amplify an oscillator sinve wave, without an op amp

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HighFrequency
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amplify an oscillator sinve wave, without an op amp

Post by HighFrequency »

Hi there! I have a wien-bridge oscillator that has an output voltage of 2.5V(pk). I need to amplify this to 10V(pk), without using an op amp. Anyone have any suggestions?
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Re: amplify an oscillator sinve wave, without an op amp

Post by Enzo »

Sure, run it through a transistor gain stage.
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Re: amplify an oscillator sinve wave, without an op amp

Post by HighFrequency »

But how do I control the gain? transistor gains are not reliable...?
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Re: amplify an oscillator sinve wave, without an op amp

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Re: amplify an oscillator sinve wave, without an op amp

Post by dyarker »

As long as hfe is significantly greater than the gain you need, a transistor circuit's gain is exactly the ratio of the collector and emitter resistors.

You want 2.5Vp amplified to 10Vp; that is a gain of 4. Assuming an NPN with hfe of at least 40 at the operating frequency, a 1K emitter resistor and 4K collector resistor, with output from the collector, will give a gain of 4 as long as the load on the output is like 80K or more. (Or calculate what collector resistance in parallel with load impedance will equal 4K.

The 1K emitter resistor also makes biasing the transistor easier because from the base side it appears to be 1K times actual hfe.

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Externet
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Re: amplify an oscillator sinve wave, without an op amp

Post by Externet »

Use a 1:4 transformer.
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Re: amplify an oscillator sinve wave, without an op amp

Post by HighFrequency »

OH SHIT!! Thanks Dale. I totally forgot about that aspect of transistors. I'm so inlove with op amps, I forgot most of my transistor theory. That should work great.
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Re: amplify an oscillator sinve wave, without an op amp

Post by philba »

out of curiosity, why no op-amp? sounds like a school assignment...
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Re: amplify an oscillator sinve wave, without an op amp

Post by HighFrequency »

You are correct sir. However, turns out when I built the circuit, the peak-peak output was 26V, not 5V. So all is corrected. Thanks for the help folks.
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