Working on a Trinity College Octave

[Gary Leonard]

I took my OM into the local shop for a setup a couple months ago, as I wasn't really happy with the condition it came to me in (bought used). The tech said he couldn't get rid of a G string buzz, and shimmed the bridge. Took it home, played it a bit and noticed that I could see under the ends of the bridge. In effect, the shim just allowed the middle of the bridge to maintain contact. I measured the action at the 13th fret, and it was 3mm, I think I want it closer to 2.

Today, I ended up taking the bridge off, peeling off the shim and glue with a sharp chisel, and sanded the foot a bit to get a better fit. The nut also came loose, and I saw some crud under the bass end of the nut, which looked like ebony dust and glue that seeped off the headstock. I scraped that off with the chisel. It also helped level things, and the top of the nut measures close to the same at the G string and E string ends (G string side is e wee bit higher).


Questions: should I glue the nut in?


Second, how do I measure the scale length, to get the bridge close to it's final position?


Third, anyone have any tips on anything else I should do to it while I have it apart?

[allenhopkins]

1. Not all nuts are glued, but I'd glue yours in -- lightly. The string tension's the most important factor keeping it in place, but you don't want it shifting around as you raise the pitch of the new strings.

2. Once the nut's in place, measure the distance from the nut to the 12th (octave) fret. The bridge should be as far from the 12th fret as the 12th fret is from the nut. There's not a completely exact equivalence, so you may have to tense up the strings to some degree, and then move the bridge slightly until you get the fretted note at the 12th fret to sound in unison with the "harmonic" -- the note you get when you just touch the string lightly above the 12th fret, then pick the string between the nut and the fret. That should set the intonation where you want it to be.

3. If your "G string buzz" wasn't related to the fourth string being too close to the fingerboard, you might check and see if there's anything rattling. Is the truss rod snug in its pocket, do any of the tuning pegs seem loose or sloppy, is the tailpiece properly screwed in, is its cover tight-fitting? You won't know if you've cured the buzz until you restring it up to pitch, so investigate any other sources of possible vibration. Tap the top and make sure none of the interior braces seem to be rattling. Hope that when you restring it and tune it to pitch, the buzz is gone.

4. Investigate an alternative place to have your repairs and adjustments done.

[multidon]

+1 on Allen’s very good advice.

I personally think nuts should be glued to keep then from shifting but lightly enough to make it so they can be removed easily if need be. A couple of small dots of Titebond will do nicely.

Allen gave you a great procedure for locating the bridge, but I would just add that one of the weak spots of the Trinity College is that bridge, which is not compensated correctly (compensated for regular mandolin rather than OM). So to set intonation the bridge will likely have to be slanted, longer on the bass side to be tolerable, and it most likely will never be perfect.

The buzz could be so many different things! If it come back check all of those things Allen lists. I think Frets.com has an article on buzz diagnosis you could go over. It sounds like a sympathetic vibration. Sometimes the strings between the bridge and the tailpiece ring sympathetically, and that can be damped with a piece of leather, felt, or rubber grommets.

[AndyV]

Gary, If the buzz only when the string is open, only when fretted up to a certain fret, or is it always there. This could help in identifying the cause.

[Gary Leonard]

Thanks all. Just re-read my post, and I made it sound like I took it in because of the G string buzz. I actually took it in because of the intonation, and to get it checked out as I bought it used. I had them put on the EJ72 mandola strings I wanted to try out, I had no clue what the strings on it were. I had no guidance to give them regarding how high I wanted the action, this is my first OM. When I went to pick it up, the tech said he adjusted truss rod, and had to shim in order to get rid of a G string buzz.

They are a good shop, good techs, and I did address the shim with them. They said bring it back in and they would fix. I actually declined, and asked for a piece of shim material in case I wanted to tackle it myself, and learn something in the process. Now that I have had it for a bit, I want to see if I can get away with a lower action, thus the work I am putting into it.

Now my problem is that the only strings I have to put on it are the Thomastik Mandola 174 mediums. At worse, if I can't deal with the lower action, I could slip the shim material under the bridge and deal with gluing and fitting it to the bridge at my next string change.

[multidon]

Gary, did you read my post? Like I said up there, the reason your intonation is a problem is most likely that bridge they put on, which is compensated like a regular mandolin bridge. While mandolins have two solid and two wound strings, mandolas and octaves have three wound and only one solid. And the wound and solid strings intonate differently. I would describe mandolin bridge compensation, going from bass to treble, as down-up-down-up. And that’s what you have. The compensation on an octave should be more like down-up-up-up. To be more clear, like going up stairs bass to treble. Heck, even a straight saddle set at the proper angle would do a better job than what they put on. I like the Trinity College instruments, I really do. But they put the wrong bridge on there, plain and simple. Unless they are replaced, beats me how anyone gets them to intonate properly.

[Gary Leonard]

Yep, I read it Don, thanks! I will eventually get the bridge replaced, or possibly rig something up with the existing bridge. Was that you that posted a picture with a piece of saddle material glued to the front of the bridge for the A strings?

I came here to post to say my adjustments were a success. I put the Thomastiks on, and I am very happy with the sound and action. I did notice a D string slot was cut way too deep, I have raised it with a bit of paper from one of the string packets. Filling that will be my next project. Intonation is close, but certainly not perfect. As I am not going anywhere past the 7th fret, I will leave it as is until I get annoyed by it.

[multidon]

No Gary, that wasn’t me, but that’s a good idea for quick DIY fix on that bridge! That solution didn’t occur to me, and I’m kind of annoyed with myself that I didn’t think of it.

Glad it’s working out for you. If you can get the set up right, it will be a good one. FWIW, my Fender OM is a TC clone, and I love the J72s.