Yes Me again,
So I get how to test a power amp with a dummy load but with a preamp can I just plug it in directly to the QA403 or should I still put it through the dummy load? My guess is the voltages aren’t that high coming out of my preamp? Sorry just don’t want to do somthing Dumb and break the poor thing (meaning the QA403) . Thanks in advance just trying to setup my bench better for different audio testing.
Hi @fmajewsk, yes, you can just plug the preamp in directly. As always, while you are getting your bearings, it’s a good idea to keep the +42 dBV full scale input. And as you get close to the performance limits imposed by the large full scale input, you can back off to lower and lower full scale inputs as needed.
Be aware that a pre-amp consisting of a few state of the art op-amps could have a THD+N of -130 dB, which is well beyond the capability of any audio analyzer in existence today. Here’s the front-page plot of the OPA1612 opamp. it’s hitting -140 dB THDN in places. And to measure these numbers, TI generally relies on an approach to “magnify” the distortion artificially (see section 8.3 of the spec).
But, you can readily measure a host of other interesting things, such as how the pre handles overload, input and output impedance, EQ performance, etc.
If testing vacuum tube gear, be mindful of simple designs that pull the output signal off the plate and, at powerup, can have high voltage on the output until the coupling capacitor charges. This spike can damage some equipment.
I also load the output with 10k Ohms as some amplifier inputs have lower input impedance.
thank you both!!! I am typically testing transistor stuff ! but thanks for the heads up!!
