Re: Remote Power Supply Connection

Iain Churches wrote
>
>> Also, transferring the filter caps to the amp would mean 
>> that both plug
>> and socket would be live at the time of parting. I have 
>> seen it said that
>> a diode in the amp solves this problem, but I wouldn't 
>> entrust my life to
>> that solution.
>
> You have to use a method (something like a sensing loop
> with a relay) to shut of the DC from the connectors if the
> cable is disconnected at either end.  If a round connector
> is chosen, it must be one one with a deep screw collar or
> bayonet latch, so there is no access to the pins while the
> connector is still making contact. That is why an octal 
> plug
> socket cannot be used, although Patrick seems to have
> found an innovative way to make that combination safe.

Not safe enough to be legal here. Innovation and safety 
don't mix well, but to his credit I don't think Patrick was 
trying to be inventive. He's done the best he can do under 
the circumstances, probably. I wasn't keen on the detail 
that the HT dies away within 10 secs IIRC. How long do 
electrocutions take? When is the most likely time a 
connection might be touched?

> Common sense would dictate the fitting and removal of
> the DC umbilical only when the amplifier and PSU have
> bveen switched off for some time.

Empty words, I'm afraid. 600V means very little to common 
sense, which anyway these days assumes that all electrical 
gizmos are fool-proof.

> A power diode, as an additional safety measure works
> well.

Additional? Works well? How well? How do you know? If the 
diode on its own isn't safe enough, and if the device isn't 
safe enough without the diode, then how does adding two 
unsafe things result in safety? You would need to know the 
two probabilities of electrocution, and whether they are 
independent, before calculating whether the resulting 
smaller probability falls below some threshold.

Except for an inadequate cord clamp at one end, my umbilical 
cords have everything everyone has suggested. I won't pass 
them on to anyone else, no matter how much common sense they 
seem to have.

> These are well-proven techniques from rack-mounted
> broadcast equipment in the tube era.
Ah, those were the days. Remember Les Harvey?

http://en.wikipedia.org/wiki/Leslie_Harvey

> But it is also important
> to comply with modern safety standards.

Which AFAIK mean that an amp with an umbilical cord can 
never legally change hands in the UK.

cheers, Ian