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

Yes, Al, the lights are fluorescent - and are older ones at that. I have been thinking of replacing them with LED, which I’m hoping will not cause the same sort of problem. The switches are newer silent type and not dimmers.

BTW, I didn’t mean to hijack the thread, but thought my experience may also shed some light on what Scott is experiencing.

I had a similar problem with the air compressor for my tonearm- the compressor is a high quality model made by Silentaire, and even the additional box supplied by the tonearm maker-Kuzma- and wired into the compressor motor connection--did not ameliorate it, nor did having the compressor connected to a dedicated line. What solved the problem -and I now use an even larger compressor with a bigger surge tank--was a large isolation transformer. Without it, you’d hear a nasty snap through the audio of the system when the compressor kicked on or off. Since you don’t necessarily have the ability to isolate the air conditioner this way, you might see if an isolation transformer will work to isolate your affected electronics--the main issues are: such transformers hum, so you need to find a place for the transformer that won’t interfere with your listening--in my case, the transformer and compressor are in what amounts to a large walk in closet that has been soundproofed; current draw of the transformer- you want one sufficient for your needs. These can be purchased as plug and play boxes, no wiring required, and you don’t necessarily need an "audiophile approved" one--I’m using a medical grade 1800 watt one from Tripplite right now, and only using one of the two motors on my compressor. Works fine, has a 15 amp breaker, four outlets and a decent cage around it. These can probably be picked up even cheaper from electrical supply houses, or used, but I’d make sure you know what you are getting. Almarg or someone else here with better electrical/electrician skills may be able to guide you better on specifics. I doubt a phono preamp (if that’s the only component affected) draws very much current.

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.