1st & 6th strings weak

[Jack Lord]

I replaced a bridge on a guitar that I had made using the same under-saddle Fishman pickup (Martin Thinline 332). On the old bridge it worked fine, on the new one the 1st and 6th strings are weak.  The spacing from the saddle to the bridge pins and the spacing between bridge pins is identical, as is the location of the pickup.  Any ideas as to what could be the problem?

[Jeff Highland]

Uneven contact pressure
either the ends of the saddle slot are lower than the centre, the sadlle underside is not straight or some other cause.
Shim under the 1st and 6th on the saddle and all should be well, may only need the thickness of a strip of tape.

[Mike Kolb]

Hmmm.... a few thoughts. Tusq or Corian saddle material seems to work better than bone for evenness of response. Make sure the bottom of the saddle slot is dead-flat. With the right jig, you can use a flat-bottom bit in a dremel to get that done. Same with the bottom of the saddle itself... make sure it's flat as a pancake.

Sometimes a .010" plastic strip under the transducer strip will help even-out the response. If you're still having problems after all that, you can take the saddle out and -very slightly- reduce the contact of the 2nd, 3rd, 4th & 5th strings by sanding a concave "smile" in the saddle material just above the corresponding areas on the pickup... and we're talking .001" or so. Not to lose contact, but just to reduce the string pressure, which will help bring all the strings into balance. In other words, if you can't bring #1 & #6 up, take #2, #3, #4 & #5 down.

[Grahame Myers]

I'd go with Mike and Jeffrey:s thoughts on this one, they've just about covered all there is to say.
As an aside, I must say that I'm not over-enamoured by these type of pickup systems, the pickup element itself that sits under the saddle is IMO too stiff to even out the pressure and avoid these kind of uneven string response problems. Although they're a quantam jump compared to the old systems one finds in old Tak's etc, where every string has its own sector on the pickup.
I think the main reason Martin (and other after-market customers) use them is the price point, they only cost about half the price of, say, a Fishmann Matrix Infinity system.
If I have the choice, or if the customer specifically asks for my advice, I prefer either the Shadow systems, which use a very flexible siliconised co-polymer as the transducer, or better still, the I-beam systems from Baggs, which are attatched to the brideplate directly under the saddle, and avoid all the problems you're having. As a bonus, they sound much more natural as well, IMO. Hope you solve the problem anyway, I just thought I'd throw in my 2 cents to give you alternatives to think about.

Grahame

[Jeffrey L. Suits]

I suggest re-routing the bottom of the saddle slot, with a jack underneath the bridge. Take a measurement of the top right behind the bridge, with a beam/dial indicator--Stewmac has this tool--and recreate the dome that string tension puts on the top.

Also, the, "Zyla clay method", may be of help.

This, and their basically one-dimensional tone, is what soured me on USTs over a decade ago.

[Jack Lord]

This suggestion by Mike seemed the easiest so I tried it first and it worked:

If you're still having problems after all that, you can take the saddle out and -very slightly- reduce the contact of the 2nd, 3rd, 4th & 5th strings by sanding a concave "smile" in the saddle material just above the corresponding areas on the pickup... and we're talking .001" or so. Not to lose contact, but just to reduce the string pressure, which will help bring all the strings into balance. In other words, if you can't bring #1 & #6 up, take #2, #3, #4 & #5 down

Thanks for all of your help.