Random audible noise from speakers even when pre amp has no active source

You might want to try some Mogami 2549 cable between your Naim 202/Hicap and active ATCs - searching through past posts on this forum, this seems to be a fairly common recommendation that appears to work very well in this application.

Have you tried disconnecting the interconnect from the 202/HC but leaving the other end connected to the speakers? If not, try that with one channel, but leave the other as normal. When the noise starts on the normal channel does it also happen with the disconnected one? If yes it is the cables. If not, then it could still be cable related, but interaction of the cable electrical characteristics with the Naim output stage. 

If it is the cable itself acting as an aerial then one thing to try could be a ferrite ring on the cable close to the ATCs. Actually, one at the preamp end may help if it is RF picked up by the cable affecting the preamp. Low cost and easy to try, at least.

Niggling in my mind is that after turning off and then back on  it takes a while to restart, while if left on it just continues. Have you tried enough times for surety?

if so, then it is not just a random local source of RFI, but something to do with what is powered up, and that suggests maybe a faulty component - but other than possibly PS (there aren’t any electronic components shared between channels, so something like a faulty capacitor should only manifest itself in one channel -  you’ve tried different PSs so its not that. Something else shared perhaps -  e.g  an arcing switch or  plug contact perhaps. Try powering with different power cable to the PS, plugged into a different mains socket. Otherwise conceivably the Burndy connections - you obviously disconnected and remade the PS end when you swapped, but no harm disconnecting and reconnecting at amp end, and doing both ends a few times to clean the contacts, or swapping with the one on the CD.

Hi IB 

No I've not tried that yet ( disconnecting the interconnect from the 202/HC but leaving the other end connected to the speakers) so will give it a go.

You're right though I've not left it alone long enough to see if it stops by itself as I've been worried about it causing damage and the stress to the cats (I have 4 and they really don't like the sound when it starts so leaving it has not been possible so far but given I've not resolved the issue the sods may have to suffer a while) but I have now instructed the other half that should it happen to simply leave it until I have had a chance to look and I will do the same

but I will have a look at the suggested cable (I have also emailed ATC to see if they can provide me a set of cables as my previous discussions they did tell me they do make such a cable) 

I have also just ordered a 'better' 6 way extension to see if this is the issue and some ferrite rings for the speaker cables 

Of course, even without surety that the interference doesn’t stop itself, and isn’t auto atically there when you turn on, there’s absolutely no harm in changing/cleaning all associated power connections 

Innocent Bystander posted:

Of course, even without surety that the interference doesn’t stop itself, and isn’t auto atically there when you turn on, there’s absolutely no harm in changing/cleaning all associated power connections 

Hi IB 

Will be doing this when the new extension arrives as I just ordered some contact cleaner and will have a happy afternoon polishing mains plugs

Just a quick update for you all on this issue.

The pre amp is being sent to Naim as this has been identified as the fault in the chain.  The interesting thing is the fluttering sound has stopped now and the issue is a constant audible 'hisss' from the speakers at all times when the pre amp is powered on.   In a quite room it it noticeable  (If i can work out how to embed audio files I'll post the recording I passed to Naim here) 

But must say really impressed with the help from both the forum and Naim in getting to the cause of this issue 

Cheers

A constant low level hiss with Naim kit sounds quite normal - unless it's excessively loud (i.e. loud from a few metres or more away) for some reason, in which case that may indicate a fault.

Hi Richard  Yes it's audible in the room if the room is quite you can hear the speakers in the listening seat which is about 4.5m away.

OK, at worst, any hiss should only just be detectable at that distance, at best only detectable when much closer, unless of course, the room acoustics exacerbate those frequencies.

Out of interest, How did you identify the pre-amp as faulty?  Did you try a different example in its place?

Hi Richard 

I made a audio recording and passed it to the fine folk at Naim after much time troubleshooitng this with them (and ATC) over the phone

But no I didn't get chance to replace the 202 as I brought it second hand I didn't feel right trying to blag a loan pre from my local dealer 

Must say though if it is normal then it's excessive as the ATC's are very quite with all other pre's I've tried on them (ATC, DCS, Mcintosh , Jeff Rowland to name a few)

Still trying to get the audio file hosted so you can have a listen though   

You can listen to the issue here  (click on the link NAC202 below where you can download the audio file) 

There is a pop at 6 seconds which is the HiCap DR being turned on then at 36 seconds you can hear the pre turning on.  This was with no source connected to the pre.

NAC202

Thanks.  Yes, I hear it!

I don't normally have the speakers on when I power up but it shows the issue and the recording was enough for Naim to say send it in. 

I did think I was going mad for a while with this but really did want to persevere as I really do like the way the Atc's and the Naim sound together even with this issues I've had