[AMRadio] Re: Clipper circuits on the GB web site...

[Donald Chester]

>From: "Brian Carling" <bcarling at cfl.rr.com>

>Aren't these diode clippers inherent distortion makers?
>When you clip AF you make unwanted harmonics, which must then be filtered 
>out. The
>resulting audio does not sound exactly like the original.
>
>Some of us who have owend Johnson Valiants fixed the awful sounding audio 
>by BYPASSING a
>circuit almost exactly like this one!
>
>On the Valiant, even if you tuirned the clipping control down to ZERO, it 
>still
>introduced some raspiness. The change to hi-fi by removing the two tubes 
>and
>then running around the circuit with a 0.1 uF capacitor was such a dramatic 
>improvement
>that I was sold on removing all clippers!
>
>It seems to me like a quality compressor-limiter device such as is used in
>recording studios or for live sound wouldgive you a vastly superior result 
>than a diode
>clipper.
>
>Comments?

I agree 100%.  The only clipping circuit that I was ever able to get to work 
was at the high level stage, accomplished by deliberately overdriving the 
class-B modulater to saturation so that it flat-topped on modulation peaks.  
I installed the lowpass filter between the modulation transformer and the 
final.  It was effective,  but I burnt out half dozen kilowatt size 
modulation in the process.  Mod transformers don't like working into a 
reactive  load such as what is presented near the filter cutoff.  When I 
finally figured out what was going on, I discontinued using the clipper.

You need extremely good low frequency response following the clipper to 
avoid phase shift distortion and maintain the clipped waveform through the 
low pass filter.  It might be possible with direct coupling used with PDM or 
analog series modulation, in conjunction with a digital lowpass filter.  
Maybe that would be a subjuct for experimentation.

Don K4KYV



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