Setting a new bridge on a Gibson A model

[FlannelTuba]

Hi Folks -

I recently fitted a new adjustable bridge from Stew Mac to my "A" model Gibson mandolin to replace the original one-peice bridge that had served its time. Having sanded the base of the new bridge to fit fairly well, but not perfect (there were still slight gaps on both sides), I installed it and strung it up. It sounded amazing—substantially better than the old original. It had a nice crisp edge and brightness. I was pleased as punch. I played it for several days and just luxuriated in the rich new sound. Even my crappy playing sounded good. THEN some little voice in my head told me I should take another shot at reducing the gaps under the bridge's feet and shoot for a more perfect seating onto the soundboard. I worked it to a much closer fit and restrung the instrument. Sadness. Gone was that beautiful sharpness and definition that I got on the relatively rough first fitting.

I am not a professional or even an amateur luthier, just a player that also happens to have a modicum of fine woodworking experience. I'm hoping that one of you more experienced and seasoned instrument builders/fixers/tinkerers can suggest what might have happened here and how I might approach finding that sweet spot that I managed to hit accidentally on my first fitting of the bridge. There must be a whole universe of techniques and tricks for bridge fitting that I have no clue about. Perhaps one of you good folks might have throw me a trick or two.

My greatest appreciation and thanks in advance.

Scott
Eugene, Or.

[Folkmusician.com]

Hi Scott,

You did the right thing, going for a better fit of the foot. If you did not take a significant amount off the foot on your second round of fitting, then all you need to do is some tuning of the bridge. Of course this is easier said than done and it is not something that is as simple as following a basic template. You can attack the bridge with a tuning fork and listen for dead or sweet spots and then adjust accordingly. This is not all that different from graduating a mandolin's top. Meaning, it depends on the particular instrument.

Now to complicate matters, the mandolin should sound better once the bridge has a chance to seat down and get some play time. You may be experiencing this as well. The new bridge was a huge improvement over the old one and the difference was obvious. The more you played it, the better it sounded. Releasing the tension and refitting the bridge, you may need to play the mandolin a while to hear a difference, but because the difference is not as extreme, and humans have trouble remembering tonal quality for any length of time, you wont get that same extreme difference as the first time, and this is perceived as not sounding as good.

It could be that the bridge looks like it is fit better, but was actually getting better contact before, or something about the bridge was changed enough to hurt the tone. Though a minor difference in the foot should not be HUGE, it can happen. The final seating of the bridge needs to be done with some downward force to get the same effect as string tension.

[FlannelTuba]

Thanks Robert.

I'm going to take your advice and let the old fellow repose for a few nights before making a final verdict on the sound. As it is, I won't have time until next weekend to give it any serious attention, so it'll have a week to vindicate itself. I will similarly allow my confidence and courage to repose before making any further alterations to the bridge. I have to say, I suspect you might be right when you suggest that what would appear to be a better seating of the bridge on the soundboard may actually be inferior. The difference was, to my ear significant. Same strings, same pick, same scales, same player, same ear, and only about an hour's time from the initial good sound to the perceived muddy sound—I'm pretty sure I introduced the mud somehow.

One observation I can make that could be a contributing factor is that in the first configuration the adjustment screws were spun all-the-way down such that the floating portion of the assembly was essentially bottomed out. My first fitting was dead on action-wise, at the absolute bottom of the thumb screws. I only adjusted it up after the second fitting, since the action dropped just enough to warrant the lift. That shouldn't matter though should it?? I suppose I could try dropping it back down just for a sound test, but I can't imagine that could make or break the deal in terms of sound quality.

For now though, it sleeps...

- Scott

[Jake Wildwood]

Scott: it does matter -- more surface area contact = easier time for the bridge to transmit vibrations. This is why one-piece bridges, when cut right, sound a few times better than adjustable bridges... but they're just not practical, usually. Well -- that's my opinion, anyway.

[FlannelTuba]

Interesting...

This gives me two thoughts. First, the original Gibson one piece bridge in its current state leaves the action decidedly high, which is one of the reasons I wanted to replace it. I imagine this is due to the neck giving in a bit over the past 96 years of tension. Conceivably, I could use the adjustable bridge to determine the optimal height, and use it as a template to rework the original. My second thought is, once I've got the new bridge set optimally, I could fashion some hardwood or even metal spacers—or washers, if you will—to precisely fill the area where the adjustment screws have left a gap and saddle everything down for a solid mechanical and acoustical connection between the bridge pieces.

I glad I checked back here on the forum before hitting the sack. Now I can sleep knowing my troubles might not have been due to faulty workmanship on my part, and that a remedy may be a fairly simple matter.

Thanks much, Jake, and Robert too for your valuable advice.

- Scott

[David Houchens]

If I remember correctly, Red Henry's bridges were slightly shorter than standard adjustable mandolin bridges on purpose. While his are one piece, maybe your mandolin responds better to the shorter span. Just a thought.

[bmac]

If the one piece bridge is high, why not just shorten it? A few minutes sanding of the base should do it, if as described. To my knowledge solid wooden bridges don't wear out. They may break due to misuse or sometimes bad manufacture, but I think normally a solid wood bridge should be good for a hundred years or two. frets.com has excellent info on bridges and adjustments.

[FlannelTuba]

Hi Bart -

I had the same thought. The only issue with the original bridge is that the groove for the outermost G string had lost its grooviness, so to speak, insomuch as it became unable to hold the string in place against a moderate downstroke, which, owing to its outermost location it tends to get a lot of. In an attempt to resolve this, the groove was re-filed somewhat carelessly many years ago by a well intentioned but ill-equipped person (uh...myself). This left the string positioned a little bit lower than its companion and left the two G strings a little too close together. Neither of these conditions affected the sound in any appreciable way, but I guess my point is, I would want to re-pave the tope edge of the bridge so I can reset not only the height, but the string grooves. Hopefully there are no major contra-indications to reworking the top edge of a bridge like this. I only need about 0.075" of lowering to get the right height.

- Scott

[FlannelTuba]

Follow up:

I stacked a few appropriate sized washers in between the top and bottom of the two-piece bridge, and lo and behold, the fine, crisp sound of the original "bottomed-out" configuration of the bridge has returned. Looks like I was losing a hugs amount of tone through the shafts of the adjustment screws. Something to note!

- Scott

[Folkmusician.com]

Hi Scott,

Glad to hear you sorted this out. Maybe there is a new one piece bridge in your future?