# Audio 100V signal to line level

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Guest

Thu Mar 24, 2016 6:56 pm

All,

I am doing some testing with an audio PA system that has the output of 100V (rms). What I am trying to do is take this 100V(rms) and bring it down to an audio line level of about 280 mV (rms). I am doing this with a resistor divider.

1.) An image of 100V (rms) input signal measured on oscilloscope is below:

http://s1070.photobucket.com/user/Mrblueblue1234/media/input_100V_zpsze4bcqkm.jpg.html

2.) I am then dividing this down to ~280mV with a resistor divider,
375k and 1k. Here is the image of the signal from the resistor divider:

As you can see the signal here looks extremely distorted on the oscilloscope! I am not sure if this is what really is happening or if it is an artifact of the oscilloscope.

3.) We have some audio equipment from the company Audio Precision here and with their equipment the signal looks much cleaner. See image below:

http://s1070.photobucket.com/user/Mrblueblue1234/media/AP_zpsaxn9km9s.jpg.html

4.) There are some transformer options out there to take a 100V signal and bring it to a line level but I wanted to see if we could do this with a less expensive resistor divider solution.

Thank you from any thoughts you have on this.

-Robert

M Philbrook
Guest

Sat Mar 26, 2016 11:14 pm

robertxmillerusa_at_gmail.com says...
Quote:

All,

I am doing some testing with an audio PA system that has the output of 100V (rms). What I am trying to do is take this 100V(rms) and bring it down to an audio line level of about 280 mV (rms). I am doing this with a resistor divider.

1.) An image of 100V (rms) input signal measured on oscilloscope is below:

http://s1070.photobucket.com/user/Mrblueblue1234/media/input_100V_zpsze4bcqkm.jpg.html

2.) I am then dividing this down to ~280mV with a resistor divider,
375k and 1k. Here is the image of the signal from the resistor divider:

As you can see the signal here looks extremely distorted on the oscilloscope! I am not sure if this is what really is happening or if it is an artifact of the oscilloscope.

3.) We have some audio equipment from the company Audio Precision here and with their equipment the signal looks much cleaner. See image below:

http://s1070.photobucket.com/user/Mrblueblue1234/media/AP_zpsaxn9km9s.jpg.html

4.) There are some transformer options out there to take a 100V signal and bring it to a line level but I wanted to see if we could do this with a less expensive resistor divider solution.

Thank you from any thoughts you have on this.

-Robert

you have what looks to me like parasitic RF being introduced in your
network.

Not knowing how your termination are being made is a big issue, too.

in the old days, and still today that is, we use parasitic chokes.
Those are carbon composite low value R's wrapped with a few turns of
magnetic wire and each end attached to the leg of the R. This inturn
captures RF on the surface and shorts it via the R, while passing
through the orginal signal.

Another note. don't use inductive type Rs

You could put a small cap across the network.

Jamie

petrus bitbyter
Guest

Mon Mar 28, 2016 7:58 pm

schreef in bericht

All,

I am doing some testing with an audio PA system that has the output of 100V
(rms). What I am trying to do is take this 100V(rms) and bring it down to
an audio line level of about 280 mV (rms). I am doing this with a resistor
divider.

1.) An image of 100V (rms) input signal measured on oscilloscope is below:

http://s1070.photobucket.com/user/Mrblueblue1234/media/input_100V_zpsze4bcqkm.jpg.html

2.) I am then dividing this down to ~280mV with a resistor divider,
375k and 1k. Here is the image of the signal from the resistor divider:

As you can see the signal here looks extremely distorted on the
oscilloscope! I am not sure if this is what really is happening or if it
is an artifact of the oscilloscope.

3.) We have some audio equipment from the company Audio Precision here and
with their equipment the signal looks much cleaner. See image below:

http://s1070.photobucket.com/user/Mrblueblue1234/media/AP_zpsaxn9km9s.jpg.html

4.) There are some transformer options out there to take a 100V signal and
bring it to a line level but I wanted to see if we could do this with a less
expensive resistor divider solution.

Thank you from any thoughts you have on this.

-Robert

Something seems to oscillate...

As mentioned already, speakers (with or without transformers) are partly
inductive loads. As the amplifier will be designed to anticipate for it, a
pure resistive load may cause the problem. So adding inductors may help.

Connecting a line to ground may cause a ground loop which in turn may cause
the oscillation. Replacing the low-value resistor by a small 1:1 transformer
may work.

petrus bitbyter

Ian Field
Guest

Sat Apr 09, 2016 2:09 am

"M Philbrook" <jamie_ka1lpa_at_charter.net> wrote in message
news:MPG.31608d6a26f08303989ec8_at_news.eternal-september.org...
Quote:
robertxmillerusa_at_gmail.com says...

All,

I am doing some testing with an audio PA system that has the output of
100V (rms). What I am trying to do is take this 100V(rms) and bring it
down to an audio line level of about 280 mV (rms). I am doing this with
a resistor divider.

1.) An image of 100V (rms) input signal measured on oscilloscope is
below:

http://s1070.photobucket.com/user/Mrblueblue1234/media/input_100V_zpsze4bcqkm.jpg.html

2.) I am then dividing this down to ~280mV with a resistor divider,
375k and 1k. Here is the image of the signal from the resistor divider:

As you can see the signal here looks extremely distorted on the
oscilloscope! I am not sure if this is what really is happening or if
it is an artifact of the oscilloscope.

3.) We have some audio equipment from the company Audio Precision here
and with their equipment the signal looks much cleaner. See image below:

http://s1070.photobucket.com/user/Mrblueblue1234/media/AP_zpsaxn9km9s.jpg.html

4.) There are some transformer options out there to take a 100V signal
and bring it to a line level but I wanted to see if we could do this with
a less expensive resistor divider solution.

Thank you from any thoughts you have on this.

-Robert

you have what looks to me like parasitic RF being introduced in your
network.

Not knowing how your termination are being made is a big issue, too.

in the old days, and still today that is, we use parasitic chokes.
Those are carbon composite low value R's wrapped with a few turns of
magnetic wire and each end attached to the leg of the R. This inturn
captures RF on the surface and shorts it via the R, while passing
through the orginal signal.

Another note. don't use inductive type Rs

You could put a small cap across the network.

That's mainly about next stage input capacitance shunting the treble.

Doesn't take a lot of input capacitance for Xc to be low relative to the
dropper end of the network.

With 100V coming in, I'd put some resistance in series with that small
capacitor so the treble notes don't overload the input.

If there's any suspicion of the next stage being a bit fragile - clamp
diodes aren't too much of an extragance.

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