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1 kHz Oscillator
great test equipment, and a great first kit

1 kHz Oscillator with less than 2 PPM of distortion (1KHZ2PPM, $79 in kit form)

1 kHz 2 PPM oscillator with enclosure 1 kHz 2 PPM oscillator PCB and components

This oscillator has state of the art distortion performance, about 2 PPM, and it's mostly second harmonic. This distortion is better than the best A2D's, D2A's, and sound cards. Typically, getting distortion this low would could at least $1000.

How do we do it? Well, start with a really careful layout. Make sure you groom where all the nonlinear currents go. Bypass the power supplies well. Use only the highest performing op-amps. Use a high selectivity topology with low distortion. Top it off with the oldest trick in the incandescent lamp used to provide the perfect balance of positive and negative feedback and LOW distortion! The only way you can get lower distortion is with an Audio Precision oscillator. The only way to measure the distortion is on an Audio Precision Distortion Analyzer in FFT Residual mode.

Like the 1KHZCLOTHED oscillator, it has stereo RCA outputs and a level control. It also runs from a pair of 9V batteries (not supplied), and has an LED power light. The specs:

Download the assembly manual for the 2 PPM oscillator.

Go to the store to order the oscillator kit.

Making Distortion Measurements

Distortion measurement equipment used to be quite expensive. However, you can use a good sound-card, the free demo version of ARTA software, and a switchable attenuator to make high resolution distortion measurements. This youtube gives you an overview of how it's done.

Building the Switchable Attenuator

In the video you'll see that I use a switchable attenuator. It does two things:

  1. It has a limiting circuit to protect the input of the sound card from accidental damage when measuring a big amplifier
  2. It has a switchable attenuator, allowing you to adjust the input to the sound card to be the biggest signal that won't cause the sound card to distort. That gives you the best measurement range in the sound card

You can download a document here that has the parts list, and shows you how to build the switchable attenuator. I don't offer this as a kit, but you can order the parts from Mouser and Amazon.

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