I’ve been using my sound card and Pete Millett’s interface for testing. However, the limitation on high frequency response is due to the sound card. A cheap, but yet effective option, is to use the Chinese digital oscilloscope Instrustar ISDS2062B which comes with built-in DDS signal generator with sweep capability. With this little piece of technology, you can sweep up to 10Mhz. The resolution is 12bit, not great for FFT but good enough for a FR analysis. For frequencies above 20kHz, you can use this device to look into things. For FFT and THD analysis, I will keep using the sound card and audio interface as usual.
When I test the device, I found that the DDS output didn’t have the stones to drive loads at HF. Therefore I went back to my workshop and built the following sweep driver. This was based on the great SSM2019 that my friend Mogens sent me:
The circuit is very simple. It’s operated from a pair of 9V batteries. So far, I’ve tested with the 20dB (actually 19dB gain due to 1kΩ resistor at hand) and 0dB gain modes.
The response is good enough for my purposes:
I can get 1.5Mhz @ 19dB or 3Mhz @ 0dB gain HF response which is great. I now need to test it again with a real load.
