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
Seems like you need to completely isolate your system electrically.  Is a dedicated circuit for your audio system in the breaker panel an option? Also, I would ask an electrician to look at the wiring to the air conditioner.  That unit should not be affecting the rest of the electrical panel in such a dramatic way.  As for power conditioning, perhaps a regenerator like the ps audio power plant could work.  There is probably a local or online dealer that will give a demo or offer a refund if not satisfied.
Mark - unfortunately, I live in an apartment complex, so any kind of rewiring is out of the question.  The PS Audio regenerator has been on my radar for a while as a reasonable solution for an apartment dweller like me.  Of course it eats up the budget I had hoped to spend on a new integrated...

Thanks, Scott
Perhaps the wiring is causing a problem, maybe even a dangerous one. The air conditioning unit shouldn't be causing so much trouble to the other electrical appliances.  It may be worth having an electrician out to investigate.  Could be something easy like the breaker circuit on the AC unit itself is bad or going bad. 
Hi Scott,

As I recall some of the phono stages you've tried in the past have had issues involving pickup of radio signals.  So in part for that reason I wouldn't totally rule out the possibility that the means by which the air conditioner is causing the issue is by coupling of RFI through the air, rather than by its effects on the power line.  Especially if the air conditioner is located in the same room as the phono stage.

And also given that a Furman power conditioner didn't resolve the problem, as some of their models provide very good filtering down to the low kHz range.  What model Furman was it?  And did it seem to make a perceivable difference in the severity of the problem?

Best regards,
-- Al
    
If I may interject, I too have had a popping sound that had begun recently, only it happens when activating certain light switches. I had recently replaced my line stage as well as my phono stage, so I didn't know where the fault may lie. The AC does not cause any problems.

The line stage is a W4S STP/SE and the phono stage: HEED QUASAR! Hmmmmmmm.
@minkwelder - interesting that you are having some issues with the Quasar, too.  I thought it sounded fantastic, but it had a surprising sensitivity to noise, especially for a unit with an outboard power supply. 

@almarg - the A/C unit is outiside the apartment (its central A/C).  I think the integrated may have as much to do with the interference as the phono stage.  It seems much louder since I started using the Jolida.  The Belles Soloist had a similar (or even more severe) issue as it reacted to every light switch in the apartment.  The only other problems I've had have been with the A/C switching on.  The Furman was an entry level model - 15i, so certainly not the most powerful unit they make.  

Thanks, Scott

Scott, ok, so it probably isn't airborne RFI that is responsible.

It appears that the two outlets on the rear of the Furman Elite 15i that are indicated as being just for video equipment incorporate some ultrasonic filtering that is not provided on the other outlets, in addition to providing the filtering the other outlets provide.  So for experimental purposes, at least, it may be worthwhile trying those outlets for the Croft and the Jolida.

Minkwelder, are the light switches you referred to controlling fluorescent or compact fluorescent lighting?  Those can generate significant noise and RFI, especially (I believe) as they get older, and especially while they are in the process of turning on.  And are the switches dimmer types, which can also be significant noise generators?

Best regards,
-- Al
 
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.  
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.
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.