Limit Amplifier output voltage

[ehsantech]

Hello
here is my op-amp amplifier

I want to limit output voltage.for example if output voltage wants to be more than 8 volt it decrease amplifier's gain and limit output voltage on 8volt(input frequency is 100khz)

Thank you

 

[Audioguru]

Few opamps amplify a signal as high as 100kHz. Many audio oscillators use a Jfet to limit the output amplitude with low distortion. Two back-to-back diodes parallel with R2 will clip the waveform producing distortion but the output will be limited.

 

[ehsantech]

Hello Dear Audioguru
Thanks for your explanation
Could you give me some sites that use the jfet as output limiter?and what should I search on the internet?

- - - Updated - - -

It can be more comfortable if we can use Bjt transistor instead of Jfet

 

[D.A.(Tony)Stewart]

Simple clipper uses no pot. Adjustable level with any matched zeners

.e.g. You can even use back//back diodes for zeners and choose ratio R instead of Pot with fixed level to convert 8V to 0.7 V to turn on clipper diodes.

R5 <<R2. for single sply. R4, R5 go to V+/2
**broken link removed**

For audio soft limiters , add diode series R to soften the knee to produce less distortion, based on R ratios as AGC . This is an active clamp but passive unity gain.. Others use gain with series Zener feedback with opt. R in series.

 

[Audioguru]

I do not like the sound produced by limiters. Some are slow to react so a loud overload blast is produced then the limiter reduces the volume.
They usually slowly increase the gain up to normal when there is no sound. On FM radio stations pop music with a strong bass beat has all the background music volume pumping up and down by the beat.

Limiters with diodes cause audio distortion.

Here is a low distortion audio limiter using a Jfet: **broken link removed**

 

[D.A.(Tony)Stewart]

I agree AGC is softer and some have pump effects on drum smash.

With a series R on diodes, the gain reduces but not clips so softer , ie compression. with no gain pumping.

With more diodes a smooth dynamic compressor can be made, without pumping gain.

High end studio compressors have fast response perhaps like AG's example.