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Transistor mic preamp
Transistor mic preamp
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Old 31st August 2015, 06:44 PM   #1
pps2086 is offline pps2086  Singapore
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Default Transistor mic preamp

I built a mic preamp just for fun out of scrap electronics. I built it to be used with an electret mic capsule and my PC soundcard. This is my first electronics build and I am amazed that it even works. Here is the schematics of what I built
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The volume is quite low. I can only hear when I speak very close to the mic. I have set the line level in my soundcard to max already. Is the volume low because I used a BC549 transistor instead of the original ?
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Old 31st August 2015, 06:49 PM   #2
Mooly is offline Mooly  United Kingdom
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Transistor mic preamp
A BC549 should be ideal I would have thought. Why don't you check the voltages on the circuit and make sure they are reasonable (as a way of proving its basically OK)

You should ideally see around one half of the supply voltage on the collector.
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Old 31st August 2015, 07:02 PM   #3
Mooly is offline Mooly  United Kingdom
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Transistor mic preamp
Its a very basic circuit tbh. The gain should be sky high at around 200 and not that well defined and repeatable because it depends a lot on the exact transistor specification. If the collector volts is low (and your sure the transistor is fitted correctly) then try increasing the 100k resistor, perhaps to as high as 1 or 2meg ohm.
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Old 31st August 2015, 07:20 PM   #4
pps2086 is offline pps2086  Singapore
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Tested collector volts to be 2.4V. Battery is at 7.5V. I forgot to disconnect the 9V battery and now it has drained.

Last edited by pps2086; 31st August 2015 at 07:26 PM.
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Old 31st August 2015, 08:32 PM   #5
sreten is offline sreten  United Kingdom
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Hi,

A PC soundcard has a standard DC output on the Mic
input for driving a Fet buffered electret microphone.
Your reinventing the wheel.

rgds, sreten.

http://www.hobby-hour.com/electronic...microphone.php

Last edited by sreten; 31st August 2015 at 08:38 PM.
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Old 31st August 2015, 10:00 PM   #6
pps2086 is offline pps2086  Singapore
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Quote:
Originally Posted by sreten View Post
Hi,

A PC soundcard has a standard DC output on the Mic
input for driving a Fet buffered electret microphone.
Your reinventing the wheel.

rgds, sreten.

Sound card microphone
It is more noisy when I use it that way. Not sure why. The mic preamp I built does not have this noise but its just much lower in volume.
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Old 31st August 2015, 10:53 PM   #7
rayma is online now rayma  United States
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Quote:
Originally Posted by pps2086 View Post
The volume is quite low.
Which mic are you using? The noise difference may just be due to the gain difference.

Last edited by rayma; 31st August 2015 at 10:55 PM.
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Old 1st September 2015, 11:18 AM   #8
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by sreten View Post
Hi,

A PC soundcard has a standard DC output on the Mic
input for driving a Fet buffered electret microphone.
Your reinventing the wheel.

rgds, sreten.

Sound card microphone
Thanks for the link.

I come here to learn and info like this is just what I need.
__________________
regards Andrew T.
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Old 2nd September 2015, 07:33 PM   #9
pps2086 is offline pps2086  Singapore
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Quote:
Originally Posted by rayma View Post
Which mic are you using? The noise difference may just be due to the gain difference.

The mic I bought seems like a clone of panasonic wm61a. If I can get the mic preamp to have more gain I can try using it as a measurement mic ( just for relative measurements) by plugging it into the line in.

I found another 2 mic preamp circuits. Will these have higher gain ?

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Transistor mic preamp
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Old 3rd September 2015, 03:16 AM   #10
pps2086 is offline pps2086  Singapore
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This is the mic capsule I have AOM-4544L-R
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