Balanced Analog Audio Measuring interface for the soundcard
I was tired to solder divider diy patches every time I needed to measure power amplifiers with a soundcard, and also by investigating how to avoid groundloops and mains related interference spectral lines. So I decided to design and build a fully balanced universal analog interface that would change a soundcard to something that resembles an audio analyser like AP, or maybe rather like QA401. I started with using such thing 2 years ago and after getting good results, I decided to make a stand-alone instrument like this. The interface, called MSYS, has 2 channels, one for low level signals up to 4Vrms, second for high level signals up to 40Vrms (at least). The gain and sensitivity is controlled by DACT stepped attenuator. Block diagram is attached, circuit diagram is attached as well, and a photo of the instrument and its rear panel. The circuit uses OPA314, AD797, OPA627 and ADA4898 chips. Dynamic range is high, distortion very low and it makes a useful tool from a conventional soundcard. Balanced input is a must if we measure a power amplifier.
Specifications
Input impedance Lo level input ….. 200k balanced
Input impedance Hi level input ….. 22k balanced
Max. input Lo level input ….. 4Vrms
Max. input Hi level input ….. 40Vrms
Level/Gain regulation ….. stepped 2dB down to -60dB
Max. Output level ….. 10Vrms single-ended, 20Vrms balanced
Frequency range ….. 0 Hz – 1.1MHz (-3dB)
Output noise level ….. -120dBV(A)
Block diagram
Rear view
Main PCB
Power amp measurement circuit
I was tired to solder divider diy patches every time I needed to measure power amplifiers with a soundcard, and also by investigating how to avoid groundloops and mains related interference spectral lines. So I decided to design and build a fully balanced universal analog interface that would change a soundcard to something that resembles an audio analyser like AP, or maybe rather like QA401. I started with using such thing 2 years ago and after getting good results, I decided to make a stand-alone instrument like this. The interface, called MSYS, has 2 channels, one for low level signals up to 4Vrms, second for high level signals up to 40Vrms (at least). The gain and sensitivity is controlled by DACT stepped attenuator. Block diagram is attached, circuit diagram is attached as well, and a photo of the instrument and its rear panel. The circuit uses OPA314, AD797, OPA627 and ADA4898 chips. Dynamic range is high, distortion very low and it makes a useful tool from a conventional soundcard. Balanced input is a must if we measure a power amplifier.
Specifications
Input impedance Lo level input ….. 200k balanced
Input impedance Hi level input ….. 22k balanced
Max. input Lo level input ….. 4Vrms
Max. input Hi level input ….. 40Vrms
Level/Gain regulation ….. stepped 2dB down to -60dB
Max. Output level ….. 10Vrms single-ended, 20Vrms balanced
Frequency range ….. 0 Hz – 1.1MHz (-3dB)
Output noise level ….. -120dBV(A)
Block diagram
Rear view
Main PCB
Power amp measurement circuit
