[TheWoodman]

Hi, I want to build a 250 stereo EQ and I wonder how to test the left / right balance. The setup manual says: Do the test with the frequency adjustment potentiometer in the middle of the band, at about 12 o’clock. Measure the central frequencies of the two channels. you get fmin and fmax.

My question is: how to measure this? Do I send an audio signal through the unit and turn (for example) the mid band volume up? And then use a frequency analyzer on the computer and look for 'bump' differences in both channels? If I use an audio signal, what kind (white, sine etc)? So, any tips how to do this measurement?

I understand the part about adding caps when channels don't match. My question is how to measure wether they match or not.

[JPK]

You can use a plugin in your DAW that generates a variable frequency sine wave (there are several free plugins available like tonegenerator) and adjust the frequency for the maximum output signal.

[TheWoodman]

Thanks for your rapid response!

Just checking if I understand this correctly, is this the method?
-         I want to check the mid frequency band of the EQ250 (central frequency for this band = approx 540 Hz)
-         I send a 540 Hz tone from a tone generator (I use Tolvan Tone) from computer to both inputs of the EQ250
-         I send the outputs back to the computer to measure the levels (in db or lufs)
-         I sweep the signal from the tone generator up and down (between 500 – 600 Hz roughly) and check the output levels for both channels
-         I make a note of the highest output level for each channel to get fmin and fmax
-         Now I can calculate k

[JPK]

Yes correct.