Thursday, January 30, 2014

This Week on Things Done at Midnight...

I recently had a hankering for a pair of Superlux HD 681s, which are some of the best cans you can buy at the bag-of-rocks price-point (or, so the internet tells me).

But before getting into such shenanigans, I thought it'd be a good idea to have a decent amp to go along with them. I found among other designs, Pete Millet's "Starving Student" hybrid headphone amp, which, as its name implies, is meant for people like me. huehuehue.

Note: The potentiometer package is a placeholder as the real pot which will have wires that run to the front panel. 

Of course, the original Pete Millet design seems to have been so widely popular that the original tubes (19J6) are virtually gone from the marketplace, which helped spawn another version using the 12AU7 (The design I'm copying, which is available here).

I haven't been able to find any measurements for the 12AU7 variety, but the 19J6 variant has an impressively flat response, and the neverending head-fi thread about this object make this venture very promising.

Opting to do this on the classier side of things, I acquired a lacie hard drive case from James as the main casing.


The plan is to cut the thing to fit the depth of the PCB and then mount the board inside with some standoffs. Unfortunately, the case doesn't come with a slot for the PCB to slide in.  

The front and back panels are going to be lasercut - a decision based on my desire to avoid having to precisely drill out the corresponding holes for the power and volume knobs. It would also allow for the power indicator LEDs to nicely illuminate the interior of the amp. 

I realize that the hole for the rear power socket  is on the wrong side according to the countersunk holes. However, this won't matter since the countersinking will be done by hand after the basic shapes are cut out.

I've decided to add aluminum accents around the tubes to hid the edges of the tube socket holes.

I sourced most of my components from digikey to save on shipping, using mouser for the odd tandem potentiometer and a few knobs. The tube sockets are from ebay.

The total component cost came in at around $50 (~$70 if you count the enclosure and shipping),although you could very easily take off ~$10 by not buying fancy aluminum knobs and a two-pole rotary switch.

To be continued...

Sunday, January 19, 2014

Batteries, A Lack of Aluminum, and Mystery Boxes

Last time on ScooterQuest™(or rather, what I did during winter break), I finished assembling the 10S2P pack. 

HDPE on the work area helps prevent accidental shorts.

Recycled from two 6S2P packs floating around MITERS, it was originally wrapped in some forearm-sized heatshrink that was at one point cut in two and then rewrapped in electrical tape. Welp. 

Of course, the whole idea of having an uninsulated pack of LiFEPO4 cells crossed my mind well before I started, so I opted to heatshrink the thing in PET. 


The cheapest source being my preferred $0.99 beverage above. Note that the 20 oz. variety appears to be the perfect size for 2P packs. Further, starting with plastic that's already near diameter of your pack will yield the best results.

It's also important to heat the plastic evenly and to assume shrinkage at the edges by at least 1cm as to avoid gaps in your insulation. 

Following the advice of Charles, I made sure to route the balance leads on the side of the pack as to avoid a burny death. 

A wheel well-type object was folded then attached to the bottom panel of the scooter to keep debris from flying into the electronics. Given that it isn't a structural feature, it was made out of sheet aluminum and attached with screws to the bottom panel. 



Speaking of missing components, I quickly realized that I needed more aluminum to build the caddy assembly. 

Since the entire thing would have to be milled, I opted to save myself the trouble and do it on the CNC. This meant modeling the parts in solidworks.





The hella switch and battery connection have been integrated into the front panel for easy access. 

In other news, I recently came across this on kickstarter. 



Their instructable revealed the inner workings.

An ATtiny that turns on a few LEDs and plays noises when activated by a crude, but effective capacitive touch plate.

Oh, and it's powered by a USB wall charger with wires soldered to the AC prongs.

 ಠ_ಠ

Don't get me wrong: it's a fairly nice object, but there were a few key design qualms that kept me from purchasing said object:
  • Several box joints are used to keep the lid and bottom together, which, in the event that the joint fails, would cause the thing to plop out of its enclosure and expose an uninsulated AC line. 
  • It's too small to be a hanging lamp, yet too large to sit on a desk without taking up too much space.
  • It's too dim a light source to justify as a functional lamp
  • Aesthetically, the joint construction lends itself to having jagged lines. 
  • The silkscreen only looks good when the thing is on. 
  • For what's inside, $49.95 is ridiculous. 
And so, I spent the following evening sourcing parts and making a model in solidworks.


The question mark spaces will be filled with black or smoky acrylic. 

The current cube configuration is 3' to a side, making it a little bigger than a tree ornament (heck, it could probably be one too). 

Its purpose is to comfortably fit on a desk as an ornament providing a bit of extra light when needed.

To be continued...