Instructables has very limited information on headphone tube amplifiers. So I have decided to help fill the gap and hopefully inspire some other builders and audiophiles. The build I have chosen is the “Millett Starving Student Hybrid Tube Amp”. Reasons being, it’s cheap (can be easily done for less than $125 for all materials except tools), sounds great, has a simple circuit and has an almost cult like following. Online support for this amp is huge, which makes questions and troubleshooting a lot easier.
There is a surplus of information about the schematic and how to wire the circuit online. So I will attempt to give you the resources about the building process excluding the schematic.
I would like to thank Pete Millett for his development of this amp and schematic. He is a brilliant and generous man and deserves credit.
Pete Millett’s original post:
Bill of Materials:
Step 1: Picking Your Components.
Now lets look at materials. Here is the standard Bill Of Materials (BOM).
My amplifier uses the exact same electrical components as above. However, I wanted to go above and beyond for sourcing an enclosure, heat sink, tubes and other materials not involved in the electronics. It was important for me to achieve an overall look that fit my tastes.
While looking at pictures, I became increasingly unimpressed and decided that there had to be a better enclosure option out there. After much distress I found what I finally was looking for. Hammond makes an enclosure designed for DIY guitar pedals that’s already polyester powder painted! It’s perfect. I then moved onto the heat sink and found one that fit the bill. Finally some awesome classic switches, aluminum milled knob and some sweet input/out connectors.
Heat Sink Mounting Grommet:
This site has some cool connectors and tube sockets:
Step 2: Drilling, Don't Scratch the Paint!!!
Step 3: Time to Wire.
Some tips include:
• Braid or twist your input cables off of the RCA inputs. Braiding/twisting helps to eliminate any RF interference.
• Braid your LED runs into the tube sockets. For some reason the negative lead picked up some RF interference when near the tubes. Braiding the leads solved this issue.
• Check for shorts. A couple of times I fired up the amp in the preliminary phases and I would get clicking or dead silence. It was a short every time. One loose strand of braided cooper wire touching a resistor or something stupid. More than likely the error is human, the chances of a failed resistor or MOSFET are incredibly low.
• Use the optional resistors from the Dsavitsk schematic; they help eliminate humming and background noise.
• Lastly, keep your runs as short as possible. Audio circuits are finicky.
So, is the heat sink really necessary? Yes, the MOSFETs melted my plastic breadboard after less than a minute of use. Those guys get hot. You don’t want to melt your MOSFETs and risk destroying your circuit.
The added LED’s were a must for me. I love the way that they look. The tubes do glow, however they’re hardly noticeable unless you’re looking for the filament. Plus the LED’s allow seeing if the circuit is on/off. I also added an additional switch just to turn the LED’s off and on. If you are wiring in the LED’s, make sure to use a resistor rated for the voltage drop. The power supply is 48v, that’s a big drop down to 3v to power the LED’s. The resistor needs to be able to dissipate that wattage. Use a resistor calculator to calculate the wattage rating needed for your resistor (http://led.linear1.org/led.wiz). I used a resistor rated for 2 watts, well above what should be required.