Baltimore Hackerspace Member Designs Modern Tube Hi-Fi System

A member of ours has been hard at work designing a really sweet modern/retro hybrid audio amplifier with a built in media center.  It’s open source, hackable, and sounds awesome.  He’s currently running a kickstarter to kick off getting them produced.  You can check out the kickstarter here.  I asked Jason to do a little writeup on his experience building the amplifier, and tell us more of the details inside.  He shares his experience below;

My name is Jason Perkins. I am co-founder of Tubecore and joined Baltimore Hackerspace in May 2013. I joined wanting to learn more about CNC machining and needed a home to prototype a project I had designed. The project started out as a modern tube amplifier built into a bluetooth speaker, but what I ended up with was a bit more.

A month after I joined I had completed the first prototype for my modern Hi-Fi audio system. Unfortunately, a week later it was destroyed by a rogue CNC at a friends house. The machine is called Kronos, is DIY and is the fastest robot I have ever seen up close. Kronos has a jog speed of 14” a second and that’s how quickly Kronos killed Duo v1.0. I highly recommend Kronos CNC to anyone looking for a Pro Level CNC that can machine billet aluminum and is advertised as being accurate down to .001” (1 mil.), while free jogging @ 14” a sec. I also highly recommend kill switches, since topping out the -z axis is what caused it to scare the crap out of me.

After we extinguished Duo v1.0, I used the opportunity to redesign and was able to make some huge improvements to the Cabinet’s engineering, the system’s design and peak performance.

The cabinets are solid hardwood. In this case African Sapele. The cabinet’s 7/8” thick main body is four pieces cut and mitered from a single board with horizontal grain that is matched all the way around. The face of the box is a burl mahogany and requires 38 precise machining operations to complete and features safe zones where additional sensors and optical hardware can be added.

The drivers are 4” full-range, composite cone drivers with machined aluminum horns and santoprene surrounds. They live in their own sealed enclosures, which are hand tuned for L-R balance and peak performance. I find these little reference-class drivers produce a big sound; warm mids and screaming highs. They reproduce clear audio from around 125Hz to well over 20Khz and are crossed at 120.

To fill in the lows I sourced the world’s smallest long-throw subwoofer and dedicated the center of the cabinet to being a ported sub enclosure. Thanks to sapele’s high density, each driver enclosure is essentially it’s own isolated environment. At high volume the case has a solid bass response that is unmatched by anything it’s size. With the sub added, the Duo’s combined tuned frequency response is 40Hz – 20KHz; clean.

For amplification I used a tube hybrid design that supplies 100w to the full range drivers and 30w to the sub. Tubecore is open source and it is my goal to have the final schematics along with the cabinet face (safe zone) diagram online by January 2014 after we produce the initial order.


With two primary functions, the Duo is a modern tube hybrid audio system that is Bluetooth enabled and features an onboard XBMC media center powered by Raspberry Pi. The raspberry is ported to the back panel and housed internally within a shielded electronics compartment which keeps the amps free of interference.

XBMC is the world’s most popular open source media center. Many would argue that XBMC is the only thing you need plugged into an HD screen. I say it’s one of two things you need plugged into your TV.

The last feature is my favorite: the control knob. The top-mounted control knob is machined from solid aluminum and countersunk into the cabinet. It controls all of the analog features including, volume, power and source selection.

The control surface features a 3” diameter and responds to the slightest touch. No data for you, but it is smooth. I really enjoy being able to “turn up the music,” for a change.

All in all, I never could have finished this project without the space. To everyone that helped me with anything, thanks, it was all for this. We will know within 45 days just how popular the Duo will be and look forward to building many more.

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