8 Channel Hum Eliminator before Tape

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thenapking
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8 Channel Hum Eliminator before Tape

Post by thenapking » Mon Jun 17, 2019 12:15 pm

I have an Otari MX 5050 BII, which is hooked up to my desk via a patchbay. Despite redoing the wiring scheme in my studio over xmas I still suffer from a lot of hum when recording, and often end up inserting cheap hum eliminators before the tape in the patchbay.
So I am considering buying an 8 channel hum eliminator like the Art T8 to insert straight before the tape machine. However I remember that Otari specify the wiring for the XLR inputs is Pin 3 Hot, with Pin 2 joined to the shield in the connector. Does this mean that if I use the existing cable to connect to the XLR inputs of the hum eliminator, then the hum eliminator XLR outs to the Otari, using regularly wired XLR cables, I will have a problem?
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Otari XLR wiring diagram
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I'm Painting Again
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Re: 8 Channel Hum Eliminator before Tape

Post by I'm Painting Again » Mon Jun 17, 2019 2:28 pm

http://rane.com/note110.html

Like 13 on the chart but switch the red and black on the XLR end

I believe using the TS outs on the art is the best because the docs don't say they're balanced while it states XLR outs are balanced

keep it unbalanced to unbalanced

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A.David.MacKinnon
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Re: 8 Channel Hum Eliminator before Tape

Post by A.David.MacKinnon » Mon Jun 17, 2019 7:33 pm

Not to derail things but this sounds like a symptom of a bigger issue.
Do you only have hum on the tape machine? Have you confirmed that your feed lines to the machine are wired properly (sounds like it but I'd double and triple check).
How's the power in the studio? Have you checked that it's actually outputting the correct voltage? It seems like a stupid question but a friend had a similar issue and discovered that their hydro was running at 160 volts due to a faulty transformer on the pole out front.
Is the tape machine on the same circuit as the rest of the studio gear? What else is on that circuit? Fridge? AC?
Does the hum go away if you remove things from the chain or move the location of any of the elements in the chain?

I'd chase down every variable in the chain to find the source of the hum before I got into buying hum eliminators. They feel like a band aid solution to a systemic problem that should be addressed in other ways.

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I'm Painting Again
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Re: 8 Channel Hum Eliminator before Tape

Post by I'm Painting Again » Mon Jun 17, 2019 8:53 pm

for sure

the hum eliminators will only work for specific types of problems - they don't elimanate hum in every situation so don't expect them to

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Re: 8 Channel Hum Eliminator before Tape

Post by kslight » Tue Jun 18, 2019 5:47 am

And I agree that if a hum eliminator did actually work that’s a symptom of a bigger problem...probably wiring related?

Sorry to not answer the question, I’ve just never heard of a hum eliminator being used like this. To me it seems like it should be worth some more troubleshooting before deferring to this solution.

thenapking
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Re: 8 Channel Hum Eliminator before Tape

Post by thenapking » Tue Jun 18, 2019 9:05 am

This is definitely symptomatic of a bigger issue, which I attempted to fix over Xmas. I improved matters, but it isn't fixed. The next step is to employ a professional tech to sort it, because I reached the limit of my knowledge, and what I can get from the internet. Some of this is due to poor design of the items - eg I have a LinnDrum whose old PSU hums terribly. Some of it is due to a mixture of balance and unbalanced kit, where I am unwilling to get rid of the unbalanced kit. The Otari is a case in point - God knows why this is unbalanced. So this is a fixing plaster for 6 months or so.
To answer specific questions:
The studio is on two separate circuits. The PC and non-audio signal items are on one circuit. Everything else is on the other. All other devices in the property are on other circuits. Each rack has power conditioners, and I have proper plug boards with RF eliminators in them. The wiring has been done so that all the audio wiring is elevated at least a foot above all the power cords. In the one place this is not possible a power lead crosses a multicore at right angles. Listening tests proved that this power cord being connected induces no hum. It is not possible to install air con in the building - the studio is also not in a room within a room. All the audio is wired according to a star-grounding system, the central ground being the ground pin on the mixing desk.
When some audio devices are patched in, yes, hum increases, however I went through each device step by step and was unable to eliminate the problems which remain. Some of these problems are are definitely eliminated by a hum destroyer. Rather than purchasing a couple more cheap hum destroyers, I wanted to look at an item of better quality, hence this rackmount item.
My question is specifically this: If I insert this hum destroyer at the patchbay end I will have no problems with the wiring and it will work, but that is a little inconvenient. So is there a problem inserting it at the tape machine end, given the wiring diagram above, and the fact that I'd be connecting the output of the hum destroyer with balanced XLRs wired in the normal way? If I understand I'm Painting Again correctly, I could do this with unbalanced connections from the jack side of the unit, to the XLR ins of the Otari.

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Re: 8 Channel Hum Eliminator before Tape

Post by Magnetic Services » Tue Jun 18, 2019 12:24 pm

I'm Painting Again wrote:
Mon Jun 17, 2019 2:28 pm
http://rane.com/note110.html

Like 13 on the chart but switch the red and black on the XLR end

I believe using the TS outs on the art is the best because the docs don't say they're balanced while it states XLR outs are balanced

keep it unbalanced to unbalanced
Beat me to it. That white paper has saved my ass too many times to count.

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