Monday, June 21, 2010

Vacuum Tube Headphone Amp

History of my hybrid tube headphone amp based on Millet "Starving Student" design.

I have a good pair of headphones, but my notebook lacks the power to drive the high-impedance of the HP speakers. I needed a new music listening device.

I spotted this web-page, and liked the design. Cheap too, so let's build it:

First, I got the 19J6 double-triodes from a collector, these components are older than me:

Then, I followed the schematics using a prototype board, and Point-to-point soldering:

The design is almost the same, switched some resistors, the capacitors are bigger for better bass response and used an IRF520 FET instead of the IRF510, because is hard to get them here in Argentina. The holes for the tubes were hard to make, but the end-result was fine:

The final assembly, using cat-5 wires for the connections:

Switched on and...only one channel work! fuck...lets do some hardware debugging then:

It turns out that the input cable was bad. The amp worked flawlessly from the start!

But the heat sinks were too hot. Lets do some calculations to see how many watts there are in each FET:

Each tube needs 19 V, .15 A (2.85 watts only for the heater!), the power supply is at 48 V, so the FET are dissipating the rest, (48V-19V)*.15A=4.35 Watts. There is no way that the small heat sinks that I installed the first time are going to dissipate that heat:

So I replaced them with a couple of motherboard north-bridge heat sinks:

Now they are still very hot, but will not catch fire... And they look bad-ass IMHO.

The amp sounded pretty good, zero noise and no distortion that I can hear. Drives my HD-650 very nicely. In this project I spent less than 300 pesos (u$s 80 dollars) and took me about 6 hours.

Power consumption: This amp is a beast, a relic from the past. Class-A, about 15 watts consumed *idle* for a total of maybe 100 mW max output. This machine pisses all over the environmental hippies:

Yeah, feel the heat whale! fuck global warming, I want my music. Why I don't just get an Ipod for my headphones? because ipods are for girls:

No way. Aqua sounds much better on my new tube amp, a machine for men.


Big brother is watching