Volume Roll-off OD/Distortion

[rschultz13]

Hi,

Some pedals allow you to roll off the overdrive/distortion by turning down the volume on your guitar. How does this work? I surely don't understand this.

And what are some pedals that do this well? Creation Labs Holy Fire is one that apparently does this.

Thanks.

[Blues Lyne]

This is a very simplified answer, but the way you usually achieve distortion is by hitting a device (transistor, tube, diode) with a larger signal than it can pass. Every thing above this limit gets clipped and the wave form is flattened creating something closer to a square wave. As you turn down the guitars volume, you are decreasing the signal hitting the device and less of the wave is getting clipped, so less distortion. If you turn down low enough, your signal will be clean again, because all of the wave is below the limits of the device.

This is a graph of a pure sine wave.


And here is a clipped wave.



The dotted line would represent the limits of the devices ability to pass the signal and you can see how it causes the wave to flatten out. As you notice in the bottom two illustrations below some of the signal falls below this line and isn't distorted and some of the signal is increased above the limits of the device and the wave form is distorted. Depending on the limits of the device and the amplitude of the signal, the guitars volume control could reduce the signal enough for it to pass through undistorted.



As I said, this is pretty simplified. In my experience designs that use transistors or tubes to create the distortion generally clean up better than designs that use diodes, but is all depends on the design. For instance a Big Muff that uses transistors, still doesn't clean up that great. The way it's designed, it's hard to get the signal small enough that it doesn't distort.

R.G Keen has a great distortion primer here http://www.geofex.com/effxfaq/distn101.htm that I got the top two illustrations from.

[Blues Lyne]

As far as pedals that do it well, the classic is the fuzz face. Many treble boosters clean up nicely. My Kingsley Jouster does it really well. I've found the COT50 and it's relatives to clean up very well. The Menatone Kar Krash, and I would assume the other Menatone amp in a box pedals, cleans up as well. Many pedals, when used with the gain low and the volume up to push the amp into more dirt, will clean up. But, it's more the amp that is cleaning up than the pedal.

[rschultz13]

Now that I understand what's going on, it seems that most pedals could do this if they were set right. There should be some threshold on guitar volume knob where above it woudl act as a clippling cleanup/control, and below would act as volume, right? I'll have to play around with this on some of my OD's.
Thanks.

[jnepo1]

The Blackstone OD is a great example of the volume roll-off. It is most dynamic when placed first in the signal unbuffered.

[Blues Lyne]

Originally Posted by rschultz13

Now that I understand what's going on, it seems that most pedals could do this if they were set right. There should be some threshold on guitar volume knob where above it woudl act as a clippling cleanup/control, and below would act as volume, right? I'll have to play around with this on some of my OD's.
Thanks.

It does seem like most would, but in reality they don't. With some pedals, rolling back the guitar's volume just changes the volume, but doesn't clean things up much. In some, it's because it's boosting the signal so much and clipping so hard, that you can't get below the clipping threshold. From my experience with a friends Redeemer (a buffer that is placed at the guitar rather than in a pedal) I think that the buffer in the input of the pedal may also effect how much it cleans up with the guitar's volume

There is more to it than that though. Often pedals that build the dirt up over multiple stages (like an amp does) clean up better than pedals that clip things heavily in one stage. In my experience, diode clipping seems to not clean up as well as driving transistors or even opamps into distortion. However, there are exceptions to every rule. The COT50 style pedals use diodes for some of the clipping, but clean up great.

The other thing that comes into play is how much difference there is in volume between the dirty tones and the clean up with the guitars volume down. Some pedals (and amps) seem to clean up well with very little change in volume. Others, have a drastic change by the time they are clean, so it's a little less useful. For instance, a Fuzz Face will often go from full fuzz to a nice clean tone by turning the guitars volume from 10 down to 7, and the clean tone isn't that much quieter than the fuzz tone.

Those are all generalizations, and as I said, there are exceptions to every rule. In the end it boils down to trying the pedals, or reading about/asking questions about other peoples experience.

[Heady Jam Fan]

Originally Posted by Blues Lyne

It does seem like most would, but in reality they don't. With some pedals, rolling back the guitar's volume just changes the volume, but doesn't clean things up much. In some, it's because it's boosting the signal so much and clipping so hard, that you can't get below the clipping threshold. From my experience with a friends Redeemer (a buffer that is placed at the guitar rather than in a pedal) I think that the buffer in the input of the pedal may also effect how much it cleans up with the guitar's volume

There is more to it than that though. Often pedals that build the dirt up over multiple stages (like an amp does) clean up better than pedals that clip things heavily in one stage. In my experience, diode clipping seems to not clean up as well as driving transistors or even opamps into distortion. However, there are exceptions to every rule. The COT50 style pedals use diodes for some of the clipping, but clean up great.

The other thing that comes into play is how much difference there is in volume between the dirty tones and the clean up with the guitars volume down. Some pedals (and amps) seem to clean up well with very little change in volume. Others, have a drastic change by the time they are clean, so it's a little less useful. For instance, a Fuzz Face will often go from full fuzz to a nice clean tone by turning the guitars volume from 10 down to 7, and the clean tone isn't that much quieter than the fuzz tone.

Those are all generalizations, and as I said, there are exceptions to every rule. In the end it boils down to trying the pedals, or reading about/asking questions about other peoples experience.

I put a simple one knob boost after my dirt pedals (MXR Micro Amp) so if there is too much volume change cleaning up a pedal, I kick on the boost and I can adjust the amount using my foot. It gives me a huge variable range of distortion from every pedal. I have used it with TS's, Low-Gains, Distortions and Fuzzes.

[Badfrog]

To answer your one question, I usually like to have the volume on the guitar to where 6 or so on the dial starts into some grit, 7-8 will have you in overdrive and 9-10 gets you into some madness (of course this all depends on the pedal).