# VCO with LM1458 op amp

Discussion in 'General Electronics Chat' started by Jonathan Shirley, Apr 22, 2015.

1. ### Jonathan Shirley Thread Starter New Member

Apr 9, 2015
15
0
Hello,

So i have been struggling with this circuit for a wee while. In the circuit simulator, the wave signal does change with the amount of C.V in (up to around 9v) but the circuit i have built myself (which is identical to schematic) my signal does change but stops raising in audio pitch at around 4.5v and is producing quite a low freq/sound. Is this the transistor size? i am unsure... anyway any help would be fantastic!

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2. ### MikeML AAC Fanatic!

Oct 2, 2009
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You want the range of input voltage to be 0V to 9V?
As the input voltage changes, what range of frequencies would you like the circuit to produce?
What do you expect the frequency out vs input voltage to linear?

Here is what I did with your circuit without knowing the answers to the above:

Colors match. Works for V(co) from 0V to 9V. It is oscillating at V(co)=0V, but too slow to show the whole period.

Last edited: Apr 23, 2015
3. ### Jonathan Shirley Thread Starter New Member

Apr 9, 2015
15
0
Wow! thanks for taking the time to do the schematic. Ideally i want the range of input voltage to be 0V to 5V. i would like to have a decent frequency range of around 0Hz to anything above 22kHz. I am unsure of you last question sorry (but whatever you would recommend). Thank you

4. ### MikeML AAC Fanatic!

Oct 2, 2009
5,450
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Wow, DC to 22kHz is tough...

5. ### Jonathan Shirley Thread Starter New Member

Apr 9, 2015
15
0
What is the max. freq in the schematic that you sent me? cheers

6. ### MikeML AAC Fanatic!

Oct 2, 2009
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You can read the range of periods right off the plot... Color of the input voltage trace matches the cooresponding color in the sawtooth.

7. ### Jonathan Shirley Thread Starter New Member

Apr 9, 2015
15
0
OK. One more question, in your schematic, is the output of the opamp your signal output? or would you use the other opamp similar to what i did in my schematic?

8. ### MikeML AAC Fanatic!

Oct 2, 2009
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I would use the buffer. Your problem was that the voltage-to-current part of the circuit wasn't working, so I focused only on getting that going...