esorensen.com

4PI Speakers and Oddwatt Amplifier

Eric Sorensen -

In 2016, I set out to design and build a sound system for our house. Going into the project, I knew I wanted to build a tube amplifier. I'm not much of an audiophile or audio "purist", but there is something fun about tube amps that made we want to build one.

I also wanted the whole system to be easy to use and fit in with our lifestyle. For this, I knew I would want to include a preamp with Airplay compatibility since that is the primary way we play music in the house.

Here are some of my early goals for the project:

  • Tube Amplifier
  • High efficiency speakers (95dB+)
  • Preamp with airplay compatibility and customizable EQ
  • Preamp support for multiple inputs
  • Extra subwoofers to smooth out the low frequency response

I been wanting to build some speakers from Wayne at pispeakers.com. He has designed a number of high efficiency speakers and freely shares information about his design philosophy and approach. The 4PI speakers were a natural fit with their high (98dB) efficiency and I chose them for the project. I used JBL2226 drivers on the low end and B&E DE250 horn drivers.

After a lot of research, I based my tube amplifier design on the Oddwatt (http://oddwattaudio.com). Bruce Heran shares a lot of information about the design and is very helpful on various online forums. With the KT88 power tubes, this amplifier is a perfect fit for the 4PI speakers.

Finally in the preamp, I included a Raspberry PI configured to operate as an airplay device using a MoodeAudio image with a HifiBerry DAC. I also added multiple switchable RCA inputs, an analog gain control, and a FreeDSP board based on a sigma-dsp chip from Analog Devices.