Clipping Diodes with Potentiometer

[jishnudg]

A very basic question - - is an arrangement like this after, say, an LPB or something, going to work - - if I want to adjust the amount of hard limiting I want? Are there any existing pedals that use it?

(sorry for the image, don't have a schematic software right now..)

https://drive.google.com/file/d/0BwMVia471c4SOTgxOURGYTNpUzQ/edit?usp=sharing

[YouAre]

A very basic question - - is an arrangement like this after, say, an LPB or something, going to work - - if I want to adjust the amount of hard limiting I want? Are there any existing pedals that use it?

(sorry for the image, don't have a schematic software right now..)

https://drive.google.com/file/d/0BwMVia471c4SOTgxOURGYTNpUzQ/edit?usp=sharing

Relevant: http://www.muzique.com/lab/warp.htm

In addition: http://www.muzique.com/lab/main.htm

Have at it!

[Quackzed]

it depends alot on the resistor feeding it from the 'after gain stage' end. if theres a 10k in series with the signal from 'after gain stage' then at the pots max resistance(100k) its 90%clean /10% clipped and is very soft clipped, to (zero ish resistance) at the pot for normal hard clipping ... just make sure theres 'some' kind of series resistor feeding this from 'after the gain stage'.

with a 100k series resistor instead of a 10k the softness is 50/50 instead of close to 90/10 so if the softness is too soft, or not noticeable on most of the pot rotation, you can raise that series resistance (10k)  till you get the range you like.

its like a voltage divider for clipping...

[jishnudg]

Exactly! A voltage divider for clipping, that's what I thought - - - I had seen Jack Ormans article but they used the potentiometer in series with the diodes so I guess that's a bit different from the voltage divider setup...?

[duck_arse]

this one on an electra, with the first silicon changed to a ge and 10kA. Ge to the ccw lug. quite nice, not overdone, easy.

[jishnudg]

Thanks! I think this'll work

[Quackzed]

i'd stick with what you have, and just throw a 50k  resistor in after the gain stage and before the pot diode setup. the electra schem will always have one side always hard clipping only one side can be set to soft clip
... your setup will go from both hard clipping to both soft clipping , you just need a resistor feeding it.

[ashcat_lt]

The clipping is actually a voltage divider of its own.  The diodes are not switches, but current-dependent resistors.   Spose that doesn't really add much to the discussion...

[Lurco]

The clipping is actually a voltage divider of its own.  The diodes are not switches, but current-dependent resistors.   Spose that doesn't really add much to the discussion...

As far as I am aware:
http://www.diystompboxes.com/smfforum/index.php?topic=104178.msg935519#msg935519
http://www.diystompboxes.com/smfforum/index.php?topic=106650.msg966040#msg966040
http://www.diystompboxes.com/smfforum/index.php?topic=106405.msg963073#msg963073

[Mark Hammer]

Almost every circuit I've ever seen that used a diode pair to ground, and was aiming for "soft clipping", used a small-value resistor pair (<1k] to do it.  And reframing diodes as current-dependent resistors helps it to make sense.

Take a look at the clipping circuit in the Pocket Rockit: http://hammer.ampage.org/files/PocketRockit.PDF

R7 and R8 are each 68R.  R8 is tied to ground through a diode pair.  When the current flowing through R7/R8 is minimal, the resistance to ground of the diode pair is high, such that the "divider", formed by R7 and R8+diodes, does not attenuate the signal at all.  When the signal is hotter, the diodes conduct, but since the R7 leg of that virtual pot is such low resistance, the attenuation/clipping will not be that drastic.  In a sense, it is functioning like a noise gate that only drops the level a bit, except it is doing so on a peak-by-peak basis.

So, how can we put this to use?

One way is to use a small-value pot in series with the diodes, as has been shown; though I doubt whether anything about 5k is going to prove particularly useful.
Another way might be to wire up a pot such that one leg is in series with the signal (i.e., a functional replacement for R7 in the Pocket Rockit schematic), and the other in series with the diodes (equivalent of R8).  Since the value of R7 in that configuration can range wide than the value of R8, something like a 10k linear pot, with a 1k, or even 470R resistor in parallel with the "R8" leg of the pot, would allow for a range of hardnesses/softnesses.