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Advice needed: re-wiring DJ Studio setup, eliminating ground loop issues

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Advice needed: re-wiring DJ Studio setup, eliminating ground loop issues

Postby VorTechS » Fri Jun 21, 2019 10:37 am

Hi all,

First time poster, so hopefully I've put this in the right place. (Apologies if not)

I currently have a DJ setup which is used to stream to an online radio station, and to Twitch but I appear to have a ground loop issue that I've not been able to solve - and would welcome any advice!

I need to sort out the wiring anyway, and so my plan is to strip everything back and re-wire/re-connect - hopefully eliminating (or reducing to bear minimum) the loop which is resulting in audible buzzing on the streams and on my speakers too.

The equipment:

- Citronic CDM10:4 MK5 Mixer
- 2 x Technics SL1210 MKII turntables
- Native Instruments Audio A6 USB Interface
- Pioneer DDJ-T1 USB Controller
- Dell Laptop
- Amplifier (forgotten brand at time of writing, but it's more of a home cinema thing than a dedicated amp as my old Rega Luna has pretty much given up)
- 2 x Monitor Audio Bronze speakers
- Sony Microphone (not sure on model, it's about 20 years old though)
- Sony Bravia TV

How it's setup:

1) Both the Pioneer DDJ-T1 and NI Audio A6 are connected to the laptop via USB
2) The SL1210 turntables are connected via RCA to the NI Audio A6 (2 channels, grounded to it too)
3) The NI Audio A6 is connected to the mixer via RCA cables (2 channels, Cd/Line-In)
4) The amplifier is connected by unbalanced RCA output from the Citronic mixer
5) The laptop (stream/recording input) is connected via 3.5mm microphone jack to unbalanced mixer 'Booth' (RCA) output
6) The microphone is plugged into the mixer (XLR socket, but by 5.25mm jack)
7) The Sony TV is connected to the laptop via DisplayPort connector

Software in use:

- Traktor Pro 3.0
- BUTT (although will be replacing with my own software, when I get it working)
- StreamLabs / OBS Studio (alternate between the two occassionally, until I decide which I want to use full time)

In an ideal world, I'd like to split the turntable output (indeed have before I started trying to work out what's causing the buzz) so that I can bypass the digital setup when needed (into dedicated channels on the mixer).

I have 3 RCA ground loop isolators available. I also have another PC that I will be introducing to take over the recording/streaming so there's less load on the laptop.

Just in case it's important (I believe it used to be many many moons ago) all power supply requirements are fulfilled by socket extensions connect to a wall outlet (which is a spur of another outlet).

Before I start stripping everything out, are there any obvious issues with the above (or proposed) setup that sets off alarm bells to anyone?

Does anyone have any advice on where, if at all, I should place the ground loop isolators?
Or should I be looking at different isolators?

Any and all advice greatly received!
Thanks!

NOTE: Because I just thought of this, the DDJ-T1 and NI Audio 6, whilst connected via USB, are also separately powered so not just relying on USB power.
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Re: Advice needed: re-wiring DJ Studio setup, eliminating ground loop issues

Postby Hugh Robjohns » Fri Jun 21, 2019 11:02 am

It's a complex rig comprising entirely of unbalanced connections, so ground loops are to be expected.

From what you've described, I would expect the most likely loops to be between the Citronic mixer, the power amp, and possibly the TV. Certainly, I'd expect the Citronic and power amp to have mains safety earths.

The laptop is probably ground-free but the situation will probably get even more complicated when you add the desktop computer as that will also have a mains safety earth to add another loop!

With systems like this, the only way of sorting it all out is to start with the core devices and make sure that's clean before adding each additional device, dealing with any hum issues at each stage.

So I'd start with the turntables into interface and build from there. I expect you'll need your ground lifters between the mixer and power amp for sure...

It sounds like everything is powered from a single wall outlet, which is good. I'd plug anything with a mains safety ground into adjacent extension board sockets closest to the cable, just to minimise the loop size.
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Re: Advice needed: re-wiring DJ Studio setup, eliminating ground loop issues

Postby VorTechS » Fri Jun 21, 2019 11:36 am

Hugh Robjohns wrote:It's a complex rig comprising entirely of unbalanced connections, so ground loops are to be expected.

In terms of 'just playing out from home' I suppose it is, but without forking out an awful lot of money (that I don't have) it's a combination the allows me to get the most out of the equipment I've built up over the last 20 years and still give me a fighting chance to 'keep up with the crowd' .

Hugh Robjohns wrote:From what you've described, I would expect the most likely loops to be between the Citronic mixer, the power amp, and possibly the TV. Certainly, I'd expect the Citronic and power amp to have mains safety earths.

The laptop is probably ground-free but the situation will probably get even more complicated when you add the desktop computer as that will also have a mains safety earth to add another loop!

Yea, adding the desktop PC can only add to the strain. I do however, (albeit probably ill-advised to use) have non-earthed power cords in my arsenal if that'll help alleviate things.

Hugh Robjohns wrote:With systems like this, the only way of sorting it all out is to start with the core devices and make sure that's clean before adding each additional device, dealing with any hum issues at each stage.

So I'd start with the turntables into interface and build from there.

To clarify thelast point...

Turntable -> A6 -> Mixer -> AMP

....without the laptop and see how that runs?

I have a feeling the A6 won't output anything without being connected to the laptop if that's what was being suggested. Although I'll give it a shot anyway!

Hugh Robjohns wrote:I expect you'll need your ground lifters between the mixer and power amp for sure...

I'll be sure to put an emphasis on that!

Hugh Robjohns wrote:It sounds like everything is powered from a single wall outlet, which is good. I'd plug anything with a mains safety ground into adjacent extension board sockets closest to the cable, just to minimise the loop size.

Ah, so the old method of separating Ground vs Non-ground devices is still a thing? Knowing how advice changes over the years, I wasn't sure. Right now, it's a double wall outlet, 2 extension cables with no regard for what's plugged into where.

I really appreciate the help and advice, thank you!
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Re: Advice needed: re-wiring DJ Studio setup, eliminating ground loop issues

Postby Hugh Robjohns » Fri Jun 21, 2019 12:51 pm

VorTechS wrote:I do however, (albeit probably ill-advised to use) have non-earthed power cords in my arsenal if that'll help alleviate things.

Nooooooooooooooooooooooooooooooooooooooooooooooooooooooo!!!!!!!!!!!!!!!!!!!!!!!

They'll only alleviate you of your life. Throw then away immediately!

Yes, removing the earth from a mains lead might stop a ground-loop problem. But it also disables the critical safety design of the mains powered equipment, and it has a long and, sadly, very well-proven record of killing people.

Ground-loops should only be sorted by breaking the loop via the audio cable screens and nowhere else! That's the only safe way. It often requires 'hum-stoppers' or line isolating transformers, or special (modified) audio cables, but it's not expensive or complicated and it works 100% safely every time. The only challenge is in figuring out the best place to break the screens.

To clarify the last point...

Turntable -> A6 -> Mixer -> AMP

....without the laptop and see how that runs?

I have a feeling the A6 won't output anything without being connected to the laptop if that's what was being suggested. Although I'll give it a shot anyway!

You'll need the laptop to configure the interface, but as it is a laptop you can run it on its battery to start with to avoid a potential mains earth connection there. (Some laptop supplies are earthed but most aren't) . So start with the decks into the interface, and check
for hums/buzzes with headphones at the interface. If that's clean, add the laptop power supply and check again. The you can try hooking up the amp and, if that then buzzes, connect via the hum-breakers and try again...

Ah, so the old method of separating Ground vs Non-ground devices is still a thing?

They don't need to be separated -- quite the reverse, really. But anything that is grounded should come from the one wall socket and all the plugs should be in adjacent sockets on an extension board. The idea is to make them all have the same ground reference voltage so that the circulating ground currents are as small as they can possibly be.

Right now, it's a double wall outlet, 2 extension cables with no regard for what's plugged into where.

Room for improvement there then! ;-)

H
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Re: Advice needed: re-wiring DJ Studio setup, eliminating ground loop issues

Postby The Elf » Fri Jun 21, 2019 1:02 pm

VorTechS wrote:Yea, adding the desktop PC can only add to the strain. I do however, (albeit probably ill-advised to use) have non-earthed power cords in my arsenal if that'll help alleviate things.
Dear lord! Bin them NOW! Seriously.

And cut them up first.

Oops - Hugh's responded.
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Re: Advice needed: re-wiring DJ Studio setup, eliminating ground loop issues

Postby ef37a » Fri Jun 21, 2019 8:59 pm

I am confused? "The SL1210 turntables are connected via RCA to the NI Audio A6 "

I have not found any information about the outputs of the SL1210s but I do not think they have built in RIAA corrected pre amps? I have an NI KA6 and know it does not have mag preamps.

If I remember the old disco rigs I serviced you will end up with two channels and a mic signal panned centrally. You wanted to split off the music channels for pre PC monitoring? I would suggest a pair of decent (Orchid?) isolating transformers at that point and then split the signal, possibly via a small passive monitor controller? However, whatever drives the transformers needs to be of low source impedance.

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Re: Advice needed: re-wiring DJ Studio setup, eliminating ground loop issues

Postby James Perrett » Fri Jun 21, 2019 9:16 pm

ef37a wrote:I am confused? "The SL1210 turntables are connected via RCA to the NI Audio A6 "

I have not found any information about the outputs of the SL1210s but I do not think they have built in RIAA corrected pre amps? I have an NI KA6 and know it does not have mag preamps.

I was thinking the same but it appears that NI also have the confusingly named Traktor Scratch A6 in their range

https://www.thomann.de/gb/native_instru ... tch_a6.htm
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Re: Advice needed: re-wiring DJ Studio setup, eliminating ground loop issues

Postby ef37a » Sat Jun 22, 2019 8:08 am

Thank you James, found it now. STILL does not give an specifications in the otherwise very comprehensive user manual! Blast you NI!

I think the 0dBfs line out is at +12dBu, 3.1V rms and so operating level around -10dBV? That would sit well with its use with more "domestic" amplification but still be enough to drive active speakers. Certainly enough drive if going into a mixer.

I am sure the Scratch A6 will have a decently low output impedance and so that would I think be the point to isolate the signals. The USB/laptop/mains charger is a common route for earth loops (AI to active speakers is another) The S A6 can work stand alone as well as bus powered* and the (not supplied?) wall rat appears to be earth free.

SO, as mentioned, earth isolate the deck feeds from the SA6. If you were up for a bit of DIY the OEP Z30A18C "600 Ohm" transformer has two independent secondary windings and so would give you two, totally isolated feeds. There will be about 6dB loss of level.

*No mention is made in the manual that having both DC power AND USB power connected is in any way harmful and I would not expect that to be the case anyway.

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Re: Advice needed: re-wiring DJ Studio setup, eliminating ground loop issues

Postby VorTechS » Wed Jul 17, 2019 9:09 am

Hi all,

I wanted to pop back and say many thanks for the advice!

Don't worry, I never used the dodgy non-earthed power cable ;)

After extensively changing connection after connection, and organising everything, the groundloop has all but disappeared - you have to have the amp on with no music playing at ridiculously loud volumes to now notice it.

One of the key factors appeared to be ensuring that both outputs from the mixer (Booth and Master) were isolated. The second, appeared to be the XLR inputs for the mic. The Citronic CDM10:4 mixer actually has 5 mic inputs, two on the 'top' which are XLR and two of which appear on the rear which are jack-based (and the 5th is an AUX 3.5mm input).

When plugged into the rear jacks, which uses one of the 4 channels on the mixer, there is no additional buzzing/hums. When plugged into the XLR, even with new XLR cables which I bought, there is a buzzing/hum present.

I had a second, very old mic, which I also plugged in, and the noise from that was, er, interesting. (Sounded like someone was murdering an old Modem)

I'm going to conclude therefore in this case, that the microphone itself is at fault here given it was all of about £20.
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Re: Advice needed: re-wiring DJ Studio setup, eliminating ground loop issues

Postby Hugh Robjohns » Wed Jul 17, 2019 10:51 am

VorTechS wrote:When plugged into the XLR, even with new XLR cables which I bought, there is a buzzing/hum present.

Difficult to diagnose remotely, but a common source of unwanted buzz/hums when using XLRs is if the connectors have been wired internally with a link between the XLR shell and Pin 1.

Most pre-made XLR cables are wired this way, and it is the technically correct method, but it can cause exactly the kind of problems you describe if the equipment you're plugging into isn't designed properly and has dodgy internal audio grounding practices!

Another possibility is that the microphone body is in contact with something which is itself grounded, forming a ground-loop.

And lastly, ultra-cheap mics, even though they have an XLR output, are often wired internally as unbalanced, so can pick up a lot of interference that can't be rejected!

H
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Re: Advice needed: re-wiring DJ Studio setup, eliminating ground loop issues

Postby ef37a » Wed Jul 17, 2019 4:33 pm

When investigating noise issues involving XLRs it is worth making up a dummy load.

A male plug has a 150 Ohm resitor soldered across pins 2 and 3 and the plug reassembled. Now you have an "end" that is totally screened and of the impedance the mic pre wants to "see" . The only noise is that of the resistor down at about -130dBu! If you don't have a handy 100 to 220R a short will do as well.

It is also worth making a silent recording with levels set for a typical session then inserting the .wav into a Real Time Analyser such as RightMark. This will not only show the frequencies you need to deal with but also stands as a "baseline" that you can check from time to time since as kit is added in and removed, things change. You will see noises you would never hear under normal circumstances.

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