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Vintage threads from the first ten years

Variable Clipping Threshold

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11/22/1999 6:44 PM
Jack	Variable Clipping Threshold Check out the design idea that I have for a variable clipping control for distortion units. It allows you to set the voltage output level at which the diodes will clip to any value vetween the Vf of the diodes and infinity (no clipping). http://www.muzique.com/misc/variclip.gif best regards, Jack

11/22/1999 7:13 PM

Great idea, and as always, very nice layout. The idea of having germanium tone without the 250mv level clamp is very attractive.

The design, as shown, however is restricted to a few select designs, most notably things in the TS-808 genre.

Could one apply the principle to diode pairs going to ground (à la Distortion+ or Bosstone), or to diode pairs in non-op-amp-based units (à la BMP)? How would this be done?

11/22/1999 8:28 PM

Could one apply the principle to diode pairs going to ground (à la Distortion+ or Bosstone), or to diode pairs in non-op-amp-based units (à la BMP)?

It would certainly work for the BMP type of circuit, but not for the diode to ground versions. In the BMP you would just substitute it for the cap and diodes from collector to base of the transistor gain stage.

I'm kicking around some other ideas for alternate clipping networks.

regards, Jack

11/22/1999 10:02 PM

quote:
"It would certainly work for the BMP type of circuit, but not for the diode to ground versions. In the BMP you would just substitute it for the cap and diodes from collector to base of the transistor gain stage."

Actually, yes it would work for diodes to ground. The diodes and resistance don't care whether they have one end tied to ground or not. In fact, the connection to the opamp places the diodes at a virtual ground at the (-) input of the opamp.

This is exactly the same setup as the earlier version I suggested with a variable pot in series with diodes to ground at the output of a Distortion Plus.

11/22/1999 11:38 PM
nic	I thought about this once. I was gonna use two pots, one on each diode to emphasize odd or even harmonics. I never took it past the notepad sketch. How useful would this be? I think there would be too many knobs on an effect. Incidentally, I thought about using this type layout on a Distortion +, RAT type distortion box. nic

11/23/1999 12:40 AM

This is exactly the same setup as the earlier version I suggested with a variable pot in series with diodes to ground at the output of a Distortion Plus.

Nope. The effect produced is much different. This circuit actually allows different clipping levels and the waveform always looks similar to that produced by diodes at a lower level. The clipped output can be +/- 4v or more. Merely adding a resistor in series with the diodes produces a change in harmonics and a distorted wave that doesn't ever get much more than +/- 1.7v.

The look and sound produced by the 2 clipping circuit resistors are much different. Plug it into EWB and you'll immediately see the comparison and how great of a difference in waveforms produced.

I haven't investigated the diode-to-ground version but I still think it is unlikely to work the same, but it might produce an interesting effect nonetheless.

regards, Jack

11/23/1999 2:05 PM

>>Actually, yes it would work for diodes to ground. The diodes and resistance don't care whether they have one end tied to ground or not.

No, sorry, in this particular case it does matter whether the diodes are connected to ground are not. If you just move the diodes from the -input to ground, it does not work the same.

This circuit allows the threshold of clipping to be adjusted while the divider/diodes to ground or diodes with a resistor in series produce a much different waveform with reduced strength harmonics.

>>How useful would this be? I think there would be too many knobs on an effect.

Too many knobs? Can there be such a thing?

Besides, who says it has to be another control. It could be a trimpot - set and forget. Or it could replace the drive control. It's another tool in the FX builders box of tricks and the added versatilty is well worth exploring.

regards, Jack

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