Hi
Not been on for quite some time, but I've put my time away to good use by amassing even more music, going to lots of gigs and much drinking of gin.
Anyhow, I have a problem with my 180, as follows...
The amp is susceptible to RF interference from my DAC (and I'd guess interference from any other source) Switch the DAC off, the noise disappears. Luckily the amp is three shelves away from the DAC, but if anything reflects it back, like having the door open, it's there. However, this is most probably related to the other issue...
There is a noticeable low level hum through the speakers at all times. The amp is one shelf below the HC, so I pulled the amp off the shelf, just to make sure this wasn't the cause. The hum worsened, and it started picking up the RF from the DAC to boot! The hum /noise is suppressed slightly if I hold the SNAIC.
If I substitute the 180 with my 140 using the same SNAIC, all of the above disappears. There is no loss of audio or any noise/crackles with the 180 that would indicate a poor connection.
The amp went for a service with this fault, in the hope that a service would rectify the issue. It clearly didn't! The service wasn't carried out by Naim btw.
I'd be most grateful to hear from anyone who could point me in the right direction on this one. My 140's lovely, but I prefer the 180!
Many Thanks,
Heath
Posted on: 06 June 2017 by Adam Zielinski
From the description it would appear to be a ground loop hum, rather than RFI.
More info, as Huge wrote, needed on specific equipment, connections, mains ciecuits...
Posted on: 06 June 2017 by Heath
The DAC doesn't affect the 140 though, so not a fault of the DAC. No hum with the 140 either. I agree that it's a possible earth issue, which could also be rendering the amp more susceptible to RFI. There are two separate noises, the hum, plus a high frequency noise, the RFI. The RFI is not present at all times, only when the amp is in close proximity to the DAC, becoming more noticeable the closer it gets. The rest of the system comprises 72, HC with SBT & CD transport in to a M-DAC with MCRU linear supply. Mains is just on the ring main. Connections are just the usual Chord phono to DIN & SNAICS.
Posted on: 07 June 2017 by Huge
Sounds like a faulty DAC - it shouldn't be emitting anythink like that amount of interference.
Incidentally it could just as easily be at ultrasonic frequency rather than at RF and fixing these two is different, so fix it at source and fix the DAC.
Posted on: 07 June 2017 by Heath
OK. So working on the assumption that the DAC was to blame, even though the 140 wasn't showing the same symptoms as the 180, I carried out some further investigations.
I had noticed previously that the MCRU PSU for the M-DAC was supplying a slightly lower voltage than the 15v required. If you hold down the volume control on the DAC when you power it up, it displays the raw digital voltage. When using this PSU, the voltage displayed was 14.2-14.5v. When I plugged the original PSU back in, the voltage displayed was 16.9v. The result is that much of the high frequency noise has disappeared, as has the hum. I do still find it strange that the 140 is not affected in the same way, as they are essentially the same amp.
MCRU are in the same town as me, in fact they are opening a retail store in Huddersfield town centre this weekend, so I will quiz them about this.
I'm still a little sceptical that this is an absolute fix, and will keep my ears open!
Thanks for your input Huge & Adam, much appreciated.
Cheers
Heath
Posted on: 07 June 2017 by Heath
Actually, scrap that. Its seems as though that was a coincidence. As the amp has warmed up, the low level hum has returned, and I'm once again getting the interference. I wish I'd kept my other, older 180, that was fine! I'm still going to question the low voltage on the MCRU PSU though.
Ah well, back to the 140 for now...
Posted on: 09 June 2017 by Richard Dane
As Witch Hat are not an approved Naim service centre I would ask members not to discuss further. Heath, I advise you to get in touch with them and take it from there. As this thread is arguably on the cusp of falling outside of forum AUP I'm going to close it now.
