Fully Integrated HiFi Studio Monitor

Studio Monitor and PCB

Have you ever wanted to build a high quality audio crossover and amplifier? [Rouslan] has put a lot of thought into making his dual amplifier studio monitor both high quality and simple to build.

With a concise schematic, a meaningful block diagram, and simulation results to boot, his well-written post has everything you need to build self-powered bi-amped speakers based on the LM4766 from Texas Instruments. It is great to see simulations which verify the functionality of the circuit, this can go a long way when working with complicated analog filters and audio circuitry. For those of you who do not have access to PSPICE (an expensive professional simulation tool), [Rouslan] uses LTspice from Linear Technology. TINA-TI from Texas Instruments is another great free alternative.

Additionally, [Rouslan] goes over the typical issues one has with a bi-amplifier studio monitor, such as phase misalignment and turn-on pop, and then provides a solution. Note that his project is powered by 20VAC, which requires an external transformer to convert the 120VAC in the wall to 20VAC. Be careful with high voltages! In the future, adding a high quality voltage regulator will most likely increase the performance.

His post finishes up with a very clean circuit board, which he ordered from OSH Park. With such a complete design, there is nothing keeping you from building your own. Go out and put that old speaker sitting in your basement to good use!

If you don’t have an old speaker sitting around, check out these very cool DIY speakers.

Build an Audio Spectrum Analyzer the Analog Way

bandpass

[Ryan] wanted a spectrum analyzer for his audio equipment. Rather than grab a micro, he did it the analog way. [Ryan] designed  a 10 band audio spectrum analyzer. This means that he needs 10 band-pass filters. As the name implies, a band-pass filter will only allow signals with frequency of a selected band to pass. Signals with frequency above or below the filter’s passband will be attenuated. The band-pass itself is constructed from a high pass and a low pass filter. [Ryan] used simple resistor capacitor (RC) filters to implement his design.

All those discrete components would quickly attenuate [Ryan's] input signal, so each stage uses two op-amps. The first stage is a buffer for each band. The second op-amp, located after the band-pass filters, is configured as a non-inverting amplifier. These amplifiers boost the individual band signals before they leave the board. [Ryan] even added an “energy filler” mode. In normal mode, the analyzer’s output will exactly follow the input signal. In “energy filler” (AKA peak detect) mode, the output will display the signal peaks,  with a slow decay down to the input signal. The energy filler mode is created by using an n-channel FET to store charge in an electrolytic capacitor.

Have we mentioned that for 10 bands, all this circuitry had to be built 10 times? Not to mention input buffering circuitry. With all this done, [Ryan] still has to build the output portion of the analyzer: 160 blue LEDs and their associated drive circuitry. Going “all analog” may seem crazy in this day and age of high-speed micro controllers and FFTs, but the simple fact is that these circuits work, and work well. The only thing to fear is perf board solder shorts. We think debugging those is half the fun.

Home Theater for One Shakes Souls, Removes Fillings

hmmmm

Sometimes an earth-shaking home theater setup just won’t do. A speaker enclosure can only fill the average sized room with so much sound. [Kevin Bastyr] has figured out a way around this. Do away with the room, and build the home theater INSIDE the speaker enclosure! [Kevin’s] creation is called Humorously Maniacal Milwaukee Makerspace Multimedia Machine, (or HMMMMMM for short). As the name implies, HMMMMMM was created at the Milwaukee Makerspace. The HMMMMMM reminds us a bit of the sensory deprivation chambers which were so popular in the 70’s. HMMMMMM’s purpose in life however, is anything but deprivation. The user (victim?) climbs through a 27” hatch and settles into a reclining position. An LCD display is mounted a comfortable distance away from the users eyes. Then movie (or brainwashing program) begins.

The sound system is what sets the HMMMMMM apart. The HMMMMMM utilises a 5.16 surround sound system. That’s 5 speakers and 16 10″ high efficiency subwoofers. We’re not sure if it would be better to call it a sound system, or a full-out frontal assault on the senses. We’re not kidding when we say senses as well. Bass this loud can be felt as much as it is heard. The HMMMMMM is has been measured at 148.6dB at 40Hz. That’s well into the hearing damage range. To be safe, HMMMMMM users must wear double hearing protection: foam earplugs and earmuffs.

[Kevin’s] graphs aren’t all smoke and mirrors either – he’s an audio engineer by trade, and made his measurements with a laboratory grade 1/2″ Bruel and Kjaer microphone. Sound pressure level testing isn’t without its dangers. During testing the 2050 watt amplifier powering HMMMMMM encountered a fan failure. The amp’s circuit board ended up scorched black with delaminated traces. The HMMMMMM however was none the worse for wear. Future plans for the HMMMMMM include RGB LEDs that flash to the beat, and a smoke machine to create that extra atmosphere when the escape hatch is opened.

Building an audio box out of thrown away boards

The last time [Mark] was at the scrap yard, he managed to find the analogue input and output cards of an old Akai DR8 studio hard drive recorder. These cards offered great possibilities (8 ADC inputs, 12 DAC outputs) so he repaired them and made a whole audio system out of them.

The repair only involved changing a couple of low dropout regulators. Afterwards, [Mark] interfaced one of his CPLD development boards so he could produce some sine waves and digitize signals generated from a PC based audio test unit. He then made the frame shown in the picture above and switched to an Altera Cyclone IV FPGA. To complete his system, he designed a small board to attach a VGA screen,  and another to use the nRF24L01 wireless module.

Inside the FPGA, [Mark] used a NIOS II soft core processor to orchestrate the complete system and display a nice user interface. He even made another system with an USB host plug to connect MIDI enabled peripherals, allowing him to wirelessly control his creation.

Boominator solar stereo keeps the music pumping even in cloudy weather

boominator

Despite 40-some years of product improvements, boomboxes today still require a half dozen D-cell batteries and measure their life in single digit hours.  After this, the batteries get chucked in the trash. Tired of the absurd cost and quantity of batteries required in a typical boombox, reddit user [anders202] has whipped up a solution that will keep the party going and the landfills empty. Using some off-the-shelf components and some impressive woodworking skills, he created the “Boominator”.

Despite its environmentally-conscious design, this green machine packs a whallop. Using its dual 10W solar panels, it can drive four woofers and tweeters to produce an estimated 102dB of sound with power to spare.  This extra juice can be used to charge its two internal 7.2Ah batteries or a cellphone using the integrated USB charging ports.  Better still, Anders chose amorphous solar panels (as opposed to crystalline) which produce power even in cloudy weather as demonstrated during a cloudy day at the Roskilde festival in Denmark.  For more information, check out the reddit comment thread.

Video demo after the jump

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Giving toys an electronic voice

sound

Whether it’s a Furby or Buzz Lightyear’s button that plays, ‘To infinity and beyond’, most digital audio applications inside toys are actually simple affairs. There’s no Arduino and wave shield, and there’s certainly no Raspi streaming audio from the Internet. No, the audio inside most toys are one or two chip devices capable of storing about a minute or so of audio. [makapuf] built an electronic board game for his kids, and in the process decided to add some digital audio. The result is very similar to what you would find in an actual engineered product, and is simple enough to be replicated by just about anyone.

[makapuf]‘s game is based on Game of the Goose, only brought into the modern world with electronic talking dice. An ATtiny2313 was chosen for the microcontroller and an AT45D 4 Megabit Flash module provided the storage for 8 bit/8khz audio.

The electronic portion of the game has a few functions. The first is calling out numbers, which is done by playing recordings of [makapuf] reading, ‘one’, ‘two’, ‘three’, … ‘twelve’, ‘thir-‘, ‘teen’ and so on. This data is pumped out over a pin on the ATtiny through a small amplifier and into a speaker. After that, the code is a simple matter of keeping track of where the players are on the board, keeping score, and generating randomish numbers.

It’s an exceptional exercise in engineering, making a quite complicated game with a bare minimum of parts. [makapuf] estimated he spent under $4 in parts, so if you’re looking to add digital audio to a project on the cheap, we can’t imagine doing better.

You can see a video of [makapuf]‘s project after the break.

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Retrotechtacular: First laser transmitter built 50 years ago

helium-neon-laser-transmitter

Most of the time we feature hokey film footage in our Retrotechtacular series, but we think this hack is as cool today as it was fifty years ago. [Clint] wrote in to tell us about Operation Red Line. It was an experiment performed May 3rd and 4th, 1963, which means the 50th anniversary just passed a few weeks ago. The hack involved sending data (audio in this case) over long distances using a laser. But back then you couldn’t just jump on eBay and order up the parts. The team had to hack together everything for themselves.

They built their own helium-neon laser tube, which is shown on the right. The gentlemen involved were engineers at a company called Electro-Optical System (EOS) by day, and Ham radio enthusiasts by night. With the blessing of their employer they were able to ply their hobby skills using the glass blowing and optical resources from their work to get the laser up and running. With that side of things taken care of they turned to the receiving end. Using a telescope and a photomultipler they were able to pick up the beam of light at a distance of about 119 miles. The pinnacle of their achievement was modulating audio on the transmitter, and demodulating it with the receiver.

[Clint] knows the guys who did this and wrote up a look back at the project on his own blog.

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