Nuts and Volts - November 2014

wood mounting screws.

The only significant negative change — if you can call it that — is the need for a three-cond jumper from the guitar to the pedal board, but even this is not a big deal since there are ready-made stereo guitar cables available. Just Google it.

Aside: Since you have done the work to decipher the active filter calculations for your schematic, I wonder if you would be able to create a nice Excel-based macro that would allow one to change RC values in your schematic and see the effects on a plotted frequency response graph.

Admittedly, I have been lazy over the years and simply played with values until I heard what I liked. Since you have done most of the legwork, it would facilitate knowing how to tweak the design without explicitly doing SPICE models.

Finally, on the subject of shielding, I prefer to use a spray-in coating rather than copper foil. You will find the adhesive of the copper strips will not be permanent and so the shield itself will fall apart. Too many interfaces. (Doesn't stick too well to wood either!)

There’s a good example of such a spray shielding material at

www.mgchemicals.com/products/ protective-coatings/emi-rfi-shielding/total-ground-carbon- conductive-coating-838.

Of course, you need to pretty much put the entire guitar inside a large plastic bag, carefully create a void in the area of the control cavity, and use painter's tape to attach the bag opening to the edge of the cavity.

For the plastic cavity cover, there are primers available for plastic. Use that first, and then spray the inside of the cover with the shielding spray. You will get adequate mating of the conductive surfaces of the cover to the cavity if you mask the cavity well.

Thanks for the great article.

Jon

Thanks for sharing your experiences of some alternatives to the guitar hotrod project. Having hung out with musicians my entire life, I just knew there would be different wants and needs, so tried to keep it general for modifications such as those you propose. The arrangement I ended up with suits my purposes perfectly, but there's no reason to expect it to match everyone else's needs as well. Long live customization!

We're all different, but I prefer to have the batteries within the guitar, obviating the need for a special cord, strap, or external pack.

Battery life has never been a problem, even back some 30 years ago when I was gigging and performing daily. I would usually replace the batteries every December 31st, whether they needed it or not. One of the guitars that I outfitted for a neighbor is on the same set of batteries these three years later. Opening the rear cavity so infrequently really isn't much of an inconvenience.

The conductive paint sounds interesting, but foil tape has worked very well for me. Just clean out the sawdust left by the manufacturer, swab the cavity with a cotton ball soaked in rubbing alcohol, and away you go. In any event, the entire cavity is filled with foam rubber making it impossible for the foil to come loose.

I suppose a person could devise an Excel worksheet for the frequency calculations (maybe my article, "Spreadsheets: The Forgotten Analog Design Tool," which appeared in the October 2006 issue of Nuts & Volts, pp. 59-63, will suggest something).

I sure found the SPICE approach to be fast and easy, however, and the visual representation of the frequency response via Bode plots is a definite plus.

Your suggestions offer a number of excellent options many readers will find useful as they personalize the project to their own needs. Thanks again for contributing them!