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Jp.
Bronze Member
65 Posts |
 Posted - 08/04/2005 : 12:15:43
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What is the difference between the overdrive circuitry and the distortion cicuitry?
How do they differ in what they do to the sound wave signal?
As my ear gets more "mature" I can hear the difference. Particularly the difference between an OD pedal in front of a S/state amp and a Valve amp. But OD to DS in front of a S/State, thats harder. |
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Jp.
Bronze Member
65 Posts |
Posted - 08/06/2005 : 14:38:24
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So no one has any idea |
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arcanon1313
Silver Member
USA
414 Posts |
Posted - 08/07/2005 : 01:17:13
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Don't quote me on this but, i beleve that the difference is the amount of gain available, an OD pedal never has the amount of gain of a distortion pedal. a good reference is a SD-1 (or a TS-9) has considerably less gain than a DS-1. |
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phenry20
Bronze Member
USA
105 Posts |
Posted - 08/07/2005 : 01:37:13
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| If you're really interested in this subject - I would HIGHLY recommend getting the Boss Book by Hal Leonard publishing that I've used as a reference on these boards and would say that between this site, the book, and harmony-central you're covered. They have charts of the curves of all of the Boss dist/od's including the switchable modes in the SD-2 or OD-2 for example. So to answer your question, I looked at the OS-2 since it's an "overdrive" and a "distortion" in one pedal. And the charts indicate that an overdrive wave "typically" is smooth and siney in it's peaks and valleys while the distortions are more square wave and choppy. Couple this with the audio disk's samples of the pedals and you're good to go. |
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sirlemonhead
Bronze Member
Ireland
64 Posts |
Posted - 08/07/2005 : 05:35:58
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I got the Boss book on his recommendation. It's VERY cool and informative. Nice interviews too ( the guy with all those SP-1s!  ) |
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phenry20
Bronze Member
USA
105 Posts |
Posted - 08/07/2005 : 05:43:23
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| Happy to hear you picked it up. You'll notice a few errors/discrepancies/inconsistencies in dates of production, etc. but overall a great source of information and MARKETING! My Boss pedal purchases grew mightily after aquiring that book. |
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bossarea
Forum Admin
United Kingdom
3652 Posts |
Posted - 08/07/2005 : 12:06:19
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I believe the difference between overdrive and distortion lies within how harmonics are added to the original signal. I think odd harmonics are what's called overdrive while even harmonics makes up distortion.
I'm out of my depths here and was hoping stinkfoot would log on and explain this to us all before I get lost in my own explanations. |
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stinkfoot
Silver Member
Sweden
181 Posts |
Posted - 08/08/2005 : 12:11:29
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First off, it's important to understand that both types (distortion and overdrive) are actually distortion - both types (and fuzz too, by the way) distort the signal by clipping/limiting the signal. You will not be flogged if you stomp on a pedal that says "overdrive" when the bandleader asks for distortion...
Distortion (the phenomenon, rather than any specific pedal or circuit) is simply what happens when you ask a circuit to produce a louder signal than it is designed for. In a fuzz pedal - as well as in an amplifier - this process will usually be as simple as that; the amplification level is turned up past what the transistors (or tubes) can handle, which squashes or clips the waveform off. In most effects pedals, the clipping is instead often simulated by introducing diodes into the circuit. The effect is largely the same - the signal's waveform wants to be bigger than the circuit allows, and therefore gets squashed or cut off.
But we do still have the two different terms attributed to various pedals, and there are a few "rules" that govern which circuit gets called what. In general, "distortion" implies that the circuit cuts the waveform off at both ends (hard clipping), whereas "overdrive" usually means that the circuit limits the waveform, leaving it slightly rounded (soft clipping).
The picture is from the excellent GM arts page, which I recommend heartily if you want to read up on all of this.
Soft clipping (or "overdrive") is usually generated with diodes in the feedback loop of an op-amp, with the tube screamer/SD-1 circuit being the most known example.
Hard clipping is usually generated with diodes connected to ground after the gain stage, with the RAT, DS-1 and Sonic Distortion as examples.
And then there are the exceptions - some circuits have diodes connected to ground and still generate soft clipping. This is partly due to the amount of gain the circuit has (how big the waveform wants to be, before the diodes clip it into the shape , due to the type of diodes used. These circuits usually use germanium diodes, which clip far easier and therefore softer than silicon diodes. The Distortion + and DOD250 are prime examples of this type of circuit.
To complicate matters further, there are also pedals that have both types at once - first a standard soft clipping stage with an op-amp (like a TS-9), and then a second hard clipping stage after the main gain stage. But for the most part, "overdrive" and "distortion" pedals will have soft and hard clipping, respectively.
/Andreas |
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bossarea
Forum Admin
United Kingdom
3652 Posts |
Posted - 08/08/2005 : 12:54:39
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Thanks for the explanation, stinkfoot.
Do you know what differences would we see if we ran the signals through a spectrum analyzer and compared the results for the hard and soft clipped circuit? As all signals are a composit of sinus waves, we should see a difference in harmonics added to the signal when we clip it.
The reason I'm asking is that I'm trying to figure out if the pseudo-answer I gave earlier has any truth in it. |
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Jp.
Bronze Member
65 Posts |
Posted - 08/08/2005 : 12:55:54
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What I'm a little confused on is the wave diagram you refer to (Ive seen it before).
Usually when you see a diagram like this its a graph. Therefore to the left of screen I expect to see a +ve and -ve value system. ie the higher the wave the louder the signal. This would then contradict the graph you present me with. I guess not being accustomed to wave signal diagrams I get confused.
When I look at that graph my mind see's a Compessor at work. Trying to even out the wave and present one straight path.
I'll do some home work and get back to you
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stinkfoot
Silver Member
Sweden
181 Posts |
Posted - 08/09/2005 : 12:14:42
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bossarea - while I think there is some truth to the harmonics theory, but I also think people tend to put too much emphasis on the odd vs even order harmonics issue. While asymmetric clipping may produce more even-order harmonics, it doesn't automatically mean a better sound than you'd get with symmetric clipping. There are plenty of other factors involved that also contribute to the sound, with the overall amount of gain in the gain stage being one of the more important ones. While asymmetric clipping can sound far better than symmetric in one circuit, it can be the complete opposite in another circuit. But the two clipping styles are different - that much is definitely true...
Jp. - I'm not sure I follow you here. A waveform like the one pictured is a graph, with positive and negative ends and 0ve in the middle. It's just that the voltage values aren't printed out in this particular one, most likely because it is simply an illustration. But I don't see how having voltage indication on the vertical axis would contradict anything I've said so far. The blue line represents how loud the signal wants to be (or in the case of a stombox, ho loud it would be if the clipping diodes were removed). The two variants of clipping are then drawn in as a reference, mostly to show how they look. But getting a clear picture is not the only reason why they are drawn in at a seemingly lower level than the unclipped signal. While a distorting amp will clip at the max level (at the same height as the blue waveform), a circuit with clipping diodes will lose a bit of volume as the clipping is applied. Also, the harder the clipping, the lower the apparent volume will be.
The compressor analogy is not too far off, though - clipping is very similar to limiting, as both have to do with neutering a signal that tries to go beyond the available headroom. The limiter is able to do this cleanly by working within its own clean headroom, and any signal lost in the process is recovered through additional amplifier stages after the limiting. The limiting in a distorting circuit is done by actually running out of headroom, which produces the distortion.
Different diode types clip at different points/levels, and will therefore limit the available output volume differently. Diodes that clip early produce more distortion with a lower output level. Diodes that clip late generate less distortion and more output level.
For instance, the MXR Distortion+ has similar gain amounts as the tube screamer, but instead of silicon diodes in the op-amp's feedback loop it has germanium clipping diodes to ground. Germanium clips earlier than silicon diodes, producing more distortion with less output level. Also, connecting the diodes to ground tend to lower the output volume, compared to having them in the feedback loop. Since the Dist+ doesn't have a second gain stage after the clipping (to recover some of the lost output level), it doesn't have very much output volume. In contrast, the Micro Amp circuit is almost exactly the same as the Distortion+, except for the clipping diodes (which the Micro Amp doesn't have). The difference in output level is quite staggering...
/Andreas |
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bossarea
Forum Admin
United Kingdom
3652 Posts |
Posted - 08/09/2005 : 12:45:53
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| Thanks for that. You're right, there's an awful lot to go into the equation here. Adding that perception of sound is individual and everyone's got different taste we find that there is room for all designs |
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Jp.
Bronze Member
65 Posts |
Posted - 08/11/2005 : 12:46:05
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Hey stinkfoot
thanks, when you exlpain it that way (and I read it four or five times) I begin to understand.
2 novice questions though.
1) Having never seen the wiring Diagram of a TS-9 I assume there are two stages to the circuitry. 1st stage for distorion 2nd stage for output recovery/signal boost. yes/no?
2) What is an "op-amp" ?
Thanks Jared
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stinkfoot
Silver Member
Sweden
181 Posts |
Posted - 08/11/2005 : 13:22:05
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I know the feeling - sometimes I too have to read things several times before I get it. And I could probably work on simplifying my answers a little too... 
But anyway, in the TS-9 and SD-1, the first stage is where the gain and clipping happens. The second stage is where the tone control is applied, and it probably does a bit of volume recovery too. After the second stage, the level control completes the basic circuit. There are lots more components in a TS-9 or SD-1 (input/output buffers, power filtering and protection, voltage divider and a complete electronic switching circuit), but the two op-amp stages do make up the core circuit.
An op-amp is actually a circuit application invented in the early '70s called "Operational Amplifier". It is a quite complicated combination of transistors (I think there's 14 different transistors involved, for instance) and other components that together make up a complete amplifier stage. For ease of use and space-saving purposes, all the components needed were then crammed into a single package, which got named "op-amp". Furthermore, the type of op-amp used in the TS-9 (various versions of the 4558 design) is a dual op-amp, with two separate op-amps bunched into one housing.
/Andreas |
Edited by - stinkfoot on 08/11/2005 13:23:08 |
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eeone
Bronze Member
Yugoslavia
121 Posts |
Posted - 08/11/2005 : 13:25:51
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quote:
Originally posted by Jp.
2) What is an "op-amp" ?
Op-amp is short for operational amplifier. Basically, it amplifies the signal brought to its input. It usually comes as a chip, but can be built with discrete components ( standard resistors, capacitors, etc.). The most widespread example is 741 op-amp.
For more details take a look here : http://www.uoguelph.ca/~antoon/gadgets/741/741.html |
Edited by - eeone on 08/11/2005 13:26:25 |
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SO GETTING JUST A little TECHNICAL...?
