RFI for the first time

That's actually quite cool - you get a radio module thrown in 'for free'...

The aerial part is normally the arm to phono amp lead(s) & its the phono amp that has the very high sensitivity to enable it to pick up these signals,   I guess moving the power plug "re-tuned" something.  My radio breakthrough is (used to be) in the Russian language,  but I also got English & German & suspected it was from the same Russian station.  My fix is to add a ferrite clamp to each of the arm to phono leads,  I don't think it matters too much where on the lead they are placed but mine are about 20cm from the amp. 

I had a problem with RF on my 52 when I lived in Kent. I never did completely eliminate it, and would get Russian radio coming through in the evening. Here's Naim's advice at the time - 

Systems where the phono amp is run unbalanced with single-ended inputs (i.e. the shells of the RCA connectors are connected to earth potential) are quite prone to this.

It sometimes occurs in unbalanced differential mode operation (where the shells of the RCA connectors are connected to zero volts but are allowed to float with respect to earth potential).  This typically occurs because of stray capacitance coupling the 0V line to earth (usually the phono amp's case), if the stray capacitance degrades the systems CMRR.

It almost never happens when using a properly screened balanced differential connection (e.g. through XLR connectors - a much better solution) and if it ever did it would actually indicate a fault in the pre-amp or cables.

The problem occurs with the first two because the + and - outputs from the cartridge are being terminated with different loads impedances wrt earth potential and stray currents flowing in this connection will appear as a signal (they're connect to the cartridge after all!); and this is why they often need the separate earth lead to provide a low resistance connection to the preamp to earth the TT's chassis.  Routing this lead close to the path the signal leads take is also a good idea.

The solution Mike has (using ferrites) is often helpful used in addition to others, as sorting out the earth connection will reduce the effect but not truly eliminate it.  Adding ferrites will improve the CMRR and further reduce the interference to provide an additional margin of protection.  Unfortunately the only way to not have the problem at all is to use a properly screened balanced differential arrangement in the same way that recording studios connect up microphones. 

Further to ferrite & Huge post on balanced config:   my Rega RB300 arm is wired with the Incognito harness,  this has pseudo balanced external (arm to amp) cables with a floating screen at the RCA end(s).   The harness has a metal slug in the arm pillar that is the star ground point for the arm tube, the bearing post, the RCA cable screen & the separate earth lead to the amp-earth.  They describe this set up as a Faraday Cage from the pillar post slug with the screen around a polythene tube inside which are the + & - signal wires, keeping the signal wires at a fixed distance from the screen.    

Still picks up Radio Russia tho' ... when the wind is from the east & the moon has a halo & its going to rain ... unless it has the ferrets 

Mike, that's easy to explain - ferrets are kleptomaniacs: they'll steal anything and hide it (I remember someone's car keys being stashed behind the freezer by one ferret).

In your case they're obviously stealing the Russian radio signal!

Later versions of the Prefix had a modification to reduce the chances of picking up RFI, older units can have this carried out as part of a service.

Also if you are running a Lingo 1 with Naim equipment I would certainly recommend having it serviced and the mains filter removed, this gives a big improvement in sound quality..

Thanks for the feedback everyone.

BTW - the Lingo was serviced earlier this year and the mains filter removed to suit the Naim amps better. Not sure if the Prefix has ever been serviced however.

How much would this be and is it worth it?

Would money be better spent buying a used olive Hicap? (it's powered from the Nac 52 at the moment)

Hi Overprint.. when you can hear radio - the term is technically  radio break through as opposed to RFI - and generally they have different symptoms and causes.

Radio break through will typically occur unless you are very close to a transmitter when there is a highly tuned (reactive) circuit such as speaker and speaker cables or an input or earth connection that has gone or is going high impedance.

So as your radio break through occurred when you changed the mains cables it might be worth checking the earth and grounding connections on the mains leads / connectors where you got the break through.

Phono inputs are also notorious for radio break through - as they are generally high impedance and also quite reactive tuned circuits.. this is why found shielding is quite important - and again this ground shielding could be connected to a main earth that is going high impedance and hence break through occurring .. or even an impedance mismatch between cartridge and phono input.

You may find a ferrite clamp looped  around the the earth grounded cable helps on the phono.. it did for me - but I had my own local radio transmitter.

As far as general radio breakthrough - the highest energies for AM long distance radio is in the evenings in the summer - this is when the radio energy is reflected the most back from the ionosphere and so radio and noise levels in .2MHz to 30Mz are at the highest - as the night passes the energy in the iomosphere depletes and so the amount of reflected radio energy depletes and so you may well find the radio breakthrough has gone in the morning.

There are variable is sun spot activity - where there are higher sun spots - there is more ionosphere energising and so there is more reflected energy. 

Sooo... the fact you heard breakthough from a non local source suggests normally that there is something on your setup is deteriorating or  has deteriorated or not not optimally setup from an impedance matching point of view  - but it affects may well vary with time of day, season and sun spot cycle. 

Simon

Thanks for the detailed info Simon. Happy to be corrected on the more technical stuff. You mention deterioration at the end - all the equipment is up to date service-wise except the Prefix which to my knowledge hasn't been serviced but I'm unsure of its age so that may be worth getting done.

BTW - I've not had any more issues since Monday but that doesn't mean it won't happen again.