Redwood Audio Amplifier

Posted on September 18, 2011 by KevinB

A few months ago I started collaborating with Jordan Waraksa on a project that is currently on display at the Haggerty Museum of Art, in a show running until the end of December. He sculpted a pair of wooden acoustic horns called Bellaphone 5 & 6 out of walnut. Each horn rests on a redwood base that houses a small speaker. If you visit the Haggerty, you’ll hear the speakers playing songs by Jordan’s band, The Vitrolum Republic. If you really love the Bellaphones and amplifier, know they are for sale.

I developed and built the electronics for the horn’s amplifier, whose chassis Jordan also sculpted from redwood. Because the chassis is wood and has no vents (for aesthetics), electrical efficiency became a high priority in order to prevent overheating. I chose to use a Maxim 98400A class D amplifier driven by a high efficiency switching 15V DC power supply. I added a digital signal processing chip from Analog Devices to increase the bandwidth of the horn and smooth out its frequency response (i.e. to improve the audio fidelity). Analog’s ADAU1701 is a remarkably powerful chip – it is more than capable of these tasks. In addition, the 1701 prevents bass notes (frequencies below 100 Hz) from reaching the small speakers (which are incapable of reproducing these low notes), which would otherwise emanate from the horns as distortion. Finally, the 1701 also adds a small amount of compression, which prevents distortion at the loudest output levels. The 1701 is actually real-time programmable via a USB connection to a computer running Analog Device’s free SigmaStudio software. It’s a tremendously user friendly GUI environment with drag and drop audio processing blocks.

Check out the inside of the amplifier as it was being assembled, prior to the addition of many ferrite beads which eliminate the audible noise from the three high efficiency switching power supplies: One powering the amp, one powering the DSP board, and one continuously charging a Motorola Cliq XT handset playing songs from the Vitrolum Republic.

Here are two more close ups, one of the amplifier:

And one of Bellaphone five and six:

Cacophonator

Posted on September 17, 2011 by KevinB

I’ve recently made several audio synthesizer / noise generating boxes. The most recent is the Cacophonator, whose circuit description and board layout are easy to find on the web. Thanks to Adam for showing me how to etch my own circuit boards – something I can now do quite easily at the Makerspace. I modified the board layout, drawn in DipTrace, so I could add SIP sockets and pin headers to tidy up the inside of the project box. The sockets also allow the board to be easily removed, despite the 20 wires running between the board and other components inside the project box. The photos below were taken before I modified the circuit by adding a momentary power switch to slowly recharge the giant power supply capacitor if held for a few seconds. I also added a LM317 adjustable voltage regulator so the power supply voltage can be reduced all the way down to 1 V DC and below. The sonic complexity of this circuit is surprising considering its small part count, and lowering the power supply voltage further adds to the chaotic behavior of the cacophonator. Careful inspection of the board will show additional components not associated with the original cacophonator, but are discussed on electro-music.com. These are used for inputting audio signals (music, for example), which come out the RCA jack quite cacophonated.

Makerspace Eight Speaker Super Surround Sound System

Posted on May 30, 2011 by KevinB

The day has finally arrived: The Makerspace Eight Speaker Super Surround Sound System (MESSSSS) is fully installed, wired and amplified. This morning MESSSSS reproduced its first 8 channel audio piece, authored using adobe audition and played back by four android devices through four 1/8″ stereo cables feeding the bank of amplifiers. More integration work remains to be completed (a dedicated computer with an 8 channel sound card plus a patch bay) but the MESSSSS is up and running!

Tea Box Radio

Posted on August 19, 2010 by BrantH

Someone bought me a gift assortment of teas last Christmas and it came in this decorative wooden box. When finished the teas, I couldn’t bring myself to throw it out so I started turning it into an iPod dock. The speakers and electronics came from a set of computer speakers. I took some measurements and made a template in AutoCAD to lay out the parts. I hope to have the panel milled out of basswood using a CNC machine shortly.