"Groundloop" noise in brand new SQ7 analog outputs

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This topic contains 15 replies, has 5 voices, and was last updated by Profile photo of Neo Neo 1 year, 5 months ago.

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  • #86832
    Profile photo of Neo
    Neo
    Participant

    Good evening everyone.

    I use my SQ7 as a 16 channel DA converter into a NEVE8816 summing mixer and then out to my monitor controller. Studio use only. Everything is connected via Dante in the digital domain. We recently upgraded all our power cables and I went about a recalibration of levels, gain structure, etc of the analog section of the signal chain. At first I thought I had found a massive ground loop as I had the typical static 50/60hz buzzing in the speakers when I turned the mixer input + monitor output gains right up (checking for noise in the system). I have been a studio tech for over 25 years and have built this particular installation around a dedicated technical earth, brand new electricity wiring, Mogami/van Damme/Klotz cabling only, etc so pretty sure there wasn’t a ground loop anywhere I couldn’t trace. Mains Power is provided via dedicated block and (very) expensive cables. Grounds are lifted where appropriate, perfect ‘star’ formation in terms of wiring.

    After MUCH faffing I realised that the “mains hum” must be coming from the SQ7, and even stranger, when switching the SQ7 on, it is silent as the night all at max gains through the summing chain, just the white noise, no interference, crackling, mains hum, etc … then about 3-4 minutes in the hum starts, it’s definitely the “sound” of the electricity getting into the the analog outs of the SQ7. Also presents itself on the headphone output. USB unplugged, firmware updated, mixer reset, all inputs and outputs (analog) unplugged, I can replicate the same problem by looping outputs 1/2 back into the mixer and listening via headphones and the master bus. If I then switch the mixer off, plug the mains power into a different outlet and switch back on, the mixer is silent again, from a few minutes, then the hum starts again.
    I haven’t noticed up to now as I mix and master at relatively low levels and the hum is barely noticeable at my mixing/listening levels + my ears are over 40 years old šŸ™‚
    I checked now however and the noise does print through as well, it isn’t just in the monitor chain. When mastering for loudness this hum could definitely be audible so I’m stumped.

    Anyone got any ideas ? Could it be that the internal fans pollute the audio with noisy electricity ? I have looked at the fan RPM counters and haven’t found any correlation between when the humming starts and whether the fans pick up speed. My studio is also quite temperate, well cooled and everything is properly ventilated. Hope it’s just a dodgy power board that could be switched out ?

    Sorry for the long rant – I spent the last week picking every cable and connection apart (hands and knees type of action) and I am at my whit’s end.

    Best,
    Peter

    #86833
    Profile photo of xyz
    xyz
    Participant

    so if everything is unplugged from your mixer and everything else is turned off and you get the hum in your headphones [cranked] after a few minutes…
    And you have tried different power socket direct into the main source?
    Is that what you are saying?

    #86838
    Profile photo of Neo
    Neo
    Participant

    Indeed. I have a dedicated electrical circuit (mains sockets) + earth, clean, 2 year old installation running quite abit of gear off it without no issues of interference, hum, noise, etc. We purpose built this studio from the ground up. Have tried cable that came with the mixer, a high end GBP 250 Belden bespoke power cable a two quid Kenable cable from amazon. All same result. And yes, everything unplugged, connect output 1 and output 2 to STR2L and STR2R for example, then crank the trim to +24db on the STR2 channel – 3/4 minutes in – a noise hum starting to appear, first a few ticks, tacks, then the whole brrrrrrrrrr (sorry for the silly wording) ā€¦ electricity hum but starts out with a few ticks/clicks (not digital). Can replicate this noise on headphone port, A/B out and AES digital out. So it’s not in my monitor chain (post mixer) and it’s not in my analog summing chain (analog out -> balanced snake -> summing mixer -> 2bus back into SQ7). Can replicate by connecting to out 3/4, 5/6, etc and the TRS ports at the back (STR1 and STR2).

    What’s telling me that there is a problem somewhere in the mixer is the fact at the noise (the electrical hum) is not present when the mixer is turned on, but switching off / disconnecting / re connecting mains power or any of the analog summing chain components has no effect, then starts to feed in a short while after – almost as one / two or some components in the mixer PSU oards (caps maybe) get charged up properly (sorry I am not an electrical engineer).
    Just for fun, and to make sure my expensive earthing system isn’t to blame I ran a 20 meter extension into the main house and plugged the mixer into a kitchen outlet, different earth, different circuit – same exact result.

    I haven’t not and won’t open up the mixer myself but from experience I’d say I have heard this kind of interference from noise fan supplies / dimmers, etc (have no dimmers anywhere in my supply circuit) – just the two fans on the SQ7 – they do run very silently though – I would not have thought that in a brand new released mixer, A&H would have designed a noise fan electrical supply circuit.

    #86839
    Profile photo of Neo
    Neo
    Participant

    Also, before I forget, unit is not connected via USB (either back or front) and I have never had any issues with the usb multi track recording facility that have been reported on here. Works actually quite well, definitely no digital noise in the system.

    Real shame as I very much like the SQ7 and it fits into my workflow perfectly. Hope I can get this one sorted as the noise floor if this is the stock behaviour isn’t good enough for studio work.

    #86840
    Profile photo of xyz
    xyz
    Participant

    If you have a scope to look at your AC would be good?
    otherwise
    I would suggest that you start an A & H ticket.

    #86843
    Profile photo of SteffenR
    SteffenR
    Participant

    To wich Bus or Signal are you listening ?

    And starting a Ticket is the next you should do

    #86847
    Profile photo of Neo
    Neo
    Participant

    Tx Steffen, how do I go about the ticket? Sorry for the stupid Q, couldntnfind any obvious links or places in the forum.
    I have gotten in touch with the retailer though who sold menthe desk.

    Tx,
    Peter

    #86863
    Profile photo of Barryjam
    Barryjam
    Participant

    Neo,

    Iā€™m sure you are well beyond this in your testing, but I once discovered my 60Hz hum was ultimately due to the mere physical proximity of a (wireless mic) power supply to my AH stage box. The hum was present even if the device powered by the PS was turned off.

    But that was immediate hum, not a delayed hum.

    Please keep us informed about what you learn.

    Barry

    #86870
    Profile photo of peterlanders
    peterlanders
    Participant

    Neo,

    To file a ticket you need to go to the support page on the main A&H website.

    #86873
    Profile photo of SteffenR
    SteffenR
    Participant
    #86874
    Profile photo of Neo
    Neo
    Participant

    Many thanks Steffen.

    @barryjam – thanks Barry, these are indeed very valuable pointers, I have made sure that I haven’t got a naughty neighbour running a HAM radio or something silly to pollute the electricity from the ‘outside’. I run a number of very sensitive pieces of analog equipment in racks right next to the SQ as well, so I’d expect there to be some interference to if there were any external issues. But indeed very good thinking.

    #86875
    Profile photo of SteffenR
    SteffenR
    Participant

    Can you move your SQ outside the studio and test it again?

    #86877
    Profile photo of Neo
    Neo
    Participant

    Hi Steffen, sorry just coming back to your earlier point about which bus I am using – I have nothing connected to analog IN or digital IN, basically no inputs. I have nothing connected to the analog OUTs except for a balanced pair of cables from analog outs 1 and 2 to STR2L/R for example, e.g. the shortest possible path to see whether there is any noise on the analog outs. I could connect four cables also to Outs 1/2/3/4 and STR1, STR2, etc ā€¦ I really notice the noise through my summing mixer as it sums all 16 outputs and then amplifies as well — at first I thought I was having a nasty groundloop in this mixing chain but through trial and error reduced it back to the mixer.

    What’s most puzzling is that the interference is not present immediately but only if I unplug the power cable and move to a different socket (any socket, I have 10+ sockets all on the same HQ dedicated earth ring) as almost if disconnecting the earth for a moment discharges a component or resets a component inside the mixer PSU == at least for a little while…

    I am travelling right now so will open a support ticket when I am back at base.

    Many thanks indeed for your help so far.

    Best,
    Peter

    #86878
    Profile photo of Neo
    Neo
    Participant

    I really didn’t want to have to take the mixer out of the desk but you are correct that is one thing I haven’t done and need to do to make sure there is no local interference, very unlikely as I have a fairly significant amount of gear racked and all playing nicely, very nicely indeed in terms of noise floor. Some of this gear is decades old some of it is new.

    I will have to try and relocate the mixer completely when I get a chance.

    Tx,
    Peter

    #87136
    Profile photo of xyz
    xyz
    Participant

    @Neo
    How did you get on with that “ground Loop Hum” ?
    Did you solve that ?
    Keen to know.

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