[Simon] wrote in to tell us about a headphone tube amp that he just built. It is based on schematics at diyaudioprojects.com that were actually featured on Hackaday in the past. [Simon's] design adds an on board regulated power supply and a volume control for the input. Effort was made to keep the PCB single sided to facilitate making this at home.
The 12AU7 is popular due to its ruggedness and tolerance for low operational voltages. This amp design uses a plate voltage of 12, although the 12AU7 can handle up to about 330. Since the 12AU7 is of the Twin Triode variety, one tube can be used to amplify both a left and right audio channel.
The case for the amplifier is laser cut plywood. The top piece is kerfed so that it can bend around the radii of the front and rear panels. The top also has a hole cut in it to allow the tube to peek out through.The pieces look nice but, unfortunately, he doesn’t show the case and amp in an assembled state.
If you’re interested in building one of these, [Simon] made all of the Eagle and Case files available. The total cost of the project was £25, about $43 US. To learn more about how tube amplifiers work, check out this Retrotechtacular from earlier in the year.
Headphone amplifiers make for simple, practical electronics projects. The Bass Bump Headphone Amp is no exception, since it’s made out of easy to source parts, and can be built on a proto-board.
We’ve seen many variants of the classic cMoy amplifier, including this pretty one. The Bass Bump differs by providing control over bass frequencies. It does this by putting a filter in front of the amplifier, with a potentiometer to select the mix of frequencies. This goes into a LM386 audio amplifier. At the output is a Zobel network to keep the impedance low at high frequencies. The amplifier can be powered from either a 9V rechargeable battery, or a USB port.
It’s a simple build, but definitely a good one to try on a rainy day. The write up explains how the analog circuitry works, and gives you full instructions on how to build it. After the break, check out a video overview of the project.
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[Jesse] sent in this headphone amp. It’s really just a board with a dedicated smd headphone amp chip(MAX9725) and a pair of smd caps recycled from an old hard drive, but it does job. I think the goal is to boost low signals rather than the usual audiophile quest for cleaner tunes.
Every so often, I like to check out the headphone amp scene at [headwize]. The headphone lovers there never seem to stop. This little amp is one of the latest creations. The latest is the mini v3 – it reflects a trend I’ve been seeing on homebrew hardware: SMD core chips and through hole components for support hardware. A 9 volt supplies power, and a pair of linear regulators. It’s a nice simple, solid design – and you’ve gotta love the thumb screws. (I’m not sure how a more efficient PWM regulated power source would affect the audio output)