Carl Thompson mods

Hello everyone,

I've done the unthinkable and made mods to one of my favorite instruments.

I got the idea from a NY jazz musician, Gene Perla who made a similar mod to his bass - a removable low C extension. My build includes no permanent mods to the bass to uphold Mr. Thompson's original intention for the instrument. It clamps through the tuning peg hole, and all components (save the string tree and gotoh tuner) were made by yours truly.

The build includes a replacement 3 string nut, a nut for the extension, the capo, rear disc, some brass work, and the extension itself. Woods used include Honduan mahogany, Desert Ironwood veneers, and a Mun Ebony fingerboard. Black Ebony was used for the capo, and the string tree (as made by THG knobs) is flamed Koa. I also built a pickup cover which uses the existing screw holes for the pickup ring of the Schaller pickup, which also fits neatly under the desert ironwood cover.

Enough talk, here's the bass. I'm happy to answer any design questions you've got. Everything was done with hand tools (dremel primarily) a bandsaw, and a lathe for the thru headstock dowel.








Cheers

 

Thanks for your replies everyone. The extension is completely playable above the E, though the technique must be altered to accommodate the additional length. This is to be expected, as the technique in fingering a C extension on an upright bass includes extended reach when not using a mechanical extension. That said, it's fairly comfortable in part because of the way Carl's basses balance and where the twelfth fret sits in relation to the body.

Making the extension completely removable and unobtrusive to the original design of the instrument was very important. There are no additional holes drilled, no original parts modified from the bass, and everything can be put back to stock in about 10 minutes. I also had the strings made by Octave4Plus, and had additional standard E strings made, so the bass can play balanced with either the low C extension installed or not.

As for the sound; the C is very deep (as you might expect for 42.75" scale), thick, and has a piano-like quality that only an extended scale can produce. When the capo is in use, the E sounds as a fingered note does; a bit less volume than an open string, so it functions as intended. The action on the bass is very low across all strings, although slightly higher for the C. Action at the 12th position is 3/64 on the G, 6/64 for the C.

All in all I'm happy with the result. It functions better than expected, and beyond the obvious changes in technique when playing beyond the E, there is no change in playability. I wouldn't have considered this project had it not been possible to achieve without permanently modifying the instrument. Carl is a genius, I mean no disrespect to his work.

Here are some pictures of Gene Perla's extension. I owe most of my inspiration to him, but there are some differences between our basses. Gene's is a more permanent mod if I'm not mistaken - it attaches on the top side of the headstock, but I'm not sure if it screws in at the nut as well? Either way, without the few pictures I've found on the web of his bass, I wouldn't have even thought of attempting it.

Cheers.