Before I get into the problem I’ve been having, my set-up consists of the Pro-Ject Debut Carbon DC with an Ortofon 2M Red cartridge -> Rega Fono Mini A2D preamp -> Pro-Ject Head Box S2 -> Sennheiser HD598 headphones. I had begun to notice a sort of low rumbling hum during lead-ins, between tracks and sometimes during especially quiet passages of music where no other low frequency information was happening. I quickly went about googling the problem and researching issues people had been having with the turntable. I found out quite fast that a substantial number of people had been complaining about motor noise with the Debut Carbon turntables, most notably with the original AC version but still with the DC version. With this in mind, I looked at the vinyl rips I had made and found that they all had the same hum I’d been experiencing, so whatever was happening during playback was also getting recorded over USB. I had a look at the recordings with a spectrum analyser and sure enough there was a low rumble at around the 50/60hz range. Upon showing the recordings of some of the particularly quiet passages of music to friends and family, everyone was in agreement that there was indeed a noticeable hum. One person in particular likened it to “an air-conditioning unit humming in the next room”. To try and get to the bottom of this, I did all kinds of troubleshooting: removing and replugging in cables, turning off my computer which is very close to my turntable in case it was causing interference etc. all to no avail. Upon cranking the volume of my headphone amp with nothing playing I noticed a different, harsher hum which I identified as ground hum. Sure enough, the system wasn’t grounded properly and after running a homemade ground cable from the barrel of the turntable’s power supply to the ground pin of a plug in the wall the ground hum all but disappeared. However, my aforementioned rumble still remained. At this point I had been googling lots of information about motor noise and had convinced myself that this was the problem I was hearing. With this in mind I brought the turntable and my other components back to the shop I had bought them from and they had a listen and could not hear anything. The hum persisted to my ears in two different rooms of the shop and although quieter, still persisted when played back through speakers. Ultimately they decided that there was no fault and that the hum I was hearing was essentially a by-product of my system and due to the fact that I was listening through headphones. Upon returning home I thought I would carry out two further tests that would determine whether or not the hum I’d been hearing was part of the record or whether it was extraneous. Firstly I removed the belt from the platter so that turning the motor on and off did not spin a record. I then turned the motor on and lowered the stylus onto a stationary record. Instant hum. Raised the stylus. No Hum. At this point I thought that that was pretty conclusive evidence that it was indeed motor noise. But to really be sure, I thought that if I played the LP at the incorrect speed of 45rpm if the hum was part of the record then the pitch would surely increase. The pitch did not increase. So with my newfound knowledge I phoned back the shop again and told them that I am convinced that it is motor noise and that I would like to try out the Rega Planar 2 and Planar 3 through my existing components for a possible upgrade. I go in and to my utter surprise; both Rega turntables exhibited the same hum, albeit to a lesser extent than my Pro-Ject. By now I was utterly confused and had no idea what I was hearing any more. I informed the shop of this and suggested that maybe this had something to do with my pre-amp and headphone amp instead. So the shop plugged a CD player into my headphone amp and when music played there was hum and as soon as I hit pause the hum vanished. Utterly relieved that we had got to the bottom of this I then realised that when making vinyl rips (in which the hum is still audible) the signal does not even reach the headphone amp as it goes out via USB at the preamp stage. At this point we tried a CD player into an actual amp with a headphone jack and there was still hum (although quieter than with my headphone amp). It was then that we decided to call it a day and that I would keep my existing hi-fi set up but that by eventually upgrading the cartridge, preamp and amp and buying speakers in the future, the problem would get better and better. The reason I have written all this up is that I’m not entirely satisfied with this answer and wonder whether anyone with more expertise would be able to inform me what this hum actually is, where it’s coming from and hopefully steps I can take to minimise or eliminate it. Perhaps it’s an issue with unclean power or cheap interconnects or maybe it’s an issue with my preamp but ultimately I would really love to get to the bottom of this. I can easily provide audio recordings and spectrum analysis pictures of everything I’ve been describing as well.