Wayne Parham Messages: 18774 Registered: January 2001
Illuminati (33rd Degree)
Intermodulation distortion (IMD) from 60Hz and 4kHz sines
The intermodulation test signal is a 60Hz sine and a 4kHz sine. Clipping in the phono stage (or measurement system) will increase IMD, as will the incorrect vertical tracking angle.
This measurement doesn't look good but it's hard to know how much of that is the measurement system and how much is the device under test. For one thing, I need to be able to change the horizontal scale so that I can see the area around 4kHz very closely. I would expect to see 3940Hz and 4060Hz components from intemodulation, but I can't see that well because of the horizontal resolution. What I can see pretty clearly are 2nd and 3rd harmonics at 8kHz and 12kHz, which tells me something else is going on. Probably clipping in the measurement amplifier or possibly the phono stage.
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