Thursday, January 8, 2015

Koss Pro4AA headphones and a 6AS7 based amplifier

The Koss Pro4AA headphones paired with a 6AS7G based amplifier I built.

I built this amp using the chasis and power supply from an old Heathkit A7 amplifier. The output transformer is fine if anyone wants to make me an offer. The schematic is similar to Aren van Waarde's found here. My power supply is different, a 5Y3GT rectifier is used in place of the pair of 1N4007 diodes he specifies. This wasn't done out of a desire for better sound. Rather, I intended a softer start for the high voltage and glowing tubes are a delight so why not use one more eh?

*this was supposed to be an amazon review of the headphones but their site is giving me grief so it gets posted here:
Excellent sound when driven with a decent source. Playing back a FLAC recording through an Audigy 2 seems to be weak on the bass. Using a separate headphone amplifier after the sound card was great without any eq changes needed. I originally bought these for their high input impedance (250 ohms) to be used with a 6AS7/6080 based OTL tube headphone amp I built. I'm happy with how it all turned out.

They're fairly heavy though well built. The headband is not designed for people with large heads so over prolonged use the plastic ridges at the base of each side of the headband do dig in a bit. The ear-cups are great, I like pleather pads and these ones are sized and stuffed the right way. The cord is chunky, this is a good thing for stationary listening but don't expect these to be great on the go. The warrenty service offered by Koss is legendarily good so I'm confident on enjoying these for years to come.

Monday, December 24, 2012

I quit!

A while ago... Half way through August 2012 I had my last day at work and headed off into the sunset. A vacation was in order so I packed everything into the Subaru and my girlfriend and I headed to Vancouver island for 10 days of exploration. Strathcona park has a healthy mosiquito population, easily discovered at any of it's beautiful forest service campsites. Other sites of interest include the McLean steam powered sawmill museum in Port Alberni which was awesome and China creek campsite which I thought was going to be a remote getaway but turned out to be a sea of RV's and boats.

After this break from this city I returned to begin.... five years of school! I am going to become an engineer, not sure which branch is the most interesting but I'm leaning towards electrical or mechanical. I settled on Capilano University as they have a solid engineering transition program (rusty math skills need a refresher) and still cost a bit less than UBC. When I got there I discovered there's no club for people who build things, so I started one.
It's going well and I've started getting kits together to run some basic microcontroller mini-workshops. My classes have been mostly enjoyable and I managed excellent grades the first term. The spring term begins January 7th with a chemistry lecture and I can't wait.

Monday, June 4, 2012


ZAAAAAAP! It works! I found this coil in storage, after replacing a few caps and cleaning up the wiring I got it running. Nice and loud...

Friday, April 20, 2012


It's happening! The background radiation of the universe is all around us and this fully operational cloud chamber visualizes it.

The apparatus has been on the floor for several weeks now with fairly solid performance. I had to rip out a fair amount of rotten material and rebuild. This:
became this:
Add lights, it's getting there:
when if in Rome (verticle mill; perfectly fit wooden braces):

All told that was about 60 hours work, $400 in materials and an $800 bill from the refrigeration service tech for the one part of the job I couldn't do (there was a slight coolant leak in the condensor assembly).

Thursday, January 26, 2012


Happy new years! 2012 is off to a quick start. Some projects have been finished just in time for the Christmas break, others seem to drag on indefinitely.

I was asked to make a statistics readout that updates important facts in real time. After looking around online I ended up picking the wrong display for cost reasons. I went with a commercial LED sign ( intended for use at a restaurant or shop that is to be programmed once and forgotten. While it had the serial port I was looking for, the manufacturer never intended it to receive live data. I ended up using Advanced Serial Port Monitor to figure out the programming protocol used when loading messages with the included PC software. After making a table of message components I set to getting an Arduino talking to the displays. Luckily they are addressable so I had a common serial bus sharing the hardware UART. After much fiddling it was done; the Arduino loads in 90 'messages' at a time which the display slowly rotates through until it needs another set of numbers. Not elegant but it worked.

Also in the new gallery; "Every 10 Seconds" an interactive exhibit about just how much gets consumed every ten seconds. Guests are asked to hold the button down for as close to ten seconds as then can. A statistic is then multiplied by their time and displayed ie; "Your time was 9.845 seconds, in that time North America consumed 78439 barrels of oil." This exhibit was created with a small form factor PC connected to an Arduino. The graphics were created using Adobe Illustrator and loaded in a PC application written in Processing. The case is rolled aluminum with supports welded inside. It was powder coated by a local shop an assembled on site. The top plaque is MDF with a vinyl graphic applied, it turned out all right but next time I would not have the printers be the ones to apply the graphic, the curved edges did not turn out so well.

My next favorite project at work will be the recommissioning of a cloud chamber. This thing has sat in storage for a decade and is exactly the sort of device I love working on. Combining high voltage, compressors, control loops, German and alcohol; the thing produces a fog of ethanol in which subatomic particles can be visualized.
It first came to the center in the early 90's from a shop in Germany specializing in scientific apparatus. Basically, an 80 x 80 cm plate of copper is chilled to - 20°C and alcohol is vaporized onto it forming a super saturated 'cloud'. Background radiation passing through this cloud causes ionized trails to become visible to guests staring into it.

To left; the electronics panel. Below; the compressor and condenser coils used to chill the plate.

My current personal project is an automotive control system. The focus is on getting a useful lambda sensor reading but extra I/O is provided for connection to other sensors and actuators. The device below is the results of my crappy welding job; a tailpipe O2 sensor mount. This will let me test out the sensor interface board without cutting into the existing exhaust system of my car.

Wednesday, September 21, 2011


Time marches on! I've been bad about updating my blog but hope to get into a weekly habit..
What's happened in the last few months? Well after months of prep, Vancouver had it's Maker Faire. Above are the rock stars responsible. (though two excellent people and a whole slew of volunteers are in fact missing form this photo)

I was lucky enough to be involved in the 2011 Illuminares festival. This fantastic yearly event has puppet makers and performance artists gather together for a night of incredible sights and live music. My small contribution was the lighting and sound systems for a giant heron puppet as well as some RGB LED controllers for a number of glowing columns. Lessons learned included;
-always buy about %15 more stock then needed when making wiring harnesses, especially if you're getting volunteer help
-lead acid batteries aren't happy discharging at even 1/2 their amp-hour rating (ie; a 5 Ahr will see a serious voltage drop if 2.5A is drawn) and this gets worse in cold weather
-don't let feature creep carry you away to the lala land of unachievable goals...

Thursday, June 9, 2011

Pneuman works!

Control system changed to a PLC, optical encoder changed to a sealed industrial unit from Omron. Still plenty of work to do but it's running!