Educate me on symmetrical and asymmetrical clipping in OD pedals

[JB6464]

Can someone explain the difference to me of symmetrical and asymmetrical clipping in overdrive pedals ? I like the sound of the TS808,Boss SD-1,and Voodoo Lab overdrives. I'm not sure what my Fulltone OCD has. Does anyone know what type of clipping they use ? The reason i'm asking is i would like a local tech to make me some custom OD pedals and i'm not sure what's the difference. Thanks.

 

[jimijames]

Re: Educate me on symmetrical and asymmetrical clipping in OD pedals

Tubescreamer - Symmetrical
SD-1 - Asymmetrical

The difference is symmetrical is smoother and less toothy, while asymmetrical is more aggressive sounding and supposedly closer to an actual amp (amps apparently distort asymmetrically)

If I had to hazard a guess, I'd say the OCD clips asymmetrically. The Voodoo Lab and the TS808 are going to use symmetrical clipping though, and that's 2 out of the 3 pedals you mentioned liking. If the guy can custom build you an overdrive, see if he'll install a switch to flip between asymmetrical and symmetrical clipping. It's a very common modification for most overdrives.

You might also want to look at the different diodes that are used in clipping circuits. The traditional tubescreamer ones are great, but there are tons more that all sound great and different - Germanium Diodes, LEDs, and a ton of different diodes that are only known by their part designation (i.e. 1N4001, 1N4372, etc.)

The diodes in a clipping circuit have a significant effect on the sound you're going to get out of an overdrive.

 

[JB6464]

Re: Educate me on symmetrical and asymmetrical clipping in OD pedals

Thanks JimiJames for your input. If i could discribe what i'm looking for it would be the clipping sounds of the SD-1 with the tones of the OCD or Voodoo lab overdrive.
The SD-1 to me has a smooth compressed clipping attack but it's tones are sqwished in the Upper mids. The tones of the Voodoo Lab Overdrive and OCD sound warmer to me but not as smooth in the clipping attack.
So i guess i'm not sure what to ask for first in my adventure down the custom pedal building path in overdrives.

 

[SrDeMaFp]

Re: Educate me on symmetrical and asymmetrical clipping in OD pedals

Tubescreamer - Symmetrical
SD-1 - Asymmetrical

The difference is symmetrical is smoother and less toothy, while asymmetrical is more aggressive sounding and supposedly closer to an actual amp (amps apparently distort asymmetrically)

If I had to hazard a guess, I'd say the OCD clips asymmetrically. The Voodoo Lab and the TS808 are going to use symmetrical clipping though, and that's 2 out of the 3 pedals you mentioned liking. If the guy can custom build you an overdrive, see if he'll install a switch to flip between asymmetrical and symmetrical clipping. It's a very common modification for most overdrives.

You might also want to look at the different diodes that are used in clipping circuits. The traditional tubescreamer ones are great, but there are tons more that all sound great and different - Germanium Diodes, LEDs, and a ton of different diodes that are only known by their part designation (i.e. 1N4001, 1N4372, etc.)

The diodes in a clipping circuit have a significant effect on the sound you're going to get out of an overdrive.

Good info, I was always curious about the difference in layman's terms.

 

[Gr8Scott]

Re: Educate me on symmetrical and asymmetrical clipping in OD pedals

I've converted a pedal from one into another style by using the same or uneven numbers of diodes on each side of the clipping section. The main difference I noticed is that the uneven number of diodes seemed to have a certain sweetness to the sound that was absent in the even diode version. Adding more diodes cause the distortion to lessen over just using one diode each way as well. I did this on the exact same pedal and then plugged it in and played it each way to educate myself on the difference. I could have hooked an extra diode on a switch to have the same effect, which would have been a better test because I could have compared the sounds more quickly that way.

I prefer the uneven clipping myself though your mileage may vary with some pedals.

 

[joelap]

Re: Educate me on symmetrical and asymmetrical clipping in OD pedals

Triodes do clip assymetrically, however the term is a bit misleading. Assymetric is anything that is, you guessed in, not symmetric. Stringing series diodes will cause it to clip assymetrically in the sense that either the positive or negative portion of the signal will clip at a higher voltage (case of SD-1, about 1.4V vs .7V). But triodes don't just clip at different voltages, they also exhibit a different character to the clipping (rounded shapes on the "knee" of the clipping itself, more pronounced on the positive side and IIRC sharper on the negative portion). Moral of the story: experiment if you can and see which one you like better, but know that adding an extra diode to one side won't make it a tube amp.

Personally, I like the positive clipper going 1N4001 + 1N34A + 1N4001 and negative clipper 1N4001 + 1N34A.

LEDs are also a good way to add some unique character, but check the voltage drops across the diode as they all clip at different voltages.

Happy experimenting.

EDIT: I'd also pose the philosophical argue that unless you are using matched diodes, all clipping is to SOME degree assymetrical.... what degree that is depends on personal taste!

 

[xxxplorer]

Re: Educate me on symmetrical and asymmetrical clipping in OD pedals

From what I researched (www.pedalarea.com was helpfull!) the OCD versions 1 through 3 are symetrical and 4 is assymetrical.

I had a BOSS SD-1 that I did the Monte Allums GT Mod too. It featured a switch to swap between assymetrical and symetrical clipping.

Reading on forums and such I thought I was going to like the assymetrical better, but I really dig symmetrical for my setup... assymetrical seemed to add a high end harshness.