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Weird Intonation Problem

I'm having what I think is a weird intonation problem with my last few builds. Maybe it's a simple fix, maybe just something stupid I am doing or overlooking. That's what I'm hoping anyways.

So, anyways, I build my three string guitar, string it up, tune it up, go to set the intonation by tweaking the location of my bridge (threaded rod, various sizes) and find that I can get the intonation correct on the first string and the last string, but not the middle string. Very frustrating. I am tuning GDG, if that makes any difference, and using phosphor bronze strings, gauges .044, .034 & .017.

Any help or insight into this would be most helpful.

Thanks,

James

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Permalink Reply by darryl kernaghan on July 30, 2015 at 3:21pm

String gauge comes into this a bit here,as your tuning is not equally stepped as compared to the original string notes ,it's nearly impossible to get perfect G d g in a straight line at the same height without adjusting your individual string gauges,usually a pretty good compromise is achievable though,i've had this problem myself and have improved it by slightly lowering/raising individual strings at the bridge,but that's not so easy with a bolt

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Permalink Reply by John Sawyer on July 30, 2015 at 5:13pm

It normally takes me a few tries to get it right. I normally put in the D string, get it adjusted right and then add the other two. It also helps me set the action,

Though I switched from bolts to wood banjo style bridges...

but that should have no effect...

Like DK said, I'd be interested in your string gauges...

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Permalink Reply by Richey Kay on July 30, 2015 at 8:36pm

Darryl is spot on here. If you want the best possible chance at perfect Intonation, you need to use equal string tension.

On a 630mm/25" scale I use 44, 28 and 20w for FCF tuning. This gives around 10kg tension on each string. With a slight angle at the bridge this usually intonates pretty much perfectly

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Permalink Reply by Richey Kay on July 30, 2015 at 8:40pm

I ran your string gauges through this tension calculator, assuming a 25" scale:

http://www.mcdonaldstrings.com/stringxxiii.html

You are getting:

G =10.8kg

D =14.8kg

G =7.1kg

This is your problem :-)

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Permalink Reply by James Mitchell on July 31, 2015 at 2:11am

Thanks for the help guys. If I read this correctly I should get a smaller gauge for the middle string?

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Permalink Reply by Richey Kay on July 31, 2015 at 3:34am

The middle string is the biggest problem, but bear in mind that you want the treble strings to be the loudest, so you would want a heavier string for that too :-)

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Permalink Reply by Rich on July 31, 2015 at 2:54am

This is a great discussion for me too.

I have had this problem - and now have a solution.

I'm gonna use the calculator to help me choose strings. It has been a bit of a guess every time.

Thanks, guys.

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Permalink Reply by jawbone on July 31, 2015 at 3:36am

I checked on line and didn't find anything - but - how do you check the string tension???
Could you take a fishing scale or something similar, hook it around a string in the middle and get a reading?? For instance, how much tension (lbs.) to lift a string 1/4", 1/2" ??

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Permalink Reply by John Sawyer on July 31, 2015 at 3:42am

There are a lot cut there.. Here is one...

http://stringtensionpro.com

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Permalink Reply by Richey Kay on July 31, 2015 at 3:42am

I don't think there's really a practical way to do it yourself Jawbone, nor is there any reason to. Have a look at the link I posted above, it just does the calculation for you.

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Permalink Reply by jawbone on July 31, 2015 at 6:07am

Thanx Rich - That's a good resource - my reason for asking was - every now and then I get in a situation where I wonder if I'm really pulling too much and it would be nice to double check some parameters before things go "Sproinggg snaaaap" :-)