Burns Brian May Red Special Upgrade Part 6: Mechanical Set-up

I described the mechanical set-up of my Brian May Red Special in detail this article: https://dsgb.net/projects/redspecial/part59/

The principle is the same with any guitar that has a floating tremolo system which is balanced by spring tension. I find that a Snark Super Tight tuner is convenient because it can be clip mounted onto the guitar headstock and set to measure vibration. I installed the pickguard first so that when the mechanical set-up process summarised below was complete, I could measure the distances from the pickguard surface to the string to allow me to calculate the required shim for each pickup.

1. Balance the Tremolo Block

  1. String up the guitar with the preferred string gauge.
  2. Tune the strings to pitch and check whether the tremolo plate is balanced approximately parallel to the guitar body (for a Fender style tremolo system).
  3. Adjust the spring tension as required by tightening or loosening the two screws at the back.
  4. Repeat steps 2 and 3 as required.

2. Set the Playing Action

  1. Decide on your preferred string action height. I get on quite well with the standard Fender action of 4/64″ (1/16″, 1.6 mm) at the 17th fret. Generally, action heights vary by no more than 0.4 mm so that a low action would be 1.2 mm and a high action would be 2.0 mm.
  2. Tune the strings to pitch (iterative process for a floating tremolo).
  3. Adjust the bridge saddle height set screws with a hex key and check the distance between the string and fret crown at the 17th fret using an appropriate implement. I used a 1/16″ or 1.5 mm drill bit.
  4. Repeat steps 2 and 3 as required. On completion, the bridge saddles will describe an arc approximately following the fretboard radius.

3. Set the Intonation Correction

  1. Tune each open string to pitch.
  2. Check the pitch at the first octave (12th fret).
  3. If flat at the 12th fret, move the bridge saddle closer to the nut (reduce the distance between the vibration nodes) by turning the spring-loaded adjusting screw. If sharp, move further away from nut (increase the distance between the vibration nodes). “flat/forward, sharp/back”.
  4. Repeat steps 2 and 3 as required until the open string and octave are both at the correct pitch, neither sharp nor flat.

4. Set the Pickup Heights Relative to the Strings

The Brian May specification Adeson Tri-Sonic pickups I deployed on this project were one of the few sets I have acquired which have extended legs to allow them to be mounted under a pickguard. Rather than use springs between the mounting lug and the underside of the pickguard to facilitate height adjustment, I prefer to make a custom sized spacer, stand-off or shim. I usually use PTFE rod with a 3.5 mm hole drilled through the centre, although wooden dowel does the same job. Once I have set the playing action to my preference, I have no requirement to change the set-up of the guitar so I prefer to have the pickups rigidly coupled to the pickguard. This is the next best situation after mounting them directly to the guitar body as they are in the original Red Special.

To estimate the required spacer height requires two measurements and knowledge of the recommended distance between either the fretted, or unfretted strings. Greg Fryer published some measurements of the distance between the pickups and the unfretted strings on Brian’s original Red Special guitar when he dismantled and restored it in 1998. I find that this set-up yields satisfactory results for Tri-Sonic pickups which have similar electromagnetic characteristics to those fitted to Brian May’s Red Special. It is certainly a good starting point for any Brian May Red Special type guitar set-up. The exact measurements can be varied iteratively from there depending on the exact output of the pickups and signal chain which you are using. With the mechanical set-up described in parts 1, 2 and 3 above complete, I measured the distance from the pickguard surface to the underside of the string and the distance from each pickup mounting lug to the top of the casing. To obtain the required spacer height, I used the following expression:

Spacer = Pickup Height – (Pickguard-to-Unfretted String – Pickup-to-Unfretted-String) – Pickguard Thickness

I then used the uncorrected spacer heights as a guide to prepare the pickguard for final checks with the strings tuned to pitch. Some minor adjustments were required and I deemed a measurement less than 0.5 mm (measured by eye with an engineering ruler) acceptable. The actual spacer heights I ended up using are within 1.0 mm of the estimated values.

Essentially, the pickup heights end up staggered as depicted in the gallery of images above. Bear in mind that Brian uses the middle and bridge pickups in phase as a default configuration around 80% of the time. The neck and middle pickups are used out of phase in the Bohemian Rhapsody solo. The current induced in each pickup coil by the vibrating string(s) will vary as a result of string vibration amplitude so it follows that the bridge pickup will have a lower induced current in it because it is nearer the node of the vibrating string where the amplitudes will be lower. The opposite is true for the neck pickup. Clearly, strings will vibrate in complex ways during playing as various harmonics are generated, but to a first approximation, having the neck pickup slightly lower than the middle and the bridge slightly higher will go some way to balancing the outputs of each pickup. Incidentally, there are some interesting videos on YouTube where people have placed cameras inside an acoustic guitar while they are playing it; the vibration modes of the strings are clearly visible.

Next article:
Part 7: Control Cavity Copper Shielding
Previous article:
Part 5: Switch Mounting Plate