This looks like a very interesting project. If you're into audio measurements, this project might also interest you.

From the Pmillett website...

Most of us DIY audio types have been using PC sound cards to make measurements.  There are excellent, inexpensive programs available to do test and measurement of audio equipment available.  Personally I use Audiotester.  If you've been around my web site you've seen FFT plots generated that way.

What has always been lacking is a decent interface between the sound card and the device under test (DUT for you geeks).  There has been much discussion in forums like DIYaudio about this, and many proposals and circuits shown, but so far I've not seen anything implemented.

The problem with sound cards is that they are designed for fixed line-level inputs and outputs.  Depending on the card this may be between 1V and 5V RMS maximum.  They are also not tolerant of overloads - accidentally deliver 20V into your sound card input and you will most likely be looking for a new sounds card.

http://www.pmillett.com/ATEST.htm

DIY'ers today have it good! There's lots of projects available on the net to build. Here's a Tube Amp Kit by OddWatt Audi. 

The manufacturers specifications for the kit are as follows:

• Rated Power Output: 25 watts (RMS)
• Input Sensitivity: 1.5V (at rated power)
• Input Impedance 100 k-ohm
• Input Terminal: Line Level RCA
• Speaker Output Taps: 4 and 8 ohms
• Distortion: less than 0.5% through half power, 1% at full power
• Frequency Response: 8Hz to 20 kHz +0/-1db at any rated power
• Signal to Noise Ratio: less than 80dB
• Tubes: Gold Lion KT88, NOS JAN Philips 5751
• Supply Voltage: 120VAC 50/60Hz
• Power Consumption: 130 watts (each monoblock)
• Weight: 6.3 kg (each monoblock amp)
• Dimensions: 205 mm (W) X 225 mm (H) X 300 mm (D

http://diyaudioprojects.com/Tubes/5751-KT88-Tube-Amp-Kit/

Mightyohm documents in his blog the making of a low cost, open source wireless streaming internet radio receiver.  All construction details, including schematics, source code, and even the design process itself will be documented on this blog. http://mightyohm.com/blog/2008/10/building-a-wifi-radio-part-1-introduction/

Doing some CNC milling work...



After a couple of hours, I have these babies...



For my TS-2 preamps


TS-2 Preamp by FiveFish Studios

Maxim offers a great explanation of DC-DC converters.

DC-DC Converter Tutorial

Abstract: Switching power supplies offer higher efficiency than traditional linear power supplies. They can step-up, step-down, and invert. Some designs can isolate output voltage from the input. This article outlines the different types of switching regulators used in DC-DC conversion. It also reviews and compares the various control techniques for these converters.

http://www.maxim-ic.com/app-notes/index.mvp/id/2031

This is not DIY per se.... you can buy this musical device ready-made. 

But for under $50, you don't need to DIY this. Just buy it. It's loads of fun too.



What's under the hood?


http://www.thinkgeek.com/electronics/portable-audio-video/c4e1/

You want things that make bleeps, noises, and other electronic noises? Then this kit is for you!

Bleep Labs Robo Audio Synths

• Enjoy making all sorts of robotic and electronic noises with this light-controlled analog synthesizer.
• Great fun for the hobbyist, musician, electronics buff, or goober who just likes making weird noises for people.
• 1/4" output jack to connect to guitar pedals, amps, etc. (no input jack)
• Thingamakit features two LEDacles and has square and triangle wave output which, coupled with the secondary photocell, means even more creative and sound control.
• Thingamagoop includes: one Thingamagoop (your choice of color) - each will have slight (very slight) sound variations as each is hand made.
• Thingamakit includes: Detailed instructions., fully labeled components, simply laid out circuit board with minimal hand wiring, two ready to blink LEDacles, "stompbox" style enclosure, and control panel and face stickers.

http://www.thinkgeek.com/electronics/musical-instruments/bf12/

This site http://scotthelmke.com/ showcases a lot of DIY microphones by the author. They look awesome. Here's a picture of a stereo microphone.



This mic is based on a pair of Transound TSB-55A cardioid electret capsules. These capsules are almost identical to the Panasonic WM-55A, but with a bit flatter low end. The two capsules are in a vertical stack, splayed out about 100 degrees. I really designed it to fit into a grand piano for live sound, but it does a nice general stereo recording as well.

I've also built stereo mics with the bigger, better Transound capsules. Those tend to be quieter, but not as flat as the TSB-55A.

Construction is a lot simpler than it looks. The body is just 1" ID copper water pipe, with the window cutouts done with a Dremel tool. The screen is brass mesh from McMaster-Carr. The capsule mount was made from various bits of brass from that little craft-metals display in the hardware store, and is mounted in a wooden plug that fits inside the mic body. Finally, the connector is a Switchcraft B4M, which fits the copper pipe almost perfectly. I used a piece rigid tubing to help the body of the connector fit nicely into mic body. This mic uses a small external power supply which is phantom-powered from a standard audio mixer. It would also be possible to build a simple power supply using a 9 volt battery and with an 1/8" stereo output, for use with a minidisc or other small recorder.

http://scotthelmke.com/stereo-mic.html

More DIY Microhones... http://scotthelmke.com/microphones.html

TS-2 Dual Channel Preamp

Powered by 12 Volts DC. (wide range, will run at lower voltage too)
Switchcraft DC jack (with locking threads)
True +48V phantom power (@ 12VDC input)
Internal Dual power supply rails +/-15V
Proven Preamp Design - based on the SC-1/mk2 design
Full size Neutrik XLR male and female jacks
12-step Grayhill gain switch
THAT and Burr-Brown chips
Anodized Aluminum Case
CNC milled and engraved front and rear panels
Approx 6.25" x 6" x 2"

The TS-2 Preamp was a limited run project.
All units are ready-made, complete, finished.
Not available in KIT form.

I only have (4) units left. Email me if interested.
$590* + shipping.
* Battery/Wall Plug not included

Thanks!

Testing an early prototype.

A DIY Tube Microphone.... and yes, it's a KIT!  What's even more awesome about this is the microphone body, grille and other stuff is included in the KIT.  Anybody that's into building DIY microphones know this is the most hardest thing to DIY... the microphone case. Not the electronics, not the power supply but the mechanical enclosure! So this kit packages everything nicely.

From the writeup:

Beautifully machined (unpainted) brass microphone body and head-grill assembly
Internal mounting cage assembly to mount circuit board, capsule, transformer and connector housings.

Components included

1 - 32mm/1in large diaphragm pressure gradient capsule (assembled)
1 - Plastic capsule mount
1 - Pre-amp circuit PCB
1 - Tube socket PCB
1 - Vacuum tube, 12AX7
1 - 9-pin tube socket
1 - 7-pin XLR male connector
2 - Ceramic insulators for both ends of C4

1 - Film Resistor,  1/2 W 10KΩ
1 - Film Resistor,  2W 100KΩ
2 - Film Resistor,  1/2 W 270KΩ
2 - Resistor, 51M
1 - Resistor, 200M
1 - Film Resistor, RJ 1/2 W 3KΩ
1 - Resistor, 1 KM
3 - Capacitor,  1μ/400V
2 - Capacitor,  .022μ/630V
1 - Capacitor,  1000 pF/630V
1 - Capacitor,  100μ/25V
3 - Capacitor,  0.1μ/63V
1 - Capacitor,  1000μ/10V
1 - Ceramic Capacitor, 2pF
1 - Transformer, turns ratio 10:1

1 - Fully assembled power supply
1 - Power cable for power supply
1 - 7-pin microphone cable

Printed documents
Schematic

I bought this kit on eBay and sure hope to find the time to build it.  I'll post pictures of my build.