Attenuating "line out" into a mic socket

I have a handheld recorder which does not have a "line in" socket. The
only input it has is a "mic" socket.

The manufacturers sell a lead which is used to attenuate the "line out"
from another device into my mic socket.

I would rather make my own lead. Obviously I don't want to alter the
frequency response.

What components would I need and in what configuration would they need
to be?

petrus bitbyter...

Specifications of mic inputs and line in- and outputs depends of the
mic input sensitivity 12uV max, input impedance 300-2k4
line input sensitivity 12uV min, input impedance 10k
but there are much more possibilities.
If you the specs of your recorder, you can calculate the resistor network
you need. If you can't, you can experiment with the network below.

+-----+-----+
| | |
| | R2 .-.
| |220k| |
| | | |
| | '-'
| | |
| | |
| | |
| R1 .-. .-.
-+ 12k| | | |<-----
| | | |
line out '-' '-'1k mic in
| |
-------+-----+-------

When the line out signal is too high, so when it is difficult to adjust the
pot in the lower part, you can rise R2 up to 1M (try some values) and lower
R1 to 10k. I don't expect the signal to be too week, but if it is you can
make both resistors 22k.

petrus bitbyter

Tomi Holger Engdahl...

You can find example circuits for this at

szekeres...

Put a 470 ohm resistor across the recorder input.
Put a 10K ohm in series feeding the hot side of the input
jack fed from the line out. Other side to common
side of input jack. If the levels need changed, the ratio needs to be adjusted
between the two resistors. 10k to 27K to reduce, 10K to 5K to increase.

David Nebenzahl...

I don't see why you can't just put a single resistor between the line
out and mike in. Since the mike input is lower impedance than the line

Mr.T...

Yes you could if you knew the input impedance of the mic input. Or simply
use trial and error.

output to start with, why would you need a load resistor; why not just

Mr.T...

How do you know that? In fact it is not usually the case. Line *outputs* are
often around 200 ohms or less, and mic inputs around 1k ohm or more.

something to reduce the voltage?

Mr.T...

That's just what a voltage divider does no matter how many resitors you use.

In any case the performance of the mic amp on these units is usually very
poor. Be prepared to be disapponted whatever lead you use.

Arny Krueger...

If you go the series resistor route, also you can easily end up with a
voltage divider with a high output impedance, which then exposes you to
losses at high frequencies. Not a problem when the input impedance of of the
equipment being driven is 5 K ohms, but a recipie for disaster when the
input impedance of of the equipment being driven is 500 K ohms.

David Nebenzahl...

Yes, but--2 things:

1. Isn't the input impedance of the little recorder likely to be

Arny Krueger...

Good design is about not taking unecessary risks.

significantly less than 500 KΩ?

2. In any case, how would a mismatched voltage divider cause high
frequency losses? (This is a request due to ignorance.) I don't see how
a resistive network, with no L or C components, could affect frequency

Arny Krueger...

The cable and gear downstream of the divider contributes the parallel C.

Mr.T...

As Arny said, there is already some shunt capacitance in the box which you
have no control over.

response at all.

szekeres...

It gets you off to an approximate attenuation level, not guessing.

invalid...

A simple resistive pad is all you need. Here is a site that descibes
several options in good detail.

Frequency response should not be a problem, but noise can be. The
idea for good audio is to have as few amplifiers in the line as
possible, and with the minimum amplification necessary.

When you bring down a line level source with a resistive pad, you are
essentially bringing the original signal closer to the noise level.
Then, because you have a mic level input, you amplify the signal again
(including the noise). It's not a problem for most applications, but
then again, for a critical studio signal, it could be.