Vacuum Tube Audio Amplifier – Update


Tube_Amp_Enclosure1Ever since I first completed this project I have wanted to build an enclosure for it. I wanted something that would decrease the risk of electric shock while also showing off the cool aspect of the vacuum tubes, ie. their characteristic glow.

In order to keep it simple I bought a sheet of aluminum that had a pattern of pre-punched holes in it at the hardware store. This allows the tubes to be ventilated while still being visible. I then made a template out of cardboard to determine what shape needed to be cut from the sheet of aluminum that could then be bent into a proper enclosure. I made sure to leave tabs on the sides so that I could secure adjacent sides of the box to one another with sheet metal screws. I then relocated the power switch to the top of the case and attached the enclosure to the wood base with screws. Overall I am fairly satisfied with this enclosure. It’s not the perfect case for a project like this since you have to remove the box to change burnt out tubes, but it is good enough for my purposes.

Tube_Amp_Enc23 Tube_Amp_Enc21About two months ago I made an enclosure for my vacuum tube amplifier. While a decent first effort, I became more frustrated with it as time went on. The poor nature of my design prevented me from accessing the tubes themselves as well as the speaker wire connection points on the main board. Also, esthetically, it blocked the view of the vacuum tubes too much.

Tube_Amp_Enc22Instead of starting over from scratch, I decided to try to reuse the existing enclosure. In order to solve my complaints with the previous design I came to the conclusion that what the amplifier really needed was a circuit board cover, not a full enclosure. To accomplish this, I shortened the enclosure by cutting off the back couple of inches of aluminum. This allowed access to the speaker wire terminals. Next I removed a couple more inches from the bottom, shortening the overall height of the enclosure. Then I cut out a rectangle in the middle of the top to allow the tubes to stick through. Finally I re-attached the case to the base board using six screws instead of four, the two additional screws in the front greatly stiffened the whole unit.

I am much more pleased with my second attempt at enclosing my vacuum tube amplifier. It is much more functional, as well as better looking.

Hard Drive Speakers

I first saw an article about hard drive speakers some time ago, but never thought about building my own until I saw this interesting project and decided to take a closer look. When I recently came into a pair of old hard drives, it was the perfect time to build my own set.

This is a very easy project to undertake. All that is required is to disassemble the hard drive (you will need some Torx screwdrivers) and solder two wires to the appropriate contacts on the hard drive’s read head. These wires are then attached to the speaker outputs of your amplifier (I used my vacuum tube amplifier to drive the speakers).

After playing with the finished speakers I found that if I restricted the read head’s movement by trapping the speaker wires between the two magnets at the base of the head’s armature (as shown) the speakers would produce much cleaner audio. By restricting the read head’s movement I prevent it from vibrating against the platters which can cause annoying scratching and rattling sounds. The downside of this is that you can no longer see the head’s armature move with the music, which is a pretty cool effect. Regardless of how you construct your own set, hard drive speakers sound best with music that contains a lot of treble. Check out the video below to hear how my speakers sound playing some Bach.

Arduino Punk Console 8 Step Sequencer

APCAPC-faceThe arduino punk console is a simple tone generator that is capable of making some cool audio sequences. I’ve always enjoyed playing around with different audio equipment (see my analog synthesizer) and this looked like a cool project when I saw it on the Make Blog. It is a fairly straightforward project that uses an arduino to handle all of the switch and potentiometer inputs and generate the tones. What is especially fantastic about this is the flexibility afforded by having a reprogrammable controller instead of a hard-wired sound generator. That said I haven’t modified the original code yet.

APC-insideWhile the original project was good (see also this Instructable), I made the following changes for my version of the arduino punk console:

  1. Eliminate the LCD screen – I wanted to make my version as cheap as possible and I thought the LCD was somewhat unnecessary for a simple project such as this since it doesn’t display very valuable information.
  2. Scratch build the arduino board – Similar to other DIY arduinos (see here & here) I’ve done before based off of the Boarduino design, I had the parts and building it myself cut the cost of the unit.
  3. 9V AC adapter power – I have found it is much more convenient to power many of my projects with an AC adapter instead of batteries as it saves having to access the inside of the unit for battery replacement and the portability provided by battery power is rarely necessary.
  4. Substitute 5K ohm potentiometers – I’m not sure why the original project used 100k ohm potentiometers, but I had a bunch of 5k’s around and they worked fine.
  5. No speaker – I was planning on using an external amplifier so I replaced the speaker with a mono 1/8″ audio jack.
  6. Eliminate the volume control potentiometer – Again, because I am using an external amplifier I don’t need another volume control.

Check out the video below of the sequencer in action:

Vacuum Tube Audio Amplifier

tube_amp1tube_amp2I have been somewhat interested in vacuum tube projects for awhile now after I refurbished an old AM radio from my grandmothers house. Although a simple project, involving cleaning the radio and replacing the old tubes with new ones, I think the main draw of a tube project is that distinct retro feeling you get when you fire up the project and it starts glowing, but in a good way. While looking around for a simple, beginners tube project I stumbled upon a fairly large community of people who had built and subsequently modded the K-502 audio amp kit from Antique Electronic Supply.

I purchased the kit and built it in a couple of hours. It is a very simple project to complete, consisting of only about two dozen parts. I had originally planned to assemble the kit in an enclosure, but my final assembly behaved poorly (I think in part due to improper grounding). I reassembled the parts on the pine board which comes with the kit and it now performs flawlessly. The amp takes a standard left and right RCA style audio input and can output up to 8 Watts of power. This may not seem like much, but with efficient speakers it gets loud enough for any common usage around the house.

I would still like to put some sort of cover over the board to minimize the risk of myself or others from coming into contact with the line voltages present. Although not the most inexpensive kit out there (compared to some solid-state kits), it is cheap compared to other tube based audio amplifier kits which can run upwards of $300. Definitely a fun project, especially if you need an extra audio amplifier.

Analog Synthesizer

synthesizer2synthesizer3I have been interested in synthesizers since I first started becoming interested in acid/new wave rock when I was in middle school. Analog synthesizers particularly interested me because they are easier to build and also cheaper, as well as having a lot of nostalgia for the original form of sound synthesis. Consequently when if first ran across the circuit board being offered at Music From Outer Space, I was very excited. The board is not only relatively inexpensive, it is also well made and was shipped very quickly. My synthesizer, pictured below, cost around $100 to make because I had to purchase the majority of the parts as well as the case. I purchased most of the parts and the case from Mouser, except for the potentiometers and the switches which I bought from Jameco. The construction of the board was fairly straight forward and took a few hours. The wiring of the board to the faceplate, however, took several ours of tedious wiring which I would not relish to repeat. In the end though I ended up with a great little unit which works great and can produce a variety of sounds. As can be seen from the photos, I also installed the mod which allows the modulation of VCO-1 with VCO-2’s output. I rearranged the faceplate accordingly to fit on my case’s aluminum plate. I had no alignment issues with the unit and it worked from the first time I turned it on. In the future I may build an audio amplifier as well as a sequencer to control the oscillators and actually produce music as opposed to just noises.

synthesizer4I had been looking for some time for a way to modify my analog synthesizer project to be powered by an AC adapter instead of the two 9 volt batteries that it had originally been designed to use. This was more complicated than it sounds since the synthesizer requires both +9V and -9V from the same power supply. After some investigation I found a circuit; that could be used to transform a single +9V input into both +9V and -9V. It is a really clever design that accomplishes this feat using a special charge pump converter IC and a couple of capacitors. As the pictures show I also changed the power switch to one that is more aesthetically pleasing than the toggle switch used previously. I also added a coaxial power socket to the back panel to accept the plug from that AC adapter. The synthesizer performs the same as it did before my modifications, however, I am now freed from having to worry about battery life.

Shortwave Regenerative Receiver

regen2regen1This project is a great way for beginning builders to hone their skills at circuit construction. The receiver plans were originally printed in a September 2000 article in QST. I built mine from scratch, not on a printed circuit board, with no ill effects due to strange parts placement. The author provides very good advice about the audio/volume and regeneration controls placement and hookup (by being careful, no shielded audio cables are necessary). Since I used a large value tuning capacitor from my junk box, I added the optional fine tuning control to add better selectivity to my receiver, which is very helpful when tuning. By following the author’s recommendations about how to assemble the receiver the average builder should have no problems with this project. When in doubt, the provided voltages on the schematic are a handy way to test your completed project.