Topic: Measuring noise level using FF 400
I'm trying to use a FF 400 sound card to measure THD+N with DSSF3 software of my DIY phono preamp. Here is the link http://www.ymec.com/products/dssf3e/
When I connect FF output to the amplifier input the noise level goes up, and shows approximately -80 dBu (around -65 in peak) in 5-100 Hz range. If I connect it to my Macbook Pro phones output, the noise level drops to -100 dBu. My amplifier is a phono preamp, and it has +30 dB gain at 1kHz. Does any have a clue why there is such a difference? I have a gut feeling that it has something to do with source impedance difference. I've tried both balanced outputs and phones. Result is the same.