doorstop electronics


music electronics that're noisy and weird 

Doorstop Monome! 

Built from a kit from

Doorstop Helmar

A voice modulation chip for children's toys wired up for either mic-level or instrument-level inputs (and, because of space limitations, only capable of mic-level output), stuffed into a metal imported cigarette tin:


Omnidirectional mic for voice or acoustic guitar: 

 Kick drum mic:


Goldtooth Zen Guitar Amp

Here's a Class A, solid state power amplifier using MOSFET switching transistors per the Zen amplifier design by Nelson Pass.  While there are some nice features, and I really like the idea of a solid state, Class A, discrete power amplifier, I think it lacks a little, and my guess is that it's the use of MOSFET drivers. To test my theory I am planning on building a nice BJT-style version.  We'll see how that runs.


Dual Preamp & Mixer for Home Recording

For a mere $75 or so, I put together a dual mic preamp (using THAT Corporation mic preamplifier ICs), plus a small mixer to combine instrument and line level inputs with one of the mic preamps.  It should be useful for home recording into the line level (stereo) input of a lap top, using the left channel for one mic preamp and the right channel for the preamp/instrument/line input.  

Tube preamp - 12AV7

I put together a tube preamp using the design developed by NewYorkDave in the Prodigy-Pro (groupdiy) forum.

The design is pretty straightforward, but he has removed the schematic from the forum so I won't post it here. Basically, though, it uses a couple of RC-coupled triode stages, with a 100k pot in a feedback loop (from the plate of triode #2 back to the cathode of triode #1) as gain control. Because gain is a modest 45 dB or so, I chose to leave it with an unbalanced output. The input transformer is an equally modest Edcor model.

This little project was my first foray into low-noise audio gear, and it shows. It works well with an SM57 mic on a guitar amp, and will try it soon with a phantom-powered mic.

Goldtoooth Wysiwyg

Here's a new box that I whipped up in a single night. It's waveshaping oscillator based off of this site. It uses a CD4040 CMOS counter to step through a CD 4051 multiplexer. A simple Schmitt trigger oscillator drives the 4040. At each step of the multiplexer is a pot - in this case, 8 linear slide pots. It's nice because it requires a single rotary pot, eight sliders, three chips (the 40106 hex inverter is the other), a 7805, a couple of capacitors, and that's it.

Each slider represents a sliver of a single duty cycle, so that you can craft a wave shape manually. The rotary pot on the right (which lacks a knob at the moment) is used to determine the pitch.

Imagine that four sliders on the left are all the way up, and four sliders on the right are all the way down; that would be a square wave. Or the farthest to the left is all the way down, the farthest to the right is all the way up, and the ones in between are sloped up from left to right; that would be a ramp wave. Now you get the idea.

In truth, a review of the signal via an oscilloscope shows that it's not so straightforward. I will need to explore ways of making it more WYSIWYG, and add other features.

This chessy ditty was made with the Wysiwyg in about twenty minutes (and it shows). Wysiwyg The Wysiwyg was sampled into Renoise using three different waveshapes, then a few effects and filters were added.

A little tube preamp

Some pics of my latest. It's a tube preamp, with volume, gain, and boost switch. Runs off a 12 VDC wallwart, and uses 12U7 tubes. The unit bypasses a triode gain stage unless the boost switch is activated.

The housing was originally some sort of instrumentation for ham radio operators; I got it a hamfest. The item originally housed a few tubes on its own, so adapting this box to hold the tubes was a little easier than starting from scratch. Plus, the box has this cool bleeding/vein-y thing going on. I inserted a red jewel lamp cover but stuck a regular red LED inside it. Originally I used a real lamp, but the lamp added a lot of hum to the circuit.

Of course, I took so long building this one - after a few wrong turns design-wise - that I am now missing a couple screws. Bummer.

More noise boxes

I built a "Wacky Sound Generator" off of the schematics provided on the "Music from Outer Space" web site and got a nice little box out of it. (Though I still prefer the old triwave picogenerator from commonsound.) Here it is:


An old triwave

A pic of one of my first concoctions - a straight triwave picogenerator (from designs put on the web by

Other pedals ...

So some bastard stole the Ugly Goldtooth pedal I built (as a wedding present, no less .. just so you know, whoever you are... you're going to hell). So I built a new one. This time it has no power led but it has a switched-in external power supply option (and a reversed color scheme). I cant get over how great this pedal sounds. It's absolutely vicious-sounding. I plan someday on expanding on it (with tremelo and pitch-shifting effects) to explore the thick synthy properties of this circuit, which is so simple and intuitive.

DIY microphone

It's amazing how good a microphone you can make for a small amount of money. I figure I don't have to buy another mic again if I'm willing to build one in a couple of hours for $15.

Below is an electret condenser mic using a 9v battery and a panasonic WM-61A cartridge from Digikey. It's a very small diaphragm (only 6 mm) and is unfortunately omnidirectional, but it gets a perfectly flat, clear response. The only problem so far has been finding a way to isolate it from room noise (like my computer's cooling fans). If you don't sweat the aesthetics (and I didn't this time), you can mount the cartridge pretty much any old way. Here, I just stuck it inside a grommet. I use a 'grip' type microphone clip to hold it. Someday I'll build one with a shock mount.

Doorstop Tooth Synth

A few weeks back I built this rack-mount synth, and it's soo satisfying I plan on building one or two more to sell (but with machine-shop quality construction, not so homemade).

The thing has three oscillators (either square or triangle wave) each from a separate 555 timer IC. These have pitch and wave control, and are modulated by a combination of two LFOs with depth, shape, and speed controls. They can be shut off individually as well. The three oscillators feed into two ring modulators for a true multitimbral tone that is thick and brittle. Mix and volume knobs finish it all off. The ring mods produce all kinds of interesting artefacts over the basic tones. I like to sample various tones and play them musically, or feed it through a sequenced gate along with some drumbeats or other parts.

I made the circuit from a Miniboard-service expresspcb ($20 each in batches of three). Could share those files with anyone who's interested....

Ugly Goldtooth

Basically a copy of Tim Escobedo's Uglyface. Uses a transistor to boost an input signal, and the boosted signal is used to reset a 555 timer IC. For the schematic, check out "Circuit Snippets" among the list of links to the left.

As usual, the knobs are unmarked.