Line level audio to mutliple locations

[Jimbo38198]

 

I have an application where I need to share unbalanced audio with multiple locations.

Previously to share audio to a remote location I have used a pair of audio baluns and CAT 6, but in this project I need to share the unbalanced audio with multiple location so I am looking for a cost effective solution that maintains the quality of the signal.

I was wondering if it was possible to to daisy chain multiple audio baluns together? For example having one send and then multiple receivers connected by daisy chaining the CAT 6 cable.

Or does anyone has a better solution?

[Mixermend]

Lots of ways to do this of course - but you could use a 1:1 transformer at each end of the line, then use further transformers to tap off the signal at various points along the line.

A few things we need to know to be certain of this strategy - how far away is the most distant location?

How many taps are needed along the route?

As long as the source has a reasonably low source impedance - and the 'loads' have medium/high impedances, whether balanced or unbalanced, this should work well.  

[sandall]

Are you talking yards or miles? Unbalanced audio will travel hundreds of feet in decent screened cable. Balanced audio using transformers at each end will travel thousands of yards in screened cable.

[sunray]

8 minutes ago, sandall said:

Are you talking yards or miles? Unbalanced audio will travel hundreds of feet in decent screened cable. Balanced audio using transformers at each end will travel thousands of yards in screened cable.

if it's correctly balanced it doesn't need to be screened. The longest unscreened audio circuit I've worked on without intermediate processing ran from Chatham to London, There may have been inductors to equalise the cable.

[sunray]

35 minutes ago, Jimbo38198 said:

 

I have an application where I need to share unbalanced audio with multiple locations.

Previously to share audio to a remote location I have used a pair of audio baluns and CAT 6, but in this project I need to share the unbalanced audio with multiple location so I am looking for a cost effective solution that maintains the quality of the signal.

I was wondering if it was possible to to daisy chain multiple audio baluns together? For example having one send and then multiple receivers connected by daisy chaining the CAT 6 cable.

Or does anyone has a better solution?

Hospital radio installation: CATII cable (telephone cable) fed with 1:1 transformer, at each point a 1:1 transformer was used to isolate from the unbalanced input to each amplifier, typically TOA500 series.

Transformers used were this style of ground loop isolators from Maplins (Sorry it was quickest to find a modified unit image):

[sandall]

19 minutes ago, sunray said:

if it's correctly balanced it doesn't need to be screened.

True (IF correctly balanced), but the screen provides a bit of mechanical protection.

[sunray]

3 minutes ago, sandall said:

True (IF correctly balanced), but the screen provides a bit of mechanical protection.

Possibly, depending on cable type and installation method.

[Jivemaster]

The answer may be multiple kilometers BUT crossings of streets etc could bring this to a close quite quickly. POTS telephone used to travel 35 miles before needing amplifiers.

If you own/control the area cable is good, if your route has to cross rivers roads or railways then probably a licensed point to point wireless link becomes more simple. 

[J Pearce]

As per other replies - add a balancing transformer at each destination and at the source. Distribute a balanced line.

Any other method of distributing audio unbalanced will bring much weeping and gnashing of teeth.

Edited January 24, 2022 by J Pearce

[sunray]

Another method I've used...

We wanted 5 or 6 PA systems fully interlinked, with distances of 500m to 2Km between each commentator.

I used a TBU, selection of Gentner and Sonifex, to allow feed-in and take-off at each location and used borrowed telephone dropwire for most of it (then had to rewind it afterwards to return😢

[Jimbo38198]

Thanks for your input.

The output and input will be from amps with unbalanced signals, the distance is not massive 100m or so and there will be 2 taps to start with.

I am not sure of the impedance of of the amps they are Cambridge Audio Azur 340A.

I will give 3 audio baluns a test to start with.

[Dave m]

just to clarify - you mean speaker amplifiers with line outputs?

or 100v line amps sending speaker voltages?

[sunray]

So I've just looked at the pathetic user manual for the impedance and voltage levels, I can't believe they have not been included.

Being phono sockets it should be a reasonably low impedance to drive the line

A HiFi amplifier picked at randommay indicate some additional line driver amplifier may be required to give a sensible signal voltage,  an alternative approach could be transformers with a voltage gain, say 1:3 or so. (ie 600Ω:5KΩ, 1KΩ:10KΩ etc).

Obviously if you have 1:1 available try those to see if they give anough drive.

 

[pmiller056]

Using screened cable to distribute unbalanced audio over more than a few metres may be unsafe.

The earth/ground/screen terminal of each bit of equipment connected will usually be linked to the earth connection of the local power circuit. Inevitably, depending on local conditions, all these different earth connections will be at slightly different potentials. Significant currents at powerline frequency will be forced to flow through the cable screen as it links the earth points of different circuits together, causing hum problems. This can be observed as 'hum bars' on video displays in some old analogue CCTV installations where screened cable is always used.

Do bear in mind that under fault conditions, a portion of the fault current will flow through the cable screen to other connected equipment, possibly causing widespread damage.

Distribute the audio as balanced line, with an isolation transformer at each tap-off. Connect the centre tap of the sending transformer only to local earth so that the line cannot become live under fault conditions. Alternatively, use a 100V line distribution system with a single suitable audio power amplifier. This will reduce the amount and complexity of remote equipment needed.