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

Hi everyone,

Back with yet another power line issue.  I have a Croft RIAA phono amp power that is causing a very loud pop whenever the AC unit kicks on and again when the fan starts a few seconds later.  In some cases the pop is so loud that it can be heard three rooms away.  It can be heard over even the loudest music peaks.  I'm afraid that it might damage the unit or the speakers, so I'm hesitant to use it.  I'm not sure if new tubes might make a difference.  I hooked a CD player up to the integrated amp (right now I'm using a Jolida hybrid while I'm shopping for a new integrated), and there is no noise when the A/C starts up if only the CD player is hooked up. 

I have tried two different power cords.  Plugged the Croft into the wall, into a PLC Thingee power conditioner, and into a Furman power conditioner.  In all cases it still pops to one degree or another.  

Any thoughts on whether it's worth hunting for the problem.  I had some similar issues with a Heed Quasar phono stage.  But haven't noticed it on a couple of other phono stages.  Seems very hit and miss.

Would welcome any advice.  Thanks!
Scott
smrex13
thekong
170 posts
 
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!


atmasphere's avatar
atmasphere
7,068 posts
 
^^ I think you can assume that is the case.

The noise is RFI, and using the power line as an antenna.
erik_squires
5,268 posts
 
You really should have your AC unit examined first, not to mention your wiring to your stereo. Lifted grounds and neutrals can do all sorts of fun things.

Ideally, it would be great to have an oscilloscope view of what was happening. For instance, if your problem was common mode, then an inexpensive isolating transformer would probably do the trick.

Among noise suppressants what I would expect would work well for you are the series mode surge suppressors available most commonly via Furman, some quite reasonably priced. They filter noise at 3kHz and above, a much lower frequency than most power strips which start around 100kHz or higher.

On the expensive side of things Richard Gray’s Power Plants would also work. The resonant circuits they use can be very effective in otherwise noisy environments. I just find them priced out of this world.

Of course, something like the PS Audio regenerators or (my favorite) PurePower units (designed by the same engineer as Jensen Transformers) should work.
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