Feature Creep and CFL Guitar Effects

So a few weeks back I came across this very interesting (to me) project. Sounds from Old CFLs. I’ve had a long off & on interest in guitar-playing, but I’ve never used guitar effects, except that one time where I strapped some back-to-back diodes into the signal path of a Roland tube amp, making a crude overdrive distortion effect.

My wife had asked that we come up with some art-meets-technology workshops. She believes that music projects would be popular in the arts community here. As I discussed this project with others, it did seem to be popular, so I set off to create a simple afternoon-long workshop where you bring in an old CFL and you exit with a hand-crafted guitar distortion effect, just like Mr. Carrel describes in his fine Make Project. As you see, this is a beautiful, simple, cheap approach to DIY, down to the 4 in2 metal electrical box that houses the finished product.

Effect box

This project started slowly because finding used CFLs proved harder than I anticipated. And I was not ready to destroy a good CFL just to get the parts I needed. Over the Christmas holiday however, while making a repair in my crawl space, I dropped my trouble light and broke the 13 watt CFL bulb inside. Soon afterward, I popped open the CFL’s base to find a set of electronic parts similar to the pictures in the Sounds from Old CFLs project.


My CFL is not typical. It has big-assed transistors in TO-126 packages. Every other CFL I’ve researched uses the tiny-cute TO-92 package. Otherwise, it has a few 1N4001 diodes, a 200v 15μf electrolytic cap, a toriod inductor and a transformer, neither of which will be useful in a guitar effects project, and a few no-descript items. Also there are few items that I’ll need to disassemble from the circuit board to see what they are.



The feature creep started when I decided that I didn’t want to use a perfboard like you see depicted in the Make Project and I didn’t care to use a breadboard either. I surmised that I could build ONE circuit board and that through component selection, exclusion, and jumpers I could create any one of the five different effect circuits presented in the project. A PCB for this project should cost sub-$10 through Batch PCB. As I hunkered down on this project I next discovered that I could use a three-contact input jack to help prevent battery drain. Soon after I found that I could add provisions for a bypass switch, so that the effect circuit was not just a lab project, it would be useful in real life. And why not add a line power jack for a wall wart power supply I thought? Back to the bypass switch, I saw that if I add a third pole, I could add an on indicator.




At this point it seems that I had it all: 5 in one effects PCB; true bypass with power indicator; automatic power off when the audio input jack is unplugged; line power input option. All of this on a PCB measuring approximately 2.75 x 1.75”. Using jumpers on the PCB, all of these features are optional. I could run a guitar-effects workshop and it would be fairly easy for someone with introductory-level skills to successfully build and use a one of these basic effects. A more advanced guitar player may need to add features at a later time. My effort with the PCB design allows the player to add for example, a bypass switch, the most useful feature to add on the road to sophistication.

But no, the feature creep is not over. An electronic circuit has to exist in the three dimensional world. At this point in the project, I reexamined the PCB layout and realized that it could use some improvement. I chose to add a ground plane to minimize circuit noise problems. I saw that the battery and the input jack should be on opposite ends of the board, not close to each other as I had placed them. Progressing from that idea, component placement could minimize trace lengths. I moved thing around to make the physical circuits less like spaghetti.

But this wasn’t enough. Guitar effect projects often end up in a project box like a Hammond 1590B enclosure. My PCB was too big to fit inside this enclosure. It should not be too difficult to make this circuit fit in the Hammond enclosure, should it? After all every guitar effect maker on earth has been able to do this.

So now I have a circuit design that fits nicely inside of a Hammond 1590B enclosure. As I  look at the PCB layout, I see that the connection points for the ¼” jacks and the bypass switch could be placed better. Where does this stop?

My PCB so far. when does this end?



~ by ratdad on January 10, 2011.

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