Hello,

I came across the following problem which I would like to solve with your
help. My brand new iRiver iFP899 provides a stereo line-in jack for
connection to any kind of source providing line-in level for direct
encoding. It can also be used as external mic input via settings in the menu
of the player.
I guess the jack input features so-called "plug-in power" which means that a
few volts of bias on the mic input is injected, which can power some small
consumer-type electret mics that don't have their own battery (although most
do have batteries anyway). I measured the input and it provides about 3.15V
(DC unloaded) for bias voltage. Funny enough, the bias voltage does not
dissappear when I switch to "line-in" mode from "external mic" mode.
Now I want to connect my hifi mixer to the device to record old vinyl
records, CDs, whole real-time mixes etc. As soon as I plug the device into
the mixer line-out output the VU meters overflow, i.e. they show full
amplitude. I guess that is due to the "wrong direction" current travelling
INTO but not OUT OF the mixer because of the bias voltage on the wire. What
tricks can I use to couple the device to my mixer so the iRiver line-input
DC bias does not reach the external source and does not affect it?

Many thanks in advance and best regards

Quinn

"Quinn Valente" wrote in message
...
Hello,

I came across the following problem which I would like to solve with your
help. My brand new iRiver iFP899 provides a stereo line-in jack for
connection to any kind of source providing line-in level for direct
encoding. It can also be used as external mic input via settings in the
menu
of the player.
I guess the jack input features so-called "plug-in power" which means that
a
few volts of bias on the mic input is injected, which can power some small
consumer-type electret mics that don't have their own battery (although
most
do have batteries anyway). I measured the input and it provides about
3.15V
(DC unloaded) for bias voltage. Funny enough, the bias voltage does not
dissappear when I switch to "line-in" mode from "external mic" mode.
Now I want to connect my hifi mixer to the device to record old vinyl
records, CDs, whole real-time mixes etc. As soon as I plug the device into
the mixer line-out output the VU meters overflow, i.e. they show full
amplitude. I guess that is due to the "wrong direction" current travelling
INTO but not OUT OF the mixer because of the bias voltage on the wire.
What
tricks can I use to couple the device to my mixer so the iRiver line-input
DC bias does not reach the external source and does not affect it?

Many thanks in advance and best regards

First make sure you are not plugging a T/S plug into a TRS socket. They
sometimes use the ring of a TRS socket for low voltage electrets (not
strictly "phantom" in that case), and using an adapter cable with the ring
unconnected will solve the problem.
Otherwise you could try a suitable non polarised capacitor in series with
the input.

MrT.

Thanks, Mr. T!

I'm sorry but I don't know what you mean by T/S plug and TRS socket. The
iRiver device has a miniature stereo jack which I connect via an adapter
cable stereo jack -- cinch. How can I implement non polarised capacitor in
series with the input? Which capacitor values are needed so that none of my
audiosignal frequencies get lost?

Regards, Quinn


"Mr.T" MrT@home schrieb im Newsbeitrag
u...

"Quinn Valente" wrote in message
...
Hello,

I came across the following problem which I would like to solve with your
help. My brand new iRiver iFP899 provides a stereo line-in jack for
connection to any kind of source providing line-in level for direct
encoding. It can also be used as external mic input via settings in the
menu
of the player.
I guess the jack input features so-called "plug-in power" which means
that
a
few volts of bias on the mic input is injected, which can power some
small
consumer-type electret mics that don't have their own battery (although
most
do have batteries anyway). I measured the input and it provides about
3.15V
(DC unloaded) for bias voltage. Funny enough, the bias voltage does not
dissappear when I switch to "line-in" mode from "external mic" mode.
Now I want to connect my hifi mixer to the device to record old vinyl
records, CDs, whole real-time mixes etc. As soon as I plug the device
into
the mixer line-out output the VU meters overflow, i.e. they show full
amplitude. I guess that is due to the "wrong direction" current
travelling
INTO but not OUT OF the mixer because of the bias voltage on the wire.
What
tricks can I use to couple the device to my mixer so the iRiver
line-input
DC bias does not reach the external source and does not affect it?

Many thanks in advance and best regards

First make sure you are not plugging a T/S plug into a TRS socket. They
sometimes use the ring of a TRS socket for low voltage electrets (not
strictly "phantom" in that case), and using an adapter cable with the ring
unconnected will solve the problem.
Otherwise you could try a suitable non polarised capacitor in series with
the input.

MrT.

"Quinn Valente" wrote in message
...
I'm sorry but I don't know what you mean by T/S plug and TRS socket.

T/S is tip-sleeve, TRS is tip-ring-sleeve.

The
iRiver device has a miniature stereo jack which I connect via an adapter
cable stereo jack -- cinch.

Assuming it is actually a stereo input, that's unusual to have voltage.
Microphone inputs are usually mono.
Have you checked to see what accessories iRiver sell for this device? I'm
betting you just need the correct lead.

How can I implement non polarised capacitor in
series with the input? Which capacitor values are needed so that none of
my
audiosignal frequencies get lost?

You would need one on each channel hot input. Size will depend on the
impedances, but at least 2 uF in most cases.

MrT.

"Mr.T" wrote ...
"Quinn Valente" wrote ...
The iRiver device has a miniature stereo jack which
I connect via an adapter cable stereo jack -- cinch.

Assuming it is actually a stereo input, that's unusual to
have voltage. Microphone inputs are usually mono.

Microphone inputs on small consumer devices like this
are typically T/R/S 3.5mm stereo mini-phone with
"plug-in power" (electret microphone bias voltage).

Have you checked to see what accessories iRiver sell
for this device? I'm betting you just need the correct lead.

How can I implement non polarised capacitor in series
with the input? Which capacitor values are needed so that
none of my audiosignal frequencies get lost?

You would need one on each channel hot input. Size will
depend on the impedances, but at least 2 uF in most cases.

I have a web page giving details of how to do this, including
selection of capacitor value. It was written for people who
want to connect professional microphones to consumer cam-
corders, but the principles and circuit are the same for your
application... http://www.rcrowley.com/CamAdapt.htm

In article , "Richard Crowley" wrote:
"Mr.T" wrote ...
"Quinn Valente" wrote ...
The iRiver device has a miniature stereo jack which
I connect via an adapter cable stereo jack -- cinch.

Assuming it is actually a stereo input, that's unusual to
have voltage. Microphone inputs are usually mono.

Microphone inputs on small consumer devices like this
are typically T/R/S 3.5mm stereo mini-phone with
"plug-in power" (electret microphone bias voltage).

Have you checked to see what accessories iRiver sell
for this device? I'm betting you just need the correct lead.

How can I implement non polarised capacitor in series
with the input? Which capacitor values are needed so that
none of my audiosignal frequencies get lost?

You would need one on each channel hot input. Size will
depend on the impedances, but at least 2 uF in most cases.

I have a web page giving details of how to do this, including
selection of capacitor value. It was written for people who
want to connect professional microphones to consumer cam-
corders, but the principles and circuit are the same for your
application... http://www.rcrowley.com/CamAdapt.htm

I noticed the Camcorder usage. On most camcorders I
have used, the input overloads on any loud sounds,
like a band playing inside. My better Sony camcorder
can handle large inputs without overloading, Well it
does overload a few feet away from a concert speaker
set. I also found a cassette unit I have overloaded. The gain
controls are often in back of the preamp stage.
So for anyone trying to mic something like this for
loud sounds, I would recommend adding attenuating resistors
before the input jack. For someone using a self powered electret
mic with biased input jack, I'm not sure of the best route for
that scenereo.

greg

"GregS" wrote in message
...
On most camcorders I
have used, the input overloads on any loud sounds,
like a band playing inside. My better Sony camcorder
can handle large inputs without overloading, Well it
does overload a few feet away from a concert speaker
set. I also found a cassette unit I have overloaded. The gain
controls are often in back of the preamp stage.
So for anyone trying to mic something like this for
loud sounds, I would recommend adding attenuating resistors
before the input jack.

Which doesn't always help since some camcorders have only automatic gain
control with an aggressive AGC action that compresses everything to
overload, even when the input signal voltage is reduced. My Canon does
unfortunately.

MrT.

"Quinn Valente" writes:

Hello,

I came across the following problem which I would like to solve with your
help. My brand new iRiver iFP899 provides a stereo line-in jack for
connection to any kind of source providing line-in level for direct
encoding. It can also be used as external mic input via settings in the menu
of the player.
I guess the jack input features so-called "plug-in power" which means that a
few volts of bias on the mic input is injected, which can power some small
consumer-type electret mics that don't have their own battery (although most
do have batteries anyway).

That's quite typical.

I measured the input and it provides about 3.15V
(DC unloaded) for bias voltage. Funny enough, the bias voltage does not
dissappear when I switch to "line-in" mode from "external mic" mode.

Funny thing. I think it hsould have dissapeared of that equipment
were well designed.

Now I want to connect my hifi mixer to the device to record old vinyl
records, CDs, whole real-time mixes etc. As soon as I plug the device into
the mixer line-out output the VU meters overflow, i.e. they show full
amplitude. I guess that is due to the "wrong direction" current travelling
INTO but not OUT OF the mixer because of the bias voltage on the wire.

Quite possible.

What
tricks can I use to couple the device to my mixer so the iRiver line-input
DC bias does not reach the external source and does not affect it?


Suitable cpaacitors on the line to block the DC and pass the AC.
Some capacitance calue that is 10 uF or higher (10 uF at 20 Hz is
around 800 ohms, not much attenuation if input impedance is
very many kilo-ohms). A plastic cpacitor would be best, but
an electrolytic paraleld with 100 nF plastic capacitor should also
work.

Other option is to use an audio signal isolation transformer
on the line connection. This transformer will not pass through
the DC, but will pass audio signals nicely. The plug-in power
is very limited in current, so I don't think that this DC
on the deivce side would not cause any serious problems to
transformer (expected 1-3 mA should nto saturate the core of most audio
transformers I think).

--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/

"Mr.T" MrT@home writes:

"Quinn Valente" wrote in message
...
I'm sorry but I don't know what you mean by T/S plug and TRS socket.

T/S is tip-sleeve, TRS is tip-ring-sleeve.

The
iRiver device has a miniature stereo jack which I connect via an adapter
cable stereo jack -- cinch.

Assuming it is actually a stereo input, that's unusual to have voltage.

There are many small portable recorders and video cameras with
stereo microphone inputs with 3.5 mm stereo jack connector.
The plug-in-power arrangement is quite commonly used in this field.

Microphone inputs are usually mono.

That's the case for the microphone inputs in PC sound cards.

Have you checked to see what accessories iRiver sell for this device? I'm
betting you just need the correct lead.

How can I implement non polarised capacitor in
series with the input? Which capacitor values are needed so that none of
my
audiosignal frequencies get lost?

You would need one on each channel hot input. Size will depend on the
impedances, but at least 2 uF in most cases.

MrT.




--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/