How to bridge 600 ohm balanced line to monitor or record?

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Fran3
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How to bridge 600 ohm balanced line to monitor or record?

Post by Fran3 » Sun Apr 07, 2019 6:29 am

Having a problem with on air audio intermittently being interrupted. Occurs randomly for a few seconds every few hours on air.
We are unsure where the problem is occurring so to try and pinpoint it we want to be able to tap on to the audio at different points along the way to either listen or record... maybe like this...

Given a balanced audio line running from device to device... for example from...
- Node A: Console audio out to EAS
- Node B: EAS to the Audio Processor input
- Node C: Audio Processor Output to the AM transmitter Audio Input

We want to be able to connect/bridge on at any node to connect...
- a pc's audio input for recording audio at that node
- or headphones to monitor at that node
- or possibly an audio amp and speaker to monitor at that node

I'm guessing we could gin-up a circuit starting with a transformer with a high-impedance primary bridged across the balanced audio line... and the other side connected to either the computer sound card's audio in jack... or to an audio amp or headphones....

But wondered what you guys would suggest...

And if the transformer solution were to be used... what transformer would we order?

Thanks for any help.

PS:
- We considered inserting an audio distribution amp at each node but that would be a pane... and then the question of weather the DA is acting up would occur

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kkiddkkidd
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Re: How to bridge 600 ohm balanced line to monitor or record?

Post by kkiddkkidd » Sun Apr 07, 2019 7:17 am

An RDL STA-1 (or STA2) is my goto for this kind of thing. Either will drive a set of headphones at low levels directly OR cleanly interface to a computer or audio amp. A DA is another option as you mentioned but more expensive. A telephone buttset is also a common quick test set.

A camera recording your audio processor / TX would show if the problem was before or after the processor.

Is your studio colocated with the TX or is there an STL?

What EAS unit do you have?

What processor and TX do you have?

You are certain that your automation system isn't stuttering...?

Regards,
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

TPT
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Re: How to bridge 600 ohm balanced line to monitor or record?

Post by TPT » Sun Apr 07, 2019 8:31 am

All three connections are (probably) balanced audio. So you don't want to hook any kind of unbalanced amp or computer across the program line, since this may introduce hum or RF into the audio.

You can find Henry matchbox devices on E-bay fairly cheap--be aware that everything is labeled backwards on these things--which will allow you to connect a balanced line (through the XLR jack) to an unbalanced feed for a computer (through the RCA jacks).

However, I would agree--if you are co-located with the transmitter--that the most likely culprit is the air computer "stuttering." Then there is always a bad connection somewhere along the line. Try shaking the wire at the output and input to each device. I've found some XLR connectors (Chinese) just don't take solder well--looks OK, but it is a bad connection. Also--if the processor output (or console) is a barrier strip--a bad crimp to a spade lug. May need to solder the lug.

Fran3
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Re: How to bridge 600 ohm balanced line to monitor or record?

Post by Fran3 » Sun Apr 07, 2019 8:40 am

Thanks folks.

Studio and transmitter are co-located in the same building.

We (think) we have eliminated the computer automation system stuttering as it also streams and the stream seems (we think) to sound fine.

However, since the interruptions are only a few seconds long... and occur only every now and then... by the time we get back to either the transmitter, audio processor or control room with the computer automation system... the problem has cleared itself up... so there is always a degree of uncertainty.

It could even be the transmitter but that currently seems unlikely.

If we can bridge the balanced audio and record on a pc... once we hear the problem we can note the time and on air content.... then listen to the recording to see if it occurred at that node...

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kkiddkkidd
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Re: How to bridge 600 ohm balanced line to monitor or record?

Post by kkiddkkidd » Sun Apr 07, 2019 9:06 am

Fran3 wrote:
Sun Apr 07, 2019 8:40 am

It could even be the transmitter but that currently seems unlikely.

If we can bridge the balanced audio and record on a pc... once we hear the problem we can note the time and on air content.... then listen to the recording to see if it occurred at that node...
Intermittent problems can be maddening to diagnose. A cheap video camera is your friend. I am experimenting with the little, cheap Wyze cams for TX site monitoring. $25ea on Amazon with amazingly good video for the price. The new versions are much advanced over the early units. I use a couple of them to monitor my vehicle in hotel parking lots but haven't tried to continuously record with one. They will record to the cloud OR to an SD card.

Just to clarify... You are using the term "node" to note locations not nodes as in networked AOIP Nodes (Axia, Wheatnet, etc). If it is the networked AOIP meaning, that brings on a whole different list of possibilities.

Assuming that you are running mono, have you tried swapping your EAS audio to the unused switcher side? I have had a couple DasDec units that would intermittently loose one stereo side or the other and IIRC was corrected with the replacement of some relays or a relay card. If it is a Sage, try either swapping to the unused side OR just unplug the XLR's and completely bypass the unit for a bit.

Regards,
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

Fran3
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Re: How to bridge 600 ohm balanced line to monitor or record?

Post by Fran3 » Sun Apr 07, 2019 2:30 pm

Thanks again for the help and suggestions.

I'm using the term "node" to designate a point along the mono analog audio path.

We will continue to work on this until we track the culprit down.

I'll try to post back when we figure out what the heck is going on.

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Dale H. Cook
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Re: How to bridge 600 ohm balanced line to monitor or record?

Post by Dale H. Cook » Mon Apr 08, 2019 4:22 am

kkiddkkidd wrote:
Sun Apr 07, 2019 7:17 am
An RDL STA-1 (or STA2) is my goto for this kind of thing.
I will second Kevin. I carry an STA-1 with me primarily for emergency monitoring of a balanced line using a laptop sound card or other unbalanced input.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html

radio_guru
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Re: How to bridge 600 ohm balanced line to monitor or record?

Post by radio_guru » Mon Apr 08, 2019 12:42 pm

Curiously, you don't mention if the audio drops about 6-10dB or goes completely out. If it drops only about 6-10dB, then one side of the balanced pair is opening (presuming electronic and not transformer termination). If the audio is going out completely, that sounds more like an equipment problem and not a wiring/termination problem....again presuming electronic and not transformer termination.

If you're in a pinch and don't want to "unbalance" anything, use a pair of 10K resistors across both + and - to either a balanced or unbalanced termination. More over, make sure to reference the site's audio common if going to unbalanced. The signal may be low to be certain. But if all you're after is confidence monitoring, it need not be pristine. Just reliable enough to hear/sample.

I admit, this is a really bubble gum way to sample the audio...but it's doable. Especially on a mono signal where channel balance is a moot point. Just don't leave it that way permanently.

Others have suggested the Henry Engineering (or for that matter anyone's) standards converter with a 10K termination if going to an unbalanced destination long term. I concur if you have the time to wait for one to arrive from an ebay lot or someone's surplus pile.

As for where to start monitoring... At the EAS box input. Divide and conquer the audio chain. And I would re-punch 66 block terminations and recrimp or solder spade lugs. I can't tell you how many poor spade lug crimps I've found over the years....on both sides of the balanced pair.

These types of drop-outs are maddening to track down. But manifest themselves readily if mechanical in nature.

Let us know what you find....

RG

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