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Need help with this certain circuit (RC phase shift system)

CalcoN

May 2, 2017
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Hello,

I need to solder this circuit, but I don't know what values should I use. Can any of you tell me approximate values or at least a way how to find them out myself?

Here is an original scheme (also without values):
osc20.gif


I edited this circuit into this

18254167_1268360953200491_766734342_n.png


So as a result I need values to solder this circuit. Can I get any help please? Thank you!
 

Audioguru

Sep 24, 2016
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The design of the 741 opamp is 49 years old and it will not do anything with a supply as low as 5V. Also its inputs are not biased correctly and it has no negative feedback. It cannot drive a speaker.
Use an LM386 audio power amplifier instead. It can be powered from only 5V but then its output power is only 0.14W into an 8 ohm speaker. It already has its inputs biased correctly and has built-in negative feedback.

Your potentiometer is shorted. If it is not shorted then it destroys the phase shifts.

Look at "transistor phase shift oscillator circuit" in Google to see parts values.
 

CalcoN

May 2, 2017
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Hey there, thank you for you reply.

I see, I will use LM386 amplifier then.

As my lecturer said, my final goal is to get alternating sound from the speaker by adjusting potentiometer (increasing or decreasing voltage). In this case, is it joined correctly into the circuit?
 

Audioguru

Sep 24, 2016
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Please describe "alternating sound".
The output of the oscillator and the amplifier is AC that is "Alternating Current".
If you want to increase and decrease the output level then use the potentiometer as a volume control between the output of the oscillator and the input of the amplifier.

Your potentiometer is shorted.
Your potentiometer has its slider disconnected from the circuit then adjusting it does nothing.
 

CalcoN

May 2, 2017
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By alternating sound I meant tone changer, would it be possible to control the tone level with potentiometer? (higher voltage - higher tone).

Well I modified the circuit, is it correct now? (on right there will be speaker, just didn't show it now)
0f9b4ddbde514d36a3b68e421f7b4119.png
 

AnalogKid

Jun 10, 2015
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The pot in post #1 does not do anything because it is shorted out.
The pot in post #5 will vary the volume or loudness, but will not change the frequency of the tone.
An LM386 will *barely* operate on a 5 V supply. Read the datasheet to see the normal operating voltage range.

To your original question, this circuit is a sine wave oscillator. The component values depend on the frequency you want, and you have not told us that. If the intent is to add a potentiometer so the oscillation frequency can be varied, that is possible - but the adjustment range will be small.

ak
 

Audioguru

Sep 24, 2016
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ALL electronic circuits need a supply bypass capacitor. Connect a 10uF to 100uF capacitor from +5V to ground.
Your volume control is backwards, it must be a voltage divider FROM the input TO the output.

The 3rd "R" has R1 and the input impedance of the transistor parallel to it which reduces its effective value. Therefore its value should be increased.

Your transistor oscillator has nothing to limit its output level so I think it will produce severe clipping distortion.
 

Attachments

  • clipping of sinewave.png
    clipping of sinewave.png
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  • volume control.png
    volume control.png
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CalcoN

May 2, 2017
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Thank you for your reply, AnalogKid. The frequency should be around 400 Hz.

Audioguru, thanks, I will use higher value of 3rd R than others.

How does my circuit look now?
47f8d1fa6d854202826005a9bb9ebb8c.png
 

Audioguru

Sep 24, 2016
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Why do you have a 10uF capacitor at the 0V circuit ground at the bottom of the circuit connected to another "ground"?
The output of the LM386 is missing the very important parts shown on the datasheet of the LM386 IC that prevent it from oscillating at a high frequency.
The capacitor in series with the speaker should be between the output of the LM386 and the speaker as shown on the datasheet of the LM386.
The +5V is missing a capacitor to ground.

Do you know how to properly bias the transistor?
 

CalcoN

May 2, 2017
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I tried my best to correct it as you said, how does it look now?

upload_2017-5-9_21-46-19.png

I'm not sure about biasing the transistor.
 

CalcoN

May 2, 2017
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I don't know why, he's talking about other things, but it's not the thing I wanted to know. So the question is, can you tell me anything should I know about this transistor while soldering this circuit?
 

Audioguru

Sep 24, 2016
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Every transistor has a part number. Yours does not have a part number.
The datasheet for the transistor lists its specifications so that you can bias it properly. You don't have the datasheet.

Maybe you are not learning about electronics. Instead maybe you are learning about how to solder wires together?
 

CalcoN

May 2, 2017
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I see, I'll try to ask my lecturer about that.

If you put it that way, I'm actually learning both, I'm avionics student and this is one of my subject work.
 
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