Rock Out Without Getting Knocked Out

June 27, 2024 by Alexander Rowsell 20 Comments

It’s a constant battle for musicians — how to practice your instrument without bothering those around you? Many of us live in apartments or shared accommodation, and having to wait until the apartment is empty or only being able to practice at certain times of day can be restrictive, especially if you need to practice for an upcoming gig or if the creative juices start flowing and it’s 3 AM! [Gavin] was having this issue and started developing Porter, a guitar/bass practice device which works with all effects pedals and is portable and rechargeable. So you can grind away your epic heavy metal solo no matter the time of day!

While there have been similar solutions, many musicians weren’t satisfied with the sound and often couldn’t support inputs from distortion pedals. They usually chewed through batteries and were just not a great solution to the problem. [Gavin] has spent the last two years fine-tuning the design. It’s a fully analog design, with built-in rechargeable batteries to boot. So it not only sounds great, but it can last as long as your practice session does with a 15-hour runtime when fully charged!

Initially, the project began as a headphone amplifier but morphed into a design specifically for guitar and bass, with preamp and power amp stages and adjustable input impedance – 500kΩ for guitars and 1MΩ for bass. The latest revision also changed to a different power amp that further reduced THD and led to an even better sound. The schematics are up on the Hackaday.io project page, but [Gavin] is also hoping to do a crowdfunding campaign to get these devices out into the hands of guitarists everywhere!

Op-Amp Challenge: Compare Op-Amps, By Listening To Them

May 7, 2023 by Jenny List 31 Comments

In the world of audiophilia there are arguments that rage over the relative merits of particular components. Sometimes this can reach silly levels as in the high-end ALPS pot we once saw chosen as a volume control whose only task was to be a DC voltage divider feeding a pin on a DSP, but there are moments where such comparisons might have a bit of merit. To allow the comparison of different op-amps in a headphone amplifier, [Stephan Martin] has created a stereo amplifier board complete with sockets to take single or dual op-amp chips.

The circuit is based upon a design from the 1990s which as far as we can see is a pretty conventional non-inverting amplifier. It has an on-board op-amp to create a virtual ground, and three sockets for either two single or one dual op-amp to create a stereo headphone amplifier.

So the burning question is this: will you notice a difference? We’re guessing that assuming the op-amps under test are to a sufficient specification with a high enough impedance input and enough output current capability, the differences might be somewhat imperceptible without an audio analyser or the hearing of a ten-year-old child.

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Drive High-Impedance Headphones With This Stylish USB DAC

October 9, 2021 by Jenny List 3 Comments

For anyone with an interest in building audio projects, it’s likely that an early project will be a headphone amplifier. They’re relatively easy to build from transistors, ICs, or tubes, and it’s possible to build one to a decent quality without being an electronic engineering genius. It’s not often though that we see one as miniaturized as [daumemo]’s USB-C DAC and headphone amplifier combo, that fits within a slightly elongated 3.5 mm jack cover as part of a small USB-to-headphone cable.

The DAC is an off-the-shelf board featuring an ALC4042 IC, it has a line-level output and a handy place to tap off a 5 volt line for the amplifier. This final part is a tiny PCB with two chips, a TPS65135 that produces clean +5 and -5 volt rails, and an INA1620 which is a high-quality audio amplifier set up for 2x gain. All this has been designed onto a very small PCB, which sits inside a 3D-printed housing along with the 3.5 mm earphone socket. The result is a very neat unit far better able do drive high-impedance headphones than the output from an unmodified DAC, but still looking as svelte as any commercial product. We like it.

This may be one of the most compact USB-to-headphone amplifiers we’ve seen, but it’s by no means the first.

Headphone Amp Features A Tiny CRT

July 7, 2015 by Adam Fabio 40 Comments

[ErikaFluff] needed an amp for her Grado open cans. Rather than build yet another boring black box, she built what may be the most awesome headphone amp ever by adding a tiny CRT which displays the current audio waveform. She packaged all this up in a customized Hammond box which makes it look like it just rolled off the line from some audiophile studio.

The amplifier in this case is based upon the CMoy, a common headphone amp design. [ErikaFluff] added a MOSFET on the output to drive his relatively low impedance (32 ohm) Grado headphones with reasonable volume. The CRT is from an old video camera viewfinder. Before LCDs were advanced and cheap enough to include in video cameras, CRTs were the only show in town. These tiny black and white screens use high voltage to scan an electron beam across a phosphor screen just like their bigger brethren.

Since she was going with an oscilloscope style vector scan rather than the raster scan the screen electronics were originally designed for, [ErikaFluff] had to create her own horizontal and vertical deflection circuits. Horizontal scan is created by a 555 timer generating a sawtooth wave at 75 Hz. Vertical deflection is via an LM386 driving a hand wound impedance matching transformer. The high voltage flyback transformer and its associated driver circuit were kept from the original CRT, though repackaged to make them as small as possible.

You might think that having a few thousand volts next to a sensitive audio amplifier would cause some noise issues. We also worried a bit about shorts causing unexpected shock treatments through the wearer’s ears. [ErikaFluff] says there is no need to for concern — the signal is fed to the CRT circuit through optocouplers. The audio circuit is also electrically split from the CRT and runs on a virtual ground. Judicious amounts of shielding tape keeps the two circuits isolated.

This may not be the most practical project, but we think it’s pretty darn cool. The response over on Reddit’s electronics subreddit seems to be positive as well. We hope [ErikaFluff] is sitting down when this post gets published!