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The "Woody" acoustic simulator file: 000067   8/21/103 3:56 am
A *very* simple attempt at mimicking an acoustic guitar with a pedal. This uses a simple exciter circuit and a bass boost to get a bit of the boom and crispness of an acoustic. Not meant to replace your Collings/Martin/Taylor/Bozo/Guild or Gibson Jumbo, but simply to have a sort of acoustic tone for those occasions where you want to have that sort of sound for rhythm guitar strumming. Works best with two single-coil pickups.

This is version 1.1. The first version inadvertently had wrong pin numbers for IC1a. Mods, comments, and especially suggestions for adapting it to a single 9v battery are welcome (

The zipfile contains the schematic, a soundfile and soundfile notes, and some pix of the one I just brought over to my friend's kid today.

Deticking a Zombie Chorus file:   DETICK~1.jpg 000066   8/11/103 2:06 pm
John Hollis' "Zombie Chorus" is a terrific little minimalist chorus unit except for one thing: most builders report an annoying audible tick produced by the LFO (in sync with the LFO speed).

While the MN3007 BBD-chip the Zombie uses normally requires a handful of additional components (one of them usually a trimpot for tuning) to provide a DC (i.e., steady voltage) bias to the input of the MN3007, John made clever use of the voltage divider circuit that provides the artificial ground (Vref or Vb in the PDF layout file at GEOFEX) to accomplish this so that users would not need to do any trimpot adjusting to have it work. This also requires the use of specific dual op-amps to hold up accurately. There may be others, but the TL062 is dependable for this.

Unfortunately, the LFO circuit also needs a bias or Vref voltage to work properly. It WILL work with the existing one, but since the Vref/Vb is not at the mid-point of the supply voltage (the resistors in the existing divider circuit, R12/13, are 10k and 15k), the LFO swings above and below the Vref asymmetrically. Since it has more voltage headroom (i.e., can swing farther) on one side of the Vref than on the other, it produces an audible tick on the half-cycle with the least headroom. This is why you hear a tick that is in sync with only the peak of the sweep in one direction and not the other.

Local builder Tim Larwill was showing me his excellent Boss CE-1 clone recently and detailed his difficulties in developing it, mentioning that he found asymmetrical LFO swing to be a source of ticking. I tucked that detail away until recently and suddenly realized that perhaps this was the source for the ticking in the Zombie.

Frustrated with the way in which the ticking was detracting from an otherwise nice little pedal, I tried an experiment in which a different (and "true") Vref/Vb was provided for just the LFO chip. Sure enough, it worked like a charm. Thanks to Tim.

The GIF is the mirror image of what RG has in the PDF file, and is exactly what you'll see on the copper side of an already etched Zombie board. It shows where to cut, what to add and where. Essentially the trace linking pins 2 and 5 of U3 (using the layout/schematic that RG Keen graciously drafted and posted) to the existing Vref/Vb is cut. Two 10k resistors are used to provide a new Vref by tying one to pin 8 of U3 (where V+ is), and the other to the nearby ground connection along the edge of the board. Their junction is now soldered to the trace in between pins 2 and 5.

This can probably be best done with 1/8w resistors (the tiny ones) but if you're like me you probably only have 1/4w ones in your bin, so be sure to cover the leads of the resistors with a bit of insulation to make sure their leads don't short out against anything unintenionally.

Thanks to John for the design, to RG for the layout and redraw, and to Tim for the idea. Four heads are better than one.

Maestroworld file: 000065   8/10/103 2:55 pm
Here is an assortment of Maestro factory schematics for fuzzes, phasers, octave dividers, brass blaster, the envelope modifier, and the ever-so-mysterious Fuzz-Phazzer.

Many thanks to Rick Lawrence for supplying them.

File is 486k, containing pdf files.

More to come (August 10, 2003)

Baseballs package file:   BASEBALLS.ZIP 000064   7/31/103 3:58 pm
Here are a couple of files that people requested, including Ambrose Chappell's original Baseballs layout, a more recent redraw of the PCB mask to correct some small errors noticed in the original, and Marjan Udekar's über-Baseballs clone called the Fuzzy Balls. I included the latter just so you could see what happens when you take a basic idea and just let your imagination go.

About half a meg in total.

file:   440mod2.gif 000063   6/25/103 8:19 pm
This is the second corrected version of the 440 schematic. I had it wrong, folks. Osamu Hoshuyama was kind enough to identify the needed changes (in red). Note that the original has the LED half of the Vactrol oriented incorrectly.

Modded Bi-Filter Follower file:   Bi-Filter_Follower_redraw_with_mixing.gif 000062   6/24/103 1:36 am
This schem adds several mods to Craig Anderton's tried and true Bi-Filter Follower (BFF). The basic drawing is from JD Sleep's generalguitargadgets site. Many thanks to him for providing something that was easy to add to. PLEASE NOTE that there is a layout for the stock BFF at JD's site but it does NOT accommodate these mods. You will either need to redesign a PC layout for them or else wire it up on perfboard.

The mods are currently untested, but there doesn't seem to be any reason why they would not work, although some component value tweaking may occur as people try it out and make suggestions. These changes will be posted as they occur.

The BFF is an LDR-based dual swept filter, similar in some ways to the Electro-Harmonix Baseballs, but better in a number of ways, and certainly very easy to mod. It is also one of the best envelope-controlled filters I've ever used for rhythm guitar. Very, very smooth.

The mods here include a range switch which spreads the two filter sections farther apart for some nice delicate textures, and a means for combining straight and filter signal together.

This latter feature is appreciatively borrowed in concept from the Lovetone Meatball and goes a bit past it. Bass players in particular complain about how swept bandpass filters tend to lose body midsweep because the bottom just disappears. Mixing in some straight signal helps to even out the sound and keep body. In effect, the swept resonant peaks "ride" on top of a full bandwidth straight signal. This mod allows the user to combine either inverted or noninverted straight signal with the filter to produce either swept resonant peaks OR swept notches, emulating an envelope controlled 4-stage phase-shifter. The user can adjust how much of the effect they produce, and can also restore the stock settings. The controls allow one to adjust output level so that even settings producing notches can still be a little louder than the bypass signal if you want.

files:   Pedals.jpg | reverb_sd.gif 000061   5/9/103 8:44 pm

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