimer Book, the basic tunings were a whole step lower - Cggg, CGcc and so on, so lower tunings are more traditional. 

"Kit" can mean a lot of things. For example, an fine instrument plus case plus a ukulele pick, a 3 inch "noter" plus a CD and book can be described as a kit. A kit can also be just plans and pieces of wood.

Particularly if buying through eBay, ShopGoodwill, or a crafts store any document, description or label should be treated as mere suggestions about possible origin. Often accessories and documents found in the same closet with an instrument are all simply thrown into one box.

That's not to criticize auction purchases, that's how I got several of mine.  

On my instruments I typically use a nut or bridge with a flat bottom and a sloped (not rounded) top with the high edge toward the fretted portion. I then carefully slope the slots to match. The VSL should run from the inside of one to the inside of the other.

If you have not studied the Folkcraft website, a visit is in order. https://folkcraft.com/

Connecticut should only indicate that this was made when the factory was there between 1979 and 2006. I don't see anything on the Folkcraft site that indicates that they made "noter style" instruments. Almost any Appalachian dulcimer can be played with either a noter or the fingers.

Since the builder of a kit can glue any label inside, there is no reason to expect to see "made from a kit" inside. A label is simply a label. 

Did you, by any chance, flip the bridge over while changing strings?

As shown in the photos, the nut is well off center. The string grooves appear to be rather tight on the strings, but it is hard to tell from the photo. Perhaps the cut-away for the outer two strings isn't as big as it should be and is creating sideways pull.

You should check string heights when you acquire a "new" instrument. There is lots of good information on how to do that here on FOTMD.

Folkcraft sells a variety of replacement bridges complete with notches.
https://folkcraft.com/pages/search-results-page?q=bridge&page=1&rb_product_type=Building%20Supplies%20%26%20Plans

I don't use tuning apps, I use clip-on tuners of various makes and models.

For a dulcimer, you want/need one with a CHROMATIC setting. Some have settings for guitar, fiddle, ukulele, etc. and in that case you need to be sure that you are using the C setting. It's usually a very small letter and easy to miss until you understand its importance.

That same thing applies with an app. I' not aware that Fender ever made dulcimers, and I wouldn't be surprised if their all only had guitar settings

Rule #1 for purchasing a dulcimer: If possible, PLAY IT.

Dulcimers come in a variety of shapes and sizes, and you need one which fits YOU. Even if you can barely play, putting it on your lap will help you decide whether it fits you.

Don't worry if you can't put it in proper tune, if one string will play you can get a pretty good sense of the tone which the body shape and size provides, and you can check for things like buzzing. Fingering each fret in order can be used to check for a warped stick or high frets. If your ear is decent, you can use Fret 7 (the octave) to roughly check fretting, nut, and bridge problems.

Generally any McSpadden, or other big name instrument, made within the past 20 years is likely to be OK if there is no visible damage, although a good look at tuners, etc. is good advice.

There are no really good price guides for used instruments except eBay and Reverb asking prices. If you can't play it, always check shipping charges, etc. since these are sometimes more than the instrument price.

Don't worry if you don't understand all this, but see if you and the instrument are a comfortable and pleasing match. You should be looking for a "lifetime companion," not a "trophy spouse." You may need more than one date, don't rush it.

You can make a stable, playable dulcimer which is only a stick. You just won't hear much without adding a sound box or putting it on a table top resonator.

The cardboard dulcimers are a good example. The structure is usually a piece of 1x2 lumber with a modest strum-hole. Once tuned and settled in, the cardboard dulcimers will often hold relative tuning for months when stored in a cloth bag, and only need a touch-up when string tension is affected by room temperature changes.

I'm not a fan of hollowed out fret boards, etc. I'm not convinced they can be proven to make better music. When I build, I like the basic stick and box construction. I think pear and hour glass box shapes, fancy woods, lots of sound holes, etc.are mostly decorative.Box size does definitely affect the sound produced.

Decoration is fine, but should be seen as such. I put ebony or mother-of-pearl dots on my simple sticks and prefer trapezoidal boxes with shaped holes to rectangles with round holes. Sometimes I paint folkish designs on the boxes.

I can appreciate fancy dulcimers just as I can appreciate an Aston-Martin car - but I drive a basic small car and enjoy playing "cheap" instruments.

I taught engineering mechanics (Statics, Dynamics, and Strength of Materials - the courses which drove students out of Engineering) for a quarter of a century. My view is based on a lot of 'book larnin.' Over the years some of us develop structural intuition just as musical intuition grows for some and not others.

My remarks are focused on "true dulcimers" with 3 or 4 strings and a stick which runs the full length of the VSL. The body is relatively narrow and the tension of the strings is modest. The sides, front, and back are sort of a stiff tube. The tension causes the body and fret board to curve very, very slightly and the wood to "creep" slightly over a period of days and "settle in."

An acoustic guitar body has only modest amounts of bracing inside, and the heavy wound steel core strings create a much larger tensile force. Solid body guitars are very different structurally.

A fiddle body is actually a complex shell shape, and the string tensions are rather low. On many fiddles the strings have a gut or nylon core.

On a modern instrument of these families the body might actually be graphite reinforced plastic. Tension will still cause minuscule bowing of the body, but there will be no creep.

There are no simple answers or explanations for such questions. I'm still trying to fully comprehend musical modes and remember chord structures.

String instruments which are played regularly are typically "kept in tune" for many decades on end.

Strings may be damaged by age or environmental factors, of course, but, in my opinion, the minute aspects of wooden bodies' shapes are better preserved if string tension it maintained. If you unbox a dulcimer with loose strings it usually takes several tunings to get it to hold properly. Tension also keeps the "bridge" and nut secure.

Wooden pegs are another matter. They and the matching holes will undergo changes in roundness with changes in humidity. That's why moving a dulcimer from Phoenix to Seattle may require attention by a luthier.

If you have a 10 million dollar violin, controlled storage conditions are probably in order, but the primary benefit goes to the gut strings and horsehair on the bow.

If your dulcimer is worth less than $10,000, keep it in the case and keep it out of rain, snow, deserts, and floods. Storing it in direct sunlight probably isn't beneficial, but a lot of wall-hanging dulcimers stay playable.

Except that mine is Dd-Aa-aa (or maybe dD-aA-aa, or aa-Aa-Dd if you prefer the reverse order)

Or like an "unreal Dulcimer." On my 6-string dulcimer, tuned in DAA with 6+ fret, I have a wound string in the middle pair tuned an octave below normal and a high D on the "bass" pair. This gives a more rich sound to the drones, and not like a mandolin.

I also like the sound of 3-string DAA noter-drone cardboard instruments.

As John and others say, depends on what you like and the mood you are in.

I ran into a problem with a wound bass string once. There was a bit of a buzz which I tracked down to a broken winding. See the attached photo.

I identified the problem when I ran my finger up and down the string. It was visible to my naked eye once I knew where to look.

A simple string change fixed it.

 Damaged Winding-labeled.jpg - 496KB

Ukulele fret boards are essentially the same width as those on dulcimers- about 1 1/2 inches. Guitar pickups are wider, but they say they can be cut. That's why I pointed to the ukulele version. 

The piezo element itself looks sort of like a black match stick with a wire on one end. As I recall, I think I just cut the height of the "bone" (probably plastic) saddle down, slide the pickup into the slot, and put the saddle back on top. Some ukulele people appear to put it along the outer edge of the bone saddle, probably raising the strings be a tiny amount.

The rest of the procedure is covered reasonably well in a number of YouTube videos. I think this one is pretty good.

Installation of ukulele pickup system

If you are doing it for the first time, you might want to do it on a cheap instrument.

It does take "some skill," but not a whole bunch. My kit came with paper templates for the holes. Other than a drill, I used only hobby/craft hand tools. The wiring is all plug-in, and the holes you cut for the tuner/controller and battery/jack boxes allow you to pass the wires for hook-up.

Since you have a serious need for a pickup, I would not suggest a stick-on mounted on the face of the dulcimer. Particularly since you say you feel sounds from other instruments on it.

I would suggest a piezo pickup under the "bridge" of the sort shown here.

https://www.ebay.com/itm/154154723887?_skw=ukulele+underbridge+pickup&itmmeta=01JR0P8CXC59HVTZEX0R9G8PKC&hash=item23e4566a2f:g:zdYAAOSwiO9fkRip&itmprp=enc%3AAQAKAAABAFkggFvd1GGDu0w3yXCmi1f1a%2FKcJRUkgjxwQyqQw7pljhCoSpJkPekGjrv%2FHmQyoDfqDnxjm6SrWceacTwHEpxive6LhrBaCArs25TycThyGZw2SwBCOiSvptCm5%2Fqzop1Fsc%2FQiJa4vvGCcKXGJPDVPubYXyW6kOSyQwGuZ3Yc3CZRgqJImQu%2F%2B6SWoTgeXfbx0g2Uo33cGOepI4b5%2B9dx0tzeZAB1uEmGVfOOhjkaI1%2F%2BVJO7Y60fW7j1TotNy7taAUvEFBrHgSRsWpZNray4sM%2Fk9HoLN2Gz0D1ObyGt3wf8uRJdkfhoChJR0GG82SBarYMYfHYCdb8cCuCEjWg%3D%7Ctkp%3ABk9SR_7OoZbAZQ

If installed with the pre-amp/tuner you add many of the features found on electric guitars, etc. I installed a similar unit on a cheap, used dulcimer, and it works. I don't use the pickup since I play quietly in an all acoustic group, but I have tested it with a 10 watt guitar amp and it works well. I do use the tuner - it doesn't get lost in my case.

The lower instrument in my photo on the left is one I made a few years ago. The VSL is about 15 inches and it has a standard string set. It is tuned to DAA, but an octave above normal - A = 440.

It has a nice sound, but I have hardly played it. I had in mind that t might be used in an ensemble for adding accent on a second verse, or whatever. I haven't had an opportunity to try that with our group.

"3 mm is ok., 2,8 or 2,9 mm too."

Adding the metric measurement is good. We should remember that "The Appalachian Dulcimer" covers the world today, and that we should routinely mention both American and SI units.

Many of us are used to thinking 1/4 inch plywood is 6mm and 3mm ply is 1/8 inch.  Actually 1/8 inch is 3.175 (3,175) mm, so "by eyeball" we are talking about the same dimension, making 2,8 mm a bit narrow for some of us.

A 3+ fret might have been used to play ancient or Eastern European tunes which have different ascending and descending scales. I think I've run across tunes where either a 3+ or 4+ was needed in DAA. Dulcimers can be highly individualized, and a "one-off" by a home builder is a possibility..

One measure might be the number of commercial producers of dulcimers. That has certainly declined.

Buying a new fretboard will cost you more than buying a 30 year old dulcimer and involve a lot more work.

I would suggest you consider buying an instrument on ShopGoodwill for $40 or less (including shipping and tax) and adding a cheap contact mic as an easy experiment. Since you will be shaping the sound with your electronics the body quality will make minimal difference.

Most of the instruments listed today on this page should serve your purposes. (I wouldn't say that to someone looking for a good acoustic instrument.)
https://shopgoodwill.com/categories/listing?st=dulcimer&sg=&c=&s=&lp=0&hp=999999&sbn=&spo=false&snpo=false&socs=false&sd=false&sca=false&caed=1%2F22%2F2025&cadb=7&scs=false&sis=false&col=1&p=1&ps=40&desc=false&ss=0&UseBuyerPrefs=true&sus=false&cln=1&catIds=&pn=&wc=false&mci=false&hmt=false&layout=grid&ihp=true

Professional Piezo Contact Microphone Pickup for Guitar Violin
ApproximatelyUS $2.57
Free Economy Shipping from Greater China
https://www.ebay.com/itm/335756608848?_skw=piezo+pickup&itmmeta=01JJ71EA19DF3XA0WECP531VMD&hash=item4e2ca74550:g:qpUAAOSwOPtneM1U&itmprp=enc%3AAQAJAAAA8HoV3kP08IDx%2BKZ9MfhVJKn2D4rzConcs1ki1Ui1XNKWM5p388NzRr7ctDbXkTg6jyJXUfQdgUK8S78UJ8CEyq5hhXsVafRrR2CmyoZFkhZIr6ptQzZxbUkoPa1y8kHxgLFENxppmRqORstXXLebiwlUtzcON8kk%2BQ%2FCVmfqUCqAghklDiAyP--nOGKZkfYA8l4lDa4g4v%2FxSWJZRKdGKAdDheOD5n6lpYerGCVv87BKQm%2Fzn6B%2FyPhEy1mITwdBR5r9powtvrK7QZKusCtkFtvkUwgn72gmxUb%2FDk4tJ%2FXl1tCRa%2BrVCKCr5R11UoHUCw%3D%3D%7Ctkp%3ABk9SR_6gueGRZQ

My knowledge is in two streams.

I use and arrange in MIDI for a crank organ with multiple voices controlled by solenoids, as well as a small MIDI synthesizer module.I don't think this has any bearing on your needs.

On the dulcimer side, I have used a $10 clip-on guitar pickup experimentally on a $40 dulcimer.. That worked as a connection to a 10 watt guitar amp.

I installed a ukulele tuner-preamp with piezo under-the-bridge installation on one on my $40 Korean dulcimers. Mostly I just use it as a tuner which never falls off or gets lost. I have tested it with a couple of small guitar amps, so I know it works, but I only play for fun with acoustic groups. I have thought it may be useful when working as a dulcimer class instructor, but found my home-made acoustic Tennessee Music Box dulcimer works well for our very small classes, and is convenient for use on a table in the front of the room.

If you already have any dulcimer, try a cheap guitar pickup first.

A solid body electric is fine, but probably expensive, and will have to be custom built with a considerable wait time.

.

It's not clear to me exactly what you propose to do.

In general, control of a synthesizer requires that the controller generate a digital signal, which is commonly in MIDI format. No pickup on an acoustic instrument can do that.

A dulcimer with a pickup CAN generate an analog audio signal which can be added as a digital stream in the output to a final audio file.

Can your system deal with input from a microphone or a common electric guitar? If not, an electric dulcimer will be no different.

I think any "set" on the market will be fine on any more-or-less standard dulcimer in CGG, DAA, DAD and DAC tuning. There is no reason to try to out smart McSpadden, or the other industry leaders

That is assuming you start a bit low and carefully tune up to the note you want. A beginner can accidentally tune a few turns too high too quickly and break a string, and I think part of the selections used in making sets make an allowance for that.

I think you can go up to 14 on the melody strings if you stick to DAA, but 12 is safer for DAD, and 10 requires less finger pressure. DAD players typically finger about 3 notes on the 14 middle string, anyway, so 14 A is playable.

Finger pressure is also dependent on string height which is also a personal choice. Have you mastered checking and adjusting that yet? Builders often leave strings a bit high to allow easy adjustment with a small file if they don't use a zero fret.

"Chromatic Dulcimers are becoming more popular" Than what?

Many, many more new violins are purchased each year than dulcimers. Probably many millions more.

I play 3/4/6-string noter-drone dulcimer for simple fun even though I'm about as comfortable on the violin. I'm not aiming for mastery of either, just my own amusement.

Why are you worried about tuner precision? Electronic turners are great for many reasons, including letting folks "tune up" backstage to the same note, instead of devoting a minute or so of on-stage time, but in my opinion, a few cents difference doesn't really matter.

In the real world when you take your dulcimer out of its case and try a tune it may sound fine, but the happy person next to you sounds out-of-tune. You get out your tuning meter and find you are a bit off because your strings are at a different temperature than they were the last time you played. In the old days, you would have said to the leader "Play me a D," and tuned to that, the group being more important than you.

Tune your middle A string as precisely as possible (in the green) and then test the tuning when you finger at frets, 3, 7, and 10. On many, perhaps most, dulcimers you will find you are a few cents sharp, but when you play music it sounds fine.

If you put your finger on the string and check the tuning, you may even find that it makes a difference where and how you place your finger.

On large organs, pairs of pipes are tuned with one a few cents sharp to produce a voice called Celeste, or a few cents flat to produce a voice called Humana. Slight dissonances make music more interesting.

As the old saying goes, "This ain't rocket science."