'Softness'/Clipping Threshold mod

[letsgocoyote]

As described in the Simple Mods in the wiki, this 'softness' mod


what exactly does it do?  i assume the pot limits the amount of signal that hits the diodes so it doesnt get clipped as much.  with pot turned all the way down/off i presume that it essentially cuts the diodes out of the circuit and would turn the circuit into booster?

im still learning so im jsut checking if this is correct.

also, what effect does using a different pot value have on this mod?  say a 10k instead of a 50k.  also, i presume you should use a linear pot.

im thinking of mishmashing some different circuit portions and building sort of a booster/overdrive pedal.  i think it would be cool to use the softness mod to get overdrive/distortion at one end and then dial it back and have clean boost.

[raulgrell]

If you used a 10k pot, the maximum "softness" setting wont be as soft. With the pot all the way down (no resistance) it would actually make the circuit as if it had no pot at all..

Regarding the taper: experiment. See which one gives you best control. My guess would be that an audio taper (log) pot would give you the best control.

[letsgocoyote]

so using a larger pot in the mod would give me a greater range of control?  from no softening to more softening?  i suppose im still pretty newbie and dont fully understand pots.  does a 50k pot go from 50k to 0 ohms?

[Mark Hammer]

1) The pot will go from 0 to 50k or from 50k to 0, depending on how you wire it.  It,s pleasingly flexible that way.

2) The diodes in that configuration clip by conducting when the signal exceeds the forward voltage of the diodes.  Think of it like a bar that only opens when the customers are thirsty enough, and stays closed the rest of the time.  The pot essentially operates like padding on the door, so that you (as bar owner/operator) can only hear them when they bang really loudly.

Now that I think about this analogy, I wonder if one could have differential clipping thresholds by having a cap and resistance in parallel.  High-frequency signals would pass through the cap as if it were an "express lane", whereas lower frequency content would necessarily pass through the resistance.  If you have read RG Keen's classic treatise on the The Technology of the Tube Screamer, you'll recall that a major partof the TS is the manner in which it filters the signal such that the mids and highs are more likely to be clipped than the lows.  Now I'm wondering if the same thing might not be achieved more easily with less forfeiture of bottom end by using the type of network described above.   Anyone ever do anything like that?

[Johan]

1) The pot will go from 0 to 50k or from 50k to 0, depending on how you wire it.  It,s pleasingly flexible that way.

2) The diodes in that configuration clip by conducting when the signal exceeds the forward voltage of the diodes.  Think of it like a bar that only opens when the customers are thirsty enough, and stays closed the rest of the time.  The pot essentially operates like padding on the door, so that you (as bar owner/operator) can only hear them when they bang really loudly.

Now that I think about this analogy, I wonder if one could have differential clipping thresholds by having a cap and resistance in parallel.  High-frequency signals would pass through the cap as if it were an "express lane", whereas lower frequency content would necessarily pass through the resistance.  If you have read RG Keen's classic treatise on the The Technology of the Tube Screamer, you'll recall that a major partof the TS is the manner in which it filters the signal such that the mids and highs are more likely to be clipped than the lows.  Now I'm wondering if the same thing might not be achieved more easily with less forfeiture of bottom end by using the type of network described above.   Anyone ever do anything like that?

I've done that on an overdrive I buillt for a bassplayerfriend.
what I did was to take the basic RAT tonecontroll ( so you could tune it in to keep the fundamental strong )and instead of the cap going straight to ground, it has to pass a set of diods. and on LOW gain setings it work, but as soon as the signal hits the rails in the preceding stage, the effect is lost. I used two batteries to get more out of the effect and I think that if you builld up several lowgain stages( so you dont slam the rails) and attenuate between them, it could be a really cool effect
j

[letsgocoyote]

1) The pot will go from 0 to 50k or from 50k to 0, depending on how you wire it.  It,s pleasingly flexible that way.

2) The diodes in that configuration clip by conducting when the signal exceeds the forward voltage of the diodes.  Think of it like a bar that only opens when the customers are thirsty enough, and stays closed the rest of the time.  The pot essentially operates like padding on the door, so that you (as bar owner/operator) can only hear them when they bang really loudly.

Now that I think about this analogy, I wonder if one could have differential clipping thresholds by having a cap and resistance in parallel.  High-frequency signals would pass through the cap as if it were an "express lane", whereas lower frequency content would necessarily pass through the resistance.  If you have read RG Keen's classic treatise on the The Technology of the Tube Screamer, you'll recall that a major partof the TS is the manner in which it filters the signal such that the mids and highs are more likely to be clipped than the lows.  Now I'm wondering if the same thing might not be achieved more easily with less forfeiture of bottom end by using the type of network described above.   Anyone ever do anything like that?

thanks thats very helpful about the pots.  im seeming to have trouble finding information on exactly how they work.  so is there any point in a pots travel where it essentially becomes an Off switch?
thanks

[Mark Hammer]

There are 2 answers.

1) At whatever point the resistance becomes large enough to do the job.  That will depend on the value and taper of the pot.  If it's a 100k pot but you have to move the wiper 3/4 of the way around to get to 20k resistance then you'll have to rotate more than if you used a 50k pot but reach 20k at the 1/3 point.  How much resistance it takes will, in turn, depend on how big the amplitude of the signal is (big fists still make a noise on the door even with padding), and any resistance just ahead of the diodes.  I've seen a number of diode-clipper distortions that purported to be "soft" clippers by having a 68R resistor in series with the signal, and then another 68R resistor in series with the diodes (imagine two 68R resistors set up like a divider, with diodes to ground on one end).  68R isn't a whole heckuva lot of resistance.

2) You can make essentially any pot an infinite resistance by lifting the back off, painting over part of the resistive strip with nail polish or some similarly durable lacquer, and placing the cover back on.  The pot will then behave normally until you rotate the wiper over the lacquered part.  At that point, it is as if there is an open circuit between the pot and the diodes.

[WGTP]

http://www.muzique.com/lab/sat.htm

Check out the Saturation  control AMZ.  Sort of like what Mark suggests. 

[letsgocoyote]

thanks that looks more like the mod im looking for
i imagine the softness and saturation mods have similar effects but the saturation mod gives you a greater range of control

[alex frias]

I put this kind of pot control but in a OpAmp negative feedback situation, on my very modified TS/Fulldrive project. It worked very well and at the minimum set it affected the attack portion of the signal.

[letsgocoyote]

i tried the AMZ saturation today and it seemed to work quite well.  i frist tried this version



but then i tried the original saturation control and feel like i had better results:


so let me try and udnerstand how the saturation control works.


the signal enters the pot, and at one end of the travel it gets all sent to the output, more or less bypassing the clipping diodes?  and at the other end of the pot it sends signal to the clipping diodes.

whereas the softness mod jsut limits some of the signal that hits the diodes, the saturation mod is more of a blend?

in playing with it, witht he pot turned down i get the saturated distorted sound, but then as i turnt he pot all the way up it both cleans up considerably as well as gives me more volume.  id almost call it a 'clean up' knob as an alternate name for saturation