Help! Preamp ground loop hum. How to fix?

Discussion in 'Audio Hardware' started by Strat-Mangler, Jan 6, 2017.

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  1. Strat-Mangler

    Strat-Mangler Personal Survival Daily Record-Breaker Thread Starter

    Location:
    Toronto
    New to vinyl and got a VPI Nomad version 2. This one can bypass its phono preamp so a different one can be used. Whatever preamp I connect, I get a nasty hum. I've tried finding different spots on the amp and turntable to ground it to but NOTHING seems to work!

    I've been at this for 3 days and I'm about to throw everything out the window. Just can't get rid of this so my only choices appear to be to use an amp with an integrated phono preamp or to use the Nomad's own preamp. Those are the only way I've been able to not have hum. I'm pulling my hair out and am frustrated beyond belief.

    Does anybody have any helpful suggestions on how to eliminate ground loop hum?
     
  2. chervokas

    chervokas Senior Member

    First of all, the ground wire on a turntable isn't likely to help you if you have a problem with a ground loop between electronic devices. That wire typically is a ground wire for the tonearm tube and maybe the turntable bearing well. It's not typically connected to anything signal related. It's not going to have an impact on a ground loop between the phono pre and the line pre/receiver or whatever you're using.

    So, if you're getting hum with various preamps inserted between the table and your line preamp, but not with an integrated or with the Nomad's own, are you getting that hum when the phono pre is connected to the line pre but with the turntable not plugged into the phono pre? Have you tried cheater plugs? Have you pulled ever connection out from the line amp except the phono pre and turned off all other electronics and light dimmers etc.? Are you using well shielded cables? Do you have environmental sources of electromagnetic radiation near the table/cabling etc? Have you located these outboard phono pres and especially their power supplies away from the table? What steps have you taken to isolated the source of the hum. Also, is it hum or buzz?
     
  3. Strat-Mangler

    Strat-Mangler Personal Survival Daily Record-Breaker Thread Starter

    Location:
    Toronto
    Thanks for your detailed reply.

    I'm using double-shielded interconnects. Not having this issue with preamps being out of the equation nor on my digital rig. This uniquely occurs when I have a preamp in the picture, no matter which one it is. I do not have cheater plugs and in fact only learned about what they are today while reading the instruction manual for the preamp.

    It's a hum, not a buzz. It occurs whether lights are on/off, whether I plug everything into the same or different outlets. The hum occurs whether the turntable is on/off. The moment the preamp is on, the hum begins. If I turn off my turntable, everything becomes silent for 1 sec (e.g. no hum for a moment) and then it comes back. No idea what that's all about. I've turned everything off with the exception of the amp and preamp with the hum still being there.

    Interestingly enough, on their revamped website, Dynavector brags about their preamp with the bulletpoint "No hum!" Check it out.

    Dynavector : P75 »

    So I'm wondering if perhaps the problem could be the turntable?
     
  4. KT88

    KT88 Senior Member

    Definitely a problem with the turntables ground scheme. A table should not hum, whether off no on, and certainly never intermittently when powered up or down. The issue is definitely there. You have also eliminated the phono preamps by trying more than one with consistent results.
    -Bill
     
  5. Strat-Mangler

    Strat-Mangler Personal Survival Daily Record-Breaker Thread Starter

    Location:
    Toronto
    Assuming this is 100% correct, what would be my options? Bring it to a tech? It has a ground lug which I needed to use when utilizing the internal preamp. That took care of the hum for that purpose. As soon as I bypass the preamp (by using jumpers on the preamp's internals), the hum appears.

    Since I am not the original purchaser, VPI has stated I'm on my own and cannot assist me in fixing it. I doubt I'd be able to since I'm not handy with a soldering iron anyway.
     
  6. chervokas

    chervokas Senior Member

    Is the hum there when the turntable is not plugged into the pre amp? Also, when troubleshooting hum, especially if I suspect a ground loop, I always do more than just switch all the components off -- I unplug all the components from each other so there are no chassis connections between anything but the components under test. The thing with the hum disappearing momentarily is weird. Maybe it's a problem with a way the bypass is wired. But you mentioned using some kind of amp with an integrated phono pre, did that not cause hum?
     
  7. Strat-Mangler

    Strat-Mangler Personal Survival Daily Record-Breaker Thread Starter

    Location:
    Toronto
    Yes. Am I screwed?
     
  8. RiCat

    RiCat Forum Resident

    Location:
    CT, USA
    If I may, from the above you get the "hum" when the pre is connected to the Arcam, is this correct? If so have you tried more than one of the high level inputs available? Have you tried one channel connecting at a time? If so is the hum there on both channels or just one? Have you tried different interconnects? Double shielded is how you described the ones you are using. The grounds may be incorrect for a phono pre to high level input use. Try any standard "stock or cheapo" you may have available. Since you report the hum both using the Dynavector and the built in pre in the TT I do not think the pre is the issue. I think the issue lies in the interconnects. Just a guess.
     
  9. chervokas

    chervokas Senior Member

    No. That means the problem is not the turntable.
     
  10. Strat-Mangler

    Strat-Mangler Personal Survival Daily Record-Breaker Thread Starter

    Location:
    Toronto
    On this amp, all channels operate exactly the same. I tried a handful of them. Tried different interconnects including some unshielded ones.

    No, there is no hum through the integrated preamp on the turntable. Only external ones.
     
  11. Strat-Mangler

    Strat-Mangler Personal Survival Daily Record-Breaker Thread Starter

    Location:
    Toronto
    I'm operating that the Nomad is the problem. Just got a prime and heard the faintest ground loop him at the store. We'll see if I get the same kind of hum when I plug the P75 through the Prime.

    I'll keep you posted. :)
     
  12. KT88

    KT88 Senior Member

    Wait, now you are bringing up that the system has hum without the table connected at all? That's a horse of another color. There is definitely something fishy going on with the built-in preamp on the thing if the ground noise comes and goes when powered up and down. That aside, if you are saying that you are getting the hum that you are complaining about without the table being connected at all, that's a new development and obviously eliminates the table from that scenario.

    Since you say that you can connect the table with its internal preamp bypassed to an amp and use the amps built-in phono without issue, yet when you connect any of several other external phono preamps you get hum with or without the table connected, let me ask you one simple question... Are you plugging the external phono stages into the amps phono input or into an aux input?
    -Bill
     
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  13. chervokas

    chervokas Senior Member

    If you have hum without the turntable plugged into the phono preamp, its 100% certain that the turntable cannot be the source of the hum.

    If the turntable's not even connected to the system and the system is humming, that should be pretty obvious: the hum isn't coming from the turntable (though of course you could have multiple sources of hum in your set up).

    Also if you have no hum when the turntable is plugged into some integrated phono pre, but you do have hum when an external phono pre is plugged into the device, it's obvious that the table is not the source of the hum.

    Probably there's some leakage current, some grounding problem with grounding scheme of your AVR (that is what your using, yes, the device mentioned in your profile?), some issue between the phono pre and something else also plugged into the AVR, or an issue involving not ground loop hum but induced hum because the phono pre (or interconnects from the table to the pre or from the pre to the AVR) are too close to the AVR's transformer or some other source of electromagnetic radiation, or you have a bad interconnect, etc. Or maybe like Bill say, you're plugging the external phono pre into the internal phono pre? I dunno it's hard to troubleshoot hum from afar. But if you have hum without the table plugged into the phono pre I can assure you that the table cannot be the source of that hum.

    Sounds like you're chasing your tail but you haven't quite yet identified the source of the problem, which should be step one. To locate the source of hum in a system the first thing you need to do is unplug every device from the AVR and from the wall. There should be no inputs connected to the AVR and no AC connections to anything in the system other than the AVR. Turn on the AVR. Is there hum? If no, add the next device you suspect -- the phono preamp. Is there hum? In this case it appears yes (though we don't know yet because I don't think you've unplugged all the AVR inputs and device power connections yet). So the things to do are switch to a different set of interconnects and/or physically relocate the phono preamp away from potential sources of electromagnetically induced noise (such as other audio components, particularly their power supplies; or electrical cords -- though at this point none should be connected to the wall except the AVRs and the phono pres; wall warts, tvs, computers, fluorescent lighting, etc) and/or try a set of cheater plugs on the phono pre. See if you can solve the noise problem at it's source. You say you've had it with multiple pres and that you have it without the turntable plugged into the pre so the problem is obviously related to the connection between the phono pre and the AVR or the phono pre and something else connected to the AVR. That's what you should be focusing on.

    Also, fwiw, every source of hum in an audio system is not a ground loop hum. That faint hum you heard in the store sound more like induced hum from the phono cartridge or exposed unshielded phono wires picking up hum from some physically nearby environmental source.
     
    Last edited: Jan 7, 2017
  14. Slick Willie

    Slick Willie Decisively Indecisive

    Location:
    sweet VA.
    While not the OP's issue, I once had hum on one of my set ups from the tables's power and audio cords running parallel to each other...another time the interconnects were too close to the wall wart.
    Sometimes these things are tricky fo' sure!
     
  15. Colin M

    Colin M Forum Resident

    It does sound as though you're "doubling" your phono amplification and plugging in the line level output of the preamp into your phono input of the integrated. How loud is a record when you play one?
     
  16. BIGGER Dave

    BIGGER Dave Forum Resident

    I have a feeling that's it!

    OP - Please verify the output of the external preamp is plugged into an AUX input on the amp. If you're plugged into the PHONO input, you'll be getting too much gain which could lead to raised noise levels which could be perceived as HUM, not to mention a multiplied RIAA curve.
     
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  17. slovell

    slovell Retired Mudshark

    Location:
    Chesnee, SC, USA
    Try daisy chaining a ground wire from component to component.
     
  18. RiCat

    RiCat Forum Resident

    Location:
    CT, USA
    Time OUT!! First from what I see the Arcam does not have a built in phono section only high level inputs. Is this correct?
    "No, there is no hum through the integrated preamp on the turntable. Only external ones." OP this is your statement quoted. Does this mean That when you connect the TT to the Arcam using the phono pre built into the TT there is no hum and the music sounds fine? If this is the case then either the Dynavector is defective or there is a mismatch between the Dynavecctor output level and the the Arcam input. What inputs are you using on the Arcam? BIGGER Dave may be partly correct? You may need to adjust the Dynavector settings/jumpers to match the input sensitivity of the Arcam. If the TT works as intended using the builtin pre then the issue is the Dynavector compatibility. Have you tried talking to your dealer or to Dynavector btw?
     
  19. Strat-Mangler

    Strat-Mangler Personal Survival Daily Record-Breaker Thread Starter

    Location:
    Toronto
    @chervokas @KT88 @RiCat @Colin M @BIGGER Dave

    Thanks for chiming in. There seems to be some miscommunication so I'll try to boil things down to their basics.

    1. The hum does NOT occur only when using the Nomad's integrated phono amp. Only scenario where no hum exists.
    2. The AVR350 does NOT have an integrated phono preamp nor a phono input.
    3. All the AVR350's inputs are identical as stated in the manual so it doesn't matter where I plug it into. Yes, I have tried numerous inputs just in case it made a difference.
    4. When using an external phono preamp, the hum occurs 100% of the time regardless of which external preamp is used.
    5. Disconnecting the turntable from the external preamp removes the hum. Reconnecting it puts back the hum.
    6. Shielded and unshielded interconnects were tried. Same as attempting to ground anything to anything. No difference whatsoever.
    7. Connecting all of the components to the same outlet or separating them made no difference either.
    8. Powering off or disconnecting everything else but the turntable, amp, and preamp made no difference either.
    9. The hum is quite loud! It's not a gentle one.
    10. I will be connecting my VPI Prime today. If the hum disappears, it'll confirm it's the Nomad which is at fault.

    Please let me know if you have any follow-up questions. I'll do my best to answer them as best I can.
     
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  20. Strat-Mangler

    Strat-Mangler Personal Survival Daily Record-Breaker Thread Starter

    Location:
    Toronto
    Didn't take me long to connect things together.

    Had the Prime connected to the Dynavector P75 preamp and there was the hum, as expected. As soon as I took a speaker wire and connected the Prime and P75's ground lugs together, the hum was eliminated 100%.

    So it's definitely the internal grounding scheme of the Nomad which is at fault. Now, I have to determine if there's a VPI-certified tech who could fix it for not too high a sum of money.

    EDIT : forgot to mention VPI stated there's a set of jumpers I can remove if there's a grounding issue from the inside of the Nomad but removing them did not address the problem.
     
    Last edited: Jan 7, 2017
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