PRS-Variax transplant guitar




These pages chart the progress of my PRS-Variax guitar build. The guitar is a handmade solid body in the style of a PRS custom 22, fitted with the electronics from a Variax 300. Anyone attempting this should visit the sites of Jeff Miller and Rose W for some invaluable inspiration. If you are planning on building your own guitar you will need a well equipped workshop and good woodworking skills, any specialist tools and jigs can be home made.


I don’t have any pictures of the neck build but it’s pretty standard. A one piece mahogany neck with a 22 fret ebony fret board. The board has abalone inlays and the head stock has veneers front and back. The neck was made with a long tenon to be glued into the body. This picture shows my home made fret board radius  jig. The fret board is held in place with double-sided tape to the base plate and the 12mm cutter in the router is run up and down the rails.



The scale length is 25 inches. To place the frets I used a fret space calculator downloaded from the internet. I put the numbers this generated into a CAD program to make a full size printout of the fret positions. These lines can then be transferred directly to the fret board from the printout. This is far more accurate than transferring measurements with a ruler and dividers.

The edges of the fret board are bound with tiger maple and have 2mm black plastic position markers.


The body is cut from a two piece slab of stripy mahogany. I rough cut it with a band saw then brought it to final size with a router and template. I use 6mm thick mdf for templates and a 12mm straight cutter with a 20mm collar in the router. This means I have to remember to make my templates 4mm undersize.

Before cutting the neck pocket the tenon is placed on top of the body and aligned on centre. Changing the overlap of body and tenon affects the eventual bridge and pickup positions and the access to the upper frets, adjust to taste. The picture shows the neck pocket cut and the neck fitted. As with all guitar building the centre line is very important, this joint must be exactly on centre.




I imported a piece of quilted maple for the top of this guitar, 12mm thick to allow for the top carving. As this piece of wood was relatively expensive I didn’t want to make any mistakes with the carving, so I cut out and carved a piece of pine board to a profile I liked. This is a shot of my home made scrub plane which is great for getting at those concave  re-curves. It is made from oak with a reground blade from a block plane.



The pine pattern was filled and sanded until the perfect shape was achieved then sealed with a couple of coats of resin.



This photo shows a set up on my copying machine. Here, I am cutting a test blank from the original pattern. This machine guides a small router in three dimensions according to the position of  a plastic stylus running on the pattern. It is great for roughing out carvings ready for sanding. Of course you can just carve your top by hand, but this is much quicker.



Maple top ready for copying



Ten minutes later



The top is screwed and taped to a base board for sanding. The screw holes are where the pickups will eventually lay. My random orbit sander makes a good job of sanding the constantly changing grain of the quilted maple top. Sand right through the grades down to 320 grit.



Here the neck tenon has been cut flush with the body.



This shot shows the top temporarily fixed to the body. The top has been cut to fit around the neck and the upper fret access has been carved in using a drum sander in a power drill.



A couple of v groves will make passages for the pickup wires



The edges are sanded using my oscillating spindle sander. This is home made from a small pillar drill and a windscreen wiper motor. I am careful to sand to a perfect finish at this stage as some areas will be difficult to sand once the neck is attached.



After the back corners of the body have been rounded over with the router and some very thorough sanding, it’s time to glue the neck to the body. I use tight bond glue for all the wooden parts.



Gluing the top. Plenty of clamps and wipe away any squeezed out glue with a damp cloth.



When the glue has dried make templates for the pickup and tremolo cavities. Attach with double sided tape and rout.



This is a test fit of the hardware. Looking good.



Some of the templates for this guitar



This guitar is intended to have variax electronics installed so I bought the cheapest used model 300 I could find. The circuitry in all the variax models is the same although the physical layout is different. The 500 model  has the switches and pots on wires (rather than soldered to a PCB) and other models come with a tremolo. So there will be some modifications to do before the transplant. This picture shows all the useful parts extracted from my model 300 variax.



I bought a PRS style tremolo with a 2 1/16 inch string spacing to accommodate the saddles from the original variax stop tail bridge.



The wires from the individual piezo elements in the saddles are brought through the base plate using new holes. The piezos are soldered to a piece of edge connector PCB glued to the block.



From here thin wires take the signals through a hole in the block to the other side where the original PCB is screwed on. This will allow connection via the 8 way socket to the main circuit board.



The rest of the electronics comes as three parts. The main circuit-board, the connector board and the plastic jack plate for jack and ethernet sockets. Mounted on the connector board are the volume and tone pots and the model selector switch. The 5 way blade switch also connects here via a short wire. The jack plate connects here via a small plug. The main board connects to the connector board via a short length of ribbon cable. I found, by manipulating the boards, that getting the electronics and controls into the right place would not be easy. The ribbon cable was too short and the layout of the controls on the connector board was restricting. It is possible to install a new longer ribbon cable but I couldn't find the required 1-mm pitch cable. I opted to extend the blade switch cable and the tone control pot.



This means the control layout (from the head stock) will be mag pickup volume, Variax model select, Variax tone, Variax volume. The mag pickup volume will have a pull switch for Variax/ mag selection and I will use the spare pole on the 5 way switch for the mag pickups.


More templates, more routing. This completes the control and tremolo cavities.



The completed jack plate rout



Cutting the rebate for the control cavity cover plate



The holes for the controls were drilled and then the depressions for the knobs were created using a coving bit in the drill press. Note the body is clamped down, proceed with caution.



The slot for the blade switch was cut using a fine bit in a dremel mounted to a router base. Guide this along a straight edge.



Test fitting the boards



At this stage I mounted the tuners, put on some strings and powered up the Variax electronics to check that everything was working and that the guitar could be adjusted to play easily. So far so good.


I made wooden cover plates which have copper screening foil on the inside and carved the tummy tuck with a rasp



With all the hardware and electronics removed its time to start the finishing process.


I will be using nitrocellulose lacquers, spraying both clear and tinted shades for a sunburst finish. I hand sand all parts down to 600 grit, wet with a damp sponge to raise the grain, then hand sand down to 600 grit again. I apply two coats of shellac sanding sealer to the mahogany parts with a cloth to fill the grain and re-sand when dry. The close grained maple doesn't need filling.


Mask off the edge binding with vinyl tape and spray the base amber coat for the sunburst. Allow to dry



Spray the outer edge in tobacco brown. This may take several passes to achieve a smooth transition from brown to amber.



I went for a similar effect on the headstock.



I made a jig to support the guitar horizontally while spraying the clear coats



Spray 11 clear-coats, 2 per day, allow to dry for a minimum of 3 days then wet sand with 1000 grit by hand until completely matt.

Spray 1 final clear coat allow to dry minimum 3 weeks. Don't be tempted to finish it yet; polishing soft lacquer can only lead to disaster.


I hand finish my guitars ( never been brave enough to put one near a buffing machine). Wet sand through the grades from 1000 to 3000 grit using small circular motions. Then work through the polishing compounds to achieve that showroom finish.


A few final details need to be completed, apply three coats of screening paint to all the cavities. As I decided to use abalone tipped knobs the model select knob had to be remade. I turned the knurling down on the new knob to a smooth finish in my lathe and then applied a new printed label. I have also included a small LED on the front surface to act as a power-on indicator and a position marker for the model select knob.







                 Any questions or comments, I can be contacted at Paul dot langwade at ntlworld dot com

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