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Old 7th Apr 2018, 6:42 pm   #1
stuart_morgan_64
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Default Electronic microphone circuit.

I have built a few of these and work very well. At the moment the gain is too high. Needs to be about half what it is now. What do I need to adjust, change to do this?

Thanks.
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Old 7th Apr 2018, 6:57 pm   #2
ThePillenwerfer
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Default Re: Electronic microphone circuit.

I had the self-same problem and nothing I tried made any difference for good or ill. I then came up with the attached. It's also much simpler in general.
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File Type: pdf Single Transistor Telephone Transmitter.pdf (100.7 KB, 214 views)
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Old 7th Apr 2018, 8:04 pm   #3
stuart_morgan_64
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Default Re: Electronic microphone circuit.

Thanks for that. PCB too and smaller. Had troubles fitting mine in some of the Belgian phones. Will give that a go tomorrow. Thank you.
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Old 7th Apr 2018, 8:06 pm   #4
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Default Re: Electronic microphone circuit.

I was thinking of making it surface mount.
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Old 8th Apr 2018, 9:51 am   #5
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Default Re: Electronic microphone circuit.

SMT is beyond my skills and eye-sight but I can certainly see the advantage. I've made them 'dead-bug' style and put them in old No 13 transmitters. The smaller round board fits inside a No 16.

I attach the PCB artwork in PNG format as that'll be easier to work with/amend as needed.
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Old 8th Apr 2018, 10:36 am   #6
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Default Re: Electronic microphone circuit.

Just in case anybody doesn't realise, you don't actually need to use a BC337 with that circuit if you don't have one handy. Any of the common general purpose types should be fine.
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Old 8th Apr 2018, 11:04 am   #7
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Default Re: Electronic microphone circuit.

Indeed, Paul. It was you who put me onto BC337s and BC327s instead on BC548s &c.
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Old 8th Apr 2018, 1:37 pm   #8
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Default Re: Electronic microphone circuit.

Thanks for all the comments. I understand the transistor isn't too critical. Square would be easier to cut. I use a electric tile cutter for PCB.To cut round I use fret saw, blades dont last too long though. Not very neat either.

I will try some of your design in the next few days.
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