Converting line level to mic level

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.

Reply to
Martin Underwood
Loading thread data ...

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.

Reply to
Charles Schuler

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

Reply to
Martin Underwood

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

Reply to
Jim Gregory

Cherck the plans at

formatting link

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.

I don't know.

--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
 Click to see the full signature
Reply to
Tomi Holger Engdahl

that you

ohm

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.

Reply to
Watson A.Name - "Watt Sun, th

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.