Have a home made amp in the workshop which is used a great deal - I tend
to listen to the radio all the time I'm in there. And of course doubles as
a test amp for anything needed. My diagrams for it are dated 1997, and
it's worked just fine since I built it.

Until last Friday. Had to turn the volume well up to hear anything.

It has balanced inputs, and the unbalanced outputs appear beside the
workbench as phonos, and are normally jumpered across to the pre-amp
inputs. The speaker outputs and inputs also appear there.

A quick fiddle showed it was the balanced to unbalanced side which had
died. Both channels. The PS for these is independant of the power amp one,
+/- 15v regulated, and its LEDs showed it working.

For some reason shrouded in the mists of time, I'd used SSM 2017 rather
than the more usual SSM 2143, etc. Perhaps to give a bit more gain. Or
perhaps just because I had loads.

Both had blown. Replaced and all is now fine.

The pre-amp shares the same PS.

Only odd thing was the severe lightening we had on Thursday - as
spectacular as I've seen in London. But it was switched off then, although
still connected to ground (and neutral)

The balanced inputs would still have been connected to my distribution
system - but everything else on that is fine. And the cabling for that is
all internal.

Any guesses?

--
*I don't suffer from insanity, I enjoy every minute of it *

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" wrote in
message ...
Have a home made amp in the workshop which is used a great
deal - I tend
to listen to the radio all the time I'm in there. And of
course doubles as
a test amp for anything needed. My diagrams for it are
dated 1997, and
it's worked just fine since I built it.

Until last Friday. Had to turn the volume well up to hear
anything.

It has balanced inputs, and the unbalanced outputs appear
beside the
workbench as phonos, and are normally jumpered across to
the pre-amp
inputs. The speaker outputs and inputs also appear there.

A quick fiddle showed it was the balanced to unbalanced
side which had
died. Both channels. The PS for these is independant of
the power amp one,
+/- 15v regulated, and its LEDs showed it working.

For some reason shrouded in the mists of time, I'd used
SSM 2017 rather
than the more usual SSM 2143, etc. Perhaps to give a bit
more gain. Or
perhaps just because I had loads.

Both had blown. Replaced and all is now fine.

The pre-amp shares the same PS.

Only odd thing was the severe lightening we had on
Thursday - as
spectacular as I've seen in London. But it was switched
off then, although
still connected to ground (and neutral)

The balanced inputs would still have been connected to my
distribution
system - but everything else on that is fine. And the
cabling for that is
all internal.

Any guesses?




You don't have to have a direct hit for damage - a coronal
discharge (like a thick glow) can also hammer things. Many
times have I been called out to radio sites and found the
equipment intact but power supply series transistors usually
o/c. Switched modes don't like it up 'em either!


--
Woody

harrogate three at ntlworld dot com

In article ,
Woody wrote:
You don't have to have a direct hit for damage - a coronal
discharge (like a thick glow) can also hammer things. Many
times have I been called out to radio sites and found the
equipment intact but power supply series transistors usually
o/c. Switched modes don't like it up 'em either!


Right. But like many others, this house is packed with electronics. And
everything else seems fine. Or rather I've not yet found anything else
broken. ;-)

--
*Everyone has a photographic memory. Some just don't have film*

Dave Plowman London SW
To e-mail, change noise into sound.

On Wed, 23 Jul 2014 16:29:37 +0100, "Dave Plowman (News)"
wrote:

Have a home made amp in the workshop which is used a great deal - I tend
to listen to the radio all the time I'm in there. And of course doubles as
a test amp for anything needed. My diagrams for it are dated 1997, and
it's worked just fine since I built it.

Until last Friday. Had to turn the volume well up to hear anything.

It has balanced inputs, and the unbalanced outputs appear beside the
workbench as phonos, and are normally jumpered across to the pre-amp
inputs. The speaker outputs and inputs also appear there.

A quick fiddle showed it was the balanced to unbalanced side which had
died. Both channels. The PS for these is independant of the power amp one,
+/- 15v regulated, and its LEDs showed it working.

For some reason shrouded in the mists of time, I'd used SSM 2017 rather
than the more usual SSM 2143, etc. Perhaps to give a bit more gain. Or
perhaps just because I had loads.

Both had blown. Replaced and all is now fine.

The pre-amp shares the same PS.

Only odd thing was the severe lightening we had on Thursday - as
spectacular as I've seen in London. But it was switched off then, although
still connected to ground (and neutral)

The balanced inputs would still have been connected to my distribution
system - but everything else on that is fine. And the cabling for that is
all internal.

Any guesses?

Best guess, based on your description of the thunderstorm, is that
the "The Free Electrity" produced a surge voltage along the balanced
line that comfortably exceeded the amplifier's input common mode
rejection by a wide margin (exacerbated by being powered down - it
might even have survived if it had been switched on and the pulse
voltage low enough).

Questioning how a local thunderstorm could cause random electrical
overloads is rather like questioning the existence of God. There's
very little point. "**** happens." to quote Forest Gump.

By '"Spectacular", may we assume you were hearing thunderclaps within
a second or so of the lightning flashes? Sound travels at 330 m/s any
such loud thunderclaps heard within a couple of seconds of the flash
would suggest ground strikes within a 700m radius. 25 to 100 KA ground
strike currents can play havoc with the local mains distribution and
telephone lines over a surprisingly large distance.

Provided you don't find any other expensive faults, just be thankful
that all that suffered was a couple of balanced line input audio
amplifier chips (and thankful that we don't suffer such spectacular
thunderstorms as a matter of routine).
--
J B Good

In article ,
Johny B Good wrote:
Best guess, based on your description of the thunderstorm, is that
the "The Free Electrity" produced a surge voltage along the balanced
line that comfortably exceeded the amplifier's input common mode
rejection by a wide margin (exacerbated by being powered down - it
might even have survived if it had been switched on and the pulse
voltage low enough).

There are 5 other amps sitting across the same line - and all switched off
when the storm happened in the middle of the night. Although those all
have SSM 2143. Or THAT 1246.

I'm not sure it was the storm that caused it - could just have been
coincidence. There is a third 2017 in the amp powered from the same PS
which is used as a mic amp when needed - but that wasn't plugged to
anything. It still works. Although it does have protection diodes across
its input because of the phantom power.

--
*I don't know what your problem is, but I'll bet it's hard to pronounce

Dave Plowman London SW
To e-mail, change noise into sound.

I had issues that day with my Microwave appearing to be dead. When I
unplugged it and replugged it it burst into life. I'm told all the digital
clocks in my house read odd times or were zeroed. I'm thinking a nasty spike
or series of pulses big enough the cause digital stuff to get brain
scrambled. Maybe you were just unlucky and got an inductive spike in the
wiring. Certainly I'f stood by the long wire aerial I have when its sparked
to ground where its wound round a hook, so it can be quit high in voltage
even if its not struck.
Brian

--
From the Sofa of Brian Gaff Reply address is active
"Dave Plowman (News)" wrote in message
...
Have a home made amp in the workshop which is used a great deal - I tend
to listen to the radio all the time I'm in there. And of course doubles as
a test amp for anything needed. My diagrams for it are dated 1997, and
it's worked just fine since I built it.

Until last Friday. Had to turn the volume well up to hear anything.

It has balanced inputs, and the unbalanced outputs appear beside the
workbench as phonos, and are normally jumpered across to the pre-amp
inputs. The speaker outputs and inputs also appear there.

A quick fiddle showed it was the balanced to unbalanced side which had
died. Both channels. The PS for these is independant of the power amp one,
+/- 15v regulated, and its LEDs showed it working.

For some reason shrouded in the mists of time, I'd used SSM 2017 rather
than the more usual SSM 2143, etc. Perhaps to give a bit more gain. Or
perhaps just because I had loads.

Both had blown. Replaced and all is now fine.

The pre-amp shares the same PS.

Only odd thing was the severe lightening we had on Thursday - as
spectacular as I've seen in London. But it was switched off then, although
still connected to ground (and neutral)

The balanced inputs would still have been connected to my distribution
system - but everything else on that is fine. And the cabling for that is
all internal.

Any guesses?

--
*I don't suffer from insanity, I enjoy every minute of it *

Dave Plowman London SW
To e-mail, change noise into sound.

On Thu, 24 Jul 2014 00:34:22 +0100, "Dave Plowman (News)"
wrote:

In article ,
Johny B Good wrote:
Best guess, based on your description of the thunderstorm, is that
the "The Free Electrity" produced a surge voltage along the balanced
line that comfortably exceeded the amplifier's input common mode
rejection by a wide margin (exacerbated by being powered down - it
might even have survived if it had been switched on and the pulse
voltage low enough).

There are 5 other amps sitting across the same line - and all switched off
when the storm happened in the middle of the night. Although those all
have SSM 2143. Or THAT 1246.

I'm not sure it was the storm that caused it - could just have been
coincidence. There is a third 2017 in the amp powered from the same PS
which is used as a mic amp when needed - but that wasn't plugged to
anything. It still works. Although it does have protection diodes across
its input because of the phantom power.

Although you didn't confirm how local the ground strikes may have
been, I don't think you can conclude anything else as to the cause of
the failure of _two_ amplifier chips connected to the same run of
cable (two balanced lines, screened or not, possibly a star quad
arrangement, but more likely the less elegant seperately screened
pairs configuration).

I've not only seen published pictures of mains cabling with its
insulation neatly stripped off, I've also dealt with at least one
telephone instrument where the subscriber got a nasty shock whilst on
the phone in a thunderstorm who had described to me how he observed
the lightning strike travelling along the telephone wiring.

Amazingly, the phone was still working, if a little on the quiet
side. It turned out that the insulation around the reciever inset
terminals had been blown off. A replacement reciever inset was all
that was required to fix that 700 series phone!

Lightning strikes can produce really bizarre effects and
consequences. No wonder it was often referred to as an "Act of God"!

If it were me considering such a strange fault, I wouldn't bother
looking any further than 'lightning damage' as being the culprit.

--
J B Good

In article ,
Johny B Good wrote:
I'm not sure it was the storm that caused it - could just have been
coincidence. There is a third 2017 in the amp powered from the same PS
which is used as a mic amp when needed - but that wasn't plugged to
anything. It still works. Although it does have protection diodes across
its input because of the phantom power.

Although you didn't confirm how local the ground strikes may have
been, I don't think you can conclude anything else as to the cause of
the failure of _two_ amplifier chips connected to the same run of
cable (two balanced lines, screened or not, possibly a star quad
arrangement, but more likely the less elegant seperately screened
pairs configuration).

Ordinary twisted pair telephone cable. 20 twisted pair stuff. Giving 5
stereo circuits. No screen.

There were no lightening strikes nearby that I know of. There was some
forked lightening in the distance, but mostly the sheet type.

No sign of any burning anywhere.


Seems it's usual to use a pair of back to back zenners across each leg of
the input with this chip. I assumed that was only when used with phantom
power so omitted them. But am told they should always be used. ;-)

--
*A hangover is the wrath of grapes.

Dave Plowman London SW
To e-mail, change noise into sound.