Gibson J45 intonation problem (solved?)

[shufflebeat]

Django owned and played the Musee de la Musique Selmer #305 from 1940 until his death in 1953 and the guitar is very well documented…

edited to add link :- https://gypsyjazzuk.wordpress.com/gypsy ... os-selmer/

Great read, thanks for that.

[Sam Spoons]

Not sure how accurate it all is, my understanding was that Selmer designed the petit bouche (oval hole) guitars to get around Mario Macaferri's patents but, yes it's an interesting read and Django led an interesting life.

[Watchmaker]

I think of the guitar as a mechanical device with some properties having greater impact on playability than others. Being made of wood, guitars can be incredibly unreliable devices! Intonation as you know is a function of string length.

With regard to changes over time, this is normal and expected for wood. It will expand and contract due to temperature and humidity (not inseparable). Also guitars are made from several species of wood, each of which reacts differently due to structure differences inherent in the wood. Meaning we can look to certain components first based on both their function and their composition.

The extent of wood's reaction is somewhat dependent on the age of the wood prior to construction. Loosely speaking, wood's reaction to atmospheric moisture content occurs in both the resins in the wood and the cellular structure of the wood itself. Cured wood reacts less extremely. It's not uncommon for high quality maple used in violins to be aged for decades. I am no fan of Gibson and have long suspected they use under aged wood. I can't prove it though.

As far as changes to intonation over time goes...if the guitar intonated fine when you bought it, I would be less inclined to think the nut height was a factor and would look to one of two primary areas where wood is known to move - the neck or the soundboard, in that order. fwiw, guitars are frequently poorly set up on nut height but its one of the trickier adjustments for a novice.

This is one area where if it works ok at the beginning, it's unlikely to ever really change due to the mechanical function it provides. The impact of nut height really doesn't extend past the 3rd fret intonation wise. Try capoing on the first fret and if it intonates properly there then maybe the nut contributes but it could also be a slightly misplaced fret. I'd try re-crowning the fret before changing nut height personally. Sometimes a higher gauge string doesn't seat properly, but a lower gauge can't sit any lower than the bottom of the notch. Break angle can also bear on intonation.

The plane along which the string resides relative to the fretboard is the key. The guitar changes underneath this plane all the time. It can change if either the neck relief moves (common) or if the saddle bows upward (less common). The saddle will never cavitate because the tension always pulls forward. Check to see if the soundboard is bowed upward at all. This indicates incomplete aging of either the sound board or bracing and can be a real bear to fix. Lower tension strings would be a good starting point.

For either condition, slightly altering the neck relief is a legitimate solution. But remember the device acts as a whole. Changing string gauge will alter the tension of the neck and the tension on the soundboard. Changing neck relief or saddle height will change string length and impact intonation all along the fretboard.

The bridge should really never move significantly. Adjusting the saddle height should be done after setting the neck relief to adjust the action, not intonation. A compensated saddle might be a good idea.

If you really want to get to grips on guitar setups, I highly recommend "the Guitar Handbook" by Ralph Denyer. It's an incredible resource that's been in my library pretty much all my life and I still turn it regularly. Literally, 47 years. I've never had to trust youtube for anything related to guitars...

[adrian_k]

Just to back up what Wonks has said, if there are intonation problems at the 12th fret this is very unlikely to be due to nut slot height, which is why I asked earlier. Adjusting neck relief may help. Can you see if the sound board has pulled up (i.e is no longer flat)? If so this will have the effect of slightly changing the geometry and can cause intonation problems. Wonks has covered all this above.

I too have had the Ralph Denyer book for years! I also have the Guitar Player Repair Guide by Dan Erlewine, and between these too rarely refer to anything else. Certainly not YouTube

Edit: from memory the J45s were ladder braced (as opposed to x-braced) and did tend to pull up over time. I don’t know about the newer ones.