1Wamp, An Open Hardware Guitar Amplifier

The folks at [ElectroSmash] recently released 1Wamp – a one watt, open hardware, Guitar amplifier packed with features. It consists of a JFET based pre-amplifier, a Big Muff Pi a.k.a BMP based Tone control and an LM386 power amplifier. The dual JFET pre-amp provides tube-like sound, the BMP provides a nice tonal range while the LM386 can drive various types of output’s ranging from headphones to speaker cabinets.

1Wamp had controls for Tone, Volume and Gain, a Speaker/Cabinet output, a headphone output with an integrated attenuator switch and an aux. input. The aux. input is handy as it adds any line level input signal to the guitar sound, allowing you to practice with metronome or MP3 backing tracks or drum bases. It runs off either a 9V battery or can be powered via an external power source. [ElectroSmash] have released all the native KiCad design files. If you’d like a quick look at the design, check out the Schematic PDF and the Bill of Materials. There’s also a handy assembly manual [PDF] that shows how to build it in five easy steps.

Their blog post provides extremely detailed circuit analysis of every part of the design, starting from the power supply filter to remove mains “hum” all the way through to PCB layout considerations for noise reduction. Oscilloscope screen shots provide signal analysis showing bias points and signal levels throughout the circuit. The choice of value for every component is explained, along with the consequences of changing those values. This makes it easy to customise the 1Wamp to suit individual tastes. We also noticed SPICE models for the recommended and alternative JFET transistors, in case you need to customise the design by changing component values.

There’s also a lot of audio amplifier trivia, references and links shared in their post. This includes a detailed analysis of the LM386 op-amp. Want to add some bling to your 1Wamp build? There are a lot of handy tips on how to add cool LED lighting to the amplifier if it is mounted in a standard metal enclosure. However, the PCB has some really nice graphics, so an acrylic-sandwich-type enclosures look best. Check out the video that walks through the features of the 1Wamp and shows off its performance. And while on the subject of Audio electronics, here’s one of their earlier projects – an open source Arduino guitar pedal.

Documentation to this level proves several things, most notably a love for this design and deep consideration for those who will use and modify this amplifier. It’s a great pattern to follow with your own Open Source designs.

26 thoughts on “1Wamp, An Open Hardware Guitar Amplifier

      1. Yeah, I like it too. But then I remember that Varg recorded one of his albums–I think it was Filosofem–by connecting his guitar to a $30 boom box, and recorded vocals with a headset mic (or a pair of headphones plugged into the microphone port, depending on who you believe). Metalheads have very different goals than folks in most other genres. >:)

        (hail satan)

      1. I thought so too, but all the diy audio circuits I’ve seen never seem to have one. So I looked it up and found a Maxim app note for white noise here: https://www.maximintegrated.com/en/images/appnotes/3469/3469Fig01.gif

        Maybe it’s common for instrumentation but my impression for audio is that the headroom of the usual chips and buffers tend to be so much higher than input signals. I guess they expect someone to power amp it by accident.

        1. Zeners make lots of noise, but only when they’re in their breakdown region. That is, they don’t start making noise until you start putting reverse current through them. So you would only get the noise while you’re overdriving the amp.

  1. The LM386 is a nice amplifier if you’re in the need for getting some audio output from your circuit. However, I wouldn’t use this part at all if there is even the remote chance that output quality is an issue. There’s really no need to build fancy circuits for your voice output or doorbell or what-have-you, an LM386 will do just fine. The LM386 works really well and it’s dirt cheap, but come on, just use a proper audio amplifier for double the price.

  2. Consider including a linear regulator and not a switcher wall wart. Also consider further adding an LC LPF to the power supply input.

    Next consider using opamp buffer stages instead of JFETs for the tone controls. A nice feature of Opamps is PSRR.

    Yes there are better linear amplfiers. The LM386 is simple and cheap, if those arent your criteria than use a better part.

    Finally, what good is this without a frequency sweep, normalized to 1kHz that also includes THD+N Ratio? Without that information you really can’t compare it to anything other than subjective “feelings.”

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