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Author Topic: How to test jack for balanced/unbalanced  (Read 17494 times)

Greg_Cameron

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Re: How to test jack for balanced/unbalanced
« Reply #10 on: November 01, 2012, 01:52:55 pm »

ok guys, the unit in question is a Vox Tonelab LE, which is several years old.

I have already checked the specs (non conclusive) and I have searched far and wide for a schematic, but cannot find one. 

The previous generation of this device had balanced/unbalanced TRS outs, the Tonelab SE.  It was spec'd in the manual as such and a service manual with schematic has been widely available on the net, which I have even though I don't know how to read it anyway, hehe. 

The newer LE does not specify if balanced or unbalanced and nobody seems to have the schematic.  I rather suspect it is not balanced, but there is still some doubt about it and so I want to find out for sure before I start buying things. 

I have also tried to contact Vox tech support via email and the answer I got from their pathetic tech support was that they are only a "humble distributorship" and don't know deep technical details that aren't spec'd in the manual.

I left all that info out because its not really helpful and I was trying to keep the discussion focused, but many asked, so there it is.

Ok, that out of the way....

The first thing I did try was to take a cable and try to push it in and out to see whether it seems that the TRS contacts are clicking or not and it does seem to, but I agree that is not completely deterministic.

I do understand what balanced audio is, I am just not exactly sure how I could, for example, plug a TRS cable into the unit, generate some sound with it and then use some kind of tester on the other end to determine whether balanced signal is being sent.

JR your test sounds like the one I should try, if I understand correctly what you're saying, I can plug a TRS cable into it, then use a meter to measure ohms: Sleeve-Tip and Sleeve-ring.  And according to you they should both be about the same, something less then 1k.  That would indicate its balanced.  If its not balanced what should I expect to see?

If you measure continuity/dead short between sleeve & ring, then the jack is unbalanced.
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John Roberts {JR}

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Re: How to test jack for balanced/unbalanced
« Reply #11 on: November 01, 2012, 03:25:57 pm »

If you measure continuity/dead short between sleeve & ring, then the jack is unbalanced.

Not to make this overly confusing, but these are guidelines not hard and fast rules, since there can be exceptions (kind of).

I have also seen unbalanced TRS jacks wired up with the ring contact floating open-circuit.

Outputs can also be transformer coupled, so while not typical, both tip and ring could measure no DCR to sleeve, but DCR to each other, or if grounded center-tap, low impedance from both to sleeve.

This is not a simple test, while one strong piece of evidence is how does it work in a noisy environment?  You can lose sleep (money and time) over trying to fix something that isn't broken, due to faulty diagnosis.

JR
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Steve Schow

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Re: How to test jack for balanced/unbalanced
« Reply #12 on: November 01, 2012, 04:08:41 pm »

ok an idea came to me.  Let's say the connector is a TRS because it clicks twice to put a plug in there.  What if I take a TS cable and plug it in to the first click only, so that the tip is touching the ring contact.  If I hear audio in that case, wouldn't  that be a pretty good indication that its probably balanced?  I guess only maybe because its possible the unit has circuitry which can output balanced or unbalanced depending on what it finds plugged in.
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John Roberts {JR}

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Re: How to test jack for balanced/unbalanced
« Reply #13 on: November 01, 2012, 04:23:41 pm »

ok an idea came to me.  Let's say the connector is a TRS because it clicks twice to put a plug in there.  What if I take a TS cable and plug it in to the first click only, so that the tip is touching the ring contact.  If I hear audio in that case, wouldn't  that be a pretty good indication that its probably balanced?  I guess only maybe because its possible the unit has circuitry which can output balanced or unbalanced depending on what it finds plugged in.

Not completely. Like I said before you can have a completely adequate balanced impedance interface with no signal on ring leg.

Also some electronic balanced outpust share voltage between two outputs so leaving one floating could lead to misleading results. Likewise a transformer winding between tip-ring, with tip floating (half plugged in TS  plug) would give no output ring-sleeve.

Like I said there are no simple "absolute" rules, just general guidelines.

JR
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Steve Schow

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Re: How to test jack for balanced/unbalanced
« Reply #14 on: November 01, 2012, 04:32:41 pm »

ok this is kind of hopeless.  I can't believe its this hard to find out. 

Do I understand correctly that I can at least determine for sure if the jack itself is TRS by testing with the ohm meter as you suggested earlier?

As to whether or not the unit is actually balancing the signal, I have no idea how to know for sure. 

I plan to run this over a long snake, so I really prefer to have a balanced signal.  I will just buy a line balancer and hope it does the right thing I guess.

thanks
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John Roberts {JR}

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Re: How to test jack for balanced/unbalanced
« Reply #15 on: November 01, 2012, 04:49:42 pm »

Yes, pretty hopeless... We still have no idea what you are trying to connect to what.

You don't need to balance the "signal", you need to balance the interface.

You would be able to buy a balanced interface checker if this was a widespread problem, but this generally isn't an issue with properly designed equipment, so no market for a dedicated tester.

Good luck, you have received about as much help as we can give without more information from you. 

JR
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Steve Schow

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Re: How to test jack for balanced/unbalanced
« Reply #16 on: November 01, 2012, 04:52:47 pm »

Uhm, that only adds to the confusion. 

Its pretty simple.  I have a device with 1/4 inch outputs which I am unable to determine from the specs whether they are balanced or not.  The previous version of the product was.  This version it not spec'd yes or no.

I need to run it through a long snake to a mixer with balanced/unbalanced inputs. 

I need to make sure I wire up the snake correctly, either TRS or TS and perhaps I will buy a line balancer because of the long run.  I prefer to run balanced.  What other info do you feel I am leaving out?

« Last Edit: November 01, 2012, 05:03:21 pm by Steve Schow »
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Chris Hindle

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Re: How to test jack for balanced/unbalanced
« Reply #17 on: November 01, 2012, 04:55:08 pm »

ok this is kind of hopeless.  I can't believe its this hard to find out. 

Do I understand correctly that I can at least determine for sure if the jack itself is TRS by testing with the ohm meter as you suggested earlier?

As to whether or not the unit is actually balancing the signal, I have no idea how to know for sure. 

I plan to run this over a long snake, so I really prefer to have a balanced signal.  I will just buy a line balancer and hope it does the right thing I guess.

thanks
Open up the unit, and count the connections on the jack / solder pads on the PCB ??
That's the first thing I would have done....
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Steve Schow

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Re: How to test jack for balanced/unbalanced
« Reply #18 on: November 01, 2012, 05:02:32 pm »

Open up the unit, and count the connections on the jack / solder pads on the PCB ??
That's the first thing I would have done....

Me too.  I opened the unit last night but the jacks are hidden behind the PCB and I didn't want take it that far apart of find out.  Some of the screws for removing the PCB are behind a lip that near as I can tell can't be accessed without bending open a metal flap of the cover that prevents access to the screws.
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John Roberts {JR}

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Re: How to test jack for balanced/unbalanced
« Reply #19 on: November 01, 2012, 05:18:34 pm »

Have you tried asking the manufacturer?

What DCR do you measure T-S and R-S? (with unit on but not passing audio).

This isn't all that hard.

JR

PS: I can't imagine a manufacturer going backwards. It cost pocket change to balance a termination with an extra resistor. The major cost there is the TRS jack not the resistor.

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Re: How to test jack for balanced/unbalanced
« Reply #19 on: November 01, 2012, 05:18:34 pm »


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