Custom Semi Acoustic Bass mods and fixes

[Andyjr1515]

Hi

I've got two more projects on the go.  Our old-gits-band's bassist has asked me to build him an EB3-style bass for November time - I'll start a new thread on that soon - but I've also been sent this little (BIG) beauty by a contact (Stuart) to see if I can make something of a bass that has sat in a case for 25 years into something that can be played and loved once more / at last.

It is a custom built semi acoustic 4 string bass:

It has some notable features:

• The body is fully carved imbuya - top and bottom
• The neck (34") and centre block are one continuous piece of timber, tip to toe
• It has a double battery compartment in the back although is wired for standard passive at the moment
• It's quite weighty - 10lbs +

However, there are some real challenges that make it presently pretty unplayable:

• The bridge, when the strings are fitted, sits high and at a steep angle
• The sit on the strap is very uncomfortable, neck heavy and makes it extremely difficult to reach the first couple of frets

Added to this, the tonal palette is limited

I have agreed with Stuart that we will tackle the issues in a logical sequence, tackling basic playability and functionality first and then, as we deem each stage successful and worth the cost / risk to continue, then move further up the wish list.

So, first thing to tackle is that positioning on the strap! 
The first job has been to fully understand how the bass has been constructed and take copious measurements. 

There are some really skillful features in the construction - the carve of the top and bottom solid imbuya body panels is stunning, inside and out.

However, the long-scale and forward positioning of the bridge is problematic, putting the farthest end of the fretboard literally out of reach for shorta***s like me

Mrs Andyjr1515 wasn't in this morning so you'll have to use your imagination with some bad small mirror shots.   Here it is hanging on the strap on its present strap pins.

 

...and here's where my fully outstretched arm gets me (I'm 5'7" so not crazily off the median scale):

Clearly, moving the bridge back is impossible because then the neck would need to be shortened. Actually, not impossible but highly, highly risky (removal of fretboard; cut, shorten and scarf neck; rejoin; replace truss rod; reglue fretboard).

But what about strap pin positions?

Here's where the pin is at the moment:

I've always found that strap pins in this position can be problematic and this one certainly is.

I un-hitched the front strap lock and tried a number of positions - practical and impractical - to feel what happened to the CofG, the pull and the settling position of the body.

I concluded that a position that might work was like where a number of acoustics have theirs - at the bottom side of the neck heel

But before I drilled a hole in this beautiful piece of wood, could I be a bit more sure?
Enter a heavily modified high-tech strap simulation rig (otherwise known as a piece of string):

The swing of the body to my right (left in the mirror image above) and the slightly neck up attitude made a massive difference:

Would it work in practice?

I drilled the hole and moved the strap pin.  Luckily MrsAndyjr1515 was back to take the photo.  Here it is, hanging free on the strap:

Even little old (both utterly descriptive terms) me can play in this position.  It feels at least 30% lighter.  But does the strap get in the way?

No       Here is the position:

...and no obstacle at all for playing up at the dusty end 

 

Stuart reckons that this already has cured the reason it got put away all those years ago.  I'm well chuffed.  We are both happy for me to go to stage two...sorting the bridge problem. 

 

[SIMpleONe89]

Wow beautiful bass! What's the backplate for?

[Andyjr1515]

40 minutes ago, SIMpleONe89 said:

Wow beautiful bass! What's the backplate for?

It's a double battery chamber. I think there were originally quite fancy electronics planned that never happened.  There are some very high standard features on the bass but one or two surprises too...

[curtisa]

Interesting project you have here, Andy. The neck/body join, being so far up the neck (pretty much all the way to the 24th fret), makes it look unnaturally huge!

Dealng with the bridge will be a challenge, especially if the neck is through-body. I was initially going to suggest you could treat it like an acoustic neck reset - steam the neck off the body, re-angle the heel block and then re-attach it - but that's not going to work if the neck extension forms the centre block.

Recess the bridge? Replace with something lower-profile? Both options will be difficult if the lateral curvature body carve continues between the two bridge posts.

[Andyjr1515]

2 hours ago, curtisa said:

Interesting project you have here, Andy. The neck/body join, being so far up the neck (pretty much all the way to the 24th fret), makes it look unnaturally huge!

Dealng with the bridge will be a challenge, especially if the neck is through-body. I was initially going to suggest you could treat it like an acoustic neck reset - steam the neck off the body, re-angle the heel block and then re-attach it - but that's not going to work if the neck extension forms the centre block.

Recess the bridge? Replace with something lower-profile? Both options will be difficult if the lateral curvature body carve continues between the two bridge posts.

Actually, the project is just my cup of tea.  Lots of 'how the heck am I going to do THAT?' moments to come, I'm sure 

I'll come to the bridge in the next post - I think I have a solution that might work and have ordered some bits for it.

The neck join....hmmm.

Based on the fact that, in many other respects, this a very high spec build - and one by a deservedly renowned luthier at that time (and still around), there is one of two possibilities :

• a straightforward miscalculation of the heel position.  It is exactly one fret out.
• a 'cut the losses' after a further customer request in what was probably a very difficult build

I say that advisedly.  Stuart, the owner and original commissioner admits freely that at - then - 21, he was a bit obsessed by articles about resonance, scale length, and pushed for a number of things the luthier advised him against, including an extra-long scale/length or neck.  Maybe there was a further push to extend the scale length once much of the hard work and cost had already been put in....

As it happens, it is a standard 34", but feels much longer because of the forward positioning of the bridge.

The surprise is the exceptionally ugly fill-in.  I would have thought some matching maple strip would have been much more in keeping and I may (depending how brave I feel) offer to try to do that as a retro because I know it bugs Stuart immensely.

 

 

 

[Andyjr1515]

So onto the bridge.

What Stuart reported was that the bridge sat very high and at an angle. It's a slightly unusual stop-tail bridge (German made - not quite sure whose) and you can see here that it's been digging into the body:

The cause of that - but not the root cause of the issue - was quite easy to work out - the bushes were very loose in deformed holes. Both bushes just lifted out. You can see the gap between the hole and the bush here:

 

The root cause, I believe, is two-fold. Firstly a basic design/installation flaw in the bridge itself. The stop tail slots into the bridge:

But there is much more distance between the ball end and the bushes than a normal stop tail. With the strings here being angled, there is a significant twisting force on both the bridge and the bushes.

Now - although I can't work out how you could install such an arrangement - it is notable that there are a couple of threaded holes at the back of the stop tail that presumably are intended for it to be screwed somehow to the body (as I say, can't imagine how that could ever be done, particularly as the bridge itself has lateral adjustment screws - certainly not possible on this type of bass):

 

 

The additional root cause can only be seen properly with a dentist's mirror.
The stop tail bushes are wider than the central maple block. You can just about see here where the drill used for the bushes holes has caught the side of the block:

To ensure the bushes have got something to drill into, there are small maple blocks glued either side. However, with the best will in the world - and that enormous twisting load on the bushes - the holes are likely to distort. You can see gaps and cracks in the bush hole sides here:

The solution in theory is:

 

• Have the bridge as just that - so that the only force on it is downwards.
• Install a separate stoptail. However, this can't be a Tune-o-matic or similar, because of the same problem - the bush centres would be wider than the central block

I did some thinking and measuring and think I've come up with a practical solution that will also look right - an archtop-jazz style trapeze stoptail and a standard t-o-m bridge.

The latter will fit within the cicumpherence of the original bush holes , plugged with walnut and re-drilled and will be fine because the side and twisting forces will have been eliminated.

 The bits are on the way - I'll update with pics when they arrive.

[Prostheta]

Have you considered just replacing the fingerboard and changing the scale length? Easier than a neck reset.

[Andyjr1515]

5 minutes ago, Prostheta said:

Have you considered just replacing the fingerboard and changing the scale length? Easier than a neck reset.

I did, but in the end moving the strap button was a lot easier .

With the moving of the button to the neck heel, it's now perfectly playable, sitting nicely on the strap and everything in reach.   The thoughts of a tidy up of the neck joint is purely aesthetic to get rid of that very unsightly ivoroid strip that just looks wrong.

[Andyjr1515]

In terms of the bridge placement, alternative placement of the bridge or standard stoptail doesn't help because the bush centres would still be outside the width of the central block.

Subsequntly, a bush based stoptail would need some wood adding to the sides of the central block, positioned and clamped through the f holes.   The carved top and back is fully glued top and bottom along the full length of the block and so isn't possible to remove without destroying the instrument.  I think a trapeze stop tail will work and, because of the style of the body will look OK.

Keep posting the thoughts, though everyone....there is usually a better way of doing things than I naturally incline towards 

[Andyjr1515]

Just to clarify, by the way, the reported 'very high bridge' wasn't in the end anything to do with the potential height adjustment of the bridge, it was simply that the bridge was being pulled and tipped forward and the bushes pulled out by the strings.  It's lucky for the owner that it didn't shoot out like a trebuchet!

[a2k]

Interesting project. Looks like a really pretty top and back.

You mention the neck and center block are one long solid piece - so do I understand correctly that the center of the body (underneath the bridge) is solid? If so, I wonder what the acoustic advantages are of having the bridge located where it is instead of closer to the tail edge of the body. 

What about moving the tail-end strap button to the back of the body and closer to the bridge? I know that's unusual, but it seems like that would help shift the position of the bass to make those low frets easier to reach. 

[Andyjr1515]

8 hours ago, a2k said:

Interesting project. Looks like a really pretty top and back.

You mention the neck and center block are one long solid piece - so do I understand correctly that the center of the body (underneath the bridge) is solid? If so, I wonder what the acoustic advantages are of having the bridge located where it is instead of closer to the tail edge of the body. 

What about moving the tail-end strap button to the back of the body and closer to the bridge? I know that's unusual, but it seems like that would help shift the position of the bass to make those low frets easier to reach. 

Hi, @a2k 

Yes - it's a very nice bass.  Very high spec, in spite of the one or two issues.

Ref the acoustic advantage, I agree - I don't think there is any advantage in perceptible terms.  How Stuart, the owner, has described himself, of 25 years ago when he commissioned it, is as 'young (21) and foolish'.  He says he had read something about maximising the waveforms in the neck itself on the basis that the longer the neck, the better would be the sound.  While there maybe something in this bit, I think we would all agree 'not at the expense of being able to play it!'  Reading between the lines, I suspect the builder had to compromise a number of times during the build 

Ref the tail-end button, yes - that was originally going to be my next step, although further round the side rather than at the back (I find back buttons problematic whatever - they tend to tip the instrument forward causing other issues).  However - and by total fluke - the one change to the heel COMPLETELY cured the playing position.  Stuart thinks I'm a genius.  I think I am a lucky b*****d! 

[Prostheta]

Fitting in a solid metal baseplate block secured to the central through tenon, drilled and tapped for the studs would obviate the need for any bushings. A big block of steel or brass perhaps. Those rear screw holes....are they tapped? I'm wondering if they were originally populated with set screws that bear onto a block underneath....perhaps that original intent, or this guess could be combined?

[Prostheta]

Whatever you decide to do with it....that awful piece of Ivoroid needs to go Dodo.

[Andyjr1515]

21 minutes ago, Prostheta said:

Fitting in a solid metal baseplate block secured to the central through tenon, drilled and tapped for the studs would obviate the need for any bushings. A big block of steel or brass perhaps. Those rear screw holes....are they tapped? I'm wondering if they were originally populated with set screws that bear onto a block underneath....perhaps that original intent, or this guess could be combined?

Yes - but still a bit weird.  Because the bridge assembly itself also has intonation screws, you would need to sort the position before you could secure the stop-bar.  I think what you say is the only practical explanation but still a bit of a weird design!  And how on earth would you be able to set or adjust the bridge height?  Very odd...

23 minutes ago, Prostheta said:

Whatever you decide to do with it....that awful piece of Ivoroid needs to go Dodo.

Absolutely it has.  This is a bit shocking, regardless of how the gap got there in the first place.  As I say, this is a notable builder (and was already, 25 years ago) and many aspects of the build are reflective of that.  

[Andyjr1515]

OK - still got to check the measurements with some real strings in place, but I reckon this is a winner:

Still probably need to plug and re-drill the holes (I say probably, because the new bushes are slightly bigger and would snugly fit in a reamer-ed hole) but I should be able to string this up later today to make sure it is all sound before the added cost of the next steps, more of which anon  

 

[Prostheta]

Hmmm. Will the bushings have enough grab though? I guess that there's no way of investigating or manoeuvring in new blocks to shore it up. I've got a borescope on delivery any day which would be ideal for this kind of work....

[Andyjr1515]

29 minutes ago, Prostheta said:

Hmmm. Will the bushings have enough grab though? I guess that there's no way of investigating or manoeuvring in new blocks to shore it up. I've got a borescope on delivery any day which would be ideal for this kind of work....

They will be absolutely fine, Carl.  Remember that there is now only downward pressure on them - no sideways or twist at all.  

If you think of, say, a Les Paul, the stop tail bushes are a very very tight fit but usually you can pull out the bridge bushes very easily indeed, even though with these you are applying side pressure with string bending.  As long as they are in the right position and don't rock they are doing their job.

Mind you, in terms of the maple block extensions that the bush holes are drilled into, I spent quite a bit of time with my dentist's mirror and a torch making absolutely sure  

[Prostheta]

I recommend nipping over to Banggood.com or some other "Chinese eBay" and dropping ten quid or so on a USB borescope. The one I have on the way should plug straight into the phone or tablet, and the camera itself is like a AAA battery on a cable. Grab one now before StewMac try and hawk the same think for ten times the cost, when in fact it'll be the exact same Chinese crap.

I say "crap", however we'll see. Any device that is good these days will conveniently be ignored as having been made in China, but if it's balls...."oh, well it's made in China".

Anyway. Where was I? Oh yes. The posts are where the majority of coupling between the strings and the body occurs. If they've wallered out at all, the hackles would rise, books would start jumping off the shelves and drawers of filing cards would fly everywhere. I might be confusing Ghostbusters with vague irritation here. We'll have to see how that pans out.

[Andyjr1515]

OK - we now have a fully functional bass.  Intonation spot on, relief OK, holding tuning and -although unquestionably long-scale - comfortable to play even for vertically challenged folk like me 

Here's how it's looking:

I'll keep an eye out for a trapeze with a slightly wider string spread to try to get slightly straighter runs, although on a bass this is probably less critical.

Now we have a playable bass, next comes adding a control hatch (yes, really!) a powered EQ and doing something about that horrible ivoroid cover strip at the neck join.

 

 

[Prostheta]

That is a tasty bass!

[Andyjr1515]

5 minutes ago, Prostheta said:

Anyway. Where was I? Oh yes. The posts are where the majority of coupling between the strings and the body occurs. If they've wallered out at all, the hackles would rise, books would start jumping off the shelves and drawers of filing cards would fly everywhere. I might be confusing Ghostbusters with vague irritation here. We'll have to see how that pans out.

Well....there is green slime coming out of the f holes now you come to mention it! 

Seriously, I'll have a peep at the cheap endoscope market - for an acoustic it would be an absolute boon!

I'm happy with the bushes on this as long as it's a vertical load - I'll draw a cross section of the construction I get a moment - it's a solid top glued to a solid centre-piece plus the maple blocks.  From a transfer of vibration, it's as close to a solid-body as you can get without the pesky centre-block having been a touch wider in the first place.  Pretty impossible to glue and clamp anything fed through the f-holes and no possibility whatsoever of removing the top.

Sounds pretty good too  

[Prostheta]

It sounds like it is very much a dyed in the wool ES-335 style bass aside from the carved back and top. Shame that the central block doesn't capture the bushings properly. It's a beaut though. That kind of wood just doesn't grow on trees any more.

[Andyjr1515]

38 minutes ago, Prostheta said:

It sounds like it is very much a dyed in the wool ES-335 style bass aside from the carved back and top. Shame that the central block doesn't capture the bushings properly. It's a beaut though. That kind of wood just doesn't grow on trees any more.

Yes - very much 335 style.  The central block missing the bushings is clearly a c**k up. There is no doubt in my mind that if it was recognised during the build, at the very least the extension pieces would have been full depth of the centre block.  As it is, they are small blocks only just thicker than the bushes length.  Pretty sure they were indeed retrofitted through the f holes.

Nice wood,  as you say

 

[Andyjr1515]

Now this is the bit where @Prostheta and a number of the others hold their heads in their hands, screaming, "Nooooooooooooooooooo!"   

Based on that we now have a fully playable instrument, the owner has asked for a control panel at the back so that in the future he can experiment more easily with alternative pickups, etc.  The starting position is going to be present pickups but plus a 3-band powered EQ - which I have confirmed can probably be fitted the 'usual' way, but he prefers the additional access.

I don't know if you remember the ES-339 I did a while ago?

This is one of those cases where I have to stress the "please don't assume this is the way to do such a task - all I am doing is describing how I personally tackled it." cautionary statement.

I cut a paper template the right shape and size, checking that it isn't going to be overly visible through the f-hole:

 

It's the one and only task I use the Dremel wibbly-wobbly router base for...simply because it has provision for a ring guide that the precision base doesn't.  It's a 1.5mm bit.  I would prefer to use a 1mm for minimising the resulting gap between cover and body but this task is no time to be having to swap broken bits:

 

I attach the template very very firmly with heavy duty 2 sided tape and clamps.  I will be doing around 10 circuits of the template so this mustn't move at all.  With the bit retracted, I also simulate running the router round the template a number of times - this is no time to have to change your grip halfway round!

 

Then first very light cut:

I repeat the procedure, dropping the bit around 1/2mm at a time until I get an initial breakthrough: 

 

I then go VERY carefully.  Ideally, I want a short bridge to be retained so the cover doesn't drop in and catch the router bit.  I cut that final short bridge with a razor saw:

 

And it's done