Pls help me reduce noise from my system! inter - connecting unbalanced to balanced

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jazztronaut
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Pls help me reduce noise from my system! inter - connecting unbalanced to balanced

Post by jazztronaut » Sun Jul 15, 2018 10:47 pm

So I've been trying to isolate a 60hz hum issue in my system. First thing I did was to connect everything to the same power outlet. I think it did improve the problem but did not solve the issue completely.

This is typically what I do when I'm recording : synth (unbalanced) -> DI Input of preamp channel strip -> JDI to various fx pedals -> audio interface. These are all connected via two Samson S-Patch patchbays (balanced) for flexibility. The idea is to be able to interconnect different fx pedals (unbalanced) on the fly in different orders.

In my setup I have all my unbalanced synth output connected to the rear of the patchy bay using TRS cables. The preamp i/o s are connected to the rear on the same patchbay, along with the inputs of the audio interface using TRS cables. On a second patchbay I have all my fx pedals connected to the back using TS cables. I patch these together in the front with TS cables.

I find that I'm still getting noises if the setup were interconnected via the patchbay. I'm assuming there is an issue with connecting unbalanced sorces to balanced input, thus in my situation, when unbalanced synth output goes into the balanced patchbay hum noises arises. With the preamp channel strip DI input Ground Lift engaged & the LINE output of the channel strip is then fed into a Radial JDI in reverse, I was able to eliminate the hum to a minimum when the patchbays were not involved.

Anyways, I'm wondering if this is where the hum is coming from? mixing unbalanced and balanced sources.

I have been doing some research regarding this issue and found these articles.

http://www.rane.com/note110.html]Sound System Interconnection
https://www.presonus.com/learn/technica ... Unbalanced

Should I try and modify my cables? Pls point out where I might be doing something wrong where balanced or unbalanced cables should be used instead.

Many Thanks!

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Re: Pls help me reduce noise from my system! inter - connecting unbalanced to balanced

Post by kslight » Mon Jul 16, 2018 5:39 am

I don’t know that I see much value in being able to re-route the order of individual pedals on a patch bay (in my own experience), so I’ve done something a bit different. What I have done is kept the chain of pedals which start and finish with the respective in and out of a Pigtronix Keymaster. The Pigtronix is on the patch bay (balanced). I think I still had a marginal amount of hum so I put an inline direct box in the input path which cleaned it up. All pedals are also powered with an isolated power brick...which is IMHO critical on a complicated pedal board.

How are you powering your pedals? If you are using a one spot wall wart or similar non-isolated power supply daisy chain...do yourself a favor and throw it out.

I have never had any problems putting synths and that type of stuff on the patch bay, that is where they all reside for me.

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Re: Pls help me reduce noise from my system! inter - connecting unbalanced to balanced

Post by floid » Mon Jul 16, 2018 8:36 am

Have you tried starting with the simplest chain and then methodically adding to it until you find the hum?
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Re: Pls help me reduce noise from my system! inter - connecting unbalanced to balanced

Post by Nick Sevilla » Mon Jul 16, 2018 9:38 am

I'm with Floid here.

Try starting with the SIMPLEST connection:

Synth - audio interface. Does that hum like crazy? Then it's the synth. No need to look further. In this case, try plugging in your DI directly after the synth, and fiddle with the "ground" switch. Does it make the hum less or makes it disappear? Good. If not, you'll need a better DI, one which actually decouples the signal with transformers. Some of these are named "dehummer" or similar "unhumming" type names.

If the synth is CLEAN, then connect the next piece, and see if the hum beings with it.

Keep adding until you find the actual culprit.

You do not say WHICH synth you are using... and also if you are suing DISTORTION pedals, which will make ANY hum horrifically louder. Add distortion after you have recorded the clean signal, not during.

Cheers and happy hunting.
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Re: Pls help me reduce noise from my system! inter - connecting unbalanced to balanced

Post by Magnetic Services » Mon Jul 16, 2018 9:57 am

That Rane paper has been ENDLESSLY useful to me. Just keep going back to it!

And try one of these for isolating and interconnecting your balanced/unbalanced stuff:

https://www.soundonsound.com/reviews/art-t8

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Re: Pls help me reduce noise from my system! inter - connecting unbalanced to balanced

Post by alexdingley » Tue Jul 17, 2018 6:43 am

When I had these struggles (and they were tricky), I found that simplifying the test was the ONLY way to really find a full solution.

Big Question
How much do you have to unplug to get the system to be 100% hum-free?

My testing methodology involved doing the following:
1. Unplug all items
2. Plugg headphones into monitoring system (console / computer I/O... / whatever you use to listen back)
3. Turned headphone pot to full volume (not while it's on my head). Give a quick listen for any hum. If none, proceed:
4. Turn headphone pot down + add one more line level item to the chain I'm monitoring but don't play anything back.... raise headphone pot to maximum again and give another quick listen for any hum. If none, proceed to repeat this step over and over.
...
5. if & when you get hum... solve that hum some way, if you're not sure how — come back to this forum & post any questions.

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Re: Pls help me reduce noise from my system! inter - connecting unbalanced to balanced

Post by vvv » Tue Jul 17, 2018 10:08 am

Really, it's a kinda basic engineering trouble-shooting approach.

I gets more complex when the problem is actually the interaction between two pieces (happens sometimes with effect pedals, or where there are impedance mis-matches), but you approach it the same way - two (or more) pieces at a time.
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