Using old microphone on PC

Short answer is it can't be done.

Longer answer: Firstly, you'll need a several microfarad capacitor in series with the signal line to isolate it, otherwise the PC input circuitry will try to feed it power. You might be able to get away without it, but turns out that's the LEAST of your problems.

You'll serious amounts of gain. Your Dynamic mic outputs less signal than a typical electret mic that would otherwise be used with a PC, so even full blast, you'll *just* be able to hear it while yelling. Certainly not viable, anyway.

Short of a pre-amplifier that's not going to happen, and since a pre-amp isn't "Simplest" it can't be done to your requirements.

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It's not the principle of the thing, it's the money

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Microphone transformer:

http://www.google.com/products/catalog?q=microphone+transformer&hl=en&prmd=imvns&bav=on.2,or.r_gc.r_pw.&biw=1280&bih=814&wrapid=tlif131651472395510&um=1&ie=UTF-8&tbm=shop&cid=8705588807110651835&sa=X&ei=qmt4TvyJJ6itsAKz-_StDQ&ved=0CJYBEPMCMAA#

The low impedance microphone needs a transformer to make it have high impedance. Go to a guitar store and buy one for $20. It has 3 holes on one end for XLR low Z and one the other end it has a 1/4 inch phone jack like a guitar cord.

"Globemaker"

The low impedance microphone needs a transformer to make it have high impedance.

** Bad advice.

Mic inputs on PCs are not high impedance.

.... Phil

Thanks all. That inexpensive transformer looks ideal, but so far not found a UK source.

I do have a few miscellaneous audio transformers, so in parallel with more googling maybe I'll experiment. It'll get me away from the PC for a while anyway ;-)

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Terry, East Grinstead, UK

Simple circuits for the casual audio electronics people

Thanks, useful article. May well get me back into my shed!

But as for

at $100 (plus international delivery) I'll pass thanks ;-)

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Terry, East Grinstead, UK

What _are_ the specs for a typical PC microphone input port? And are there even specs, or does the circuit just happen to be what the manufacturer felt like using at the time?

I gather that it's designed for electret microphones, then -- that makes lots of sense. In theory that means that you could make a preamp that would be powered by the PC, but that's only "simplest" if you have a well- stocked junkbox, some knowledge, and some time.

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www.wescottdesign.com

Thanks Tim. I'm thinking about experimenting with that F-99B (seems a shame to waste a fairly expensive mic) but it means cleaning up my shed and workbench first - something I've been putting off for a couple of years!

I have the first two of those requirements, but time is in short supply.

The circuits in the article referenced by bw up-thread are one starting point, if I do make the initial effort.

I could even avoid the spring clean by doing some bread-boarding here at my PC. ;-)

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Terry, East Grinstead, UK

I once had a mic like that so I slapped together a bog-basic common emitter amplifier as a preamp.

(page 1 is all full of formulas and stuff - yech!)

Of course, for stereo you'd have to build two of them. ;-)

Have Fun! Rich

You have here a low impedance, dynamic mic, whose output is likely very low. The mic socket expects a lot higher voltage signal, from a cheap, high impedance microphone. The gain just isn't there.

Get a (or, seeing what newsgroup this is, build yourself a) microphone preamplifier. Because the impedance of the mic is low, you can get away with a low input impedance, like 1000 ohms.

You can also boost the level passively with a transformer. A transformer will also make the impedance of the mic input look lower to the mic. But that's okay because the mic has low impedance, and is designed for a low-ish impedance input.

This mic does not have balanced outputs. It is single-ended, and so it will pick up noise. This limits the cable length you can use, even though it is low impedance.

For this you can do common base, too!

Rich, Kaz: thanks both.

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Terry, East Grinstead, UK

If you are going to build a preamp anyway, you may want to connect it to Line In instead of Mic In. Although Mic In is about 10 times more sensitive (say, 100 mV vs 1V full-scale), it may be more than 10 times noisier. It also has (in the sound cards I've tested) a reduced frequency response of about 9 kHz or so, instead of the full 20 kHz. (That's not a problem for the originally-intended use with voice, probably even a good thing.)

I've also seen some sound chipsets that have strange behavior on Mic In, which might be related to the reduced frequency range. Looks like it is sampling at a reduced rate (maybe 18 kHz instead of 48 kHz) and then using sample rate conversion to get back to 48 kHz equivalent. But there seems to be minimal anti-aliasing on the original conversion, so high frequencies (above 9 kHz) wrap back down with hardly any attenuation. This would be a Very Bad Thing for music recording.

Mic In is always mono-only, with the Left (white) line carrying the signal. The Right (red) line is only used for phantom power for the electret's built-in FET preamp, which I seem to recall is typically 5V through a 4.7K resistor (or something like that). But I think some (most?) setups may apply that directly to the Left. That bias doesn't cause a problem since the sound card input is AC coupled.

Best regards,

Bob Masta DAQARTA v6.02 Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, Sound Level Meter Frequency Counter, FREE Signal Generator Pitch Track, Pitch-to-MIDI Science with your sound card!

Yes, this is also true - at the time, I was too lazy to figure out how to bias a common base circuit properly. :-)

Thanks! Rich

Thanks Bob. That seems to square with the circuits above, yes?

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Terry, East Grinstead, UK

Yes, the:

reference squares with my experience regarding connections.

Best regards,

Bob Masta DAQARTA v6.02 Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, Sound Level Meter Frequency Counter, FREE Signal Generator Pitch Track, Pitch-to-MIDI Science with your sound card!