Series II - Dealing with unbalanced inserts

[Anthony Cornish]

Hey all,

I've been working with a local studio the last few weeks getting a Series II set up.

As you might know, the insert patch is unbalanced, with Tip not connected, Ring to hot, and 

Sleeve to ground shield.

We're having issues with significant noise going to outboard gear, particularly if it has an output transformer. Input seems to be fine.

Isolating the output via and unbalancing transformer works to some extent to remove the hum. However the Radial ones we are using drops the signal by around 10dB.

All cabling utilises the Hot and Shield only. Cold is left unterminated at either end. Trying to link the cold to ground directly or via 10ohm resistor has no effect in reducing hum and noise.

Surely there must be a simple solution to this other than using a tonne of transformers to unbalance the outboard gear?

I'm also very curious as to the correct earthing of the console, in relation to the outboard and the power supply.

Anyone with any assistance would be greatly appreciated. We can get by for now, but need to address it as soon as practical.

Anthony.

[ik...@zimbelaudio.com]

Hi Anthony,

    Need more info...

-what is the current grounding set-up for the console and PS?

-What is the frequency of the hum?

-You say the inputs of the outboard gear are ok...if you Send to a device, and then listen to the output on a test set or other means independent of the desk (small mixer, headphone amp...) is the send from the console actually clean, or are you just not hearing the input hum until you connect the output back to the desk?

-does the desk have the short TT jacks in the PB? If so, it's actually the RING and Shield that connect when you insert a TRS TT plug in there. The TIP would just be hanging in space, beyond the end of the socket...assuming it's not shorting against something like a metal frame etc.

-You are probably losing -6dB with the iso-transformers. Any transformer, iso, or output, is going to need to be tied to 0v at the low side...it has to be terminated.

Please report back...

~Ike Zimbel~

   Wireless frequency coordination specialist.

   Manufacturer's Representative

   Radio Active Designs (Canada)

       ~416-720-0887~

FCC:WRBX645

   http://www.zimbelaudio.com/wireless-frequency-coordination/

 

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From: neote...@googlegroups.com <neote...@googlegroups.com> on behalf of Anthony Cornish <anthony...@gmail.com>
Sent: July 8, 2025 6:44 AM
To: Neotek <neote...@googlegroups.com>
Subject: [Neotek] Series II - Dealing with unbalanced inserts

 

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[Anthony Cornish]

Hi Ike,

I did respond at length to this, but realised it never sent. Anyway here goes again.

Yesterday I was at the studio and fixed a whole bunch of stuff. Many broken traces on the underside of the board.

Unbalanced outboard gear is fine, but anything with a transformer input / output is a no-go, as the insert patch bay and aux patch bays are unbalanced. Interesting that they have wired the whole console with the ring of the patch as the signal. I have no idea the logic in this.

So noise aside, which was not presenting an issue, what is the common way to wire up transformer balanced gear to an unbalanced Neotek?

I tried using transformer isolation (1:1) with one side of the secondary winding tied to ground, but that cut the signal down considerably - maybe 15 to 20dB, so probably need to go 2:1 due to having only one phase.

Any advice is really appreciated.

Anthony.

[Anthony Cornish]

Hi Ike,

I keep replying to this but it never goes through!

Anyway, we have sorted out all issues except how to interface with transformer input gear. As the EDAC outputs are only ground and hot (on the ring of the TRS patchbay), we need to tie the cold down to ground at the equipment rack end. This creates a bit of noise, so am hoping to use an unbalanced to balanced transformer to do the job. But that is needed on the input AND output of the gear!

Is there a simple way to do this?

Example being they have an LA2A and want to insert it on a channel.

Anthony.

On Wednesday, July 9, 2025 at 12:46:41 AM UTC+10 ik...@zimbelaudio.com wrote:

[Chris N.]

Good timing. Interested in this as I am now starting to plan out interconnection to my S1E in the not too distant future...

To view this discussion visit https://groups.google.com/d/msgid/neotekusers/87ab2ada-1411-4e18-b08e-d2726936c1ccn%40googlegroups.com.

[Matt Syson]

As a general plan, wire everything as balanced throughout and then Unbalance at the last possible moment (connector) and then work through any hum or interference issues individually after that. Transformer balanced gear is especially handy to keep hums at bay and will be happy unbalanced at the 'far end' of any cabling. 

To view this discussion visit https://groups.google.com/d/msgid/neotekusers/CAEb4gF26Pum-nxHPdEXeuGnbfRVefC-%2Bs3dP4R%2BZuvzE0hEFLw%40mail.gmail.com.

Virus-free.www.avg.com

[Matt Walsh]

Also, there's a 99% chance it's not going to be a problem. I've wired up high end stuff to random pieces of crap over the years and it's all been fine. 

To view this discussion visit https://groups.google.com/d/msgid/neotekusers/3391d7bf-5adc-438f-881e-09943469971e%40mseaudio.plus.com.

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[Chris N.]

Hi Matt,

Thanks for your reply to this thread.

I'm a little confused by your advice. If I'm interpreting you correctly, everything at the punchblock is balanced and if necessary, unbalanced at the connector of the outboard.

My recollection from year's past is that it's usually best to connect the shield at the input and to cut the shield at the output. Was this misguided advice I received in my youth?

Thanks,

Chris

To view this discussion visit https://groups.google.com/d/msgid/neotekusers/3391d7bf-5adc-438f-881e-09943469971e%40mseaudio.plus.com.

[Matt Syson]

Hi

Yes unbalance at the input and or output of the outboard gear as the 'self balancing of the Neotek BALANCED outputs will effectively 'read' the unbalance at the outboard's connector. Similarly for balanced Neotek inputs. The cut the grounds off advice from years ago was usually effective for mains frequency hums but needs updating for the modern world with HF switchmode supplies (wall warts) and mobile phones and bluetooth gear putting out significant level of Microwave energy which can get into anything. Wiring everything as balanced will allow easy changes if or when you change your outboard and the fine tuning of your noise prevention can be done inside XLRs or jacks on the outboard. It is near impossible to guarantee a noise free setup with so many variables out there. With the HF noise issues it seems that grounding everything as often and with as thick wiring everywhere is actually better than the old 'star earth' concept which simply adds a load of antennas to your mix of wiring because the wavelength of RF is a matter of inches to a few feet so a 1 foot piece of wire can receive a fair amount of RF (someone else could calculate the frequency but phone microwave is in the order of 5 inches I believe). Doing alterations on remote gear is usually easier than crammed at the back of a desk!

Good luck

Matt

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[Chris N.]

Thanks for the clarification/elaboration Matt!

To view this discussion visit https://groups.google.com/d/msgid/neotekusers/0473a3ef-ca90-4bf6-8259-c714582fa5e3%40mseaudio.plus.com.

[ik...@zimbelaudio.com]

I agree with Matt S that you should keep all wiring balanced for as long as possible. This means using 2-conductor-shielded cable everywhere, even if source and destination are known to be unbalanced. What this does is allows you to take advantage of the properties of the balanced wiring by using a "quasi-balanced" scheme wherein the "+" side of the twisted pair is your signal and the "-" side is the return path, while the shield acts as a shield, even if it's only connected at one end.

    I also agree that the unbalancing should be done at the device end. So, if you have an older device that has barrier strips for connections, and is transformer balanced, like an LA-2a, or a Pultec, you would tie the low side of the transformer to the 0v/Gnd terminal on the barrier strip. This will take care of the -6dB loss you get when a transformer is un-terminated on one end. Whether you connect one, both, or none of the shield connections at the barrier strip is a studio wiring/trouble-shooting decision. BIG NOTE: There was a time in the 1980's where transformers were considered to be a sonic problem rather than today's bringers of toasty-iron-goodness. To that end, I have seen a variety of vintage gear that had the input iron bypassed at some point (presumably in the '80's, when studios had full-time techs). This list includes an LA-2a, an EQP-1A, and a pair of LA-3's. I restored all of those to their original configuration, but the OP could be dealing with units that have had that done.

    Having said all that, MOST outputs, on MOST Neotek desks that I have seen are un-balanced (the exception being the main 2-Mix outputs on the Elite, Elan, E-whatever desks...not sure about the S-1,2-3's). To that end, it's also very possible that the internal wiring on the O/P's desk is 1-conductor+shield, in which case you will not get the advantages mentioned above inside the desk.

    To sum up, you should be able to un-balance a device as described above (or with suitable adaptors), put it on the bench and see unity gain through the device, IOW with no level loss. If you are NOT able to do that, then you are not un-balancing the device properly (NOTE: this is WRT transformer balanced devices only, and, varies widely with actively balanced output devices). Put another way, level losses when making un-balanced connections are one issue, and ground hum is another. So, step one is being able to insert a device and make the round-trip at unity gain. Once you've accomplished that you will know that the signal path is correct. If it hums, that hopefully becomes a matter of lifting or connecting shields.

~Ike Zimbel~

   Wireless frequency coordination specialist.

   Manufacturer's Representative

   Radio Active Designs (Canada) 

       ~416-720-0887~

FCC:WRBX645

   http://www.zimbelaudio.com/wireless-frequency-coordination/

 

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From: neote...@googlegroups.com <neote...@googlegroups.com> on behalf of Matt Syson <matt....@mseaudio.plus.com>
Sent: August 26, 2025 1:01 PM
To: neote...@googlegroups.com <neote...@googlegroups.com>
Subject: Re: [Neotek] Series II - Dealing with unbalanced inserts

 

To view this discussion visit https://groups.google.com/d/msgid/neotekusers/3391d7bf-5adc-438f-881e-09943469971e%40mseaudio.plus.com.