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previous: Mark Hammer I get your gist, but I was thinking... -- 9/28/1999 8:48 PM

Re: Question about selecting bandwidth in diode clipping circuits

9/29/1999 12:05 PM
GFR	Re: Question about selecting bandwidth in diode clipping circuits Mark If you put a cap in series with the clipping diodes: When the diodes are "off", no current is flowing through them. With no current to charge the cap, no voltage will develop across it. If there's no voltage across the cap then the voltage at the diodes will be the same as f the cap was not there. So they will start conducting at the same level, independently of frequency. When the diodes turn "on" you have a cap to ground, just like a guitar tone control. You will get a treble cut that depends on the input signal. That's what Petri heard as "bassier" - just less treble. LXH2's Marshall simulator used this to mimic the fx that the frequency response of a power amp changes when overdriven (because feedback can't compensate the response anymore). If you want a frequency content dependant clipper I think you could do something like this: 1) Split the signal in two paths, one will have flat response and the other will have bass cut like in a TS. 2) Use the bass-cut signal to turn on/off a pair of transistor B-E junctions. 3) Tie the collector of these transistors to the output of the flat response path. This way you are clipping the full spectrum signal based on the level of the filtered signal. Not so complicated, with not so many parts and you just need a single pot for "more" - you only need to ajust the gain of the filtered path to have different clipping thresholds. AND... you could use the output of the filtered path too if you want, or simply clip the output of flat signal. This would give you three fx in one box: full range distortion, full range freq dependant distortion and midrange hump distortion.

9/29/1999 12:05 PM

GFR

Re: Question about selecting bandwidth in diode clipping circuits

Mark

If you put a cap in series with the clipping diodes:

When the diodes are "off", no current is flowing through them. With no current to charge the cap, no voltage will develop across it. If there's no voltage across the cap then the voltage at the diodes will be the same as f the cap was not there. So they will start conducting at the same level, independently of frequency.

When the diodes turn "on" you have a cap to ground, just like a guitar tone control. You will get a treble cut that depends on the input signal. That's what Petri heard as "bassier" - just less treble.

LXH2's Marshall simulator used this to mimic the fx that the frequency response of a power amp changes when overdriven (because feedback can't compensate the response anymore).

If you want a frequency content dependant clipper I think you could do something like this:

1) Split the signal in two paths, one will have flat response and the other will have bass cut like in a TS.

2) Use the bass-cut signal to turn on/off a pair of transistor B-E junctions.

3) Tie the collector of these transistors to the output of the flat response path.

This way you are clipping the full spectrum signal based on the level of the filtered signal.

Not so complicated, with not so many parts and you just need a single pot for "more" - you only need to ajust the gain of the filtered path to have different clipping thresholds.

AND... you could use the output of the filtered path too if you want, or simply clip the output of flat signal. This would give you three fx in one box: full range distortion, full range freq dependant distortion and midrange hump distortion.