Recently, I had the great fortune to get in on a group buy of sorts, for a modified version of the Starving Student Millet Hybrid amplifier. The SSMH started life as a simple but ingenious hybrid (tube and solid state) design by Pete Millett, in which he used the heating element of the tubes to put a load on the MOSFETs of the amplifier, cutting complexity and cost. Originally, it was a very basic amplifier with a budget-minded soul, built into whatever enclosure was handy with point to point (P2P) wiring. You can see the original build at his site here, and the forum thread following it’s history here.

DIY forum user Dsavitsk then improved on the design with some slight modifications to the circuit. He also developed an equally ingenious way to mount the amp in an enclosure – a PCB would be developed and attached to the sliding top of a standard Hammond enclosure, allowing the tubes to be mounted to the “underside” of the PCB and stick out through the case. This would eliminate the P2P wiring that caused many problems in DIY builds of the amp – problems with grounding and bad connections had plagued countless hobbyists.

Collaborating with Tom Blanchard of Beezar Audio, the two developed PCBs and set the project in motion. Tom took on the arduous task of organizing the procurement of the increasingly rare 19J6 vacuum tubes, the custom-machined Hammond cases, and all the other various parts needed to develop kits of the SMMH.

I was lucky enough to get in on this undertaking and purchase a kit, and after a couple months (during which the cases were machined), I recently took delivery of the kit and quickly put it together.

The ease of construction of this amp is a great testament to the amount of work that Tom, Dsavitsk, and originally Pete put into this design. I had the amp completed from start to finish in less than 5 hours, with no serious problems. With me and DIY projects, that’s unheard of. Tom made it extremely smooth with his excellent instructions. I flipped the power switch, watched the glow of the tube heaters and LEDs come to life, and plugged in my headphones and source. I wouldn’t call myself an Audiophile, but the sound of this amplifier far outranks anything I’ve listened to, and blows my own basic DIY amps out of the water. Plus, it looks amazing on my desk. Glass tubes? How quaint!

For those looking for a great audio project with that old-school tube feel, there are still PCBs and tubes available, with a chance that more custom cases will become available. [EDIT] As of February 2010, the supply of 19J6 tubes has been nearly exhausted and no more PCBs or kits based on this tube will be produced unless a stash is found in the corner of a warehouse somewhere. The possibility of doing this build point-to-point still exists if you want to buy the tubes in small quantities at high prices, and there are modifications that can be made to use this design with more common tubes – see the SSMH website or the Head-Fi thread for details.

Even if this amp seems like too much of an undertaking, I highly recommend dabbling in DIY audio – a great place to start is the classic CMoy headphone amp in a mint tin. Tangent has some of the most complete instructions here.

Un-Disclaimer: I’m in no way involved with Beezar audio or anyone else mentioned in the post; this was just an awesome project that came together through the power of the DIY community.

Arduinos with Buzzers

The most basic way to create audio using the Arduino is essentially bit-banging one of the digital pins – write high and low at the frequency you wish to generate. The downside is that this creates a nearly square wave, which sound very harsh and unnatural. Also, the “high” is 5V, which is a very high amplitude to be supplying to headphones. Constant use at this amplitude (volume) will probably damage the drivers in earbuds – use the cheap earbuds that came with your MP3 player. Using a standard 8ohm buzzer is of course the preferred method if you have one lying around. I found a buzz function online to control this – pass it the pin to buzz on, the frequency, and the length, and it does the work for you.

void buzz(int targetPin, long frequency, long length) {
long delayValue = 1000000/frequency/2; // calculate the delay value between transitions
//// 1 second's worth of microseconds, divided by the frequency, then split in half since
//// there are two phases to each cycle
long numCycles = frequency * length/ 1000; // calculate the number of cycles for proper timing
//// multiply frequency, which is really cycles per second, by the number of seconds to
//// get the total number of cycles to produce
for (long i=0; i < numCycles; i++){ // for the calculated length of time...
digitalWrite(targetPin,HIGH); // write the buzzer pin high to push out the diaphram
delayMicroseconds(delayValue); // wait for the calculated delay value
digitalWrite(targetPin,LOW); // write the buzzer pin low to pull back the diaphram
delayMicroseconds(delayValue); // wait againf or the calculated delay value
}
}


The downside is that this uses the delay function. That means your controller can't do anything else while waiting for the end of the delay. You would also have to use a delay function between the notes to create spaces. This is sufficient for a small buzzer project, but if you're looking to do more complex things (especially signals other than square wave), try consulting the Arduino Playground.

I was able to find a script for the Mario Bros theme online, and covert it into a series of buzz and delay calls. Not all the notes are correct and some of the spacing is off, but it's good enough to get the idea. The entire Arduino script is available here.