Help with loud pop when AC kicks on - phono amp problem

Isolation transformer. I use four of them, and very good value they are. Plitron makes a good one - medical grade too.

I also had this problem with my phone stage, using the integrated transformers eliminated the problem completely.  

I tried all of the AC product devices and AC power cords.  They did not solve the problem.

Some phono units pick up the voltage arc that happens on the thermostat.  There are ways to control the wave form of that arc but most HVAC techs do not have the background to understand the issues.

The problem is caused by the switching that turns the air conditioner system on and off. Assuming its a relay of some sort, its contacts are supposed to be bypassed by a small capacitance to prevent arcing (which creates bursts of RFI) of the contacts as they open and close.

I am sure this capacitor is present in the air conditioning system but it has failed. The relay that operates it will not be far behind as the contacts are now subject to arcing as they operate. It would be a good idea to get this serviced.

Proper grounding of the preamp can assist with making the preamp less susceptible to this sort of noise. If properly grounded, the chassis of the preamp will be grounded by the ground prong of the power cord. The actual circuit ground of the preamp will not be the chassis, but will float at chassis potential and will be the same thing as the shield connection of the RCA inputs. Meanwhile the tone arm ground will connect to the chassis of the preamp. In this way you will have the maximum immunity to noise of this type.

Unfortunately many preamps are improperly grounded, which means that IMMV; resulting in things like isolation transformers and such to fix this problem. But the most elegant way to do it is to have the phono circuit grounded properly to begin with.  

Assuming its a relay of some sort, its contacts are supposed to be bypassed by a small capacitance to prevent arcing (which creates bursts of RFI) of the contacts as they open and close.

Hi Ralph, does that mean the noise is actually airborne, instead of traveling through the power line itself? I have had the same problem with a single end tube phono and the compressor for an airbearing arm. I found that even moving the compressor by a couple of feet (when the pump was already around 30 feet away from the phono in another room) could make a big difference to the volume of the pop. So, I suspected that the noise was airborne.

I then switched to a SS phono with single end input / balance output , and the noise went away. I always thought it was due to the balanced output, but with your description, maybe that new phono just had better grounding!

^^ I think you can assume that is the case.

The noise is RFI, and using the power line as an antenna.