Author Topic: Test and adjustment signal for BOSS-NF1(Wien bridge oscillator).Opinions, please  (Read 1876 times)

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onelife

I decided to make BOSS-NF1. Bellow the schematics there was instruction for adjustment of the effect. Since I don't have such a device as sinewave generator with frequency of 1kHz and -45dbm I decided that this should be the first thing I should do(after some research I understood that this oscillator could be used also in other effects adjustment processes). I found that the best solution(according to me) is the Wien-Bridge Oscillator due to the fact that is simple, provides steady sine at frequency of 1kHz and it is really cheap. It was hard to find the best schematic but I think did it (you would be the second to tell me what do you think of the schematic) :). So I made a simple simulation with Proteus 7 and I am really satisfied with the results.
Now I am going to explain what did I do, and I hope more people would tell their opinions.
Ok, first of all this is the schematic that I have used:

It is made with op-amp 741 and two diodes, and of course the wien-bridge which consists of Resisors-R3,R4 and capacitors-C1,C3. The om-amp starts when its gain is greater than 3. And this is achieved by the variable resistor-VR1. When it is moved to the left, at some value the gain becomes greater than 3 and the op-amp starts to provide signal with a rectangular-shaped form. After that I should reduce the value of RV1 - to the maximum right, so the signal could turn into a sine.
The two diodes provide stable value for the gain (It should be G=3 all the time for a steady sine signal), and if the G=3 diodes are off. When the voltage is positive D1 turns on and R5 is connected in parallel causing G to drop to 3.Conversely, when voltage is negative D2 turns on and R6 is connected in parallel , so the gain drops to 3 again. This ensures stable sine signal.
Frequency is measure with the following equation f=1/2*pi*R*C, R=R3=R4=15k, C=C1=C3=10nF, and at these values the frequency is 1061Hz ~ 1kHz. So if you like you can change that values according to your needs. It is important to note that this op-amp provides steady signal until frequency reaches 1Mhz. At the output I have put a voltage divider realized with the resistors R7 and R8 due to the fact that -45dBm = 0.0044V at resistor of 600 Ohms (that I was told by someone from this forum - thanks for that :) it really helped me).
So the final result can be seen at the oscilloscope. The yellow sine is the sine provided from the Wien-bridge, and the blue sine is a result from a sine generator with the same characteristics,  integrated in the software(i think it is ideal without any noises and distortions). There is an offset at the voltage of only 2mV , so I thinks this is really satisfying.  

And, that's all. I have sine signal at 1kHz, and -45dBm need for the test. Now I am going to make the BOSS-NF1 circuit in the Proteus program so I could simulate it and take some results. I hope this will happen soon.
Please tell me your opinions, I know it would be useful for me.
« Last Edit: March 04, 2012, 02:33:01 PM by onelife »