Finally, after a few days of assembly process, my final project is ready!
Final project: the tube amp + DAC + remote digital audio transfer (incoherent speach is due to 20+ hours without a sleep)
Impressions
Although a bit brutal, the system looks aestheticaly appealing. Surely, it is a bit of a stretch to call it "portable".
Audio quality overall is great thanks to the recognized amplifier design and a good pair of wide-range speakers. In my (subjective) opinion, the mids and highs are the strong side of this system. The lows are present, but not sufficient for certain genres of music (electronic, for instance). Direct comparison of the sound emitted by bare speakers with the sound of the enclosed ones leads to a tremendous positive effect of the enclosure (obviously). The system has no unnecessary resonances or vibrations, which one could find in poorly designed wooden or plastic enclosures.
Low levels of 60Hz hum is present even after numerous attempts to elimitate it (i.e connecting the 12VDC filament supply, substituting the capacitors with the ones of higher quality, wrapping up in steel enclosure). However, the AM-radio effect is completely gone, which is probably due to the Faraday-cage effect of the chassis.
What was done before
The idea of concrete speakers is not new and this example of german high quality speakers was one of the sources that inspired me to try it out. As for the tube amps, there exists a large community of hobbyists that tackle DIY tube amps designs. Finally, the remote audio transfer is also something that we take for granted nowadays.
What is new
While there is little technological/conceptual novelty in my final project, the attempts to build the systems from the components that are mass-produced (enclosures, knobs, PCB) essentially from scratch are infrequent. This process is super fun, but also teaches how to respect all the technological advances that exist in the modern world. I have never realized that designing, assempling and fitting all the components would be so non-trivial.
Further steps
The resulting project, though partially complete, also represents work in progress. For the next iterations, the following steps should be completed:
Either finding/developing the appropriate libraries for the serial communication with the current bluetooth module or swapping to the more handy Bluetooth module (to the NRF series, for instance) and learning how to use the I2C protocol
Developing the UI with the code for pushing the audio files and the firmware for receiving these files via the bluetooth in real time.
Getting rid of 60 Hz hum in audio channels. This noise not significant and also volume-independent, but is still present
Adding the third "woofer" channel with the embedded solid-state circuit. This would improve the low-frequency response. Luckily, there is enough space inside the designed amplifier enclosure.
Designing and making the ported speaker design. Ideally, the internal volume should be larger and walls thickness - thinner. This will improve low-frequency response without much of an increase in the speakers weight.
Going to lower levels of "how to make almost anything": making the DIY tubes, designing the custom tube amplifier circuit, making the DIY speakers.
Skills used
The final project intergrated a variety of skills that I learned throughout the semester. Having a simple idea for the final project has essentially helped me to always stay on track (which is very difficult to do in such fleeting weekly-project-based classes) and master a variety of Cad-design tools and various fabrication instruments. Here is a short list of incorporated techniques:
Molding and casting (volume knob control and speakers)
Milling (wooden framework, fabrications of mold, PCBs for DAC and clapper switch circuits)
Sheet metal (chassis and transformers enclosure)
Electronics production (tube amp, clapper switch circuits)
Electronics design (DAC + bluetooth)
Price
The amount spent for this final project can be separated into two parts: necessary spendings and unnecessary. Since a lot in this project was for pure fun and esthetics, I have quite a lot of unnecessary spendings
Speakers. 40$ for the pair of speakers plush ~10$ for 16kg of Hydrostone + 15$ for foam (mold). This could be reduced with diy or cheap speakers (~5-10$ for a pair), but I wanted to have full-range speakers.
Tube amp. ~300$ for the tube kit, audio wires and interconnects, ports, and a few upgrated elements (capacitors, current limiters). This is largely an unnecessary amount of spendings, which one could easily shrink down to ~100 dollars if knowing what components to order exactly (I was not in this position with a lack of experience with tube and audio amps). This price tag is mainly defined by audio and power transformers which are often quite pricy.
Audio transfer. ~15$ for the bluetooth, Xmega and audio Op-amps.
Steel enclosure. Thanks to the provided by CBA resources, this was essentially for free, but one might spend ~40 dollars for the comparable sheets of steel
Total of ~400 dollars, which can be reduced to ~150-200$ if being frugal. However, there exists another opportunity for a reduction in price. Swtiching from the tube amp to the solid state design can guarantee to reduce the total price to about ~100$ (solid state amps is my next goal).
Issues that I faced (on a high level)
Building enclosures and assembling parts require a significant amount of effort. I underestimated the amount of debugging that I eventually needed
The rate limiting steps for me were coming up with ideas and 3D cadding. While I had a chance to train and master the latter (Fusion 360!), improving the former would be less trivial. I thinkg that my time for ideas generation has been greatly diminished due my inherent eager for a perfection (which everyone always needs to fight hard in order to be at the optimum performance)
The majority of my unnecessary spendings were made during the first month of the class. As the class progressed, I fell in love with the idea of making everything myself and thus, spending very little amount of money. Neil in his class has taught me how to respect being frugal.
Performing low-level audio transfer is far from straightforward. (Just like reaching a robust Bluetooth data transfer is).