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?
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.
greg
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Specifications of mic inputs and line in- and outputs depends of the manufacturer. One I ever found says: 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| | | |
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.
Beachcomber
GregS spake thus:
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 output to start with, why would you need a load resistor; why not just something to reduce the voltage?
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Yes you could if you knew the input impedance of the mic input. Or simply use trial and error.
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.
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.
MrT.
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.
It gets you off to an approximate attenuation level, not guessing.
greg
Arny Krueger spake thus:
Yes, but--2 things:
-- Pierre, mon ami. Jetez encore un Scientologiste dans le baquet d'acide. - from a posting in alt.religion.scientology titled "France recommends dissolving Scientologists"
Good design is about not taking unecessary risks.
The cable and gear downstream of the divider contributes the parallel C.
Arny Krueger spake thus:
For a company designing a product for sale, that would be a consideration. For a guy trying to get a signal into an el cheapo handheld recorder, I don't think it makes any difference.
What if the single resistor was right at the microphone plug? No significant C then, right?
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As Arny said, there is already some shunt capacitance in the box which you have no control over.
MrT.
I can't believe that so much air has been warmed (figuratively speaking) over a ten cent resistor.
Not so, even equipment that is specifically designed to have low input capacitance like oscilliscopes and other test equipment, has input capacitances in the range of 15-35 pF.
Equipment with high input impedance did not die with the days of the tube. Direct boxes are very common and by definition have very high input impedances.
You can find example circuits for this at
-- Tomi Engdahl (http://www.iki.fi/then/) Take a look at my electronics web links and documents at http://www.epanorama.net/
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