Tag: Pete Millet’s soundcard interface

Sound Card interface (revisited)

For  measuring my system, I was struggling with not having a floating USB sound card to use with Pete Millett’s interface. I found a cheap alternative (Focusrite Scarlett 2i2) which can do ASIO 96kHZ and 24-bit.

focusrite loopback FR

Above is the response with internal loopback at 1Vrms on the 2Vrms scale of the SC interface.The distortion is really good below 0.01% just above 25Hz:

focusrite loopback THD

With the balanced input and outputs the noise level is really low. Below -120dB mostly across the entire 20Hz – 50kHz band. Inband noise level is below 100uV when the DAC volume is at highest level and the ASIO generator is muted:focusrite no signal

For distortion testing this USB audio interface has a very good oscillator output performance. Check out the 100mV level below:
focusrite loopback 100mV

The Noise Inspector

Detecting those little creatures from the bottom

When recently measured the performance of my CCS designs, I found that I wasn’t able to measure below -114dBV (2uV) and therefore limited my ability to measure CCS impedance. I was also keen to measure inductors, transformers and other reactive components to derive 2 or 3 component models for more accurate simulations during the design process. A preamplifier was in order, so I looked at options with some of the ICs I had at hand. A very nice suggestion from Burr Brown/Texas Instruments is shown below. The INA106 is a precision 10x differential amplifier. Not a cheap device, but quality does comes with it unfortunately. When coupled with a pair of OPA37, a very accurate differential preamplifier can be built with extremely low noise and distortion:20140118-184418.jpg

Continue reading “The Noise Inspector”