My New Old Amplifier

A long time ago, I built my own amplifier. This was a fun project, and the results were pretty decent. I never did post the results of the project, so here’s a picture of the results.

Obviously, I put a cover on there, and the end result looks fairly decent (a throwback to the 70s, when wood was commonplace on electronics).

On the front of this unit (not shown), I have a log potentiometer that served as the “preamplification stage” (basically, a volume control). Over the course of this amp’s life, this volume control would drive me absolutely bonkers because at about 10% of the volume level, the left speaker would shoot up to about 50% until you went down to 5% volume level.

I set up some speakers in the office recently, and decided to use the amplifier a little more. I realized quickly that I could just leave the amp playing at full volume, and simply control the audio level on my MOTU Traveler. This worked great.

So, this past weekend, I went to the “electronics lab” (basically, my basement) and decided to modify my amp a little more. I removed the connections to the volume control, and now the unit behaves more like a pure amplifier.

During this exercise, I reorganized a lot of the internal wiring, and decided that I should really separate this project into a power supply unit, and an amplifier unit. This would allow me to more easily experiment with other amplifier designs, and also a nicer (read: smaller) case layout.

I wish I had more time to play with these projects…

3 Responses to “My New Old Amplifier”

  1. SuperMegaUltraGroovy » Blog Archive » Kookaburra in transit! Says:

    [...] It turns out that the volumeless amplifier idea didn’t last very long. Once the amplifier got hooked up to my MacBook Pro’s internal audio source, the granularity of the volume control was not nearly enough for day to day use. Also, thinking of headroom, it’s always best to have a digitally controlled output attenuated in the analog domain, rather than digitally. [...]

  2. Josh Says:

    Were you using a Pot with an audio taper winding? The symptoms that you describe with your volume control sound like you are using a Pot with a linear winding.

  3. chris Says:

    It was definitely a logarithmic audio pot. It even had stereo operation! (Two sets of pins.)

    Judging from where I bought it (surplus electronics store), it was probably faulty out of the box…

Leave a Reply