variable clipping based on old elektor circuit

[Steben]

Ok, bear with me... here we go.

This base circuit is from Elektor. It is used in a guitar amp design in 1986. Designed as a "tube" like soft clipping. Very promising
Main problem is I never heard of someone who actually built it.

Here comes the thing. If one can alter the voltage supplying the lot, one can have a different transient curve. Supply sag can easily be emulated, since the clipping tresholds are changed by the supply voltage. "Sag" is a small change in voltage. Yet if we make the bias resistors around the base of transistors pots we have a control over the working point. The higher the working point, the less the combination of diodes has a large portion in the curve definition, giving a harder clipping result. At around 3.5V we have the probable clipping of the opamp driving the circuit in front. Setting the working point to this 3.5V will give hard opamp clipping only. The lower the working point, the more "round" the curve, making the total more softer. The only drawback is the difference in output levels with different settings and the larger signal we need at hard clipping settings (higher treshold). This means we cannot change the character in a single control. The working point will act as a "headroom" control (sort swapping between neg feedback amp and low wattage non feedback)

[Fancy Lime]

Hi Steven,

I did some fairly extensive experimenting with diode ladders in the feedback path of an opamp. Slightly different but same basic concept. It did clip very gradually and softly. It also sounded quite dull and boring when set to very soft clipping. I have since come to the conclusion that what I perceive as the typical "tube like clipping" sound is not soft clipping as such. Rather, it seems to me, hard clipping with a soft knee sounds tube-like. So, yes, I think you might want 2 controls: one for the "maximum hardness" of the clipping and one for the "knee roundness". Definitely an interesting circuit to play with.

Andy

[Steben]

Hi Steven,

I did some fairly extensive experimenting with diode ladders in the feedback path of an opamp. Slightly different but same basic concept. It did clip very gradually and softly. It also sounded quite dull and boring when set to very soft clipping. I have since come to the conclusion that what I perceive as the typical "tube like clipping" sound is not soft clipping as such. Rather, it seems to me, hard clipping with a soft knee sounds tube-like. So, yes, I think you might want 2 controls: one for the "maximum hardness" of the clipping and one for the "knee roundness". Definitely an interesting circuit to play with.

Andy

True, plexis for example are quite hard clipping.  Thats why high gain sounds are easily emulated by clippers or 386 chips. Ac30 on the other hand much rounder.

[pinkjimiphoton]

i DID build that, and posted it years ago.
forget what the hell i called it, but it was based on i think arsenio nova's tube sound overdrive.
very kind, for lack of a better term, clipping. def worth a breadboard bro

[Steben]

i DID build that, and posted it years ago.
forget what the hell i called it, but it was based on i think arsenio nova's tube sound overdrive.
very kind, for lack of a better term, clipping. def worth a breadboard bro

Omg, now i am hung on finding that thread. didnt have sound samples i guess.

[pinkjimiphoton]

sorry i can't be more help. i lost some stuff in a hard drive near disaster a year or so ago, but thie info should be on here or FSB somewhere. it was probably close to 10 years ago. my memory kinda sux!

[Steben]

sorry i can't be more help. i lost some stuff in a hard drive near disaster a year or so ago, but thie info should be on here or FSB somewhere. it was probably close to 10 years ago. my memory kinda sux!

So off I went to FSB.
This is what I found