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Author Topic: How to test jack for balanced/unbalanced  (Read 17493 times)

Steve Schow

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How to test jack for balanced/unbalanced
« on: October 31, 2012, 11:11:09 pm »

I have a slightly odd question.  I have a piece of gear that I am uncertain whether it has balanced TRS or unbalanced TS output jacks on back.  The previous model had balanced TRS jacks, but this model does not state either way in the docs.  I need to run the cables a fair distance so I either have to know for sure they are balanced TRS, or else I will get a box to convert them to balanced before sending over the snake.

Can anyone help me figure out how to test the jacks to find out if they are balanced or unbalanced?

Please explain in novice terms as I am rather new to multimeters, etc.
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Mark McFarlane

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Re: How to test jack for balanced/unbalanced
« Reply #1 on: November 01, 2012, 02:17:49 am »

I have a slightly odd question.  I have a piece of gear that I am uncertain whether it has balanced TRS or unbalanced TS output jacks on back.  The previous model had balanced TRS jacks, but this model does not state either way in the docs.  I need to run the cables a fair distance so I either have to know for sure they are balanced TRS, or else I will get a box to convert them to balanced before sending over the snake.

Can anyone help me figure out how to test the jacks to find out if they are balanced or unbalanced?

Please explain in novice terms as I am rather new to multimeters, etc.


The first and easiest test is to insert a 1/4 TS or TRS plug into the jack. If you feel resistance with about 1/2" of travel left then the jack is probably balanced.  If you have a guitar handy (which is not balanced) you can use this to calibrate your 'feel' for unbalanced. If the console has inserts you can use them to calibrate your feel for a TRS female jack.  The unbalanced TS jack will give resistance at about 1/4" of remaining travel, the TRS jack at about 1/2".  Think about it, you have two 'prongs' that have to touch the T & S.  Look at a picture of a 1/4" female TRS (stereo) jack online and when you understand the design you can probably feel it.

Edit:  I leave this to one of the experts here on how to use the multimeter...  I proposed a test but quickly realized it wont work.
 
« Last Edit: November 01, 2012, 02:22:39 am by Mark McFarlane »
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Chris Chambers

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Re: How to test jack for balanced/unbalanced
« Reply #2 on: November 01, 2012, 05:23:23 am »

What's the piece of equipment in question?

Ivan Beaver

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Re: How to test jack for balanced/unbalanced
« Reply #3 on: November 01, 2012, 06:42:30 am »

The first and easiest test is to insert a 1/4 TS or TRS plug into the jack. If you feel resistance with about 1/2" of travel left then the jack is probably balanced.  If you have a guitar handy (which is not balanced) you can use this to calibrate your 'feel' for unbalanced. If the console has inserts you can use them to calibrate your feel for a TRS female jack.  The unbalanced TS jack will give resistance at about 1/4" of remaining travel, the TRS jack at about 1/2".  Think about it, you have two 'prongs' that have to touch the T & S.  Look at a picture of a 1/4" female TRS (stereo) jack online and when you understand the design you can probably feel it.

Edit:  I leave this to one of the experts here on how to use the multimeter...  I proposed a test but quickly realized it wont work.
Agreed that if it doesn't pass this test-it is unbalanced.  However it is common practice to simply use the same jack (TRS) for both balanced and unbalanced.

The reason is simple.  Same part number-so that they can buy a larger quantity (for lower costs)-only use 1 part number and so forth.

If it is "quasi balanced" then you can just measure the resistance between the Ring and ground.  It should be in the 100-200 ish range.

If it reads open-then there is still a possibility it provides a balanced output.  You could then rig a cable to provide a  unbalanced output (for testing) and hook it between the ring and ground and see if you get a signal.  If you do-then it is balanced.

Or he could provide the model number and see if anybody knows-or look at  a schematic or call the manufacturer etc.

Of course without more details-who knows.

Not to be rude-but it is quite amazing the number of people that ask questions about gear-coverage etc and yet provide no details to actually help them out.
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John Roberts {JR}

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Re: How to test jack for balanced/unbalanced
« Reply #4 on: November 01, 2012, 09:48:32 am »

Measure the resistance to ground or sleeve from both tip and ring. It should be < 1k ohm and close to the same resistance on both. Note: Make this measurement with the unit turned on, since one or both outputs will be connected to circuitry that could be undefined impedance without power.

JR
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Jordan Wolf

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Re: How to test jack for balanced/unbalanced
« Reply #5 on: November 01, 2012, 11:24:49 am »

Can anyone help me figure out how to test the jacks to find out if they are balanced or unbalanced?
Steve,

I find that differential, balanced outputs sound "odd" when listened to via headphones when compared to the signal from that unit's headphone output.  Use the same source material for monitoring, and you should hear the difference.

Do realize: it's the device's circuitry that determines what is "balanced" or not; it just requires both legs to have the same impedance referenced to signal ground (a la JR's post above).  The "differential" side of things is one (very effective) method of reducing/eliminating the effect(s) of external interference on the desired signal.
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John Roberts {JR}

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Re: How to test jack for balanced/unbalanced
« Reply #6 on: November 01, 2012, 11:38:23 am »

Steve,

I find that differential, balanced outputs sound "odd" when listened to via headphones when compared to the signal from that unit's headphone output.  Use the same source material for monitoring, and you should hear the difference.

Do realize: it's the device's circuitry that determines what is "balanced" or not; it just requires both legs to have the same impedance referenced to signal ground (a la JR's post above).  The "differential" side of things is one (very effective) method of reducing/eliminating the effect(s) of external interference on the desired signal.

If you get sound in both ears, that is a useful positive test, but sound in only one ear, does not confirm the negative. You can still have a balanced impedance termination with only one hot leg driven with audio.

JR
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Don Boomer

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Re: How to test jack for balanced/unbalanced
« Reply #7 on: November 01, 2012, 11:39:45 am »


Not to be rude-but it is quite amazing the number of people that ask questions about gear-coverage etc and yet provide no details to actually help them out.

+1  ...  It's all in the details so please list them including specific model numbers.  I makes it much easier to answer the question.
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Jordan Wolf

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Re: How to test jack for balanced/unbalanced
« Reply #8 on: November 01, 2012, 11:51:15 am »

If you get sound in both ears, that is a useful positive test, but sound in only one ear, does not confirm the negative...
That is important to note - thanks for pointing that out, JR.
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Jordan Wolf
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Steve Schow

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Re: How to test jack for balanced/unbalanced
« Reply #9 on: November 01, 2012, 01:19:32 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?


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Re: How to test jack for balanced/unbalanced
« Reply #9 on: November 01, 2012, 01:19:32 pm »


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