Parametric Distortion/Clipper

[markseel]

I made a circuit that allows five *independent* adjustments of signal amplification and clipping functions that's to be used in an analog distortion effects pedal.

This "distortion" stage can be adjusted as follows:

1) Overall signal gain
2) Positive signal clipping threshold (similar to a bias adjustment)
3) Negative signal clipping threshold (similar to a bias adjustment)
4) Positive signal clipping 'hardness/softness'
5) Negative signal clipping 'hardness/softness'

Here's some results of circuit simulation:
https://picasaweb.google.com/mark.seel/NextAudioDigitalAudioSignalProcessor#5595921178366273282


The graphs show output for the following adjustments:

Graph1: Gain = 22K, 0K <= Bias1 <= 50K, 0K <= Bias2 <= 50K, Clip1 = 10K, Clip2 = 10K
Graph2: Gain = 22K, 0K <= Bias1 <= 50K, 0K <= Bias2 <= 50K, Clip1 = 50K, Clip2 = 50K
Graph3: Gain = 22K, Bias1 = 25K, Bias2 = 25K, 10K <= Clip1 <= 50K, 10K <= Clip2 <= 50K
Graph4: 10K <= Gain <= 50K, Bias1 = 25K, Bias2 = 25K, Clip1 = 25K, Clip2 = 25K
Graph5: 10K <= Gain <= 50K, 0K <= Bias1 = 50K, Bias2 = 25K, Clip1 = 25K, Clip2 = 25K,
Graph6: 10K <= Gain <= 50K, Bias1 = 25K, Bias2 = 25K, 10K <= Clip1 = 50K, Clip2 = 25K

I was going to control each of these five parameters using digi-pots (hence posting this in the Digital and DSP forum) but it could be used with 5 regular pots too (all pots are 50 Kohm)

With a couple of these stages and some pre and post filtering (that would also presumably be controlled parametrically) I would think you could simulate all kinds of distortion sounds completely in the analog domain but with the option of using digital control to perform complex adjustments with a small set of pot controls (by mapping one control to a number of adjustments with look-up tables or formulas that control multiple digi-pots).

Anywho, thoughts on the parametric clipper?  Anyone interested in the actual circuit?  Anyone interested in a PCB for a stompbox project?

[PRR]

Forum does not embed "https://" links; some assumption about "secure HTTP".

Therefore your image does not show in-message.

Google defaults to https links but will often accept "http" for the same file.

[crane]

Graphs seem really nice and flexible
Would you mind posting actual schematic?
My idea is that 5 controls is too much for a distortion, howere it would be nice to use trimpots inside a stompbox to adjust for the tone you're looking for.

[markseel]

Here's the schematic:

http://picasaweb.google.com/mark.seel/NextAudioDigitalAudioSignalProcessor#5596590609927868386

I can't get the image to show inline.  What am I doing wrong?   

[crane]

hmm, isnt that2120 obselete and expensive part to get?

[markseel]

The circuit I made uses the THAT2180.
They're easy to get.  Mouser has them in stock.
You can use any THAT corp VCA that has both positive and negative control ports.
Some of their VCA's have just one port but the circuit could be modified for that.
The THAT2180 or THAT2181 can be replaced with the THAT2162 that has two VCA's and runs off of a lower supply voltage. Just change R1 and R2 appropriately.

[PRR]

I can't get the image to show inline.  What am I doing wrong?   

I think you linked to the _album_, not the _image_.

[borman09]

Nice explanation.Very helpful.

[Galego]

16v hmmm... what digipots could you use with that voltage?

[caspercody]

Do you have any sound clips?

[markseel]

16v hmmm... what digipots could you use with that voltage?

Analog Devices sells digi-pots that have separate logic and signal voltage supplies supporting bipolar analog signals up to +/- 16.5V (or uni-polar supply up to 33V).
http://www.analog.com/en/digital-to-analog-converters/digital-potentiometers/products/index.html

... or you could use the THAT2162 and use a 5 volt supply:

The THAT2180 or THAT2181 can be replaced with the THAT2162 that has two VCA's and runs off of a lower supply voltage. Just change R1 and R2 appropriately.

[markseel]

Do you have any sound clips?

No, sorry.