In a previous post I detailed the setup I’ve begun to use to learn about measuring the distortion of some of my amplifiers. Acknowledging this setup is rudimentary, for those wishing to tinker further there are of course many options. As ever, improvements can be made by the utilisation of better (read more expensive) equipment such as the audio interface used. Additionally, another avenue is the use of a low noise high precision generator as an independent reference source. A DIY kit that purports to perform at the level of the most expensive equipment available peaked my interest.
The instrument is the Akitika 1kHz 2ppm Oscillator. The designer describes it thus: “Harmonics are typically more than 114 dB below the fundamental, making the distortion 2 part per million or less. This puts it in the realm of the most expensive, best performing test equipment in existence. It can be used for distortion testing of the highest performing equipment.“
The kit comes from the US, so UK customers should factor in approximately £24, which includes VAT and the customs processing fee to pay to Royal Mail, on top of the purchase price and postage. The package contains everything required to build the oscillator, including an enclosure, with the exception of the required 2x9V batteries. Everything appears to be good quality, well designed and fits well. An excellent build manual is available for download.
In addition to the oscillator, the Akitika website also has a schematic to build a switchable attenuator. This performs two functions:
“It has a limiting circuit to protect the input of the sound card from accidental damage when measuring a big amplifier. 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.“
I bought a 6 position switch, reused an enclosure from one of my old CMoy amps and everything else came from my own stock of parts, so this was a very cheap build.
I’ve just started a new job and so I’m very busy at the moment, but I hope to start getting to grips with the actual measurements in the next few months. Eventually I hope to obtain a better interface as well and it will be an interesting exercise to compare the UCA202 to this.