Amplifier Test Setup

The heart of the test setup is the Quantasylum QA403 Audio Analyzer.  The included software has a number of automated tests, including frequency response sweeps and measuring THD+N vs. power output.  I purchased a QA451B Programmable Load to go along with the Audio Analyzer.  The QA451B can handle up to about 200W for short bursts, it attenuates the signal down by 12 dBV before sending it to the analyzer, and it includes a 6th order low pass to filter out some high frequency ripple inherent in many Class D amps.  It can also be used with external loads when testing higher power amps.  I do have several pro audio amps in house, so will be utilizing this feature.

I also added a variable DC power supply (0-60V, 0-5A) that could cover most of the desktop and mini amps that are powered using a wall wart or other output DC power supply.  Many of those amps can run using a range of voltages and one advantage of being able to test is having some data to make decisions on what voltage to run at.  

I'm starting out running the setup off of a 10 year old laptop that has a docking station, which gives a little extra USB power.  So far, the computer hasn't been a limitation.  

When I do work my way up to testing higher power amps, I have a few load resistors to try out.  These Vishay Milwaukee resistors are 4 ohms each and can take 420W continuously (and 10 times that for 5 second bursts).  These are about a foot long...  I acquired them cheap, but I do know inductance is very low (I ran impedance sweeps on a couple of them with Praxis and the resistance did not vary more than 0.01 ohms up to 20 kHz.