[Tristan Chambers] picked up an old speaker box some friends acquired at a yard sale. It didn’t have any inputs, and there weren’t any tuning knobs like a radio would have, so it’s a mystery what this was originally used for. [Tristan] traced out the circuit and figured out where he could input audio signals which allowed him to hook up an iPod, but it was mono and not very loud. He ended building his own vacuum tube preamp from a schematic he found on the Internet so that he could use it with an electric guitar. As the video after the break shows, the box not only puts out some pretty good sound but it’s nice and loud too.
amplifier138 Articles
Making Mobile Audio Work At Home
[Nikita] made a great find while cleaning out his garage: a set of audio amplifiers from a 1986 Volvo. After a bit of testing, he dislodged a stuck relay and set out to use these amps for a home audio system. He grabbed some left over brackets from his TV mount and used them as rail mounts. On the back he wired standard speaker connectors and RCA connectors to the wiring harness for the amplifiers. The final aspect is powering up the device, for which he used his ATX psu previously modified as a bench supply. 130-Watts of power for the cost of a few connectors.
We surprise to find we haven’t covered this common ATX bench-supply conversion before. What we have seen is an adapter to use one as a bench supply.
Amplifier Built Inside A 9v Battery
It’s pretty creative to use a 9v battery as an enclosure. That’s what [Osgeld] did when building this amplifier. There are several advantages; they’re easy to find, it keeps a bit of the dead battery out of the landfill, and this method provides a built-in connector for a 9v power source. In this case the circuit is built around a LM386 audio amplifier. It’s glued to the back of a potentiometer and wired up with the other components for a package smaller than a quarter. A stereo jack reside in the side of the battery case with a cable and alligator clips for connection with a speaker. Now the amp can be quickly connect to any 4-8 ohm speaker.
Center Speaker Amp For An IPod
A few weeks ago we saw [Jaroslaw’s] universal credit card spoofer. Now he’s sent in a project that incorporates an amplifier into a center speaker for use with an iPod or any device with an audio jack.
The build has two main components; an LM4950 audio amplifier and a center channel speaker he picked up for $3 at Goodwill. The circuit used is straight from the datasheet and he’s provided the four necessary resistor values for you in his writeup. An old set of headphones was butchered for the audio connector and DC power can be provided by any 6-12V source.
The final circuit was built on some protoboard. The speaker housing has plenty of room to fit everything in for a nice finished look. Pretty simple, and except for the IC, this should be an easy salvage project for most folks.
Electronic Stethoscope
[Vik] sent in this simple little project. He purchased a $3 spy ear, a simple 3 transistor amplifier, and attached a stethoscope end. Little modification was necessary, mainly just scraping a bit more space in the microphone tube. The end result is a super cheap electronic stethascope that can be hooked to a computer or other speakers for multiple people to listen to.
Using VFDs As Amplifiers
[HP Friedrichs] sent us this cool writeup on how to use scrapped Vacuum Fluorescent Display tubes as amplifiers. For those unfamiliar, a VFD is a display device common to electronics. Many have been replaced by LCD, but you can still find them in modern products. [Friedrichs] points out that his 2008 ford has a VFD for the multimedia display.
Since these units are basically tubes, he figured that you should be able to use them as a tube amp. After some testing, he found it to be quite adequate. The project includes tons of background information on how tubes work, how VFDs work and how to utilize it for amplification. In the picture above, you can see him using one (middle) to amplify a home made radio (right).
Hacking The MINI Cooper
[war6763] sent us this hack to power an amplifier in a MINI Cooper. Apparently, aside from being unconventionally handsome, they’re also unconventionally wired. Amplifiers are generally wired to the ignition or stereo and turned on when the car is turned on. Due to some strange wiring, this just isn’t possible in the MINI Cooper. Some people use the cigarette lighter to power on their amplifier, but [war6763] wanted something that left his cigarette lighter free for other things. He built a circuit that monitors the cars built in USB input line and turns his amp on and off accordingly. The entire unit cost around $10.00. You can see the video demonstration after the break.