Log Guitar Uses Tube As A Bridge, Actually Is The Blues

In the never ending quest to replicate the tone of depression-era blues records, [Valve Child] managed to build the most backwoods guitar ever seen.

The body of [Valve Child]’s slide guitar was taken from the limb of a red gum tree felled during a wind storm. After taking a chainsaw, router, and sander to the guitar, [Valve] sealed it with linseed oil.

The real beauty of this build comes from the bridge and electronics: the pickup is made from six stacks of magnets encased in hot glue and wound with enamel wire. The bridge of the guitar is actually made from a 6GM8 dual triode. Not only does this provide the guitar with a wonderful brassy sound, the tube serves as a wonderful low-tech preamp when powered by a 6 volt battery.

The three strings on the guitar are tuned DAD, perfect for the likes of [Robert Johnson], or, for the younger kids, [Jack White]. Surprisingly, [Valve Child]’s guitar actually sounds really good. as heard in the video demo after the break.

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[Dino’s] JFET Guitar Preamp With Piezo Pickup

This week, with a little help from a Roomba, [Dino] built a guitar pickup and preamp that sounds marvelous. A pickup takes vibrations from the guitar and turns them into an electrical signal which can then be amplified and broadcast. He grabbed a long-dead Roomba which has slowly but surely been donating its organs for his weekly projects. After plucking out a piezo element he grabbed a bag of Junction gate Field-Effect Transistors (JFET) and built a preamp circuit around one of them.

JFETs operate in much the same way as MOSFETs (which we took a look at last week). [Dino’s] design adds a few resistors and capacitors to tune the gain and decouple the circuit from the input and power rails. He epoxied the piezo element inside the guitar and connected leads between it and a jack mounted in the body. As always, he does an excellent job of explaining the concepts behind the design and outlining the build techniques that he used. We’ve embedded his video after the break.

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Quick And Easy Audio Preamp

npn_transistor_audio_preamp

The most recent installment of [Dino Segovis’] Hack a Week covers the construction of a simple NPN transistor audio preamp. Some time ago, he built a small audio amplifier using an LM386 which worked well, but didn’t quite get his music as loud as he would like it. He decided to build a preamp to complement his amplifier, and demonstrates how you too can build one with just a small handful of components.

As the name probably suggests, the cornerstone of this amplifier is an NPN transistor. He explains that a forward bias is applied to the base-emitter junction, which results in the transistor operating halfway between its cut-off and saturation regions. Both halves of the input audio signal are superimposed on this bias voltage, resulting in a decent amount of gain across both channels from a relatively small package.

The preamp isn’t going to win any awards among audiophiles, but it is definitely a great beginner project. Its a novel way of demonstrating how transistors work, while producing a useful takeaway piece of audio equipment at the same time.

Continue reading to see a video showing just how big an effect [Dino’s] NPN preamp had on his music.

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Build A Tetrahedral Ambisonic Microphone

[Dan Hemingson’s] been refining a design for building a tetrahedral ambisonic recording system. This is a set of four microphones used to record audio that can later be mixed down for a three-dimensional listening experience. His goal is an easy and inexpensive build while maintaining the highest fidelity standards possible. Lucky for us he’s made a set of extremely detailed build instructions you can use to make your own. In addition to the mounting bracket seen above he has also developed a pre-amp module that connects to the four mics; it’s part of the build instructions with schematic and board layout files available as well.

[Thanks Isaac]

Tube Preamp With A Dazzling Wood Case

It’s been a while since we’ve looked in on the world of vacuum tube audio equipment. [Bruce] just finished documenting a tube preamp he built. He actually made a couple of these with slightly different cases but they use the same circuit design. We found his discussion of common errors made when tying into ground quite interesting. It seems that many folks struggle with noise in their circuits because of ground loops. There’s some details about isolating the signal ground from a metal chassis, and also an admonition about not connecting the input or output jacks directly the chassis.
If you like this, don’t miss on of our favorite tube projects, [Bruce’s] Poddwatt.

Headphone Tube Preamp Kit

If you’re curious about tube amps but don’t have a firm enough knowledge base to dive right in you might want to try a kit. [Mark Houston] reviewed one such kit and we enjoyed reading about his experiences. It comes with everything you need save soldering tools, an enclosure, and the final connectors ([Mark] used RCA connectors). There is a full schematic available and the assembly instructions take you through tube matching and using that piece of copper coil you see in the picture to wind your own inductor. Consider trying this primer before you jump into building a single tube, multiple tube, or an amplifier of your own design.

[Thanks Gio]

In-cable Guitar Preamp


[Bryan] sent in this old but excellent guitar cable hack. [J. Donald Tillman] managed to fit a fet based pre-amp inside the 1/4″ connector of a guitar cable. It’s phantom powered – so it’ll leach power from the sound board/mixer. I’m just impressed that he fit the thing inside there.

On a side note, This is the kind of crap that gives hackers a bad name. I hope the jerks behind it end up as Soylent Green.