Hacklet 85: Alternative Audio Amplifiers

When you think of amplifiers, you’re probably thinking of audio or some big ‘ol power amps for radios. While interesting, there are some very interesting ‘alternative’ amplifiers floating around hackaday.io that are more than just power amps, and exceedingly useful, to boot.

1601181393316190625[Ronald] bought an XMS amplifier a few years ago, and although it worked well, every time he changed the input, the loudness had to be toggled. One thing led to another, and he realized this amplifier had a four-channel audio processor that could be controlled by I2C. This was the beginning of his Network Amplifier.

Inside the box is a Raspberry Pi that controls a PT2314-based amplifier. Also included is a 2×16 character LCD, a few LEDs, switches, and a rotary encoder.  There was an Android app that controlled the amplifier, but this was discarded for a better looking web-based solution. Now [Ronald] has every audio source available over WiFi.

973501443636885535What if you want an audio amplifier without a speaker? Wait, what? That’s what [DeepSOIC] is doing with his experiments in ion wind loudspeakers.

‘Ion wind lifters’ have been around for decades now, mostly in the labs of slightly off-kilter people who believe this is the technology aliens are using to visit earth. Nevertheless, ion wind lifters produce an airflow, and if you make that wind variable, you get sound. Pretty cool, huh?

The amplifier for this project uses a tube to modulate kilovolt supply through the ion ‘blower’. Does it work? Sure does. [DeepSOIC] got a piece of 0.2 mm nichrome wire to discharge ions into the air, after which the ions drift into the second electrode. The result is sound, and the entire project is built deadbug style. It really doesn’t get cooler than this.


2981611414932529525Continuing with the tube amp trend, [Marcel] built the cheapest little tube amp around.

The design of an audio tube amp is fairly simple business. First, you start with a big ‘ol transformer, and rectify the AC into DC. This gets fed into a preamp tube, and this is fed into a bigger power tube.

In about 50 years of development, tube designers had the technology down pat by the mid 1950s, and triode/pentode tubes were created. This allowed tube designers to condense two amplifier stages into a single tube. While this setup was usually used for cheap, toy-like electronics, you can still buy the ECL82 tube today.

[Marcel] took one of these tubes, added a rectifier tube, transformer, and big cap to create the simplest possible tube amp. Use it for guitars, use it for hi-fis, it’s all the same. It’s not going to sound great, but it is a very easy amp to build.

All of these interesting audio amplifier projects are curated on this new list! If you have a build that amplifies sound in an interesting way, don’t be shy, just drop [Adam] a message on Hackaday.io and he’ll add it. That’s it for this week’s Hacklet. As always, see you next week. Same hack time, same hack channel, bringing you the best of Hackaday.io!

Controlling Guitar Amps With Servos

[fichl] plays electric guitar, and with that hobby comes an incredible amount of knob twisting and dial turning. This comes at a cost; he can’t change the settings on his small amp without taking his hands off the guitar. While larger, more expensive amps have multiple channels and footswitches, this tiny amp does not. Instead of upgrading, [fichl] came up with a device that turns his single channel amp into a completely programmable one, with just an Arduino and a handful of servos.

The amp in question – an Orange Dark Terror head – has just three knobs on the front of the chassis, volume, shape, and gain. [fichl] had the idea of controlling these knobs electronically, and the simplest solution he came up with is cheap hobby servos. These servos are mounted in an aluminum box, and mount to the knobs with a few shaft couplings.

The footswitch is the brains of the setup, with three buttons, four LEDs, and a DIN-5 output jack that delivers power, ground, and three PWM signals to the servo box. With the help of an Arduino Nano, [fichl] can change any of the knobs independently, or switch between twelve programmed settings. It’s an interesting setup, and something that could serve as a prototype for a much larger system on a much larger amp.

Hacklet 75 – Guitar Projects

Some things just go hand in hand. Hacking and guitars are one perfect example. A huge number of hackers, makers, and engineers have at least dabbled in playing the guitar. Even those who don’t play have heard the swan song of the wayward guitarist “Bro, you fix amps?”. Seriously, once your guitar toting friends find out you tinker in electronics, you’ll never be left wanting for pizza or beer. This week’s Hacklet is about some of the best guitar projects on Hackaday.io!

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Instrumentation Amplifiers and How to Measure Miniscule Change

These days there a large number of sensors and analog circuits that are “controller friendly” meaning that their output signal is easily interfaced to the built-in Analog to Digital Convertors (ADCs) often found in today’s micro-controllers. This means that the signals typically are already amplified, often filtered, and corrected for offset and linearity. But when faced with very low level signals, or signals buried in a larger signal an Instrumentation Amplifier may be what’s needed. The qualities of an Instrumentation Amplifier include:

  • A differential amplifier with high impedance and low bias current on both inputs.
  • Low noise and low drift when amplifying very small signals.
  • The ability to reject a voltage that is present on both inputs, referred to as Common Mode Rejection Ratio (CMRR)

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Speaker Cabinet Boom Box Build

When you get that itch to build something, it’s difficult to stop unless you achieve a feeling of accomplishment. And that’s how it was with [Rohit’s] boombox build.

He started out with a failing stereo. He figured he could build a replacement himself that played digital media but his attempts at mating microcontrollers and SD cards was thwarted. His backup plan was to hit DX for a cheap player and he was not disappointed. The faceplate he found has slots for USB and SD card, 7-segment displays for feedback, and both buttons and a remote for control. But this little player is meant to feed an amplifier. Why buy one when you can build one?

[Rohit] chose ST Micro’s little AMP called the TDA2030 in a Pentawatt package (this name for a zig-zag in-line package is new to us). We couldn’t find stocked chips from the usual suspects but there are distributors with singles in the $3.50-5 range. [Rohit] tried running it without a heat sink and it gets hot fast! If anyone has opinions on this choice of chip (or alternatives) we’d love to hear them.

But we digress. With an amp taken care of he moved onto sourcing speakers. A bit of repair work on an upright set got them working again. The bulky speaker box has more than enough room for the amp and front-end, both of which are pretty tiny. The result is a standalone music player that he can be proud of having hacked it together himself.

Keep those filaments lit, Design your own Vacuum Tube Audio Equipment

It was a cold January Saturday night in Chicago and we had big plans. Buddy Guy’s Legends bar was packed. We setup directly under one of the PA speakers less than 15′ from the stage. Time to celebrate. Skip the glass, one pitcher each and keep them coming. We’re about to make bootleg recording history. Conversation evolved into bloviation on what our cover art would look like, certainly it would be a photo of our battery powered tube mic pre-amp recently created in my basement lab. We had four hours to kill before Buddy’s appearance. Our rate of Goose Island and Guinness consumption would put us at three-sheets to the wind by 11. Must focus. It’s time, Buddy was on. Much fumbling about and forgetting how to turn on the Japanese-made 24 bit digital recorder with its nested LCD menus, cryptic buttons, and late 90’s firmware. Make it work. We did, just in time for the bouncers to notice the boom mike and battery packs. Wait, wait… maybe we should talk about why tube amps are worth this kind of trouble first.

Yes, vacuum tubes do sound better than transistors (before you hate in the comments check out this scholarly article on the topic). The difficulty is cost; tube gear is very expensive because it uses lots of copper, iron, often point-to-point wired by hand, and requires a heavy metal chassis to support all of these parts. But with this high cost comes good economic justification for building your own gear.

This is one of the last frontiers of do-it-yourself that is actually worth doing.

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Build a Simple Audio Amp

[Ynze] has built an audio amplifier that looks and sounds great. His amplifier uses a National Instruments (now TI) LM3886 Overture series 68 Watt power amp. The LM3886 places [Ynze’s] amp squarely in the “Gainclone” catagory. Gainclone or Chipamp are terms long used by the DIY community to describe audio amps based upon highly integrated semiconductor amplifiers. The Gainclone name stems from the original Gaincard audio amplifier sold by 47 labs. The Gaincard used less than $100 USD of parts when it was introduced in 1999. It sounded good enough to command a $3300 USD price tag on the audiophile market. The low parts count and simple construction spawned the audio DIY community to build their own versions of the Gaincard. Hundreds of variants exist now, and wading through the different versions can be a bit of a daunting task. [Ynze] found a basic design that works, and built from there.

One of the interesting things about [Ynze’s] amp, as well as many of the Gainclones, is the fact that they use no circuit board. All wiring is done point to point. resistors are soldered directly to the pins of the amplifier chip. This can be some tricky soldering for beginners, but several PCB kits are available. [Ynze] built his amp in two cases. One case holds the power supply, and the other contains the amplifier itself. [Ynze] is using a large toroid transformer to drop his local 230V mains down to +25V and -25V. The amplifier circuit itself is simple – a few discrete components surround the LM3886 and it’s heat sink. [Ynze] also did some very nice carpentry work on his wood chassis. The resulting amp looks like it’s right out of the 1960’s – but hides 1990’s electronics inside.

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