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 ...

Arfa

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... ;-)

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


It sounds like they made a deal with Lucas... ;-)
Denon was left with a difficult choice when designing the British model.
They either had to make it quirky in a way that Brits would appreciate,
or to follow the great tradition of British automobile makers and
provide a way to make it leak some type of fluid.

They chose the less expensive choice.........

Smarty wrote:

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


It sounds like they made a deal with Lucas... ;-)
Denon was left with a difficult choice when designing the British model.
They either had to make it quirky in a way that Brits would appreciate,
or to follow the great tradition of British automobile makers and
provide a way to make it leak some type of fluid.

They chose the less expensive choice.........


It's much better to have it leak, than to make a deal with the prince
of dorkness. ;-)

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... ;-)

On Wed, 2 Jan 2013 16:45:12 -0000, "Arfa Daily"
put finger to keyboard and composed:

The reported problems were that the sound level fluctuated on both channels,
and that the headphone socket did not cut the speakers.

My old Mitsubishi CRT TV had two headphone sockets. One cut the
speaker, the other did not. Presumably it was to allow a hearing
impaired individual to listen to the TV via headphones while their
partner listened via the speaker. I can't imagine that this would
apply in the Denon case, though.

I'm trying to envisage some kind of safety issue, but I can't think of
any that make sense. There have been times when I've received a
deafening blast from my headphones at switch-on, or when selecting a
signal source, but that's not something that would be remedied by
unswitched speaker outputs.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Franc Zabkar wrote:
On Wed, 2 Jan 2013 16:45:12 -0000, "Arfa Daily"
put finger to keyboard and composed:

The reported problems were that the sound level fluctuated on both channels,
and that the headphone socket did not cut the speakers.

My old Mitsubishi CRT TV had two headphone sockets. One cut the
speaker, the other did not. Presumably it was to allow a hearing

I recall this. It's on par with picture-in-picture for actual usefulness.

Franc Zabkar wrote:

On Wed, 2 Jan 2013 16:45:12 -0000, "Arfa Daily"
put finger to keyboard and composed:

The reported problems were that the sound level fluctuated on both channels,
and that the headphone socket did not cut the speakers.

My old Mitsubishi CRT TV had two headphone sockets. One cut the
speaker, the other did not. Presumably it was to allow a hearing
impaired individual to listen to the TV via headphones while their
partner listened via the speaker. I can't imagine that this would
apply in the Denon case, though.

I'm trying to envisage some kind of safety issue, but I can't think of
any that make sense.


It sounds like they needed to remove one more part to meet a price
point.

"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

"Franc Zabkar" wrote in message
...
On Wed, 2 Jan 2013 16:45:12 -0000, "Arfa Daily"
put finger to keyboard and composed:

The reported problems were that the sound level fluctuated on both
channels,
and that the headphone socket did not cut the speakers.

My old Mitsubishi CRT TV had two headphone sockets. One cut the
speaker, the other did not. Presumably it was to allow a hearing
impaired individual to listen to the TV via headphones while their
partner listened via the speaker. I can't imagine that this would
apply in the Denon case, though.

I'm trying to envisage some kind of safety issue, but I can't think of
any that make sense. There have been times when I've received a
deafening blast from my headphones at switch-on, or when selecting a
signal source, but that's not something that would be remedied by
unswitched speaker outputs.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.


The headphone socket on my current TV is always live, but it has its own
software level control, and of course, there is a remote 'mute' function, so
the internal speakers can be turned off if I want to listen to something on
there, whilst the missus is messing about on her laptop, or whatever.
Interestingly, the on-screen 'mute' symbol disappears after about 2 minutes.
On my workshop TV, you get a bloody great red loudspeaker symbol with a bar
through it, all the time it is muted ...

With 40 yeras of experience in this game, and added to the all the combined
years of the rest of us on here, if we can't come up with a sensible reason,
then you have to assume that there *is* no sense to it. I hate it when you
get a puzzle like this though. I really would like to know what the designer
was thinking when he did this for the "English" model only. By that, do they
actually mean the "UK" model ? I can't imagine that any different version
was shipped to N.I. or Wales or Scotland. That would be a bit like having
one version for Texas, and a different one for Colorado ...

Arfa

On Fri, 4 Jan 2013 01:03:02 -0000, "Arfa Daily"
put finger to keyboard and composed:

On my workshop TV, you get a bloody great red loudspeaker symbol with a bar
through it, all the time it is muted ...

LG?

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

"Arfa Daily"


With 40 yeras of experience in this game, and added to the all the
combined years of the rest of us on here, if we can't come up with a
sensible reason, then you have to assume that there *is* no sense to it. I
hate it when you get a puzzle like this though. I really would like to
know what the designer was thinking when he did this for the "English"
model only. By that, do they actually mean the "UK" model ?

** Yes.

The motive back then was the British hi-fi press's obsession with "damping
factor" or DF.

By omitting the wiring to and from the HP jack, Denon were able to publish
an impressive number for DF and the folk in sales thought this to be a good
idea, at least for the UK market.


..... Phil

"Michael A. Terrell" wrote in message
m...

Franc Zabkar wrote:

On Wed, 2 Jan 2013 16:45:12 -0000, "Arfa Daily"
put finger to keyboard and composed:

The reported problems were that the sound level fluctuated on both
channels,
and that the headphone socket did not cut the speakers.

My old Mitsubishi CRT TV had two headphone sockets. One cut the
speaker, the other did not. Presumably it was to allow a hearing
impaired individual to listen to the TV via headphones while their
partner listened via the speaker. I can't imagine that this would
apply in the Denon case, though.

I'm trying to envisage some kind of safety issue, but I can't think of
any that make sense.


It sounds like they needed to remove one more part to meet a price
point.


But why for just one regional model ? You could save the same amount of
money between a switched and unswitched socket by fitting a cheaper volume
knob ...

Arfa

"Franc Zabkar" wrote in message
...
On Fri, 4 Jan 2013 01:03:02 -0000, "Arfa Daily"
put finger to keyboard and composed:

On my workshop TV, you get a bloody great red loudspeaker symbol with a
bar
through it, all the time it is muted ...

LG?

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.


It's actually a Bush. Two generations ago, Bush were a very well respected
indigenous manufacturer of quality consumer electronics. When I was a kid,
our household TV was a Bush. My first transistor radio which was built on a
metal chassis which had wiring points all over it (and which I've still got
somewhere) was a Bush. About one generation ago, they formed an amalgamation
with Murphy, another quality UK manufacturer, under the Rank Organisation
umbrella to become Rank Bush Murphy or RBM. It was still a wholly UK
manufacturing operation, and still produced quality products. Some years
back, like most manufacturing here and as I understand it, in the U.S. also,
they packed it all in.

Always having an eye to the main chance, some bunch of Ying Tongs bought the
Bush and Murphy names, and started badging their crap with them, and
exporting them back to the UK. Because Bush stuff used to be good, and
there's plenty of my age that had Bush stuff in their homes when they were
kids, it has continued to sell well, but most of it is now real cheapo Far
East stuff that'll just about last out its warranty if you are lucky. It's
real 'shed' and supermarket quality stuff.

To be fair, the TV in my workshop is not too bad, as long as all you are
interested in is having a picture, rather than having a 'good' picture. The
only reason that I have it is that it was 'inherited' from a dealer that I
did some work for, and he supplied the set for monitoring purposes as part
of the deal.

Is it LG inside ? I don't know. It could be, I suppose, but I doubt that it
would warrant having a chassis from a well known manufacturer like them in
it. However, if the big red speaker on the screen is characteristic of the
LG you are thinking of, then maybe it is an LG chassis ...

Arfa

Arfa Daily wrote:

"Michael A. Terrell" wrote in message
m...

Franc Zabkar wrote:

On Wed, 2 Jan 2013 16:45:12 -0000, "Arfa Daily"
put finger to keyboard and composed:

The reported problems were that the sound level fluctuated on both
channels,
and that the headphone socket did not cut the speakers.

My old Mitsubishi CRT TV had two headphone sockets. One cut the
speaker, the other did not. Presumably it was to allow a hearing
impaired individual to listen to the TV via headphones while their
partner listened via the speaker. I can't imagine that this would
apply in the Denon case, though.

I'm trying to envisage some kind of safety issue, but I can't think of
any that make sense.


It sounds like they needed to remove one more part to meet a price
point.


But why for just one regional model ? You could save the same amount of
money between a switched and unswitched socket by fitting a cheaper volume
knob ...


A marketing decison: No one really uses headphones anymore! ;-)

"Phil Allison" wrote in message
...

"Arfa Daily"


With 40 yeras of experience in this game, and added to the all the
combined years of the rest of us on here, if we can't come up with a
sensible reason, then you have to assume that there *is* no sense to it.
I hate it when you get a puzzle like this though. I really would like to
know what the designer was thinking when he did this for the "English"
model only. By that, do they actually mean the "UK" model ?

** Yes.

The motive back then was the British hi-fi press's obsession with "damping
factor" or DF.

By omitting the wiring to and from the HP jack, Denon were able to publish
an impressive number for DF and the folk in sales thought this to be a
good idea, at least for the UK market.


.... Phil



There is a degree of 'sense' to that thought, Phil. I seem to recall that
Peter Walker of Quad fame espoused similar opinions a bit further back than
this unit comes from, and cited it as the reason for refusing to fit
headphone sockets to their products ...

Arfa

On Wed, 2 Jan 2013 16:45:12 -0000, "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 ...

Arfa

I have seen lots of Japanese and some other amplifiers that do not have
speaker cutouts on the headphone jack; but _ALL_ of them had proper
speaker switches of some sort.

YMMV

?-)

On Wed, 02 Jan 2013 16:13:02 -0500, Smarty wrote:

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


It sounds like they made a deal with Lucas... ;-)
Denon was left with a difficult choice when designing the British model.
They either had to make it quirky in a way that Brits would appreciate,
or to follow the great tradition of British automobile makers and
provide a way to make it leak some type of fluid.

They chose the less expensive choice.........




You cost me about 6 paper towels and a mouthful of wine. Worst of all
some of it came out of my nose.

?-)

On 1/3/2013 3:45 AM, 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 ...

Arfa

**Sounds like the Pommy hi fi press influence to me. Headphone socket
switches are not the highest quality method of switching a speaker level
audio signal available.

--
Trevor Wilson www.rageaudio.com.au

Trevor Wilson wrote:

On 1/3/2013 3:45 AM, 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 ...
?
? Arfa

**Sounds like the Pommy hi fi press influence to me. Headphone socket
switches are not the highest quality method of switching a speaker level
audio signal available.


That's because they use cheap plastic junk, rather that commercial
grade jacks like these:

http://www.switchcraft.com/Drawings/14b_cd.pdf

I've seen these in equipment that is used daily for decades with no
problems.

"Michael A. Terrell"

Trevor Wilson wrote:


**Sounds like the Pommy hi fi press influence to me. Headphone socket
switches are not the highest quality method of switching a speaker level
audio signal available.


That's because they use cheap plastic junk, rather that commercial
grade jacks like these:

http://www.switchcraft.com/Drawings/14b_cd.pdf

I've seen these in equipment that is used daily for decades with no
problems.


** That sort of stereo jack cannot perform speaker switching on a hi-fi
amplifer.

You need ones that have a pair of independent contacts.


...... Phil

http://www.switchcraft.com/Drawings/14b_cd.pdf

That sort of stereo jack cannot perform speaker switching
on a hi-fi amplifier.

Sure it can. It's just not a good idea. You don't want to run the amp's output
through such a "cheap 'n dirty" "switch".


You need ones that have a pair of independent contacts.

???

Arfa

I have seen lots of Japanese and some other amplifiers that do not have
speaker cutouts on the headphone jack; but _ALL_ of them had proper
speaker switches of some sort.

YMMV

?-)

Yep, me too, which is why I couldn't see the point of having this
arrangement ...

Arfa

"William Sommer****** is getting WORSE "

http://www.switchcraft.com/Drawings/14b_cd.pdf

That sort of stereo jack cannot perform speaker switching
on a hi-fi amplifier.

Sure it can.

** The only way such a jack could perform speaker switching is if the amp's
output were connected DIRECT to the headphone contacts - something no
sane amp maker would ever do.


You need ones that have a pair of independent contacts.

???


** Wot an ignorant, ****ing **** you are.


..... Phil

Phil Allison wrote:

"Michael A. Terrell"
?
? Trevor Wilson wrote:
?
??
?? **Sounds like the Pommy hi fi press influence to me. Headphone socket
?? switches are not the highest quality method of switching a speaker level
?? audio signal available.
?
?
? That's because they use cheap plastic junk, rather that commercial
? grade jacks like these:
?
? http://www.switchcraft.com/Drawings/14b_cd.pdf
?
? I've seen these in equipment that is used daily for decades with no
? problems.
?

** That sort of stereo jack cannot perform speaker switching on a hi-fi
amplifer.

You need ones that have a pair of independent contacts.


They make those, as well. I was pointing out the construction of the
jack. Their long frame series have additional switches. They are the
same grade that were used in telephone switchboards & audio patch panels
in studios. The point is that they would ad $10 to $10 to the retail
price of the units.

As far as putting resistors in series with the 'cans', it's also
possible to use the extra switches to reduce the drive to the amplifier.

On 09/01/2013 02:09, Arfa Daily wrote:


Arfa

I have seen lots of Japanese and some other amplifiers that do not have
speaker cutouts on the headphone jack; but _ALL_ of them had proper
speaker switches of some sort.

YMMV

?-)

Yep, me too, which is why I couldn't see the point of having this
arrangement ...

Arfa
Surely the best solution would be a 'user' control to mute the speakers
at will? Best of both worlds.

"William Sommerwerck" wrote in message ...

http://www.switchcraft.com/Drawings/14b_cd.pdf

That sort of stereo jack cannot perform speaker switching
on a hi-fi amplifier.

Sure it can. It's just not a good idea. You don't want to run the amp's
output
through such a "cheap 'n dirty" "switch".


You need ones that have a pair of independent contacts.

???


Presumably to switch a remote relay.



Gareth.

Gareth Magennis wrote:

"William Sommerwerck" wrote in message ...

http://www.switchcraft.com/Drawings/14b_cd.pdf

That sort of stereo jack cannot perform speaker switching
on a hi-fi amplifier.

Sure it can. It's just not a good idea. You don't want to run the amp's
output
through such a "cheap 'n dirty" "switch".

You need ones that have a pair of independent contacts.

???

Presumably to switch a remote relay.


No. They switched a pair of resistors in line with the headphones to
reduce the drive. I recall a lot of 180 Ohm resistors on the back of
headphone jacks.

"Michael A. Terrell" wrote in message
...


Gareth Magennis wrote:

"William Sommerwerck" wrote in message ...

http://www.switchcraft.com/Drawings/14b_cd.pdf

That sort of stereo jack cannot perform speaker switching
on a hi-fi amplifier.

Sure it can. It's just not a good idea. You don't want to run the amp's
output
through such a "cheap 'n dirty" "switch".

You need ones that have a pair of independent contacts.

???

Presumably to switch a remote relay.


No. They switched a pair of resistors in line with the headphones to
reduce the drive. I recall a lot of 180 Ohm resistors on the back of
headphone jacks.


Yes, that would surely still rely on the switched headphone jack passing
the amplifiers power, or not, via its puny switch to the speakers.

What you really need is a pair of independent contacts in the headphone
socket that makes a circuit when a headphone jack is inserted.

This pair of contacts will then remotely switch the speakers off.


These sockets do actually exist.


Gareth.

Gareth Magennis wrote:

"Michael A. Terrell" wrote in message
...

Gareth Magennis wrote:

"William Sommerwerck" wrote in message ...

http://www.switchcraft.com/Drawings/14b_cd.pdf

That sort of stereo jack cannot perform speaker switching
on a hi-fi amplifier.

Sure it can. It's just not a good idea. You don't want to run the amp's
output
through such a "cheap 'n dirty" "switch".

You need ones that have a pair of independent contacts.

???

Presumably to switch a remote relay.

No. They switched a pair of resistors in line with the headphones to
reduce the drive. I recall a lot of 180 Ohm resistors on the back of
headphone jacks.

Yes, that would surely still rely on the switched headphone jack passing
the amplifiers power, or not, via its puny switch to the speakers.

What you really need is a pair of independent contacts in the headphone
socket that makes a circuit when a headphone jack is inserted.

This pair of contacts will then remotely switch the speakers off.

These sockets do actually exist.


They have been around since the '60s.

"Gareth Magennis" wrote in message
...


"William Sommerwerck" wrote in message ...

http://www.switchcraft.com/Drawings/14b_cd.pdf

That sort of stereo jack cannot perform speaker switching
on a hi-fi amplifier.

Sure it can. It's just not a good idea. You don't want to run the amp's
output
through such a "cheap 'n dirty" "switch".


You need ones that have a pair of independent contacts.

???


Presumably to switch a remote relay.



Gareth.


The late model Denon's I've seen use a switch in the headphone jack to
control the speaker relays.

Mark Z.

"Gareth Magennis"

You need ones that have a pair of independent contacts.

???

Presumably to switch a remote relay.


** Not at all.

These stereo jacks have two sets of isolated, NC contacts that will do the
job just fine with amplifiers up to say 80 wpc.

See items 3 & 4 on this page:

http://www.minute-man.com/acatalog/1...reo_Jacks.html



.... Phil

"Gareth Magennis" wrote in message
...


"Michael A. Terrell" wrote in message
...


Gareth Magennis wrote:

"William Sommerwerck" wrote in message
...

http://www.switchcraft.com/Drawings/14b_cd.pdf

That sort of stereo jack cannot perform speaker switching
on a hi-fi amplifier.

Sure it can. It's just not a good idea. You don't want to run the amp's
output
through such a "cheap 'n dirty" "switch".

You need ones that have a pair of independent contacts.

???

Presumably to switch a remote relay.


No. They switched a pair of resistors in line with the headphones to
reduce the drive. I recall a lot of 180 Ohm resistors on the back of
headphone jacks.


Yes, that would surely still rely on the switched headphone jack passing
the amplifiers power, or not, via its puny switch to the speakers.

What you really need is a pair of independent contacts in the headphone
socket that makes a circuit when a headphone jack is inserted.

This pair of contacts will then remotely switch the speakers off.


These sockets do actually exist.


Gareth.


The system of speaker switching that you are suggesting, is often used on
home cinema systems or AV amps where there are 6 channels to be switched
off. For instance, my Sony HCD - S800 home cinema unit that I use for
optical decoding and surround processing on my TV, has an independent set of
contacts on it that tell the system control micro that headphones have been
jacked in. It responds by cutting off the six speaker protection relays on
the ends of the amps. The actual stereo signal for the headphones is derived
from an independent small amplifier, with a power output more appropriate to
driving them.

Arfa