Powering an In-wall Amp

[MrTea]

Hi Guys

I've just acquired an "in wall" amplifier primarily intended for use in
classroom situations, but I am intending to try it as part of my whole
house audio project.

It's a Nuvo NV-Wa30.

It has simple inputs on the back for DC in, Inputs A/B and then outputs
for a pair of speakers.

The power is supplied using a long cable connected to an adapter which
in turn is plugged into the mains (the adapter is similar to those used
for laptops, so you plug a cable into the mains which in turn is
plugged into the adapter)

I want to do a tidy install of this so was hoping to run power to the
Amp "neatly" but I'm not sure how! The problem is I don't just want the
DC adapter "hanging" out of the wall somewhere.

I think I have a few options.

1) Extend the cable so I can run it all the way back to my node 0 and
just plug it in there.
2) Come up with some kind of DC wall socket thing (connected to the
amp), then modify my adapter cable so it can be plugged and can
therefore be plugged in to this socket.

Any thoughts or suggestions would be appreciated (apologies if any of
the above doesn't make much sense!)

[Robert Green]

"MrTea" <hilton.jon@gmail.com> wrote in message

<stuff snipped>

> The power is supplied using a long cable connected to an adapter which
> in turn is plugged into the mains (the adapter is similar to those used
> for laptops, so you plug a cable into the mains which in turn is
> plugged into the adapter)

Sounds like a typical coaxial power plug. Is the metal tip about 1/2" long
with a hollow center? Does it look like any of these:

http://www.radioshack.com/sm-dc-power-connectors--fi-2032284_cp-2032058.2032
231.html

> I want to do a tidy install of this so was hoping to run power to the
> Amp "neatly" but I'm not sure how! The problem is I don't just want the
> DC adapter "hanging" out of the wall somewhere.
>
> I think I have a few options.
>
> 1) Extend the cable so I can run it all the way back to my node 0 and
> just plug it in there.

Might work, might not. The voltage may drop too much after a long cable run
to be useful (which is why AC and not DC is running throughout most of the
world's homes - AC voltage doesn't drop the way DC does with long wire
runs).

> 2) Come up with some kind of DC wall socket thing (connected to the
> amp), then modify my adapter cable so it can be plugged and can
> therefore be plugged in to this socket.

You can find panel mount jacks for your power supply's plug - but be aware
that there are at least 20 very similar looking plugs - you have to get an
exact fit. That's determined by the inner and outer diameters of the power
plug and to a lesser extent, the length as well. If you have a Radio Shack
nearby, they would have such panel jacks. It would be a simple matter to
buy a blank wall plate, drill a hole for the jack and a retrofit wall box
and power it through that. This is such a jack:

http://www.radioshack.com/sm-size-m-panel-mount-coaxial-power-jack-w-switch-
-pi-2102491.html

When they say "with switch" it means that there is a connection to break an
internal circuit when the plug is inserted. This is often used when a
device has both internal batteries AND a power input jack. The jack
responds to the insertion of a plug by disconnecting the batteries so they
aren't getting voltage from the power supply and will not be likely to
explode as a result.

> Any thoughts or suggestions would be appreciated (apologies if any of
> the above doesn't make much sense!)

HTH,

--
Bobby G.

[MrTea]

> <stuff snipped>
>
> > The power is supplied using a long cable connected to an adapter which
> > in turn is plugged into the mains (the adapter is similar to those used
> > for laptops, so you plug a cable into the mains which in turn is
> > plugged into the adapter)
>
> Sounds like a typical coaxial power plug. Is the metal tip about 1/2" long
> with a hollow center? Does it look like any of these:

I should probably clarify my original description.

The cable itself is attached to an adapter, not dissimilar to a typical
laptop PSU e.g

http://www.irqcomputers.co.uk/contentitempage.aspx?contentid=74930

However at the other end (the bit which goes to the amplifier), there
is currently no plug on the end if it, just the two bare cables.

[Robert Green]

"MrTea" <hilton.jon@gmail.com> wrote in message
news:1143123605.848355.313100@v46g2000cwv.googlegr oups.com...
> > <stuff snipped>
> >
> > > The power is supplied using a long cable connected to an adapter which
> > > in turn is plugged into the mains (the adapter is similar to those
used
> > > for laptops, so you plug a cable into the mains which in turn is
> > > plugged into the adapter)
> >
> > Sounds like a typical coaxial power plug. Is the metal tip about 1/2"
long
> > with a hollow center? Does it look like any of these:
>
> I should probably clarify my original description.
>
> The cable itself is attached to an adapter, not dissimilar to a typical
> laptop PSU e.g
>
> http://www.irqcomputers.co.uk/contentitempage.aspx?contentid=74930
>
> However at the other end (the bit which goes to the amplifier), there
> is currently no plug on the end if it, just the two bare cables.

I'm not following, I'm afraid. Does the amplifier have a power jack or does
it just connect to the power supply with screw terminals? I suppose you
should start again from the beginning just so that we are clear. Where will
you be mounting this device? Are you trying to conceal the power supply,
connect the power supply or both?

--
Bobby G.

[MrTea]

That's OK I should probably learn how to describe things better!

To answer your question directly, the amp has screw terminals for power
connection.

Therefore the supplied adapter has a long cable on it which has bare
wires at the end (for connecting to the amp).

The adapter has an output rating of +24v (1.75A)

What I don't want, is to connect this cable to the amp and then have
the cable (with adapter hanging off it) poking out of a wall somewhere.


Following your previous post I am coming round to the following idea..

Purchase a DC socket (one of these)...

http://www.maplin.co.uk/Module.aspx?TabID=1&DOY=23m3&ModuleNo=1407&criteria=

Anda plug (one of these)..

http://www.maplin.co.uk/module.aspx?TabID=1&criteria=dc%20plug&ModuleNo=5439&doy=23m3

Because the existing cable (attached to the adapter) is longer than I
require, I could make a cut in it and put as much as I need in the
wall, connected to the amp at one end, and my DC socket at the other,
then pop the plug on the end of the remaining cable (from the adapter)
and plug this into the socket.

I hope that's cleared things up a bit. My mention of a laptop adapter
probably confused things, all I meant to point out was that the adapter
itself has a socket for an IEC (Kettle) lead

Hope that's clear! Thanks for your patience and persistance!

[Robert Green]

By George, I think you've got it. Those two adapters should work nicely,
especially if you're shortening, not lengthening the power cable.

--
Bobby G.


"MrTea" <hilton.jon@gmail.com> wrote in message
news:1143126898.891822.226300@i40g2000cwc.googlegr oups.com...
> That's OK I should probably learn how to describe things better!
>
> To answer your question directly, the amp has screw terminals for power
> connection.
>
> Therefore the supplied adapter has a long cable on it which has bare
> wires at the end (for connecting to the amp).
>
> The adapter has an output rating of +24v (1.75A)
>
> What I don't want, is to connect this cable to the amp and then have
> the cable (with adapter hanging off it) poking out of a wall somewhere.
>
>
> Following your previous post I am coming round to the following idea..
>
> Purchase a DC socket (one of these)...
>
>
http://www.maplin.co.uk/Module.aspx?TabID=1&DOY=23m3&ModuleNo=1407&criteria=
>
> Anda plug (one of these)..
>
>
http://www.maplin.co.uk/module.aspx?TabID=1&criteria=dc%20plug&ModuleNo=5439
&doy=23m3
>
> Because the existing cable (attached to the adapter) is longer than I
> require, I could make a cut in it and put as much as I need in the
> wall, connected to the amp at one end, and my DC socket at the other,
> then pop the plug on the end of the remaining cable (from the adapter)
> and plug this into the socket.
>
> I hope that's cleared things up a bit. My mention of a laptop adapter
> probably confused things, all I meant to point out was that the adapter
> itself has a socket for an IEC (Kettle) lead
>
> Hope that's clear! Thanks for your patience and persistance!
>

[Dan Lanciani]

In article <o9ydncNa9chJPb_Z4p2dnA@rcn.net>, ROBERT_GREEN1963@YAH00.COM (Robert Green) writes:

| Might work, might not. The voltage may drop too much after a long cable run
| to be useful (which is why AC and not DC is running throughout most of the
| world's homes - AC voltage doesn't drop the way DC does with long wire
| runs).

To a first approximation (good for anything you might be doing in a home
with 50/60Hz AC and DC power distribution) AC voltage "drops" exactly the
way DC does with long wire runs. For power transmission on the level of
grid interconnects the losses with DC are sufficiently _less_ than with
AC that it becomes economical to use DC even after you factor in the cost
and losses of conversion equipment on each end.

Dan Lanciani
ddl@danlan.*com

[Byron Hynes]

So, realistically, could I run 12V DC (or so) through my 2500 sq ft house
to get rid of some wall warts? (Possibly driving it off a solar panel/battery,
for that matter).

> In article <o9ydncNa9chJPb_Z4p2dnA@rcn.net>,
> ROBERT_GREEN1963@YAH00.COM (Robert Green) writes:
>
> | Might work, might not. The voltage may drop too much after a long
> cable run
> | to be useful (which is why AC and not DC is running throughout most
> of the
> | world's homes - AC voltage doesn't drop the way DC does with long
> wire
> | runs).
> To a first approximation (good for anything you might be doing in a
> home with 50/60Hz AC and DC power distribution) AC voltage "drops"
> exactly the way DC does with long wire runs. For power transmission
> on the level of grid interconnects the losses with DC are sufficiently
> _less_ than with AC that it becomes economical to use DC even after
> you factor in the cost and losses of conversion equipment on each end.
>
> Dan Lanciani
> ddl@danlan.*com

[Robert L Bass]

> So, realistically, could I run 12V DC (or so) through my 2500 sq ft house
> to get rid of some wall warts? (Possibly driving it off a solar panel/battery,
> for that matter).

Absolutely. I did the same thing in my CT home many years ago.
Run the wire to mud rings (look like junction boxes only there's
no back) in each location. Over the mud rings place single-gang
plates with appropriate jacks mounted. Home run 16/2 from each
location and you'll be fine as long as the power supply is of
adequate size. If the DC current requirements are small, run
18/2.

Altronix and ELK Products both make reliable DC power supplies in
various capacities.

--

Regards,
Robert L Bass

Bass Burglar Alarms
The Online DIY Store
http://www.BassBurglarAlarms.com

--

Never underestimate the power of very stupid people in large
groups.

[Dan Lanciani]

In article <50cb70803eda48c81ca3ed807842@newsgroups.comcast.ne t>, bph@byronetta.com (Byron Hynes) writes:

|So, realistically, could I run 12V DC (or so) through my 2500 sq ft house
|to get rid of some wall warts? (Possibly driving it off a solar panel/battery,
|for that matter).

The problem I usually encounter with such schemes is that many of the
little gadgets that are powered by wall warts depend on those wall warts
for isolation. That is, the negative power supply input may well not
be the same as the negative/ground connection of any i/o, audio in/out,
etc. of the device. Some devices that don't otherwise depend on the
isolation try to help you by putting a bridge rectifier at the supply
input. That means that the internal ground/common is going to be one
diode drop away from the power input negative.

If you power two or more devices that need isolation from a common supply
and if those devices are directly or indirectly interconnected then you
can get some pretty strange behavior or even damage. If the devices have
no external connections or if you can be sure that the connections are either
isolated or referenced to the same ground then you should be ok. In general,
I find it sufficiently difficult to be sure of this that I don't replace
multiple wall warts with a single supply even when they are all on the same
power strip...

Dan Lanciani
ddl@danlan.*com

[Byron Hynes]

Thanks.

> In article <50cb70803eda48c81ca3ed807842@newsgroups.comcast.ne t>,
> bph@byronetta.com (Byron Hynes) writes:
>
> |So, realistically, could I run 12V DC (or so) through my 2500 sq ft
> house |to get rid of some wall warts? (Possibly driving it off a solar
> panel/battery, |for that matter).
>
> The problem I usually encounter with such schemes is that many of the
> little gadgets that are powered by wall warts depend on those wall
> warts
> for isolation. That is, the negative power supply input may well not
> be the same as the negative/ground connection of any i/o, audio
> in/out,
> etc. of the device. Some devices that don't otherwise depend on the
> isolation try to help you by putting a bridge rectifier at the supply
> input. That means that the internal ground/common is going to be one
> diode drop away from the power input negative.
> If you power two or more devices that need isolation from a common
> supply
> and if those devices are directly or indirectly interconnected then
> you
> can get some pretty strange behavior or even damage. If the devices
> have
> no external connections or if you can be sure that the connections are
> either
> isolated or referenced to the same ground then you should be ok. In
> general,
> I find it sufficiently difficult to be sure of this that I don't
> replace
> multiple wall warts with a single supply even when they are all on the
> same
> power strip...
> Dan Lanciani
> ddl@danlan.*com

[Robert Green]

"Dan Lanciani" <ddl@danlan.*com> wrote in message

> | Might work, might not. The voltage may drop too much after a long cable
run
> | to be useful (which is why AC and not DC is running throughout most of
the
> | world's homes - AC voltage doesn't drop the way DC does with long wire
> | runs).
>
> To a first approximation (good for anything you might be doing in a home
> with 50/60Hz AC and DC power distribution) AC voltage "drops" exactly the
> way DC does with long wire runs. For power transmission on the level of
> grid interconnects the losses with DC are sufficiently _less_ than with
> AC that it becomes economical to use DC even after you factor in the cost
> and losses of conversion equipment on each end.

I thought the payback came from HVDC having a lower overall voltage compared
to AC's peak-to-peak and that allowed using existing transmission cables
designed for AC to transmit more power without overloading the wire
insulation and standoffs.

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

says: "Above a certain break-even distance (about 50 km for submarine
cables, and perhaps 600-800 km for overhead cables), the lower cost of the
HVDC electrical conductors outweighs the cost of the electronics."

HVDC has a lot of other important benefits that will insure its commercial
success. It can tie two unsynchronized AC systems together and it's better
at powering long cable runs like undersea cables where the line capacitance
becomes a serious issue for AC power transmission.

I should have worded my comment about voltage dropoff differently. AC has
been the traditional method of power distribution because when
Tesla/Westinghouse and Edison were fighting over AC v. DC for the national
power grid, there were no DC voltage convertors. AC at that time could be
easily transformed to higher voltages where the voltage drop is not as
significant. Use of a higher voltage leads to more efficient transmission
of power which is one reason why large appliances are powered by 220VAC. The
same amount of power can be transmitted with a lower current by increasing
the voltage. Edison power stations had to be local - the DC systems
couldn't power anything much beyond a mile from the source. Westinghouse's
AC system could send HVAC for hundreds of miles and transform it down to a
safe voltage at local substations.

But this all has little to do with creating a home-brew 12VDC distribution
system. My limited experience with running long DC wires is that the
voltage drop-off for 12VDC is greater than 110VAC simply because the voltage
is lower. Some of the DC powered cameras I use come with variable voltage
PS's that can be spun up to about 18VDC. By the time it reaches the camera,
it's back down to 12VDC. Without that voltage boost the attenuation is so
great that the cameras won't operate reliably. I suppose I could run 12/2
or heavier cable and cut down on the voltage drop, but that wouldn't be
practical.

Perhaps the EE's out there can tell us what the voltage drop would be for
both 110VAC and 12VDC over a 250' length of 12/2 wire.

All the above is of little consequence since as you point out, few wall wart
powered devices can be counted on to have no interaction with other devices
on the same power bus. I suspect that electronics designed for auto or RV
use can be attached to a 12VDC bus without serious interaction because
that's how they are connected to the car/RV battery, but I haven't checked
to make sure.

--
Bobby G.