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Old 12th November 2008, 03:16 PM   #1
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Default Driving 8 Ohm Speaker

Hello,

I think I am in the right section to post this question. Well here goes. I am trying to build a dynamic Mic amplifier to drive a 8 ohm speaker but the speaker doesn't give any output. I am using a single transistor as a pre-amp.

circuit 1 see attachment


Then I feed the output of the above circuit into a push-pull configuration with more or less unity voltage gain but Supposedly gives current gain.

circuit 2 see attachment

looking with oscilloscope on circuit above (Push_pull) I get about 4vP-P(c2). When I then plug in 8 Ohm speaker at( C2 to GND) the output signal vanishes!!


Anybody know why??
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File Type: jpg 4 test.jpg (31.7 KB, 172 views)
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Old 12th November 2008, 04:26 PM   #2
Ted205 is offline Ted205  United Kingdom
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solid state section
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Old 12th November 2008, 06:09 PM   #3
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Default Driving 8 Ohm speaker help required

Hello,

I think I am in the right section to post this question. Well here goes. I am trying to build a dynamic Mic amplifier to drive a 8 ohm speaker but the speaker doesn't give any output. I am using a single transistor as a pre-amp.

circuit 1 see attachment


Then I feed the output of the above circuit into a push-pull configuration with more or less unity voltage gain but Supposedly gives current gain.

circuit 2 see attachment

looking with oscilloscope on circuit above (Push_pull) I get about 4vP-P(c2). When I then plug in 8 Ohm speaker at( C2 to GND) the output signal vanishes!!


Anybody know why??
Attached Images
File Type: jpg 4_test.jpg (31.7 KB, 121 views)
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Old 12th November 2008, 06:09 PM   #4
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Right you are will copy over to solid state.

Cheers
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Old 12th November 2008, 07:04 PM   #5
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It appears that your attachments are playing hide and seek, and currently it is hiding. Some may be seeking, but have not found.


Peace,

Dave
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Old 12th November 2008, 07:24 PM   #6
lineup is offline lineup  Sweden
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Default Re: Driving 8 Ohm speaker help required

When input feed from one (dynamic) microphone for 8 Ohm speaker out ...
1. we need a lot of voltage gain
even for a low level out, we may need amplify x100
2. we need a power supply giving at least at least like 25 mA
3. we need the output stage having high enough input impedance
not to reduce the voltage amplifier gain too much
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Old 12th November 2008, 07:29 PM   #7
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If you wanted chipamp, howabout nte1516 (NEC UPC1212C) Op Amp? That's a "soft clip" chip, and if you get the mic too hott or too close, the output is rounded a bit. That's pretty sweet for stopping some customary problems with microphones. The device will drive an 8 ohm speaker. Options are driving the speaker with BTL config or using the device to drive line level.
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Old 12th November 2008, 08:41 PM   #8
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Two threads have been merged.
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Old 12th November 2008, 09:08 PM   #9
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Thanks guys
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