Acoustic Guitar Repair : Gibson J 30





Towards the end on 2010 I had a telephone call from Valencia in Spain.

It was an owner of a Gibson J 30 acoustic who explained that he was having a problem with the soundboard on the guitar. He described how the soundboard was lifting badly behind the bridge, which was causing the bridge to “ride-up”. This, in turn, was causing a high playing action.

My first question was to ask if there wasn’t anyone in or around Valencia that could repair the guitar; Spain being the land of the Classical guitar with a Luthier on every street corner. I was interested to hear that American-made steel strung guitars such as this J 30 were outside of the local Spanish Luthiers comfort zone and their ethos to such a problem is: “If in doubt replace the soundboard”. Which conveniently side-steps the issue and also would change the guitar’s identity and characteristics forever.

After exchanging a few more ideas and discussing the possible causes of the problem I agreed to take on the repair. Several days later the guitar arrived by special carrier and I was able to take an in-depth look.

The bellying problem is shown in this photo.

Research and Background

The J 30 is a delicate and finely made instrument.  Made between 1985-1997, this guitar is a dreadnought size flat top acoustic with square shoulders. More info here…

With further investigation I was able to discover that the J 30 was (possibly) an experimental model by Gibson using a parabolic soundboard. This made me sit up and listen! Was the soundboard supposed to be this shape? All soundboards have a slight curve built into them to help with strength and stiffness. It would appear Gibson flirted with the parabolic idea on the J 30. However, if this shape was built into the design it wasn’t working very well.


Investigating the problem

The neck angle is correct; therefore this is not a possible cause.

This photo is taken through the sound-hole and shows a mirror image of the bridge plate. The size of the plate certainly could contribute to the bellying problem.

Click image to enlarge

In this photo of the soundboard, you will notice a very wide growth-ring pattern. Without writing a lengthy explanation as to why this could add to the problem (perhaps another time) it must suffice to say that the tighter or closer together the growth-rings the stronger the soundboard. Therefore this very wide growth-ring pattern could contribute to the deformation in the soundboard.

Click image to enlarge

Here’s a close-up of edge of the bridge. In this photograph stress lines have formed around the bridge wings. This could be due to the rotating effect of the bridge at its extremities or a loose brace.

Click image to enlarge

To sum up,  we have deformation in the soundboard due to the following possible causes:

  • A probable parabolic shape built into the soundboard
  • Dubious soundboard strength due to a wide growth-ring pattern
  • A bridge-plate that is not helping to stiffen that crucial area of the soundboard
  • Possible loose brace

A Possible Solution

  • There is nothing that can be done with the soundboard quality apart from following the Spanish Luthiers advice. However, the soundboard could be gently eased into a flatter parabola.
  • The bridge-plate could be exchanged for a larger and sturdier replacement to help flatten the soundboard
  • The bridge could be removed and the underside subtlety shaped to help flatten the soundboard




The Repair

The internal braces are checked: all in order.

The bridge and bridge-plate are gently moistened and heated. This softens the glue and ensures easy removal.

Once removed and while the area of the soundboard around the bridge and bridge-plate are in a “moist” state, the soundboard is gently eased into a flatter shape.  It is left to dry-out in a quiet part of the workshop for a few weeks.

A new bridge-plate is made up. This is designed slightly larger, slightly thicker than the original and is made from quarter-sawn Rosewood for extra sturdiness.

After several weeks of drying-out time the new Rosewood bridge-plate is glued into place. Whilst the glue is drying the soundboard is kept in its flatter shape.

After several days in clamp the bridge is refitted.  All the while the soundboard is held in its flatter shape. (no photo available)

After a few days the guitar is strung up, tuned to concert pitch and monitored. Several days later all seems well.


The Before and After Assessment

Before                                                                                     After


Improvements

The shape of the soundboard has improved considerably. Although still in is Parabolic state it has become less extreme at the soundboard edges resulting in the bridge sitting slightly lower and thus giving a better playing action, better feel and better sound quality.

The J 30 has improved considerably with the work that was carried out. It plays beautifully and now has that lush Gibson sound again. This repair was considered a success and the owner back in Spain was delighted. All that remains is to organise the shipping back to Valencia.


Contact

A few days after shipment I received this email:

Hi Graham

The guitar arrived safe and sound yesterday and plays beautifully.
Thank you once again for your excellent service, I really do
appreciate it.

Saludos

Michael

More photos on Flickr…





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