"Tim Schwartz" wrote in message
...
Happy New Year Arfa,

Well, maybe they felt that the British either use headphone or speakers,
and most people don't own both?

On the other hand, your description makes me thing that if you fitted the
switching jack to the board, you could add the switching the customer
desired...

The even dumber part is to run the speaker wires to the headphone jack
board at all if you are not going to switch them, adding all the extra
wiring for no reason, and adding the resistance of the wiring to the
speaker lines.

Best regards,
Tim Schwartz
Bristol Electronics


P.S. Who said there was a point?



On 1/2/2013 3:51 PM, Michael A. Terrell wrote:

Arfa Daily wrote:

Today, a Denon amplifier model PMA 250 II crossed my bench. Quite old,
but
then Denon gear is usually pretty good quality and long lived, and well
designed - or so I thought ...

The reported problems were that the sound level fluctuated on both
channels,
and that the headphone socket did not cut the speakers. The first
problem
was cured in short order by treating the function switch to a dose of
squidget juice. I gave all of the other switches and controls a little
tickle as well, for completeness.

Then I jacked in a set of headphones, and the owner was correct - the
speakers kept running. There were five wires going across to the
sub-board
at the front that the socket was on, so it looked promising that it
should
switch, but I was a bit puzzled as to why it actually wasn't. The socket
and
board is secured to the inner front panel by a slide-on clip, so I
whipped
the outer front panel off, pulled the clip, and withdrew the board and
socket so I could have a look underneath and see what was going on. I
was
mighty surprised to see that although the PCB had all the right pads and
holes for a five pin socket, only a 3 pin was fitted. Two of the wires
in
the 5 wire ribbon were in fact connected to nothing other than dead-end
tracks. I put it back together, and went on-line to see if I could find
a
user manual. When I did, I looked up the section on controls and
connectors,
and found this entry :

"PHONES

The jack is used for connecting the headphones.
When the headphones are plugged in, the sound will cease to come from
the
speakers (except for the English model)."

WTF is that about ? I could maybe at a pinch understand it if there was
a
front panel speaker selector switch such as you see on some amps, like
"OFF,
A, B, A+B", but there is no such switch on this, nor any other way that
I
can see of disabling the speakers, short of disconnecting them. What is
the
point, then, of having a headphone socket at all ? Why would you design
it
to take a switched socket, and then exclude one model from using the
feature, effectively rendering the socket pretty much useless for its
intended purpose ? Why in particular exclude the "English" model ? It's
not
as though there are any regulations here concerning headphone sockets,
and
in fact I don't think that I have ever seen another amp that didn't
switch
the speakers when phones were plugged in.

Because I knew that the owner was not going to believe this either, I
printed off the manual page and highlighted the relevant text, before
returning it to the store that sent it in to me ...


It sounds like they made a deal with Lucas... ;-)



Happy new year to you too ! I don't suppose it makes that much odds with the
wiring, as it's a piece of 5 way ribbon cable, but it does of course require
that two wire links are fitted somewhere - although I don't recall seeing
them at the socket PCB, so perhaps they are the other end. At the end of the
day, it's quite an old amp and it is what it is. I'm not about to start
messing about modding it, unless the owner says specifically that he wants
to pay for it as a 'proper' job. I would guess that it's either sat in his
attic for years and he's forgotten about this little foible, or he's bought
it on FleaBay and didn't realise. No matter how you look at it though, I
still think that it's a thoroughly ****-street piece of design work, and I
can't see any point in having the socket fitted at all, if it's not going to
cut the speakers ...

Arfa