[sdiy] Transporting line level audio in home / buzz-free USB wall warts?

Mr&MrsAccount hbissell at wowway.com
Fri Jul 21 15:28:36 CEST 2023

70 volt line is a speaker distribution method where the signal is sent from a central amplifier at a higher voltage and lower current to overcome resistive losses in the speaker cable 
and use smaller gauge wire.  Very much like AC distribution systems.  Individual speakers have a step-down transformer that matches their impedance. These secondary transformers are 
tapped for wattage, i.e. 5W, 10W, 20W ... so that each zone can have the volume adjusted for similar coverage. 
The transformer coupling isolates each zone so there is no possibility of disturbing the system from induced noise or ground issues (no local grounds are needed).   
The drawback is usually the transformers are too small for good bass response and often use is limited to P.A. or background music. 
I have used transformers on the system with secondary resistive attenuation as feed points to other amplifier systems (for example outdoor portable PA systems). It works very well but you get whatever 
background noise or distortion is in the main system added to the signal, so the noise floor is worse. but if the main system is OK usually the additional feed is good as well. 
Gordon... we call it 70V line here in the USA as well. I've seen 100V and I think they mean essentially the same thing with a higher voltage (100V). 
Another problem is that building code often consider "70V line" to be a high voltage and may require wires in conduit, even though there is virtually zero fire or shock hazard. There is a "25V" line 
as well but even that is too high to be considered low voltage.  I usually am careful to call the wires "speaker wires" in which case no one has any complaints about installation. 
One could use a distribution amplifier with multiple transformers to distribute line level audio, it would work excellently if the transformers are carefully selected. 

-----Original Message-----

From: Gordonjcp <gordonjcp at gjcp.net>
To: synth-diy <synth-diy at synth-diy.org>
Date: Friday, 21 July 2023 8:30 AM EDT
Subject: Re: [sdiy] Transporting line level audio in home / buzz-free USB wall warts?

On Fri, Jul 21, 2023 at 01:15:23AM -0700, brianw wrote: 
> I've been meaning to ask: What are you referring to with regard to "70V"? 

Presumably 70V line, which is what Americans call 100V line. It's the kind of thing you use for Tannoys in large establishments. I look after several hundred such installs at work. 


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