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Vintage Telephony and Telecomms Vintage Telephones, Telephony and Telecomms Equipment |
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7th Apr 2018, 6:42 pm | #1 |
Heptode
Join Date: Aug 2004
Location: Woodbridge, Suffolk, UK.
Posts: 501
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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. |
7th Apr 2018, 6:57 pm | #2 |
Octode
Join Date: Mar 2011
Location: Sheffield, South Yorkshire, UK.
Posts: 1,453
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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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7th Apr 2018, 8:04 pm | #3 |
Heptode
Join Date: Aug 2004
Location: Woodbridge, Suffolk, UK.
Posts: 501
|
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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7th Apr 2018, 8:06 pm | #4 |
Heptode
Join Date: Aug 2004
Location: Woodbridge, Suffolk, UK.
Posts: 501
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Re: Electronic microphone circuit.
I was thinking of making it surface mount.
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8th Apr 2018, 9:51 am | #5 |
Octode
Join Date: Mar 2011
Location: Sheffield, South Yorkshire, UK.
Posts: 1,453
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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. |
8th Apr 2018, 10:36 am | #6 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,970
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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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8th Apr 2018, 11:04 am | #7 |
Octode
Join Date: Mar 2011
Location: Sheffield, South Yorkshire, UK.
Posts: 1,453
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Re: Electronic microphone circuit.
Indeed, Paul. It was you who put me onto BC337s and BC327s instead on BC548s &c.
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8th Apr 2018, 1:37 pm | #8 |
Heptode
Join Date: Aug 2004
Location: Woodbridge, Suffolk, UK.
Posts: 501
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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. |