rec.arts.theatre.stagecraft

David McCall wrote:
>"Scott Dorsey" wrote in message
>> We have plenty of iso boxes with 1:1 transformers that allow anyone
>> to break signal grounds at any point. Anyone that does an outdoor
>> festival without such things is not competent.
>>
>Back when I was doing concert sound in the late 60s these things were
>available, but not at all common.

Part of that is because in the late 60s, everything was transformer-isolated
and there was already a transformer in the input and the output of the console
and on the input of the amp. So telescoping a ground was all you needed to
do to get transformer isolation.

These days transformers are too expensive and folks often consider them too
much of a source of possible audio degradation for everything to come with
transformer-isolation. So instead we have more iso boxes on the truck.

In the sixties, here in the US, if you knew someone that worked at the phone
company you could get them to bring you "repeat coils" which were used
for long distance circuit isolation and loading, and which were some of the
best audio transformers available at the time.

>> It has been against the NEC here in the US, at least since the early
>> seventies.
>>
>That sounds about right. I don't remember grounded outlets being very common
>in the early 60s and don't remember any in the 50s. I still run into quite a
>few
>outlets with no ground even today. If you are lucky, the box will be
>grounded and
>you can just use an adapter. If the box isn't grounded, then I guess you
>should
>start looking for a water pipe.

In the US, you see a lot of those in homes, but not many left in commercial
locations. They turn up in old churches, though, as do things like DC
outlets...
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."