Don Pearce wrote:
On Tue, 22 Aug 2006 14:17:01 +0100, Rob
wrote:

Dave Plowman (News) wrote:
In article ,
Rob wrote:
I take it your physics teacher had a degree in physical education? Because
it's basically rubbish. Although some devices like projectors have cooling
fans which are meant to run after powering down, but I'll bet he wasn't
thinking of those.

No, she (it was a 'she', Dave, and not a 'he' - Ms Lyons, class 3C, BVGS
Birmingham 1976) was/is a physics graduate although she didn't have a
PhD - or at least she didn't use the title 'Dr' (most of the other
staff did). I'm afraid I can't remember if she was a member of any
chartered or similar organisation - sorry.
I was trying to remember last night - I asked her 'why?', and I'm pretty
sure the answer had the word 'surge' in it, and tailed off into a 'this
doesn't apply to everything but as a rule you shouldn't switch a
switched device on or off at the mains. Device first, mains second'. I
tried it with my system - 3 valve amps, TT and CD, and left them
switched on at the appliance and just flip the switch at the mains.
Mighty convenience, but hell of a thump at the speakers when it's
switched on, fine when switched off.
That's rather different as there's no way you could switch all the devices
simultaneously except at the socket.

Indeed - it would be tricky - 6 switches!

But I'd be worried if a valve power amp produced a thump at the speakers
when powered up.

No, that's the curious thing - just a little 'blip' when the main supply
is switched in/on at the appliance. I'm not sure of the reason when
they're all put on at once, although I could easily isolate the rogue. I
have a feeling it is the power amp though - the guy who serviced it said
it's best to switch on the standby first, wait a minute, then switch on
the main thing.

Are you sure? The usual way is main first, then standby later.
Switching on the standby first does nothing until the main is on.


Yes, I'm sure. It's a Beard P100. The amp was originally fitted with a
'soft start', that would actually amplify, albeit at low volumes. The
problem was that owners kept them in this 'standby' mode all the time,
and early valve failure was common. Mine has been rewired so that
standby does something (all the valves light up but no sound), and power
brings with it sound.

The worst offender on the switch on thump syndrome is the CD - a
throoughly modern Marantz. I tend to switch that on first, followed by
everything else, finsihing with the power amp.

Rob

It sounds like the amp is the common factor here, and thus also the
problem.


Yes, I think it is the amp, but if the only way is to follow the
suggested power-up routine, then life goes on.

Rob