In telephone line there's a vcc of about 44.6 V.
Is it too dangerous according to you if I pick this vcc to power
supply a small headphone amplifier?
Could this create some problem to telephone line?????
audiomix

Audiomix wrote:
In telephone line there's a vcc of about 44.6 V.

More than that. Should be around 48V coming from the telco, into a 600 ohm
load.

Is it too dangerous according to you if I pick this vcc to power
supply a small headphone amplifier?

You won't be able to get much current out of it, so don't expect it to
sound very good. But if you have something line-powered and it's all
transformer-isolated from everything else, there's no reason you can't
steal a little line current.

Could this create some problem to telephone line?????

Not unless you drop the load below 600 ohms. Be aware that you'll regularly
see ringing current around 100V, which is more likely apt to spike up to 300V
or so on a typical line from the inductance of the ringers if there are other
phones on the pair. Also you'll see test voltages around 200V sometimes.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

On 10 May 2004 08:55:22 -0400, (Scott Dorsey) wrote:

Audiomix wrote:
In telephone line there's a vcc of about 44.6 V.

More than that. Should be around 48V coming from the telco, into a 600 ohm
load.

Is it too dangerous according to you if I pick this vcc to power
supply a small headphone amplifier?

You won't be able to get much current out of it, so don't expect it to
sound very good. But if you have something line-powered and it's all
transformer-isolated from everything else, there's no reason you can't
steal a little line current.

TPC (The Phone Company) has some pretty strict rules about drawing
current from the line when you're not making a call. I don't recall
offhand the exact numbers, but I think you're not allowed to take more
than about 10 microamps when on-hook.

There are also rules about going off-hook automatically. I remember
hearing about some cordless phone manufacturer who had the idea of
going offhook for a few seconds every hour in order to keep the phone
battery charged from the power on the phone line. TPC nixed this
idea.

I worked on a project once that provided a blinky LED to indicate the
presence of waiting voicemail. It had to run on batteries, because we
couldn't draw enough current from the line for one micropower
processor and an intermittent duty LED.

-- PJW


Could this create some problem to telephone line?????

Not unless you drop the load below 600 ohms. Be aware that you'll regularly
see ringing current around 100V, which is more likely apt to spike up to 300V
or so on a typical line from the inductance of the ringers if there are other
phones on the pair. Also you'll see test voltages around 200V sometimes.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

?

You won't be able to get much current out of it, so don't expect it to
sound very good. But if you have something line-powered and it's all
transformer-isolated from everything else, there's no reason you can't
steal a little line current.

For example a 9 volt battery........by the way which is the minimum
voltage ampere supply for a small headphone amplifier????
Do you know a simple scheme of that????
Thanks to everyone
audiomix

Audiomix wrote:
?

You won't be able to get much current out of it, so don't expect it to
sound very good. But if you have something line-powered and it's all
transformer-isolated from everything else, there's no reason you can't
steal a little line current.

For example a 9 volt battery........

Oh, no, you won't get anywhere near as much current as you will out of a
9-volt battery.

by the way which is the minimum
voltage ampere supply for a small headphone amplifier????

For what sort of application? Typical cheapie consumer gear is seldom
above to drive more than the rail voltage... figure 9V into a 50 ohm load.
This makes it unusable for 600 ohm professional headphones.

Do you know a simple scheme of that????

Any amplifier circuit will do. Even a cheap op-amp will drive low-Z
headphones to an acceptable level in some cases.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

A remarkable variety of telephone-line-powered
devices can be seen here...
http://www.sandman.com/telco.html

"Audiomix" wrote in message
om...
In telephone line there's a vcc of about 44.6 V.
Is it too dangerous according to you if I pick this vcc to power

48V DC (open Circuit) at 20mA (Short Circuit) + 75V AC (RMS) Ring
current....

supply a small headphone amplifier?

Not without looping the Line but I guess you dont need to listen to a phone
line unless you loop it . You should be able to merely connect the
Headphones across the line there is usually enough level from the Audio to
drive a 200-600 pair of phones nicely.

Could this create some problem to telephone line?????

Dunno tell us more about what you want to achieve ....

audiomix

On 10 May 2004 08:55:22 -0400, (Scott Dorsey) wrote:

Audiomix wrote:
In telephone line there's a vcc of about 44.6 V.

More than that. Should be around 48V coming from the telco, into a 600 ohm
load.

Argh. The 48V figure is for open-circuit. If the OP is using a
cheap and/or old mechanical-movement meter, it might indicate 44.6V,
both for the loading, and for it's lack of accuracy. The phone line
open-circuit voiltage itself might vary a volt or two.
Put a 600 ohm load on an open telephone line, and the voltage will
drop (maybe even to zero for a half-second or so while the CO switches
batteries - I've seen it) to anywhere from 5 to 15 volts or so, and
the CO will send dial tone. I hope it's a 1 watt or larger resistor.
If it's much smaller it will get hot.

Is it too dangerous according to you if I pick this vcc to power
supply a small headphone amplifier?

You won't be able to get much current out of it,

You can usually get close 20mA at up to 19V, but that's far from
guaranteed. I've seen the curves with the 'operating area' of voltage
vs. current, but I don't remember the numbers offhand. If I recall
they (the LSSGR) specified at least a half-dozen coordinates.

so don't expect it to
sound very good. But if you have something line-powered and it's all
transformer-isolated from everything else, there's no reason you can't
steal a little line current.

Could this create some problem to telephone line?????

Phone companies don't want you to pull significant current from the
phone line unless you're going off-hook, and they don't want you to go
off-hook if you're not making a call. You can get on-hook current
through a 5 megohm resistor (this limits current to the 10 uA someone
else mentioned), but that will barely charge a high-quality,
low-leakage capacitor.

To the OP: I'm not sure I understand what you want to do. Do you
want to listen over the phone through "standard" stereo headphones?
I would use something like transformer isolation (a cheap telephone
transformer out of an old modem would be ideal) and an off-the-self
headphone amplifier. Or even an off-the-shelf Radio Shack speaker
phoneline monitor (I don't know the model but I used one ten years
ago) with the speaker connections disconnected from the speaker and
connected to a headphone jack. Is there some reason you can't do this?

Not unless you drop the load below 600 ohms. Be aware that you'll regularly
see ringing current around 100V, which is more likely apt to spike up to 300V
or so on a typical line from the inductance of the ringers if there are other
phones on the pair. Also you'll see test voltages around 200V sometimes.

Those are all on-hook signals. If you go off hook, they don't apply
(for very long, anyway).

--scott

-----
http://mindspring.com/~benbradley

On 10 May 2004 08:55:22 -0400, (Scott Dorsey) wrote:

Audiomix wrote:
In telephone line there's a vcc of about 44.6 V.

More than that. Should be around 48V coming from the telco, into a 600 ohm
load.

Argh. The 48V figure is for open-circuit. If the OP is using a
cheap and/or old mechanical-movement meter, it might indicate 44.6V,
both for the loading, and for it's lack of accuracy. The phone line
open-circuit voiltage itself might vary a volt or two.
Put a 600 ohm load on an open telephone line, and the voltage will
drop (maybe even to zero for a half-second or so while the CO switches
batteries - I've seen it) to anywhere from 5 to 15 volts or so, and
the CO will send dial tone. I hope it's a 1 watt or larger resistor.
If it's much smaller it will get hot.

Is it too dangerous according to you if I pick this vcc to power
supply a small headphone amplifier?

You won't be able to get much current out of it,

You can usually get close 20mA at up to 19V, but that's far from
guaranteed. I've seen the curves with the 'operating area' of voltage
vs. current, but I don't remember the numbers offhand. If I recall
they (the LSSGR) specified at least a half-dozen coordinates.

so don't expect it to
sound very good. But if you have something line-powered and it's all
transformer-isolated from everything else, there's no reason you can't
steal a little line current.

Could this create some problem to telephone line?????

Phone companies don't want you to pull significant current from the
phone line unless you're going off-hook, and they don't want you to go
off-hook if you're not making a call. You can get on-hook current
through a 5 megohm resistor (this limits current to the 10 uA someone
else mentioned), but that will barely charge a high-quality,
low-leakage capacitor.

To the OP: I'm not sure I understand what you want to do. Do you
want to listen over the phone through "standard" stereo headphones?
I would use something like transformer isolation (a cheap telephone
transformer out of an old modem would be ideal) and an off-the-self
headphone amplifier. Or even an off-the-shelf Radio Shack speaker
phoneline monitor (I don't know the model but I used one ten years
ago) with the speaker connections disconnected from the speaker and
connected to a headphone jack. Is there some reason you can't do this?

Not unless you drop the load below 600 ohms. Be aware that you'll regularly
see ringing current around 100V, which is more likely apt to spike up to 300V
or so on a typical line from the inductance of the ringers if there are other
phones on the pair. Also you'll see test voltages around 200V sometimes.

Those are all on-hook signals. If you go off hook, they don't apply
(for very long, anyway).

--scott

-----
http://mindspring.com/~benbradley

If you want to listen to a telephone curly cord you can use
http://www.retellrecorders.co.uk/rec...achine/650.htm and plug an audio
headset into the stereo socket on the front.
Ruth

"Audiomix" wrote in message
om...
In telephone line there's a vcc of about 44.6 V.
Is it too dangerous according to you if I pick this vcc to power
supply a small headphone amplifier?
Could this create some problem to telephone line?????
audiomix