Madeira A-20 intonation issue

[Sperry]

Thanksgiving Day I made a detour to pick this guitar up. The kid said it was his moms, and from the oval label and squared headstock, I'm guessing it is an early '70s Japanese copy.

The intonation is off. Even with high action, a 12th-fret harmonic and its fretted counterpart are lightyears off.

Scale length is 650mm (25.59") measured down the middle of the fret board.

Other A-20s I've seen do not have a compensated bridge saddle. Rather than assume the bridge is misplaced, can I determine if the nut is misplaced? That the fretboard is somehow too long at that end?





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[Bill Yellow]

I had a Madeira M30 (flame maple laminate back & sides dreadnaught), I bought in about 1978.

It had a similar adjustable saddle.

The intonation, action and finish were appalling in comparison with today's entry level. But it got me started.

[Sperry]

I was imagining the nut being a mm off would create this intonation issue. A tech just told me the Madeira scale length is 25.5", so I guess it is a bridge issue.

After checking out the tundraman website, I find the first couple frets measure correctly from the nut for a 25.5" scale. Looks like the bridge is off by 2.3mm ...

[jbbgibson]

Advertised scale lengths are not accurate. They are rounded off and serve as information purposes only for buyers. It was quite common with inexpensive guitars to have intonation way off. They have come a long way since then.

To determine the actual scale length measure from the where the fretboard meets the nut to the exact center of the 12th fret. Then multiply by 2. This tells you where the break point of the saddle should be. Since the saddle is usually slanted from the 1st to 6th strings, measure this on the fretboard's center line. Special tools are made to do this and are not that expensive.

So your saddle is off in which direction?

Don't even consider trying to compensate at the nut end. If you move that nut the distance between it and every fret will now change and you will compound the problem.

Moving that bridge would be a big issue because of the existing pin holes, so you want to avoid that.

So your best bet is to move the saddle slot within the bridge IF (and that's a big if) there is room, I would remove the bridge, cut a piece of wood (looks like rosewood) and glue it in the existing saddle slot. Sand it down and make it pretty then cut a new one in the proper place. If there is no room for moving the slot, I would buy an oversize blank and make a new bridge.

This is a specialized skill and some more expensive equipment so it may be time for a trip to your local luthier if you don't have it.

[Sperry]

Originally Posted by jbbgibson

measure from the where the fretboard meets the nut to the exact center of the 12th fret. Then multiply by 2.

Simple as it sounds, I did not think of this. Common sense is how I make money in my trade, which this obviously is not.

Using your method, the bridge is about 2.5mm too far back from the 12th fret.

I cleaned the Madeira up, applied a good fingerboard oil to the fretboard, and installed new strings. We'll see how it sounds tomorrow after the strings have stretched. My thinking? The guitar will suit my brother for playing chords near the nut.

The bridge is not suited for shortening the scale by moving the saddle slot.

If the guitar truly has a remarkable tone, which I doubt from preliminary strumming on the new strings, I'll do my first bridge reset.

Truth be told, I want to give this to my brother so I can get back my 1996 Guild D4, which does have a truly remarkable tone.

The guitar certain looks nice cleaned up, with near -zero- fret wear.

[jbbgibson]

If you get the action where it needs to be your brother will be all smiles. He probably has no clue on what intonation is and what a bad one sounds like. Hope you get the D-4 back. Had one of those and loved it.

[Sperry]

Thanks for your guidance, Mr. Gibson.

There is, upon closer examination, enough room to create a new saddle slot on the bridge. I can also modify the current cradle holding the saddle, and scoot the saddle almost one mm closer to the nut.

Lets say I wanted to cut a saddle slot without a router. Would I use a saw blade, then a series of files?

The new strings are stretching. The guitar sounds fine. Except for the intonation issue.

[charles Tauber]

Your first photo is rather blurry but shows some sort of "material" at the nut, between the nut and the end of the fingerboard. Does that show that the nut is not seated agains the end of the fingerboard and the gap filled with some material?

Assuming the nut is in the right place, and that it is the 25.5" scale length, 647.7 mm, the high E string should break over the saddle at about 1 to 2 mm longer than that, about 649 mm from the nut. At the low E is should break over the saddle at 2 to 3 mm longer, about 650 mm.

Accurately measure from nut to saddle those two strings. You may be able to shape the saddle so that the point at which the strings break over the saddle is closer to the fingerboard, shortening the actual vibrating string length so that it is at or nearer the ideal. That assumes that the fretted notes sound flat.

[Jim.S]

Sperry, you have said the 12th frett intonation is off, is it sharp or flat? That is is the fretted note at the 12th fret sharp or flat of the open note on the same string.

[Sperry]

Originally Posted by charles Tauber

Does that show that the nut is not seated agains the end of the fingerboard and the gap filled with some material?

Assuming the nut is in the right place, and that it is the 25.5" scale length, 647.7 mm, the high E string should break over the saddle at about 1 to 2 mm longer than that, about 649 mm from the nut. At the low E is should break over the saddle at 2 to 3 mm longer, about 650 mm.

You may be able to shape the saddle ... closer to the fingerboard ... assumes that the fretted notes sound flat.

The high E side has filler, the other, not. Measurements to the first two frets, 1 & 26/64ths, and 2 & 50/64ths.

My first thought too, Charles. But I found tundraman's site, and measured the first few nut-to-fret distances. Nut seems to be in the right place. The slots are cut a little close for a 1 11/16ths, though! One of my bone nut blanks may be fit to this guitar.

Scale length appears to be 1/16" longer than 25.5" measured right up the middle. But best I can figure, the string is breaking over the saddle 650mm on the low E, and just shy of 648mm (647.7mm) on the high.

Originally Posted by Jim.S

Sperry, you have said the 12th frett intonation is off, is it sharp or flat? That is is the fretted note at the 12th fret sharp or flat of the open note on the same string.

Jim, the fretted pitch is higher than the harmonic, even allowing for high action. The sharp pitch is noticeable even at the 7th fret, and a digital tuner picks up the issue at the 2nd fret.
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I'm going to hand off the guitar to my brother, a casual strummer, for a few weeks while I make a new nut for the Hohner which came in last week (plays great, different sound). I'll mull over the Madeira for a bit.

I want to get a more accurate nut-to-fret measurement before deciding the Madeira bridge is misplaced.

While I have not cyphered out which direction the bridge would go (by fooling around with a mandolin bridge), something tells me longer bridge, lower note. There is easily enough meat on the saddle to lengthen the scale length a millimeter.

Interesting note, the cheaper Indonesian Hohner has a saddle with multiple compensations, also has challenged action, but has great pitch all over the fingerboard.

[charles Tauber]

Originally Posted by Sperry

the fretted pitch is higher than the harmonic... There is easily enough meat on the saddle to lengthen the scale length a millimeter.

That is the answer. Lengthen the actual vibrating string length by moving the breaking point of the string over the saddle away from the nut.

[Sperry]

Thanks for the confirmation. I pulled out my hundredths ruler, 1.43" & 2.78" to the 1st and second. That jives with a 25.5" scale using an online calculator.

What is the preferred string spacing on a 1 11/16" nut?

[Wozer]

It would also appear as if you have the following option:

completely remove the saddle mechanism and replace it with a Somogyi styled saddle (e.g. very thick and allowing for a lot of intonation movement)

[jbbgibson]

Originally Posted by Sperry

Lets say I wanted to cut a saddle slot without a router. Would I use a saw blade, then a series of files?

Although all things are possible, I would not want to cut a slot without a router unless it was something like an old Gibson bridge that had the slot cut all the way through. I use a Dremel with a very small down cut bit along with the StewMac router base. I set up boards to use as a fences to make sure it cuts the slot exactly where it needs to go.

Its critical to get this right. Maybe with a skill set I don't have it can be done with hand tools, but its certainly not for the less than highly experienced. I guess I am more interested in accuracy so I go for the best tools to achieve that.

[Sperry]

I went with Plan C:

I removed the saddle, flipped it around, and reinstalled it. Lowered the E & A at the nut. Good to go.

Think I was looking for a problem that was not there, the saddle fell out at some point and was installed backwards?

Can't imagine I picked up more than 0.5mm or .075mm, but it sure sounds better!

Reminds me of the story of the guy who bought a car for $50 which was jumping all over the place, he swapped out the bent rims, after which he had a perfectly-running vehicle.