Adjusting dual truss rods

[Rockin John]

For my first foray into the world of the fretless 6, I bought a second hand Harper (a German made bass: they sell on Ebay a fair amount).

I think it's probably assembled from Far Eastern made components. But its not bad to be honest and it sounds really quite good so, for the money, I'm pleased!

Anyway, there was a small hump in the neck at about 4th 'fret'. I backed the rods off and, gradually, the hump lessened to the point where the bass is pretty good and playable with quite a low action.

What concerned me though, was that the adjusting Allen heads of the rods were in completely different positions. The C string side rod's adj. head is about 1/2" further forward (towards the headstock) than the B string side.

Whilst I've done plenty of adjustments on my own, single rod basses and am therefore used to it I've never owned a dual rod instrument so just have no idea what to expect. On the face of it it seemed the C side rod wasn't working although both rods feel nicely stiff to turn.

I contaced Harper via the Bay but they very disinterested in my plight.

Wisdom, advice, etc greatly appreciated.

Thanks.

John

[202dy]

Clarification: Are the truss rod adjusting nuts bearing against parallel positions? Or is the rod being extracted as the nut is turned?

Pictures would be a lot of help.

[Rockin John]

Hello 202'

On the face of it, the C side rod is being wound out of the neck. I have not tried to wind it out, just back off the rods to remove this hump which, largely, has been successful.

I'll see what happens about pictures. I've only got a mobile phone so it might be difficult.

It might be possible to visualise the situation by the following:-

With the bass on a flat surface (say a bed) and the strings face the ceiling, the headstock points toward you so is roughly at your knees, and the body of the bass points away from you.

Look down on the neck with your eyes over the top nut. Then imagine the fingerboard is not there but the top nut still is there. The adjusting (Allen) head of the C side rod is forward of the nut (= closer to you) whilst the head of the B side rod is behind the nut (= further away from you).

That's a pretty good approximation to what I meant in the original post.

Thanks.

John

[202dy]

Is the bearing edge e.g. the area the nut or jam plate comes into contact with the wood in the neck, parallel to one another? If not, it might not matter.

How much of the rod is proud of the bass side nut? Treble side?

[Rockin John]

202dy said:

Is the bearing edge e.g. the area the nut or jam plate comes into contact with the wood in the neck, parallel to one another? If not, it might not matter.

I see what you're getting at but its impossible to tell. Any bearing surface is buried somewhere under the top nut, inside the neck. The only things you can see of the truss rod mechanism are the Allen adjustment screw heads of each rod.

202dy said:

How much of the rod is proud of the bass side nut? Treble side?

Well, the treble side Allen head is somewhere between 1/4" and 1/2" further forward (towards the headstock) than the bass side Allen head. Having said that, both Allen heads sit well under the little plastic truss rod cover on the headstock.

It may be naive, but I was expecting both Allen heads to be in very similar positions when both rods were correctly adjusted, not the best part of 1/2" apart.

This is, after all, a budget bass made in all probability from Far Eastern parts: I doubt whether these are push-pull rods but I just dont know. The bass plays really quite well with low action.

Seems to me the previous owner must have adjusted the rods. Either that or he was prepared not to be able to use the first 6 or 8" of the fingerboard due to mal adjustment, and he must have accepted that when he bought the bass from new. I Just dont know.....

Best.

John