Graphic Equalizer

No, you aren’t looking at a 30 year old Teac graphic equalizer that somebody modified. The MWA-002 Network Music Player created by [GuzziGuy] is built entirely from new components, and easily ranks up there with some of the most gorgeous pieces of homebrew audio gear we’ve ever seen. Combining modular hardware with modern manufacturing techniques, this 1980s inspired build is a testament to how far we’ve come in terms of what’s possible for the dedicated hacker and maker.

The enclosure, though it looks all the world like a repurposed piece of vintage hardware, was built with the help of a CNC router. It’s constructed from pieces of solid oak, plywood, and veneered MDF that have all been meticulously routed out and cut. Even the front panel text was engraved with the CNC and then filled in with black paint to make the letters pop.

Internally, the MWA-002 is powered by a Raspberry Pi 3 running Mopidy to play both local tracks and streaming audio. Not satisfied with the Pi’s built-in capabilities, [GuzziGuy] is using a Behringer UCA202 to produce CD-quality audio, which is then fed into a TPA3116 amplifier. In turn, the output from the amplifier is terminated in a set of female jacks on the player. Just like the stereo equipment of yore, this player is designed to be connected to a larger audio system and doesn’t have any internal speakers.

The primary display is a 256×64 Futaba GP1212A02A FVD which has that era-appropriate glow while still delivering modern features. [GuzziGuy] says it was more difficult to interface with this I2C display than the LCDs he used in the past due to the lack of available libraries, but we think the final product is proof it was worth the effort. He bought both the VFD spectrum analyzer and LED VU meter as turn-key modules, but the center equalizer controls are completely custom; with dual MCP3008 ADCs to read the state of the sliders and the Linux Audio Developer’s Simple Plugin API (LADSPA) to tweak the Pi’s audio output accordingly.

We’re no strangers to beautiful pieces of audio gear here at Hackaday, but generally speaking, most projects involve modernizing or augmenting an existing device. While those projects are to be admired, the engineering that goes into creating something of this caliber from modular components and raw building materials is really an accomplishment on a whole different level.

There was a time when any hi-fi worth its salt had a little row of sliders on its front panel, a graphic equalizer. On a hi-fi these arrays of variable gain notch filters were little more than a fancy version of a tone control, but in professional audio and PA systems they are used with many more bands to precisely equalise a venue and remove any unwanted resonances.

On modern hi-fi the task is performed in software, but [Grant Giesbrecht] wanted an analogue equalizer more in the scheme of those fancy tone controls than the professional devices. His project makes for a fascinating foray into analogue filter design, as well as an understanding of how an equalizer combines multiple filters. Unexpectedly their outputs are not mixed because it proves surprisingly difficult to ensure all the filters have the same gain, instead they are in series with the signal path passing through all filters.

The resulting equalizer is neatly built upon a PCB with a 4-AA-cell power supply, and makes for a self-contained audio component. Unexpectedly such analogue equalizer have been few and far between here at Hackaday so it’s particularly pleasing to see. We’re more used to graphical displays for off-the-shelf devices.