Overdrive vs Distortion

[jwblant]

Hey ya'll!

I've been looking at a few schematic and actually just finished a Timmy-clone build last night, but I began wondering about the differences between overdrive/distortion.  Now, I'm not talking about sonic properties or technical differences as far as what the circuit does.  I'm talking about actual, physical differences between the circuit/schematic between the two. 

I've heard that overdrives use germanium diodes where distortions use silicon, but the Timmy I built is an overdrive and it uses silicon in the feedback of an opamp.  Can anyone shed some light on this situation? 

Thanks ya'll!

Willy B

[Earthscum]

Basically a distortion does just that... it distorts the signal. You can use whatever means you find necessary to destroy the signal.

Overdrive leaves at least remnants of the original signal at the output. The Tube Screamer is an overdrive, and it uses silicon 1n4148's or equivalent.

A fet driving another fet into clipping can be considered "overdrive" territory, but if you add one more fet, and maybe even another, the signal eventually gets large enough that it's losing large amounts if the top and bottom, getting nearer and nearer a square wave.

[Pablo1234]

overdrive is distortion and visa versa. Their is no real rational to it, their all distortion.
Someone should really define it and make it a standard but that requires everyone to follow the standard.
This is how I define it
Overdrive is a gain pushing an amp or pedal into distortion
Fuzz is fuzzy sounding less dynamic and compressed sounding
Crunch is crunchy sounding with dynamics
And their all distortion.

[Keppy]

^ What he said. They're the same thing. I usually see them differentiated only by degree. A little clipping=overdrive; tons of clipping=distortion.

[jwblant]

Well technically, OD has a "soft-clipping" that leaves most of the signal intact and distortion has a more "hard-clipping" that further distorts the signal more, which could also be argued is simply "more distortion." 

Regardless of what you call it, what are some differences between OD/dist or low gain/high gain pedals or whatever you want to call it?  What increases/decreases the gain in this circuits?  Also, what are some of your favorite circuit layouts for these types of drive?  (i.e. as Earthscum suggested, a FET into a FET or diodes in feedback loop of opamp, etc...)

[Earthscum]

I hate to admit it, but I'm quickly becoming a fan of the Tube Screamer format.

My personal preferences are Jfets for circuits that you want a subtle or no tonestack on, and feedback clipping in transistors (Big Muff, variants, parts) with different filtering schemes. For me, as a bassist, I really love the BMP tone stack, and you have to take filtering into consideration when talking distortion. Generally, whenever you are making higher order harmonics through clipping, you want to tame them down a bit. An intuitive filter can make all the difference in the world in sound, and sometimes almost makes the type of device a moot point... rather up to the designer considering gain needs, and the filter does all the shaping.

[LucifersTrip]

correct me if I'm wrong, but the OP asked:

"Now, I'm not talking about sonic properties or technical differences as far as what the circuit does.  I'm talking about actual, physical differences between the circuit/schematic between the two.
I've heard that overdrives use germanium diodes where distortions use silicon"

yet, everyone answered exactly what the OP did not want

But unfortunately, there is no real answer to the Op's question. There are loads of different types of circuits/schematics that will produce BOTH distortions AND overdrives...There is no specific type of circuit that produces one or the other.

...and BOTH distortions AND overdrives can use germanium or silicon

[flintstoned]

Overdrive---- one ic
Distortion--- two or more ic's

[LucifersTrip]

Overdrive---- one ic

3
http://analogguru.an.ohost.de/193/schematics/Maxon_OD-880_OverDrive.gif

Distortion--- two or more ic's

1
http://www.freeinfosociety.com/electronics/schematics/audio/pictures/distortionplus.gif

[Gurner]

Overdrive ....a verb, ie setting the parameters of a signal/circuit so that once the said signal travels through the circuit, it starts clipping thereby resulting in distortion  

[newfish]

I'm with the, "soft, 'feedback clipping' = Overdrive (Tubescreasmer, SD-1, etc...) ,
and the hard 'clipping to ground' (SD-1, Rat, etc) = Distortion" opinion.

Of course, the Big Muff is the exception to this sweeping generalisation.  Masses of clipping from 2 x 'feedback loop' clipping.

It's distortion!

[petemoore]

  Linear by definition is linear.
   Non-linearization of a signal waveshape is by 'proper' definition: distortion.
  The definition of distortion has been irrevocably distorted to have meanings such as 'overdrive', which can have the net result of creating distortion.
   Without an amazing increase in related subject content, 99% of the time, distortion, overdrive and to a lesser degree 'fuzz' can be interchanged randomly. "Tube Sound Fuzz" isn't actually fuzzy sounding, many 'overdrives' are much more fuzzy or distorted than the most famous one.
   Hopefully this is confusing enough to relate to some degree how confusing [and often downright misleading] the use of these terms has become.
  Some sound sampling and circuit schematic observations [as well as building/modding/testing a number of them] provide at least some idea of how 'right on' or 'out there' the associated texts, names and terminologies might be.
   

[Keppy]

correct me if I'm wrong, but the OP asked:

"Now, I'm not talking about sonic properties or technical differences as far as what the circuit does.  I'm talking about actual, physical differences between the circuit/schematic between the two.
I've heard that overdrives use germanium diodes where distortions use silicon"

yet, everyone answered exactly what the OP did not want

But unfortunately, there is no real answer to the Op's question. There are loads of different types of circuits/schematics that will produce BOTH distortions AND overdrives...There is no specific type of circuit that produces one or the other.

...and BOTH distortions AND overdrives can use germanium or silicon

That's the point of what several of us have been saying. The OP asked for physical differences, when there really are none. These terms, as commonly (mis?)applied, are interchangeable. We're just splitting hairs and attempting to justify it in a variety of ways.

[teemuk]

^ This.

When you overdrive things they distort.


Overdriving is the name for the process, distortion is the name for the product from it. Furthermore some may use words like "fuzz" or "crunch" to describe the characteristic tone of the distorting signal. People have a habit of using terms interchangeably - especially if they don't quite understand what the terms are all about - so we're kinda wandering to the same realm where some people talk about "gain" while they really were meaning amount and magnitude of distortion in the signal instead.

That's all there is to it. You won't find any deeper meanings because there aren't any.

[Mark Hammer]

At one level, I would agree wholeheartedly with teemuk.  At another level, I think there are differences.  Certaily he is correct in asserting that you've basically got your linear operating range, and your non-linear range, where the harmonic content starts getting added.  However, the question - which comes up regularly - is also partly prompted by the labels used "out there".  If the labels were completely incoherent, and things like a Big Muff were called "overdrive" and a Bluesbreaker was called a "fuzz", I suspect people would begin to ignore the labels, and the question wouldn't come up quite as often.  The thing is that, although the boundaries are not entirely crisp, there is modest coherence to the use of the labels across the industry (and across the industry's history).  So, naturally, people want to know more about what falls under what heading, and if there is something they can and should look for which will help them to place a circuit squarely within a category, or perhaps permit it to be considered as able to straddle 2 or even all three categories.

For me, one of the central principles guiding all of this is the fact that a guitar signal changes from the moment the string is picked/plucked.  It changes both in amplitude and in spectral content.  It has a sudden burst of wide-bandwidth energy for a brief period, then quickly "settles down" to a lower amplitude with noticeably less harmonic content.

This reality sits alongside the other guiding principle of what I like to call "proximity to clip".  Generating harmonic content that was not there in the original signal depends on the difference in amplitude between the signal, and the limits of the circuit to pass and amplify the input signal without generating additional harmonic content.  If the signal remains well below that point, nothing changes much.  If the signal is dangerously near, or well above that point, content gets added.
But here is where the two concepts interact.  If the signal changes level over time, then some parts can exceed that threshold, while others remain safely below it.  Our use of the terms "overdrive", "distortion", and "fuzz" depend on a) how long the signal remains above that threshold, and b) what harmonic components get generated or at least passed to the output.

If only the initial peak results on adding harmonic content, such that the attack is exaggerated, we tend to label that as "overdrive", especially if it consists mostly of lower order harmonics.  If the amount of gain applied is such that the signal remains above clipping threshold for a longish time - enough to make it sound like a steady-state signal - we generally refer to that as fuzz.  "Distortion" tends to be that zone where clipping continues a bit past the initial attack, and contains more higher-order harmonic content; generally enough to render the notes less clearly defined.  By this sort of definition, you can imagine that some circuits can be "transformed" by the addition of gain stages ahead of them that render the signal well above the clipping threshold for a longer period.  You can also see how altering the clipping threshold by the use of LEDs or extra diodes, results in circuits that only have their effect on the initial attack of the notes, rather than for a more prolonged period.  Finally, you can see how the very same circuit can effectively straddle several categories by providing a threshold and gain capable of generating some clipping during peaks or more prolonged clipping after the peaks, with sufficient EQ control to let those higher-order harmonics come through...or not.  Those sorts of pedals straddle both "overdrive" and "distortion" boundaries.  Some folks appreciate that flexibility, and some folks would rather zero in on one category per pedal and allow more precision dialing.

Whether manufacturers label such pedals appropriately is a whole other matter.  But that's my story, and I'm pretty much sticking to it.

[R.G.]

Really, folks, the answer to this was turned up decades ago.

The difference between overdrive and distortion is the identity and mood of whomever wrote the advertising. The eternal puffing and sophistry of advertising writers is the only difference.

There is no physical difference; at most it's a sloppy inexact attempt to nail words on to some point on a continuum of sensations, much like an attempt to nail jello to a tree. It fits almost everywhere you put it, but it's really hard to make it be still.

Remember "one man's meat is another man's poison" or it's derivatives "one man's fish is another man's poisson" and "one man's ceiling is another man's floor".

[arawn]

on consideration of the question the best answer I can give is this: Overdrives most commonly have their clipping diodes in a feedback network of some sort, while "most" distortions have clipping diodes to ground outside of a feedback loop. althought i think rg is more right on this question os he is on all others.

[Astronaurt]

I really don't see that there is any "rule" or even a general Guide-line to what diode configuration determines What your distortion box is gonna be. The BazzFuss has one diode fed back from a Tranny's emitter to base, and that can be about as fuzzy as it anything with a low threshold Silicon diode. A friend of mine built one with a green LED with a very high threshold voltage, and it sounded more like a Tubescreamer-esque overdrive. The vocabulary being used is just confusing the actual facts here. I'm going to define "Distortion" as simply Amplitude distortion; when the Amplitude relationships of a signal coming out are different from what came in.

There are only two considerations when trying to generate amplitude distortion, and that is "What is the threshold of Clipping?" and "What is the amplitude of the signal going into this threshold?" If you feed a signal with a maximum amplitude of 0.8v into a circuit with a clipping threshold of 0.7v, that 0.1v, approximately 12%, of the signal is clipped off resulting in a small amount of distortion. We would probably call it a middle of the road kind of overdrive. If you feed a signal with a max amplitude of 8v into the exact same circuit then obviously you're clipping off 7.3v, more like 90% of the signal, which would be so much fuzz your ears bleed. 

Now what happens when you feed a signal with a max amplitude of 8 volts into a different circuit with a clipping threshold of 7v? The exact same relationship as before, about 12% of the signal is chopped off. so of course you would get a sound that is likely to be pretty close to the first example. Like I said before, the important thing is what level amplitude is driving what threshold of clipping. The precise components and their exact arrangement really does not matter. It's simply the job of the circuit designer to set up these two conditions in whatever way they deem necessary - if you want something that sounds distorted as all hell, you could drive 1 op-amp into an ultra low voltage diode, slap on a volume pot and call it a day. You could use the EXACT SAME SET-UP, and just attenuate the input signal to a tiny fraction of what it was coming in, and it would be that much more tame.

@ jwblant, honestly just look up the schematics of all your favorite pedals, see what they do and how they do it, and experiment yourself to find the tone that you want. One of the funnest parts for me about building is having an idea, trying it out, and having it turn out completely not like I expected; but somehow a lot more interesting than I could have ever imagined.

[brett]

+1 for RG's comment...

The eternal puffing and sophistry of advertising writers is the only difference.

Plus the endless discussion in threads - we might as well be discussing whether ceramic or electro caps are better.
Consider this: Tubescreamer = both.

[jwblant]

Thanks guys.  You've really helped a lot.  A lot of good discussion going on.  I think Arawan kinda pointed in what I was orginally asking about as far as OD (or pedals commonly referred to as OD)=diodes in feedback and dist (or pedals commonly referred to as dist)=diodes to ground after feedback.  However, Teemuk made a good point too about overdrive is the process and distortion is the result.  Kinda sums a lotta things up.

Just wanna thank all ya'll for your input! It all helped me out a lot!