[sdiy] Clipping Amplifier questions...

[Bret Truchan]

Thanks Harry,

I wired it up as you suggested, and of course it works great.  Phew.  I'm 
glad I didn't have to try and sleep with that technical issue dancing around 
in my head.  I understand what you mean about the amplifier having a gain of 
one when the zeners conduct.  It just hadn't dawned on me before.

Thanks again!!
- Bret

>Hi Bret (et al)
>
>The circuit as shown cannot work.  It will have inverting gain of whatever
>the resistor ratios are... but when the zeners conduct it will have a gain 
>of
>ONE.
>For a clipper, you want the output level to be limited so that it does not
>increase.
>
>Someone might have thought this worked... if they chose a really high gain 
>on
>a small signal (guitar fuzzbox?)... and they saw the sudden reduction in 
>gain as
>
>being a sign of  "clipping"  In other words if the normal gain is 100, and 
>the
>limiting
>gain is 1 ... it will act sort of like a clipper.  But if the normal gain 
>is 2
>its going to
>really suck !
>
>A better way would be to use the amplifier as an amplifer...and clip the 
>output
>with
>a series resistor and the zener diodes directly...  or use two inverting
>amplifiers and
>make one a clipping amp...
>
>H^) harry
>
>Bret Truchan wrote:
>
> > Hello!
> >
> > Does anyone happen to have the book "Practical Electronics for 
>Inventors"?
> > In it, there's a very nice looking circuit that they call the 
>"Noninverting
> > Clipper Amplifier" (page 245).  If you don't, I made a copy by hand
> > (http://www.voxglitch.com/images/clip_amp.jpg)
> >
> > I can't, for the life of me, get this wee-little circuit to work.  The
> > circuit is a normal op-amp based amplifier, but an addition of two zener
> > diodes accross the feedback loop was supposed to limit the voltage (both
> > positive and negative) to the cutoff voltages of the zener diodes.
> >
> > I intended to use this amplifier circuit for one of the inputs to a 
>module.
> > The module has an imbeded effects board, which has a 4V maximum rating 
>on
> > it's audio input.
> >
> > I had _thought_ that I had it working at one point and I created a PCB 
>with
> > the circuit on it.  However, it doesn't seem to be doing the job.  The 
>zener
> > diodes are 3.3V, but I can measure a full 12V on the output line of the
> > op-amp.  I wired up the op-amp circuit again on a breadboard and got the
> > same results.  Something is afoul.  I'm using TL082 op-amps.
> >
> > If anyone can take a moment to look at the circuit in question, I would 
>be
> > very happy.  Or, if I'm approaching this in the wrong way, let me know.  
>My
> > intention was to have an input that I could control the level on (via
> > potentiometer), but also have the input voltage clipped below 4 volts to
> > protect the imbedded effects unit.
> >
> > Thanks!
> > - Bret
> >
> > _________________________________________________________________
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