Bose L1 Tower PA Repair

This is a repair of Bose L1 tower PA system. These skinny tower speakers are somewhat of a marvel because they are designed to stand behind the musician (aimed RIGHT AT the microphone) and don’t generate feedback. Ah, the miracles of DSP.

It turns out these PA’s have a frequent failure in their power supply. Read on for details.

1st generation Bose L1 tower PA system

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Tormach PCNC 770 DIY Enclosure

I recently got a Tormach PCNC 770 CNC milling machine. So far, I’m very happy with it (but have not cut much yet). I figured that since I wouldn’t be using flood cooling, that I could get away without a full enclosure. But even with mist rather than flood, chips were shot everywhere, so I decided to roll my own enclosure using 80/20 parts

There are lot of similar designs on-line, but the one I used most for guidance was by sauni68 on YouTube:

His was a design for a PCNC 1100, but his video still has several good tips that are appropriate for the 770.

Photo Feb 19, 4 47 45 PM

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TouchDRO Machine Position Digital Readout

This is a outstanding machine DRO for hobbyists, not just an outstanding DIY project, but a super DRO even compared to high-end pro setups. The beauty of TouchDRO is that it uses a (cheap) Android tablet for the display and control (I used a 1st-generation Nexus tablet – $50 on eBay) and then the scales connect to a small box that wirelessly sends data to the tablet via Bluetooth.

More info and pics to follow. Below are a schematic and a link to the TouchDRO website.

TouchDRO MSP430

TouchDRO Link:

This particular circuit is designed for quadrature-output scales only. It will not work with the cheaper Chinese “caliper” or other similar scales. Examples of quadrature output scales are optical scales and some magnetic scales. In my particular case, I used magnetic read heads made by Renishaw and linear magnetic tape that I purchased used on eBay.

Below are links to Eagle files for the above circuit. Note that you can get an MSP430 Launchpad board for less than building the above board, but I wanted a specific size with particular connectors for my read heads, so I made my own board and got PCBs made at OSH Park.

Eagle schematic:

Eagle PCB layout:

Or, if you want to just use my layout, you can order boards from OSH Park here:

Read heads are Renishaw LM10s off eBay for about $100 each. These are can be expensive, but I wanted the tiny size. I also got the linear magnetic scale tape off eBay.


Z-scale mounted. 0.25″x1″ aluminum bar with channel milled to hold magnetic tape and stainless steel cover tape.
X-scale mounted. Small overhang has to be to the front of the cross slide (rather than the back) to not interfere with the milling column.
Both X and Z read heads in fixed positions on saddle. No scale wires are dragged by the saddle or cross slide since TouchDRO sends position to the tablet wirelessly via Bluetooth. White wire is power to MSP430 & transmitter box.
MPS430 Touch DRO circuitry and Bluetooth module on OSH Park board fits in small plastic box.
Tablet holder before gray paint
2014-09-25 22.18.32
Tablet mount on the machine

Brass Rod Bender for Banjo Hooks

This is bender specifically made to put a very tight radius bend in 5/32″ brass rod for banjo hooks. The original design was modified from this:,8229.html  but required a few revisions to get the desired result. Finally, when I was able to force the rod into a tight radius bend, some would crack. I learned that they needed to be heated with a torch before bending, but don’t have to be bent while hot.

The key difference between this and the little universal bender (besides less “slop” and tighter-tolerance fittings) is the movable round die is a “cam” that can be pivoted (with a 3/4″ wrench) and forced tightly against the stationary die while the bend is being made.

This was also my first exercise with hardening O1 tool steel. There are tons of guides on line covering this topic so I won’t go into detail here. Having the working surfaces hardened may not be necessary for bending brass but I wanted to play with O1 steel and this was pretty forgiving applications for a first try. It went quite well.


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