Feedback Generator (1993)

(Click on Jimi to hear  
 his feedback virtuosity)
Cool! Where's 
my drill??!?! 

I built this device in an effort to sound like Jimi without bothering the neighbors or blowing out my eardrums. The concept is very simple...sound travels through solids a lot better than it does through air. So if you apply the vibrations of the guitar sound right to the guitar, Hendrix-like feedback effects will happen with way less power than if they go through air between the speaker and the guitar. The first part of the device is a rackmount box with a post-modern design:

Diagram of stuff inside ugly silver box:

          |                                  |    Audible
          |                              +------> guitar 
  Clean   |      Craig         Craig    /    |    output 
  Guitar >-O  O-Anderton--O  O-Anderton+     |
  Sound   | \   Compressor  /  Spluffer \    |
          | O--------------O             v   |
          |   DPDT Bypass            Craig   |
          |      Relay              Anderton |
          |         ^             Tube Sound |
          |         |                 Fuzz   |
          |        /                    |    |
          |    Feedback                 v    |
          |    On/Off             Guts from  |   
   On Sw--|--->Flip               battery-   |
  Off Sw--|--->Flop               powered    |
          |        \            practice amp |
          |         \                   |    |
          |          \                  O    |
          |           +--------------->/     |
          |                             O    |
          |                             |    |
                             To feedback transducer

A transducer is used to apply the guitar vibrations to the guitar in some way. Two possible ways to do this are:

  1. Drill huge hole in back of guitar with Forstner bits and install transducer there.
  2. Attach transducer to a guitar slide and run it across the strings. Additional cool screeching noises can be created by holding the transducer next to the pickup in use. Control frequency of screech with guitar tone pot.

Hey, kids! Make your own feedback transducer!

  1. Buy a small cheesy 8 ohm speaker like this one from Mouser. Radio Shack used to have them, but they don't anymore.
  2. Cut off the speaker cone with a Xacto knife, leaving the wires intact.
  3. Use tin snips or wire cutters to cut off the outer metal frame except for three tabs for screws, and the little terminal strip.
  4. Super glue a dime onto the voice coil. This is necessary to provide mechanical resistance so the coil won't burn up.


Here is me using the guitar-mounted version of the feedback generator on Pat Jordan's tune "Dolls" from the album With My Bathroom Fixtures I Shall Rule The World by Iconoclast:

(255K mp3)
Here is me playing with the guitar slide version: (196K mp3)
Here is me playing Happy Birthday with a more recent (July 2005) kludged-together feedback generator. I did this one for my sister's birthday. (721K mp3)

Related Devices

Of course, after I built this I realized others have used the same idea: Sustainiac Model C.

Someone told me there was a device many years ago called the "Feedback Extravaganza" or something that worked like this. If anyone knows anything about this, please email me.

The Fernandes Sustainer uses a different method to get a similar result. It uses an electromagnetic driver (a pickup being used backwards) to drive the strings rather than an acoustic transducer.

Pedalboard Version

Lately (August 2005) I've been working a pedalboard version of the feedback generator using a bunch of Danelectro mini-pedals. I'll keep the page updated as I make progress.

           +----------+       +-----+
           |Surf&Turf |       |PB&J |       +------------+
Guitar --->|Compressor+--+--->|Delay+------>|Roland GP-16+--> Audible output                      |
           +----------+  |    +-----+       +------------+
              |   Pedal-controlled   |
              |   short delay        |
              |(Modified Hash Browns |
              | Flanger inside Dunlop|
              | rocker pedal; pedal  |
              | controls delay time) |
                 |    T-Bone    |
                 |  Distortion  |
                 |    Fish &     |
                 |   Chips EQ    |
              |    Bacon & Eggs      |
              |      Mini Amp        |
              |    (modified for     |
              |   speaker output     |
              | and less distortion) |

Mod Details

  1. Hash Browns Flanger

    1. No dry signal in output
    2. Pot controls delay time, not LFO depth

      Changing the phase relationship between the guitar string and the signal to the feedback transducer can cause the feedback to jump to a different harmonic of the note you're playing. I modified my Hash Browns Flanger so that it outputs only delayed signal, and the delay time is controlled by the pot that was originally the "Depth" pot. After my mod, the LFO that normally sweeps the flanger's delay time has been disabled, and the delay time stays fixed when you are not moving the pot.

      Effect of delay time on feedback (483K mp3)

Adding long delay to feedback signals

Putting an echo effect with a longer delay time in the chain (PB&J Delay) causes wonderful beating effects when the transducer is moved along the string and the old echoes beat against the new ones.

Echo beating (636K mp3)