montreal

My 20-year-old CT-400 amp occasionally generated popcorn noise in one of the two channels. I noted this problem on this forum prior to 2008. I traced the noise back to the second op-amp stage of the input since the noise continued when I cross wired the first op-amp stage from left to right and the noise disappeared when I closed the volume control on the back of the amp.  Swapping the Motorola 2-stage op-amp chip did not change the situation.

Then my neighbour moved away 18 months ago and I have not had the problem since. My conclusion was that one of the neighbour's domestic wireless devices (wifi router or cordless phone) may have been broadcasting into my basement and then via the cabling into the Crown amp.

Another corrective measure which I undertook 5 years ago to reduce (but not entirely eliminate) the frequency of incidents of popcorn noise was to hot wire the internal fan on 24/7 in order to maintain a lower chassis temperature when idling.

Now that the noise appears to be permanently gone, I am thinking about removing the fan bypass jumper wire in order to reduce wear and tear on the fan and create a quieter background in the home theatre room.

If the popcorn noise stays completely away without the fan operating continuously, then I will conclude that the neighborhood wireless transmitters had something to do with the popcorn noise.