Question Pro-Ject Debut Carbon DC - mysterious hum

Discussion in 'Hi-Fi Stereo Systems & Separates' started by Reubzen, Aug 1, 2018.

  1. Reubzen

    Reubzen
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    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.
     
  2. Nat64

    Nat64
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    I had a quick google on this and tbh it seems to be a common problem.
    I was interested because my mates keep telling me that their belt driven turn tables are better than my direct drive technics.
    I thought the whole idea of a belt drive turn table was to isolate the motor from the rest of the unit to stop any hum, noise ot whatever you want to call it. I'd say you have conclusively proved its a fail in that respect.
    I take my hat off to you for persevering, but personally I would take that turntable back and buy something else.
    Anyway, I found this.........clearly you are not alone.

    Does the new Project Debut Carbon DC fix the motor hum problem?

    Good luck.
     
  3. Reubzen

    Reubzen
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    I would completely agree with you and it was my plan to take it back and buy something else but I heard what sounded to me to be the same hum with the Rega Planar 2 and Planar 3 running through my same preamp and headphone amp so that's why I wasn't sure
     
  4. Deleted member 781788

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    Lets see if I got it right:
    1- the belt removed, stylus on a stationary groove and motor turned on = HUMM
    2- same as above, but pitch control fully up = HUMM but at same frequency (are you sure?)
    3- as above but motor off = Silence
    if the above applies it is an electrical noise.
    Somehow the mains humm is leaking into the system, usually trough bad earthing/cabling or bad shielding, specially that you have some humm present even when turntable is switched off.
    I blame your amplifier!
    Bear in mind pitch control usually changes the speed by +/- 5% - so the ear may not be able to tell if the Humm is 50Hz or 55Hz, hence the question Are you sure.
     
    Last edited by a moderator: Aug 2, 2018
  5. Reubzen

    Reubzen
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    That's all correct yes except that I changed speeds between 33 and 45 and recorded the same excerpt of music at both speeds and I can confirm that the hum is the exact same frequency as I was flicking between the two recordings and it remained at a constant pitch
     
  6. Deleted member 781788

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    it is electrical then.
    the 33/45 speed selector is a mechanical one, so the motor still rotates at the same speed.
    The only thing that changes the motor speed (frequency) is the pitch control.
     
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  7. Reubzen

    Reubzen
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    Would the motor hum change with the speed of the record though? The speed is changed by the belt so I wouldn't have thought that the motor would emit a different pitch. However looking more closely, the hum does seem to be 50hz so it probably is electrical. In that case, how would I go about reducing/eliminating this? Thanks so much for your help by the way :)
     
  8. jonno73

    jonno73
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  9. jonno73

    jonno73
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    Nb - it’s a PSU not a brush, so no idea why the link says that!!!

    Just search for ‘Pro-ject HighPower It’
     
  10. Deleted member 781788

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    we usually start at the end and work backwards to eliminate the culprit.
    disconnect everything from your amp, but power , speakers.
    switch on, turn volume up and listen.
    start with input switch, then connect inputs to the amp one by one to see when the humm appears.
    Come back to me.
     
  11. Reubzen

    Reubzen
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  12. Reubzen

    Reubzen
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    My headphone amp only has one phono input and with nothing plugged in it's absolutely silent even on max volume. I'm not sure how to then determine whether it's the pre-amp or the turntable at fault.
     
  13. Khazul

    Khazul
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    Yes, I've often been told the same, but have yet to be convinced to have a serious look at anything else (well except the new GR maybe if I ever decide I don't need two decks any more) :)

    However it seems my technics decks (SL1210M5G) are silent as the grave whatever I plug them into here (dj mixer, dj audio interface or my Yamaha amp) so long as the ground lead is connected properly and I don't do something stupid like plugging it into a power outlet on the other side of the room via a long extension lead.
     
    Last edited: Aug 2, 2018
  14. Reubzen

    Reubzen
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    I just bought a new Pro-Ject preamp and the hum is still there. I am at an absolute loss now. I really really don't understand where this is coming from anymore. Absolute silence with the volume fully cranked and then as soon as I lower the stylus there's hum
     
  15. Reubzen

    Reubzen
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    My turntable, preamp and headphone amp are now all DC powered and all made by Pro-Ject just to clarify
     
  16. jonno73

    jonno73
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    Have you connected the ground wire from Turntable to Phono Amp?
     
  17. Khazul

    Khazul
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    Hmm - I wonder if there is a damaged screen on the cartridge wires and its actually the change of position of the arm and hence wire that is exposing the issue.

    While I don't think it is static, have you tried anti-static treatment? My deck has metal platter so only the mat and record that can accumulate charge not the platter as well.
     
  18. Deleted member 781788

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    have you?

    Working backwards means this:
    - so the amp is silent.
    - connect the preamp, do not connect it to the turntable in any way, keep the preamp switched off, but connected to the main amp, is there hum? (1)
    - switch on the preamp, still not connected to the turntable, is there any hum? (2)
    - carefully use tweezers to disconnect the wires from the cartridge at the head shell (all 4) , connect the phono cable from turntable to the preamp (switched on) , is there any hum? (3)
    - finally connect all wires to the cartridge and try again. is there any hum? (4)

    (1) = check interconnects from preamp to the amp - try disconnecting earth wire on the mains cable from the amp.
    (2) = assuming the previous did not apply - the preamp(s) are the culprit (1 in 100)
    (3) = check turntable phono interconnects to the pre amp - make sure the extra earth wire from the turntable is connected to the preamp body.
    (4) = the cartridge is faulty and has internal wiring issues.
    (5) = get an exorcist, priest, rabbi or a mullah (if you can fit them in one room) !
     
    Last edited by a moderator: Aug 7, 2018

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