Archive for the ‘Warranty Void if’ Category

First Commission

January 20, 2011

I have been commissioned by the founders of to create a retro nixie tube display to display the site’s traffic. Working on the project has been fun. I’m using some off the shelf stuff for economy’s sake: a nixie tube clock found on ebay, an arduino, and an arduino ethernet shield. The device will go onto the internet and retrieve the site statistics periodically and display them in the warm glow of excited neon.


Free Tube Amp

June 29, 2010

My friends Mikey and Wendy gave me this thing they found at a yard sale. They were hoping to sell it for something on ebay, but it turned out to not have any input jacks or knobs. A radio? but no tuning nob or switches. It was full of tubes and had speakers. Clearly it could be used as an amplifier somehow!

I traced out the tone and volume circuitry, and found it in the middle of a chain of four tubes. I disconnected the wire going from the output of the volume potentiometer (wiper contact) to the input (grid) of the next tube. I left the current limiting resistor. Then I just installed a 1/4 inch jack on the back, connecting the sleeve to the ground on the circuit board and the tip to the current limiting resistor going to the grid of the first of two amplifier tubes. And, there it was, a PA amplifier. It worked great with line level signals from my ipod etc, and I got a small amount of sound from a guitar, but it wasn’t loud enough to use as a guitar amp.

To boost the guitar signals I built a preamplifier circuit based on the 12AX7 tube. I found a useful schematic on the “cooperative tube guitar amp project” online at I just copied the preamp section of the basic amplifier design. I drew from the +300 volt supply already on the circuit board which I found by looking up the plate pins of the other tubes and metering it out.

With this addition the amp not only gets nice and loud but distorts when it’s turned up all the way. It sounds great too! Listen to my friend Andy shredding in this video:

The guitar (if I may add) was found in the dumpster behind a local thrift store – making this ear smashing hair thrashing metal machining rig virtually free.

If you enjoyed this article please check out my other Electroacoustics posts on


January 16, 2009

My friend Zevin and I had a circuit bending jam session in preparation for an electroacoustic noise show that we are putting together. On our way to my house we stopped at the dumpster behind a thrift shop and scored a crumby old HP inkjet printer. After ripping off the cover, because I couldn’t find my torx wrenches, we discovered that the motor that drives the belt that moves the heads back and forth is DC. This changes everything, since driving a DC motor is just a matter of driving some current through it, apposed to a stepper motor which would require drive circuitry and logic. We hooked the motor up to the output of my stereo amp, and started experimenting with different signals, using Pure Data.

Here’s one, using a saw tooth wave:

And here’s another, using a random signal between -1 and 1, changing every 10th of a second:

Finally the hack came to perfection when we taped a screw driver to the head and drove the amp with a pulse shaped like a single cycle of a saw tooth signal, using the ~vline object in Pd. Then we triggered the ~vline object using a step sequencer I wrote a while ago in Pd, and put a large steel drum in harms way.

This contraption will definitely play a role in our music project. It’s hard to say how yet. It could be used, as is, to strike a barrel or it could even strike a conventional drum. But there are many other possibilities.

I was most inspired during this hack by the acoustic recordings on Aphex Twin’s album drukqs, which I thought were made using devices such as the one above. But Zevin noticed that they are actually compositions on prepared piano, a method developed by John Cage that uses a standard piano. The misunderstanding lead to a unique project, that might not have happened otherwise.

Hacking NWS

January 9, 2009

I figured out recently that you can get access to raw weather station data through NOAA’s site. Just go to the site and type in your zip code. Then scroll down and look on the right for a station close to you.nws-santafe
For me it was the station at the Santa Fe water treatment facility. The link is to a flat text file full of scrumptious data. I’m mostly interested in the temperature, so I keep my eye on the “Tmp” column. Keep in mind that the dates are in UTC format, so you will have to adjust.
If you’re interested in seeing the data visually there’s no need to parse or plot. NOAA has done it for us. Take the URL of the data file and change the URL to call a different script. Instead of raws_flat.cgi, call time_mesowest.cgi with the same location info after.

For me the URL to the raw data is:

I change the URL to this:

You should get a nice plot of all the data that looks like this:


This has been useful for checking the performance of the cold frame we built in the front yard, and figuring out how well the light bulb in the chicken coop worked, etc. There’s no need to set up a microcontroller outside to record temperature data. It’s already been done for you!

Electroacoustic musings

January 9, 2009

I took apart a big old laser printer yesterday and found some nice electromagnets. Here’s what I did with them, and an old autoharp I found at a tag sale this summer.


The strings on the autoharp are steel, and thus are somewhat ferrous. I placed the magnets close to the strings with a bracket repurposed from the printer. Then I ran an oscillating current through the magnets to vibrate the strings. I think a saw tooth wave works the best. The strings resonated at different frequencies, producing a dynamic harmonic mash that I think sounds great. I accomplished this by hooking the electromagnets to the speaker outputs of a stereo amplifier, and driving a signal into the amp from my computer running Pure Data. The other thing you can do is play music through it. Jimmy Hendrix works well, but as of late I have been running the local country station through it; the undulating resonations please the ear far better than “boot scoot and boogie.” The electromagnets are about 150 ohms at DC, so this is totally safe. In fact I had trouble getting too much power into them because of their high impedance. The volume knob is turned all the way up on the amp to get a medium volume level out of the electrozither.

electrozither coils

Next, I taped a piezoelectric transducer to the body of the autoharp and fed it’s output into my computer. I set up a feedback loop this way, producing some even more interesting sounds. The only problem with this setup is that I’m getting a lot of 60hz hum from the wires going to the piezo transducer, so there’s always a foreign signal exciting the loop. I’d like total quiet to be a possible state of the feedback loop. To get around this, and also to effect the timbre of the instrument, I’ve been experimenting with putting filters in the feedback loop. A resonant lowpass filter works pretty well when the Q is high. This also cuts out the 60 hz hum, which sadly is jagged and can be heard in virtually every area of the sound spectrum, not just the low end.


Here is a recording of the electrozither feeding back on itself with a three band EQ on the feedback loop for one channel, and a resonant low pass filter on the other channel. The rattling you hear is one of the strings, lose, vibrating up and down in the varying electromagnetic field. It looks quite supernatural.

I hope to get more of these electromagnets. With only two, a great deal of of sonic possibilities have yet to be realized.

transformer rewound

December 25, 2008

tx cored

tx rewound

The rewound transformer now reads about 11 volts coming out of the secondary coil. With two of these wired in series I’d get a total output from the welder at 22 volts. This is less than I was anticipating. I think I may have ended up with smaller transformers than those used in the instructable.

Plasma arcs weee!

December 23, 2008

Since seeing some arc welding this weekend in T or C I’ve been recollecting the parts for my microwave transformer arc welder project. Whilst contemplating the design I thought I’d have a little fun with high voltage arcs and scare my housemate at the same time. I wired the transformer up unmodified, and let’er rip.

Note: This is probably super dangerous, so don’t do it.

The transformer is used in a microwave to drive the magnetron tube. It produces a supper high voltage for this purpose, and from what I can tell at a relatively high current compared to a flyback transformer for example.

The next step for my arc wealder is to cut out one of the windings and replace it with heavy guage wire. You can read all about this on the instructable I got the idea from here.