sound buzz

[Bobby Dip]

Originally Posted by wa2ise

I assume that the set is an intercarrier design. What usually happens to create such buzz is the video carrier momentarily disappearing when there is peak white in the video. Peak white corresponds to the lowest RF level in the modulated TV channel, and a misbiased or misaligned video IF stage going into cutoff killing the video carrier when the peak white happens. The video detector creates the 4.5MHz sound carrier by beating the sound carrier against the video carrier, and if that video carrier isn't there, you get no sound carrier into the 4.5MHz sound IF. These sound "holes" end up sounding like the buzz you're hearing.

I have a TV that suffers from this, but I cheated by reducing the amplitude of the video feeding the RF modulator. Leaving more RF amplitude when peak white happens.

Thanks for the explanation, WA2ISE. I used to have a B&W set back in the 70's that buzzed whenever the station put up digital lettering. Sounds like it's not the set's fault, if the station is over modulating!

Bobby D.