[sdiy] Clipping Amplifier questions...

[Czech Martin]

Note that real zener (avalance) action will typically
set in about 6-8 V, depending on doping profiles.
There is a limit on how much doping can be made, so
the avalanche can not be made to start much lower.

"Zener" diodes with less voltage are often normal diode strings
in forward conduction. They show no sharp zener clamping
slope, but a soft characteristic which will sometimes
make correct circuit function impossible.

m.c.

> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Bret Truchan
> Sent: Samstag, 27. März 2004 03:12
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] Clipping Amplifier questions...
> 
> 
> 
> 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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