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Topic: Capsule for PC Mic input (Read 12355 times) previous topic - next topic
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Re: Capsule for PC Mic input

Reply #25 –
Quote from: pelmazo on
This one works. The circuit doesn't provide capsule bias, so I assume your divider was connected in front of C1. The combination of C1, C2 and R1 is weird. It almost seems as if C1 was meant to be the capsule itself.

Yeah, I put the voltage divider before C1. I can only guess that R1 and C2 are meant to provide some sort of HF filtering but I don't really know.

Quote
Both circuits are crude, to say the very least. They are likely to distort, even if you can make them work. An amplifier based on an OpAmp would be easier to get working properly.

I don't seem to have any distortion using the second circuit with 10k for R2. With higher resistance it was overloading the input but I can't say whether it would have sounded distorted going into a higher level input. As I get sufficient gain from a single transistor for the mic input, I can only guess that the dual-stage circuit is designed to produce line level output and that using a single transistor with a higher resistor for R2 does produce too much distortion. The only problem I have with the circuit now is what seems to be electrical hum, so if I could filter that out it would be fine. I don't think I had this hum with the first circuit but it might just have been hidden by the white noise.

I bought these ICs
http://www.ebay.co.uk/itm/272112949843
http://www.ebay.co.uk/itm/351591053501

but didn't realise how tiny they are, so I doubt I'll be able to do anything with them. I also ordered this
http://www.ebay.co.uk/itm/191890795602

and when it arrives I plan to try desoldering the capsule (which might not be great) and running some wires from the board to my capsule, so that it can sit on the end of my boom with the board attached to the base.

Quote
Your reasoning assumes an unloaded voltage divider. However, the capsule loads it, which makes your calculation wrong. You should be able to measure this easily with a multimeter when you compare the voltage of the divider without and with the capsule connected.

Ah OK, I'll have to check what it reads when loaded then.