Tuesday, October 13, 2015

Restoring a set of Blonder-Tongue Audio Batons

A long-ago project, these two Blonder-Tongue Audio Batons were a complete teardown and refit, as best I could make them with limited parts. These were one of the first active audio EQs, and used 12AX7 vacuum tubes to provide 9 bands of adjustment.

These units were purchased from a seller in Antique Radio Classifieds, as-is, not working. And not working they were. Someone had punched out several of the potentiometers to put more tubes on the chassis. The wiring and components, already old, was hacked up beyond recognition. One of the units was missing it's case, and had only a few of the signature spiral columns for the adjustments.

The only thing I could do was a complete teardown of the chassis. Everything except for the terminal strips and the transformer were removed. The holes in the front were repaired by soldering washers with the correct inner hole size into the chassis, so pots could be remounted. All new components were purchased - Orange Drops, Nichicon, and IC capacitors, metal film resistors, new tube sockets and the best quality pots I could get my hands on were placed into the chassis. Filament wiring was all twisted to reduce noise. I wound up with a layout more compact than the factory one, although not by much.

Since I didn't have a case for the one, I re-purposed a SESCom rack-mount chassis for it. The chassis fit in nicely, and I moved all the potentiometers to the front panel. These were placed in an arc, two VU meters flanking, and a dim green pilot in the middle. The other unit, it's case in moderately good shape, was left alone save the addition of some band labels where the previous owner had attacked the front panel with a scraper.

I added some circuitry to handle the VU meters, and a centralized switch to allow both units to be turned on from the rack chassis. All audio and power routed through the larger unit.

I was really pleased with how they turned out, but I really didn't have room for them and ended up selling them to a studio a few years later.

 I took a number of pictures beforehand, but, being pre-digital, I seem to have lost some of them. These two, a bad shot of the original case and the chassis/VU meter unit, are all I have left. I'm hoping to find the person I sold them to, I'd like to get some more shots.

If you have these, please contact me. I don't want them, just photographs if they are still like this.

Thursday, September 10, 2015

Spectrum Analyzer Display Driver Board.

Another board from my Spectrum Analyzer project, this was supposed to be the display driver.

I had originally intended to have a dedicated right and left channel, and a scanned 10 channel audio analysis function for the various frequencies being monitored.

The project used LM3914N bar/dot drivers recovered from another device, as well as recycled board and 10-turn trimpots from a hamvention purchase. I got as far as this before shelving it.

Eventually, I did build something with one of the LM3914Ns, a single audio level meter using fluorescent tubes. It was created for a friend who was "going to open a club." I'm sure it's still in it's box, somewhere...

Monday, August 31, 2015

An old Audio Spectrum Analyzer project.

Several years ago I had a rack of stereo components that I had collected over the years. Tape deck, FM unit, dedicated amps, CD player, the works. I always though it would be kind of cool to have a nice analyzer unit for the audio. Instead of buying one, I decided that I was going to build one using some already designed circuits and some interesting displays.

I had originally intended to use what I've heard called "Pinball Displays" recovered from old HP equipment. Instead of (expensive!) Nixie Tubes, these were just neon bulbs inserted into an array marked 0-9, which lit up to indicate the digit. I had planned on replacing the neon bulbs with multicolor LEDs. 10 channels of bouncing lights with the option to have rectified outputs to drive analog meters.

The analyzer channels themselves were simply copied from a consumer unit that was available cheaply. The rest of the circuitry, including the precision instrument rectifier board and dot-driver was adapted from reference designs. Everything was going to be mounted modular and connected with DB connectors for easy installation and removal.

One side of the 10-channel filter board and it's accompanying precision instrument rectifier board:

However, like a lot of things, it changed. My audio rack gave way to a laptop with a good DAC, which gave way to a streaming audio device connected to a remote network share. All of that old equipment simply became dead weight, and was either sold, or donated because it no longer held value.

I was never able to get enough of the displays to complete the project, and other things like 1N34 germanium diodes became harder to find. I decided to shelve the project shortly after selling off the audio equipment, and I've been trying to figure out what to do with these things ever since - beside just using them as a talking point on job interviews...

Wednesday, August 26, 2015

Cheap crap bought online, and how to fix (some of) it.

I've always had a few alarm signs scattered around the place, but they've faded to the point of being useless. So a few summers ago, I decided to get some new ones. These signs included a nice little solar powered LED device that you could attach to the sign's pole to illuminate it at night. Cool little things, they lasted all of a season before quitting.

The units are held together with 4 poor quality screws that had almost rusted to nothing. A rubber plug covered the switch. State of the fasteners notwithstanding, everything was still doing it's job of keeping the case sealed and debris free.

It's a simple circuit, the solar panel trickle charges the battery. A transistor turns the LEDs on at night, and I assume keeps the battery from discharging through the panel. The blue-topped switch turns the entire assembly on and off.  This switch appears to be my problem.

I was able to jiggle it with the rubber seal off, and get the LEDs to light once more. Since it doesn't appear to be corroded, I'm guessing the thing is just of poor enough quality to not work. I could care less about turning it on or off, (why is this even needed? Who knows?) and the fix was to solderblob the pins together.

No more problems with bad switches, and something that should not have been there in the first place was fixed. My signs are lit once more.

Monday, August 24, 2015

An outdoor sensor, built on the cheap.

A while back, I wanted to start adding some temperature sensors to my place. The eventual intent is to tie it all in to a control system of sorts. Eventually...

I looked at a bunch of different ways of reading data. The Raspberry Pi was the logical choice, since it supports a lot of different input methods right out of the box, including 1-wire devices. I eventually settled on a commercially available product designed for data center monitoring that I was able to purchase on the cheap from an auction site. It has a whole host of inputs and outputs, and has a built in alarm and email server, all in a nice rack mount case.

Since this thing is targeting commercial customers, the sensor prices are commercial prices. Expensive! But all the components they use are just standard 1-wire devices in special packages. Their outdoor sensor is around $100, which is too much for a hobbyist.

I set out to replicate that outdoor sensor. I disassembled one of the other sensors received with the original purchase (it was dead) to see how they wired it, and got to work.

Materials needed:

  • A Maxim DS18x20. I used DS18S20 to maintain compatibility with my device.
  • Some cable and connectors as needed. I used 4-wire telephone cable.
  • A thin metal tube, cut to about 1.5" or so, cleaned and deburred. Size for your sensor.
  • A cap to fit the tube.
  • Some heat shrink tubing.
  • Two-part epoxy. You may need to experiment to find epoxy that doesn't corrode your leads.
  • Tool Dip.
  • Some sort of mount.

  • Solder the cable directly to the sensor's legs. You'll want to have heat shrink on the wires to slide up afterwards. Make sure all the joint are clean and solid, and shrink the tubing on.
  • Put your cap on the tube and slide the assembled sensor into the tube. Ideally, you'll want to have the outer jacket protruding from the bottom of the tube. Use heat shrink as needed to provide protection for the cable jacket as needed.
  • Fill the tube with epoxy and allow to cure. 
  • Place another piece of shrink at the bottom of the tube to hold the cable in place, if needed.
  • Dip the entire assembly in Tool Dip and allow to cure.
To mount the sensor, I used a simple stainless hose clamp. Nothing fancy, but it holds the sensor tightly and keeps it out away from the mounting surface.

I'm guessing there is some small delay in the sensor's reading, due to the mass of the material around it. It's not terribly important in my application, and this setup has been working flawlessly for the past few years.

Total cost was probably $10, and could be cheaper depending on how well stocked your junk box is.

Sunday, August 23, 2015

My first production board

One of the projects I've been working with is an interface board for an embedded computer system. While I've never designed anything like this before, I've worked with board for 20+ years and have a decent idea of how things should look. The board was designed in NI Multisim, and routed with NI Ultiboard. Both of those tools were unfamiliar to me, so I learned how to use those at the same time I learned how to lay out a board.

It's of moderate complexity, but is doing quite a bit:

  • Provides power for the CPU and on board storage drives
  • Brings a SATA port up for easy access and offers two choices of storage
  • Provides customer USB ports, so they don't have to plug directly into the CPU
  • Provides several troubleshooting indicators
  • Buffers and provides ESD protection for customer-level serial outputs
In all, the most complex thing about this board was drawing all of the components from often incomplete or just plain wrong datasheets. But all said and done, this board turned out pretty nice for a first-time designer. I will admit to making a wiring error on the backside, but that's why we run a prototype before actual production. It's been corrected and all is working as it should.