Sunday, March 6, 2011

Guitar Shielding

Does your guitar hum? Got a noisy guitar? Shield it.

Do the following first:
  • Obtain a wiring schematic of your guitar.
  • No schematic?
  • Make a schematic or photograph all connects carefully
  • Check continuity to know which wire is connected to what (very simple terms here!)
  • Remove all old wires and components
  • Clean all components that will be reused
  • Shield the instrument (easier said than done - read a book about it!)
  • Solder all connections together using a decent soldering iron and solder (wire too)
  • Check continuity
  • Install components in the instrument (chronological sequence will vary with each instrument)
  • Double check continuity.
  • Button it up and enjoy.

This is a recent project of mine that wasn't nearly as simple as described because the PCB pre-amp was suspected of malfunction. I created a shielded test box to isolate problematic possibilities.

This was what the Factory sold to the public!

There was a lot of junk inside this cavity and I don't know what happened to the original battery clip but when I opened up this unit - The battery was wrapped in a napkin.

The Volume and Tone control cavity was grounded to the wire bridge in the main cavity - Still - the guitar had a troublesome hum. This hum was omni-present because this is a nylon string guitar with piezoelectric under-saddle pickup.

It is important to have secure wire connections. I used shrink tubing to insure a robust wire harness.

This is the shielding with the bad PCB Styrofoam insulation.

I ran many iterations to determine the source of 60 cycle hum. The pcb had some cold joints and bad components. I used my O-scope to pin-point the faulty component. Replace the component. Then I constructed a new insulation barrier for the pcb. The former PCB insulation was Styrofoam that was breaking down. The old insulation barrier was removed and I shielded EVERY CAVITY in the guitar.

This is what the shielded instrument looks like with the new wires, wire harness and components installed.

The guitar is now quiet as a mouse. Prior to this modification the guitar was annoying to play due to persistent hum noise. If I wished to use this guitar for a gig I had to adjust my all the amp settings to get barely passable tone. In addition, playing the guitar through a tube amp was not an option as the guitar would only work half decent on a solid state amp.

This guitar has a new life. Got hum - Try shielding! Scott \m/

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