[time-nuts] TSC5110A noise floor?

[AC0XU (Jim)]

I have repaired this unit. The ZCD modules each had a blown 7809  9V regulator.

The design of these ZCDs is interesting. They are entirely enclosed except for a pair of 7809/7909 +-9V regulators which hang out one side. My guess is that the VRs, being noise generators, were determined to be better outside the can.

I didn't try it, but it occured to me that there might be some benefit in replacing the 7809/7909 pair with low noise equivalents, but maybe there is a second VR stage or just adequate filtering so it wouldn't matter.

Does anyonw know what sets the noise floor of a DMTD device using ZCDs such as the TSC5110A?  Also, I believe that the 53100A has a lower noise floor - how was this achieved?

Thanks!
Jim