Crack Voltage fluctuation/volume matching

[PT]

Hello,

I am very fresh into audio measurements, so please take my observations with a grain of salt. Yesterday I volume matched Crack and Topping A90 headphone amps for listening test purposes. Checking that match with a toy scope (first time I am hooking up, I got 105mV Vpp on the A90 and 155mV Vpp on the Bottlehead crack. This was done with 1kHz sine wave, both amplifiers were fed from the same DAC. Crack sine wave also seemed to "drift" from the initial zero all the time. Screenshots attached. Let me know what do you think on that.

 

[Paul Birkeland]

That may be a little bit of DC drift on the outputs because of the coupling caps, did you try setting this with headphones plugged in?

 

[PT]

Hi,

Thanks for a prompt reply. That was tested right speaker in, left speaker on the scope. Should I do a “loaded” measurement?

 

[Paul Birkeland]

A load may help stabilize that.

 

[PT]

Tested with 300 Ohm load, the drift is barely noticable.
Thanks for the tip!