I’m new to QuantAsylum and am expecting UPS to deliver my QA-403 later today! I’ve already been reading a lot on this site and am really looking forward to getting up to speed on the software, once I have the hardware in hand to play around with.
I’ve been accumulating gear for years and have been doing what I’d characterize as “very basic” bench testing of vintage preamps, power amps, integrated amps and receivers using a homebrew of ARTA software, a Motu M-2 USB Audio Interface, bench DVM’s, and a DSO. Mainly I do Frequency Reponse plots and spectrum analysis to get THD+N at 1kHz and at various power levels (usually 1W rms and peak “non-clipping” power).
So I’m looking to the QA-403 to enable me to do more sophisticated, rigorous and repeatable testing. But I fully expect to be on a learning curve for a while. So I’m hoping maybe you all can help me with a little advice/sanity checking as I get started? Thanks in advance!
Also, I’m interested in a reasonable degree of precision, but not going crazy over “ultra-precise” measurements. In other words, for my purposes I am not concerned with THD+N to the 5th decimal place. I’m much more concerned with repeatability and usability, and 3 decimal places is generally more than enough for the gear I measure. If I can eventually end up getting “reasonably” reliable results down to the 4th decimal from the QA and my setup (cables/loads/environment/procedures and practices/etc.) then I will be ecstatic.
Okay, so for power amp measurements I have some really nice Vishay Dale industrial non-inductive load resistors that I’ve been pretty happy with. And I’m planning to take advantage of the built-in attenuation options of the QA-403, but I also am planning on building in a -6dB attenuation network to provide for headroom and minimize the possibility of doing something dumb. Below is a schematic of my plan, I will mount it all in a metal enclosure with a heatsink. So do I have the basic idea correct?
And then can anyone give practical advice on what would be a solid choice for interconnecting the signal back to the QA-403 inputs? Advantages/disadvantages of using the QA-403 inputs single-ended with basic RG58C/U 50 Ohm BNC cables? Or is differential input really the only game in town? Getting the differential cabling done correctly seems a little intimidating based on a few of the threads I’ve seen on here, so maybe I look at tackling differential later on?
Cheers! - Steve