Isolation transformer

[ubxf]

Hello,
I'm trying to help a church with a hum in their PA system. The main church has 8 speakers . The trouble is that they send a speaker cable to and adjacent building 20 meters away and feed that to an amp that in turn powers 12 outdoor speakers > That not surprisingly is creating hum in every speaker . I was thinking to send a line level feed from the mixer in the church to the second building amp and also add an audio isolation transformer . Would a 600:600 be good or a 10K:10K ? Another twist is that the system was originally designed as a 70V but over the years the amp got replaced by regular amps .

 

[ccaudle]

send a speaker cable to and adjacent building 20 meters away and feed that to an amp

So the feed to the amp is two-conductor unshielded cable? Line level signal sent on speaker wire, or a high level signal from the output of an amplifier sent, which is then attenuated at the input of the amplifier and used as input signal?
Is the amp an unbalanced input, or balanced input amplifier? Two-wire or three-wire power entry on the amplifier?

creating hum in every speaker

Did you mean literally every speaker, or every outdoor speaker? Are the indoor speakers also affected?

adjacent building 20 meters away

Above ground or underground feed? When sending signals between buildings you really need to consider power faults and lightning induced ground differences.
Do the buildings have separate power entrances with separate protective earth rods at the power entry?

@MisterCMRR are you familiar with any isolation transformers which are made for inter-building use, e.g. have GDT overvoltage protection or similar heavy duty protection capabilities to account for power faults or earth potential differences during thunderstorms?

 

[ubxf]

Thank you for your response, I have to go back and investigate properly to be 100%sure but from the quick evaluation
feed to the amp is two-conductor unshielded cable? yes
high level signal from the output of an amplifier sent, which is then attenuated at the input of the amplifier and used as input signal? yes
Is the amp an unbalanced input, or balanced input amplifier? Two-wire or three-wire power entry on the amplifier? I need to check but I think balanced
Did you mean literally every speaker, or every outdoor speaker? Are the indoor speakers also affected? yes
Above ground or underground feed? above ground
Do the buildings have separate power entrances with separate protective earth rods at the power entry? I don't think so but I have to check.

 

[ubxf]

I read this application paper and I will follow recommendations
https://www.jensen-transformers.com/wp-content/uploads/2014/08/an004.pdf
Maybe use this transformer
https://www.jensen-transformers.com/product/pi-xx/

 

[JohnRoberts]

They are sending a speaker cable to feed audio into another amplifier? Most amplifier signal equipment inputs are not designed to accept speaker level signals. When using active powered equipment in different buildings, each with their own utility service, it is not unusual to have significant potential differences between safety grounds.

#1 If you pad down the speaker level signal with a resistive pad that will not only reduce the signal level but attenuate the ground potential differences.

#2 A small audio transformer can generally isolate the two safety grounds.

JR

 

[sodderboy]

600:600. It's not a science project.
Top shelf Jensen Inside™ solution
Mid shelf solution
Bottom shelf is the same on Amazon, mostly for cars.
The Radio Shack Ground Loop Isolator has a proud history on this site, and I was using it long before in all sorts of applications. For a stereo feed between church systems it is great! Wire it balanced with hot on 2 (tip) and shield on 3 (ring) no pin 1 (sleeve) connection.
If the amp and speakers work quietly with a local source, then isolate your external feed and enjoy the praise.
Mike