Converting line level to mic level

[Martin Underwood]

I have a laptop that just has mic in and line out sockets. If I want to
record from a line level source, what is needed to convert line level to mic
level so I can connect the line level source to the mic socket?

I presume each channel needs a potential divider:


-------------------- R1 -------------------------
|
line level R2 mic level
|
-------------------------------------------------


But what are the correct values of resistors to match the line level output
(eg from the tape recorder) and the mic level input to the laptop.

Alternatively, do suppliers such as Maplin (in the UK) sell converter cables
with those resistors built in?


I've tried simply turning the laptop's sound card level right down. While
this gives a signal that is not clipped, it's highly asymmetric: the peaks
extend much higher above the zero level than they do below it. Consequently
there is a lot of audible distortion.

 

[Charles Schuler]

I don't have the interest to research the levels, but will suggest that you
try a simple voltage divider with a 56,000 ohm resistor and a 1,000 ohm
resistor.

 

[Martin Underwood]

"Charles Schuler" <charleschuler@comcast.net> wrote in message
news:MLqdnYz94voSBMTfRVn-2g@comcast.com...

I don't have the interest to research the levels, but will suggest that you
try a simple voltage divider with a 56,000 ohm resistor and a 1,000 ohm
resistor.

Thank you. I'll try that. Now where did I put my resistors...?

 

[Jim Gregory]

You need end-product level to simulate a dynamic mic's impedance, typically
between 150 and 300 Ohms.
The "Mic" i/p load impedance at the laptop would be around 1k5r.
Assuming Source AF reference level of 200mV to 750mV rms

Suggestions:
if Source is balanced [floating]
42dB approx pad .... 50dB approx pad
R1 series [per leg] 10k ... 22k
R2 shunt 200r ----> to mic i/p

if Source is unbalanced
42dB approx pad .... 50dB approx pad
R1 series 20k .... 43k
R2 shunt 200r ----> to mic i/p

use 1/4W or 1/8W 2% metal oxide - not carbon

"Martin Underwood" <me@privacy.net> wrote in message
news:42590fa5$0$63427$ed2e19e4@ptn-nntp-reader04.plus.net...

I have a laptop that just has mic in and line out sockets. If I want to
record from a line level source, what is needed to convert line level to
mic level so I can connect the line level source to the mic socket?

I presume each channel needs a potential divider:


-------------------- R1 -------------------------
|
line level R2 mic level
|
-------------------------------------------------


But what are the correct values of resistors to match the line level
output (eg from the tape recorder) and the mic level input to the laptop.

Alternatively, do suppliers such as Maplin (in the UK) sell converter
cables with those resistors built in?


I've tried simply turning the laptop's sound card level right down. While
this gives a signal that is not clipped, it's highly asymmetric: the peaks
extend much higher above the zero level than they do below it.
Consequently there is a lot of audible distortion.

 

[Tomi Holger Engdahl]

"Martin Underwood" <me@privacy.net> writes:

I have a laptop that just has mic in and line out sockets. If I want to
record from a line level source, what is needed to convert line level to mic
level so I can connect the line level source to the mic socket?

I presume each channel needs a potential divider:


-------------------- R1 -------------------------
|
line level R2 mic level
|
-------------------------------------------------


But what are the correct values of resistors to match the line level output
(eg from the tape recorder) and the mic level input to the laptop.

Cherck the plans at
http://www.epanorama.net/circuits/line_to_mic.html

Especially this one:

20 dB PAD for line to electret microphone input
This circuit is designed to interface consumer (-10 dBu) signals to
microphone input that is designed for two-were electret microphone
capsules. This circuit provides around 20 dB of signal attenuation
(typically enough to make thigns work, if more attenuation is needed
use higher R1 value) and blocks the DC bias used in the electret
microphone input to get to the line signal side (C1 does this). This
circuit look like around 1 kohm signal source to at the mic side, whic
matches pretty well to electret capsule characteristics (similar
impedance and provides DC path for bias to go to ground).


C1
+Line level in --||----R1----+-- +Mic level output
+ |
|
+----R2----+
|
Ground (input)----+--------------- Ground (output)


R2 = 1 kohm
R1 = 10 kohm
C1 = 10 uF

NOTE: The polarity of C1 is marked to the circuit in case you use an
electrolytic capacitor. A "dry" plastic or ceramic capacitor is
preferred in this circuit.

Alternatively, do suppliers such as Maplin (in the UK) sell converter cables
with those resistors built in?

I don't know.

I've tried simply turning the laptop's sound card level right down. While
this gives a signal that is not clipped, it's highly asymmetric: the peaks
extend much higher above the zero level than they do below it. Consequently
there is a lot of audible distortion.

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

 

[Watson A.Name - \"Watt Su]

"Charles Schuler" <charleschuler@comcast.net> wrote in message
news:MLqdnYz94voSBMTfRVn-2g@comcast.com...

I don't have the interest to research the levels, but will suggest
that you
try a simple voltage divider with a 56,000 ohm resistor and a 1,000
ohm
resistor.

The usual is 100,000 and 1,000 ohms. Some stores (I think Radio Shack
in the U.S.) sell a cable with the resistors built-in.