Qa401+qa450+qa480 + ahb2

[HeineB]

Hi,

I want to measure how accurate my QA setup is and are looking at using the Benchmark AHB2 as a reference. I am hoping we will get the same results as seen on audiosciencereview where the amp measured a low of 113 THD+N. This can of course not be archived by QA450+QA401 alone but need some assistance. I was lucky to obtain one of the few QA480’s - and I was hoping to bring this into play to replicate the audiosciencereview numbers.
I’m hpoing to get some help and advice on how to proceed. I’ve been reluctant to put the QA480 into the chain - as I’m not certain if it can handle the levels.
So first question is would be - will it be safe to loop the output from the QA450 into the input of the QA480 and that output into the QA401? For 5W@4Ohm and 150W@8Ohm?

I’ve included my regular measurement from measurering only using QA401+QA450 - where I hit the

-97 THD+N.

I would appreciate all help, suggestions and advice that anyone can provide.

[matt]

Hi Heine, can you confirm if the AHB2 output is push pull or single ended? If single ended, then I think you could go QA480 output into AHB2, and AHB2 into load (QA450 or other), and then tap off the active side of the load and run that into the notch and then notch into QA401. The QA480 rails are +/-15V, so as long as the signal going into the QA480 notch is below 29Vpp or so (~25W into 4 ohms) it will be OK. I think a 5W into 4 ohms would be an ideal test point.

Before you put the AHB into the mix, you can sweep the QA480 into the QA401 with to learn the limits of the QA401 both with and without the notch. Using the AMP THD versus IO Level you can measure the QA401 DAC in isolation. And using the “AMP THD versus IO using the QA480” you can measure the QA401 ADC in isolation.