The diode clipper clips the signal the same as the same circuit in a guitar fuzz effects circuit. But if there is a resistor in series with the diodes then the clipping distortion is reduced.

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Uncle $crooge

 

thank you for your reply Jony130 as well as helping teach me simulate. if you are referring to the previous post where i had the gain set at 3 for the circuit without amp stab, i purposely set it to those parameters to have a closer view..under normal parameters, i get an overall flat line..which is correctly represented when the gain is exactly 3 returning no oscillations. am i having the correct concept? i stand corrected..other than that the parameters on my time transient analysis are identical to yours.=)

referring to your second circuit with the diode bridge. i would like to ask why resistances of R3,R4 and R6 are assigned those values of 10k, 4.7k and 2.35k (VR set to 0.5) respectively.From the gain formula 1+R2/R1..after the diodes get turned on and R5 is bypassed, wouldnt the gain drop to 2.41K? or is there some little resistance still available from the diode bridge resistor(R5)?

 

with those values of resistances, i just realized that the pk to pk voltage of that circuit is reduced to approx +- 3V although the power rail is +-15V..ive asked that question too earlier ...is the lowering of amplitude down to +-3V something intentional? ( i do get a really nice sine wave) or should the output sine wave oscillate from pk-pk according to the power rail values?

 

You don't want rail-to-rail oscillations. You're getting a good sine wave because you're intentionally not going to the rail.

__________________
You don't need a quadraphonic Blaupunkt -- you need a curve
ball.

 

ahh i see i see...thank you so much!!!

as for the clipping form 15V to appprox 3V .how does the diodes clip so much voltage when it only has 0.7V drop?
when the diodes start conducting, is the resistance parallel to it still "resisting" or is it totally bypassed?

 

I already posted on this. Look back over the thread.

__________________
You don't need a quadraphonic Blaupunkt -- you need a curve
ball.

 

sorry for the oversight.
when the gain becomes 2.5. the gain is no longer unity thus not providing oscillatory conditions..however, the loop gain becomes less than 1 (2.5*(1/3))
=0.83


so when the signal starts to get big and the diodes short out the resistor, it becomes a damped system making the amplitudes to be clipped down?

 

Yes!

I love when we reach that Ah-Ha! moment.

__________________
You don't need a quadraphonic Blaupunkt -- you need a curve
ball.

 

=D
i love those too! haha...once again im indebted to you.=)
cant believe that someone with your expertise got laid off...anyway its their loss..
thank you once again!!!=)

 

The simplified equation for Vo looks like this:
Vo = (3 * R1 * Vd) / (2 * R1 - R2)
Where:
Vd = diode forward voltage = 0.4V...0.55V

 

You need the gain-setting resistors to cause a gain of slightly less than 3 so the diodes can adjust the output level.
In your circuit with a minimum gain of 3 the opamp output will reach clipping and the diodes will not do anything.

__________________
Uncle $crooge

 

Message removed. Poster was confused.

EDIT: I think the equation should be: Vo = 3R1Vd/R3.

__________________
You don't need a quadraphonic Blaupunkt -- you need a curve
ball.

 

does that mean after diode adjustments, the gain will be set back to a maximum value of 3?

 

Yes.
You want the diodes to conduct only a little and only at the peaks of the sine-wave for the lowest amount of clipping distortion from the diodes.

Note that the voltage of the diodes is temperature sensitive so the output level will change a little when the temperature changes.
Note that diodes in a clear case are light sensitive and the output of the oscillator might become modulated by light.

__________________
Uncle $crooge

 

if the diodes conduct only a little, does that mean there is still some shunt resistance in between the diodes thus increasing the gain back to 3?
how does the resistors know how to auto adjust back to 3 or do i have to use a VR to tune it until the values adjust perfectly..