Headphone amp testing question

[jkim]

Perhaps this question is best answered by Amir, but anyone familiar with this matter may as well.

When testing a headphone amp or DAC output with 1 kHz sine tone, Amir's AP dashboard result shows "Input: Analog Balanced 2 Ch. 200 kohm" at the bottom status bar.

My question is, does this test NOT use any resistor in parallel with the input?

I ask this question because I use E1DA Cosmos scaler and found, with its input impedance of 200 kOhm, some input signals are SO sensitive to cable noise and AC hum.

Today I was trying to test a headphone amp output with a 1 kHz sine tone. The headphone amp has a built-in power supply plugged to the mains. I couldn't get a clean noise floor without using some load on its HP out. Directly connecting it to the scaler's 200 kohm input gives too much noise, which is resolved with some load like 300 ohm or by connecting it to Cosmos ADC directly (input impedance < 2 kohm).

Am I missing something?

 

[NTK]

The "200 kohm" is the input impedance setting of the AP analyzer that reads the signals. The load Amir uses for headphone amplifier testing is this one.

Neurochrome HP-LOAD Review (Headphone Dummy Load)

This is a review and detailed measurements of the Neurochrome HP-LOAD "dummy load." It was kindly donated to me by its designer, and our valued member, @tomchr. It costs US $1,499 from him direct. I don't know why but for some reason, companies sell you instruments for tens of thousands of...

www.audiosciencereview.com

 

[jkim]

I am referring to no load testing in which Amir does not specify a load value.

Like this:

What's confusing is, in some cases, Amir indicates it's 600 Ohm. Like this:

Then, let's suppose he uses a 600 ohm load for headphone amp "no load" testing. How about preamp or DAC testing? Does he really connect it to AP's 200 kOhm input directly? I suspect that may not be the case. But I am more curious about his headphone amp test settings.