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Common transistors - A drawing of some common transistor types and their pin designations. I keep this one pinned to the shelf above my soldering iron.   New 1 Jun 2002

Prevent Dull Volume Controls - It is sometimes noted that a volume control causes the sound to be "dulled" as it is turned down. This is caused by the series resistance of the pot interacting with the capacitance of the next stage to form a low pass filter and a resulting high frequency loss. To counteract this, a small capacitor is added from the input to the wiper on the volume control. This small value capacitor has a low impedance at high frequencies and provides a bypass around the series resistance of the pot as the volume contyrol is turned down. Some experimentation with the value of the capacitor will be necessary as the amount of boost required depends on the value of the pot and the capacitance of the following stage, but 150pF to 470pF is a good starting range for C1.   New 29 Apr 2002

DPDT switch - A diagram on how to wire a dpdt footswitch for true bypass   New 1 Apr 2002

Breadboarding? - If you are working with one of the solderless breadboards like they sell at Radio Shack, be aware that it has a lot inherent capacitance that can often make a circuit behave in a manner totally different than when it is put on a pcb. High gain and high impedances are sources of trouble with these plug-in boards. Watch out for it!   New 29 Mar 2002

Acoustic Guitar Microphone - Try the Radio Shack lapel mic (part no. 33-3013) inside your guitar; move it around to find the best placement. You'll be surprized at the sound from this $25 microphone!   New 1 Jan 2002

  • Paul Verticchio submitted the following comments (thanks!):
    The mic is a house branded Audio Technica. It's available from most AT dealers at a price lower than RS...except when it's on sale. Suggestion (or "here's what I did a year ago"...):
    Rebuild (reproduce with better components) the ECM power supply and outboard it to a cast alum. Hammond or Bud box. Use a 9v battery for DC power supply (increases headroom). Use 1/4" phone plugs and jacks for ease of future maintainence.

    VERY carefully hot melt glue the ECM capsule to the bottom of a soundhole mounted magnetic pickup at the edge that faces the bridge. I used a S.Duncan Woody.

    While the glue is still pliable, angle the ECM capsule so that it will point toward the bass side lower bout of the guitar. Mix the two signals with an active mixer & tweak with the mixer's channel EQ's. You wont believe the incredibly NATURAL sound that comes trough a QUALITY S.R. system. Yes Virginia, this setup will still sound like crap through a regular lo-fi guitar amp.

    2 tips:
    1. only run the Mag signal back through the monitors for more gain before feedback.
    2. Effects should also be used only on the mag output.

    Seems that Seymour sells an "conceptually identical" product for a MSRP of around $300!!!! What I described can be yours for less than $100...even if you pay full bore retail.


Wah Inductor Sub - FYI, I measured the inductance of the 1k:8 Radio Shack transformer that is recommended as a sub for the 500mH wah choke and found the primary to measure 530mH, which is a little high but still useable. It will make the center frequency of the filter slightly different than with a real wah inductor.

Here are some inductance mesaurements for some of the small Mouser transformers that might be useful in filter circuits:

  • 42TU016 - Primary 380mH, Secondary 380mH
  • 42TM022 - Primary 833mH, Secondary 261mH
  • 42TM021 - Primary >2H, Secondary 408mH
  • 42TM019 - Primary >2H, Secondary 343mH
  • 42KM019 - Primary >2H, Secondary 1mH
  Revised 29 Mar 2002

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