Puzzling amplifier phase response

Hi,

I measured an amplifier a few weeks ago and the result was as expected.



I tried repeating the same measurement yesterday and this was the result:



I had this problem once before and after turning everything off and on again it went away. Now I can't get a normal phase response and I'm having the same problem with a second amplifier although the point of phase reversal is different.

Any suggestions as to what I might be doing wrong please?

John Mulcahy said:

It is an inverted response. Possible causes:

• Amp connections swapped
• Soundcard used for measurement is inverting
• The "Invert" box on REW's soundcard references input options is checked (or not checked if it used to be)
• The "Invert impulse" box is checked in the Impulse graph controls

Click to expand...

Thanks John. Since I made the original plot I rebuilt my BNC to XLR cable. I must have reversed the connections. I checked the "Invert" box on the REW soundcard preferences and all returned to normal.