Does my new (second hand) 12 string Guild need a repair?

[MilesWilley]

Hello folks.

I took a punt on a Guild GAD F212 through ebay and I'm seeking some advice on how serious the slight bulge behind the bridge is. A couple of pictures attached. It plays great and the intonation is fine at the moment - I'd like to keep it if possible, but I don't want to hold on to something that could cost a big repair further down the line. It only arrived yesterday so I could return it.

Basically, is the extent of this bulge serious? Or is it to be expected and no big deal? 

Any advice gratefully received!

 

 

 

[Gibson29]

All guitars have a bulge.

[garthman]

Hello and welcome.

Most acoustic guitars develop a top bulge behind the bridge as they age due to the tension of the strings. It often happens sooner with a 12 string guitar because the string tension is 50% greater. If the break angle of the strings (that is the angle of the strings from the top of the saddle to the pin hole) is reasonable the guitar should play and sound OK. You can help reduce string tension by either tuning the guitar down a couple of semitones or using lighter gauge strings.

There is a device called a "Bridge Doctor" that you can fit inside the guitar to reduce and sometimes correct a bulging top. Another fix for poor break angle is to sand down the bridge in the area around the pinholes to lower it thereby increasing the angle of the strings over the saddle. Obviously this may affect the value of the guitar but if you don't plan to sell it that's not a problem.

[Freeman Keller]

I don't come around much anymore but I have to chime in.  The dome in your top is perfectly normal and is desirable.  It is built into the guitar with the shape of the braces.  A spherical dome is much stronger and stiffer than a flat plate.  Over the life of the guitar the dome may increase slightly, that also is normal.    If it becomes too much (along with some other changes in geometry) it will be time for a neck reset.   I'm assuming that you have measured the neck angle and that it is OK.

One thing that you should be very aware of is that if your guitar dries out, becomes dehydrate, the dome will flatten out and eventually the top may become concave.   The action will get low and buzzy, the top may actually split.   I use the fact that the top of a guitar has its dome shape as one indicator that it is properly humidified.

One last comment, the "bridge doctor" will (usually) reduce the dome but it introduces its own set of problems.  If anyone is considering using one please contact me and I'll try to talk you out of it.

 

Now back under my rock.  

 

[Emory]

Listen to Freeman... he's forgotten more than I'll ever know.

From ebay, from where to where? If maybe from different enough area bulge may be due in part to different humidity, etc.

I bring that up because I got a Tacoma jumbo in Oregon & brought back to Thailand (very different levels of humidity). The top swelled, perhaps due in part to Tacoma's floating braces design. Kept shaving bridge to have passable action.... eventually it settled down...

Maybe loosen strings and just wait. How long? don't know. Took me time to adjust to humidity differences Thailand and Oregon

Lovely lovely from what I could see in photos

 

[Freeman Keller]

Its been my humble experience that a guitar does not "swell up" unless maybe you have extremely high humidity.   I build guitars with a 25 foot spherical radius in the top which means that if I lay a straight edge across the lower bout behind the bridge I typically have around 1/8 gap at both sides at the edge.   You maybe have a bit more than that but that is to be expected with a 12 string - they do have half again the tension on the top (depending on your strings and tuning) but it should be braced for that.

It is worth while talking about strings and tuning, lets see if the OP comes back and tells what he is running.   I might even check back to see....

[Mikeo]

This should be a nice reminder with the winter months soon approaching to hydrate your acoustic instruments.

The guitar looks fine.

You should have a slight bulge on the back side too. Flats tops aren't exactly flat.

 

Hey Keller nice to see you drop in.

 

 

 

[DeepEnd]

As Freeman and others have said, the bulge isn't necessarily a cause for concern unless the whole bridge is tilted toward the neck. Since there are no pics from an appropriate angle I'll assume it isn't. What might be a cause for concern is the dip between the bridge and the neck, visible in the second pic. If you're lucky the guitar is simply dehydrated. If you're not the fretboard may be pushing the top down and deforming it, indicating there's a neck reset in your future.