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

Chromatest J. Pantsmaker chromatest at azburners.org
Fri Jul 21 16:43:12 CEST 2023


Others have said what it is already.  In the states (at least at some
point) 70V RMS was used because it's less than 100V Peak.  Anything using
the "cheap" wires over 100V had to be in conduit.  70V RMS would never go
over 100V, so it didn't need to be in conduit.
https://www.lowellmfg.com/wp-content/uploads/What-is-a-25V-70V-or-100V-Speaker-System.pdf

On Fri, Jul 21, 2023 at 6:29 AM Mr&MrsAccount <hbissell at wowway.com> wrote:

> 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.
>
>
>
>
> ------------------------------
> *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.
>
> Gordon
>
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