I bought a MusicMan Stingray bass clone. It's a nice-looking bass (see picture) with a pretty decent sound despite its low price. It has an active circuit with an humbucking pickup that effectively blocks the AC buzz even at high volumes. But it also had an irritating interference from some FM or AM radio station. Not advertised on the package! The RF was not very noticeable at low volumes, but it came out quite clearly otherwise.
So if you have a similar problem with your "generic" bass or guitar, you may find this instructable useful.
Of course I had to make sure that the problem was not with other components of my setup, so I replaced cables, tested the bass with my son's guitar amp (at low volumes -- I didn't want to buy him a new one) and even used a battery-powered headphone amp, but the radio station was still there. I eventually plugged my son's guitars to the bass amp -- lots of hum, but no RF interference. So please test your setup and make sure the problem is with your instrument before trying anything, otherwise you will only frustrate yourself!
Now I'll show you the method used to solve the problem, which was surprisingly effective considering the simple and inexpensive materials I used and that it took me slightly over 3 hours. So let's get started!
Important: be sure you are handy with tools and have good soldering skills. Don't blame me if anything goes wrong!
Step 1: What You'll Need
You'll need (see notes below):
- Philips screwdrivers
- Wire cutters
- X-acto knife or scissors
- Heat shrink tubing
- Double-sided adhesive tape
- Electrical tape
- Aluminum foil
- One or two towels or a blanket
- 3.5 mm shielded cable
- Some kraft paper
- Soldering iron
- Camera or phone with camera
- Instead of kitchen foil, you should by all means use copper tape for a much more professional result. See here for an excellent example.
- Use some towels or blanket to protect your instrument from scratches, soldering blobs, etc.
- I've used a 3.5 mm microphone cable, but any good quality shielded cable should work.
- The kraft paper can be taken from a shopping bag or box.
- The camera is for taking pics so you don't get confused when you need to solder the wires back together.
Step 2: Disassembly
In my particular model, the only disassembly needed was to removing the eight screws that hold the chromed control plate in place and the two screws from the output jack plate. Other basses or guitars may need different steps to expose the wiring and circuitry.
As I've said before, I like the way this bass looks -- from the outside. The second pic shows how cheaply constructed it is under the hood. What a mess! Wires were way too long and there were a couple of bad solder joints too. The unbranded, dangling black box contains the active circuitry and most of the wiring. You can also see a close-up of the output jack, complete with bad quality cable and no shielding at all. The only thing that can be called "shielding" is the black conductive paint (I know it is conductive because I've tested it with my multimeter). No wonder it picks up RF signals!
Step 3: Tidying Up
I used my phone to take pictures of all wiring and also took some notes so I wouldn't mistake anything. I rotated the two center pots a little bit so as to make more room for the black box between them. In the picture you can see it just before I peeled the tape. Beware as some tapes will make a very strong bond with the chromed plate. I know this because in my first attempt I fixed it across the plate instead of lengthwise. This was stupid because the assembly didn't fit back in the bass compartment!
Then I proceeded to cut the wires that come from circuit box to more suitable lengths, and re-solder them in place. The result is shown in the other photos and you can see it is much neater. These pictures were taken before I realized I've reversed two of the wires, so please be smarter than me and double-check everything.
Step 4: Shielding
Next it was time to shield things. Starting with the output jack, I replaced the original cable with a good quality shielded cable. You can see that I've placed a thick cardboard around the jack and fastened it with white electric tape so the foil around the jack wouldn't touch any undesirable points. I've also soldered extra wire strands to make a good electric contact with the aluminum as shown below. Finally I've wrapped the whole jack with the foil and used a reasonable length of electric tape around it to avoid any damages to the thin foil.
More cardboard and electric tape was applied to the control plate to isolate all places that could accidentally touch the shielding. Everything was then wrapped in foil as you can see in the pictures.
Of course if you have a suitable copper tape you can do a much better job than I did.
Step 5: Reassembly
For the all-important test, I soldered all wires between the bass and the control plate then put the plates back in place (no screws yet) to check if there was any audible difference. To my surprise, it worked much better than expected. No RF interference anymore! In the process I've discovered that the aluminum foil around the control plate and pots didn't seem to have any effect, so in the end I removed it. The final step was to tighten the screws back in place. Done!
I hope you liked this instructable. Please post your comments, criticisms or corrections. Enjoy!
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