The Jazz Guitar Chord Dictionary
  1. #1

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    I have a 1934 Epiphone Spartan, round-hole archtop. They were only made for about one year: I acquired it as a total wreck, and have rebuilt it, including a new carved back. After alot of work, I got it back together, and strung it up last January. After playing it since then, I have to admit, I'm underwhelmed by the sound: it's greatly lacking in volume, especially compared to it's f-hole brethren. Since it's already lost(IMO) it's originality, and value(before I got it!), I'm considering removing the back, and rebracing it, to improve the sound. I'm looking for suggestions from anyone who's built a round hole archtop,or has worked on good-sounding vintage examples, and can comment on or suggest other bracing layouts. Below are photos of the guitar, as I received it, the original bracing, and progress pics.possible rebracing of vintage round hole archtop-img_2666-jpgpossible rebracing of vintage round hole archtop-1934-epiphone-spartan-jpgpossible rebracing of vintage round hole archtop-img_1847-jpgpossible rebracing of vintage round hole archtop-img_2369-jpgpossible rebracing of vintage round hole archtop-img_2402-jpgpossible rebracing of vintage round hole archtop-img_2455-jpgpossible rebracing of vintage round hole archtop-img_2503-jpgpossible rebracing of vintage round hole archtop-img_2542-jpgpossible rebracing of vintage round hole archtop-img_2469-jpg

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  3. #2

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    I'm not qualified to make suggestions on bracing, but I do want to say hella job bringing that one back from the brink. Amazing save! Great work so far.

    Sent from my SM-G960U using Tapatalk

  4. #3

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    I would suggest asking at a luthier's forum like mimf.com and luthiersforum.com.

  5. #4

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    Out of curiosity how thick is the back plate and did you carve in a recurve? How much does she weigh?

  6. #5

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    I’m no luthier, but it seems unusual to have the tone bars so close together toward the bottom of the guitar. They also seem very stout and extend all the way to the end, which might over-constrain the vibration. You might google archtop tone bars and try an arrangement that other luthiers prefer. I wonder if X-bracing might help the tone, but since you want more volume, you’re more likely to get that with parallel bracing. Of course the thickness of the top may also be a factor.

    I hope you’ll report back on what you decide to do and how it works.

  7. #6

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    Matt, when the new back was carved, the only template I had, was the original back, shattered and incomplete(likely pressed, but possibly carved maple), and I took measurements off that. The new back(hard bird's eye maple) was carved by a luthier friend with CNC, and then I final scraped and sanded it. I'll check my measurements, and report back. The recurve, I now think, is inadequate: I now also have a '36 Spartan, with a carved walnut back, which has a lovely deep recurve. The new, hard maple back may be part of the problem. I'll check the weight of the guitar.

    I believe the 'reverse' splay of the existing tone bars is part of the issue: the narrowing toward the end block would seem to stiffen the top, under the bridge. I'm not aware of any other archtop, with tone bars, using this arrangement. Gibsons tone bars were more truly parallel, not splayed(is that correct?), and Epiphone tone bars(in the f-hole guitars) splayed from narrow at the neck block, to wider at the end block. I'm actually think an x-brace might help(or at least parallel tone bars, like a Gibson). I would not call the original bars stout, based on my observations: they match(in cross section) those that were in a '34 Epiphone Sorrentino archtop, which was a lovely, robust sounding instrument.

  8. #7

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    Thanks, Dave. I asked about thickness of the back because the photo makes it look a bit thick. The back plate can have a major influence on sound. Hard maple can probably be carved a bit thinner than some of the softer types of maple. Somewhere around 3/16" thick for all areas other than the recurve at somewhere around 1/8"thick would be a good starting point. My guess is you may even be able to go a bit thinner with hard maple. Pressing on the top and back with 1 of your thumbs is a good way to check for how much flex or deflection your plates have. I can use one thumb and exert about 30 pounds of pressure. Try that at the bridge area and at the center of the back and see if your plates flex noticeably. This may help with judging how heavy the bracing is also. You may want to calculate the down force at the bridge and try to match that with your thumb pressure. You should have some flexing at the bridge when you reach the same downforce as the bridge has at full string tension. You have her looking good BTW

  9. #8

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    The guitar weighs 4lbs 9oz. The back thickness is, along the centerline, about .200", tapering to about .186", toward the ends. The recurve does indeed appear too thick, varies from about .128", to .157" and .167": I can definitely thin it to a consistent .125". I can also thin the centerline to a consistent 3/16", or .1875"(and, given I used hard maple for the new back, maybe thin it even more?). I do have Benedetto's book on building archtops, and I looked at his numbers, which agree with Matt's. The original top, while inconsistent(and suffering from a long, badly repaired and sanded crack on the bass side(making the thickness reading doubly inconsistent), does have a thinned area(down to .109" or so), around the edge of the lower bout, but farther from the edge than the recurve. I do think that the 'reverse' splay of the tone bars is not helping: it's contrary to accepted tone bar placement, and, I think, overly stiffens the top under the bridge. Hmmmm....I've spent so much time bringing this one back, it would be nice to do something more, to make it sound better.