THD at max gain on od/dist pedals?

[Alpha579]

Does anyone know the THD on some standard OD/dist pedals when the gain is maxxed? Because i just wanted to know so i could compare...
Alex

[smoguzbenjamin]

Lots and lots and lots :twisted:

Let's put it this way. My dad has an EE degree. He thinks that 0,2% THD is totally unacceptable, while I can't even hear the difference between totally clean, and 0,2% THD. Think of how horrified he must be when I say "I'm going to use this input stage to kick the 2nd FET into overdrive" :mrgreen:

[Alpha579]

LOL!
I just simulated a BSIABii, and with the gain dimed and an input signal of 100mv @ 1Khz, it pumps out 42.89 THD!!! I gotta build that someday...

[Paul Perry (Frostwave)]

I don't think a single measure will be very useful, at a minimum I'd like a THD, plus an idea of the amount of 2nd & 3rd harmonic, plus intermodulation.
Which is why, really, there is no substitute for ears.. after all, look at thoise hi-fi guys arguing about the diff between two amps each of less than .02% :roll:

[WGTP]

Paul is right, there are infinite combinations of harmonics and distortion types that go into 50% (hotter pickup) THD which would all sound slightly different.  I guess the 2nd & 3rd harmonic balance with the fundamental, in addition to the level of IM distortion are big factors.  That is intersting info.  The Jfet designs are supposed to be lower in IM distortion I think, is why so many of us like them??? :?:

With our distortions, we really are moving between a different instrument at 50% THD and the basic guitar sound with 1%THD.  

[Alpha579]

:oops: whats IM distortion :oops:

[stm]

As far as I know, a good overdrive circuit may or may not have high levels of THD. What matters for a good sound is the balance between the different order harmonics.

It is believed that producing mainly low order terms i.e, 2nd, 3rd and 5th is desirable.  On the other hand, terms like 7th, 9th, etc. harmonics are unmusical because they are not harmonically related to the fundamental, and thus tend to sound harsh to the ears.

The above, of course is a matter of taste.  I heard the other day Boss Hyper Fuzz pedal, and found the sound horrible (to mi ears) full of high order harmonics, but the owner just loved the sound  :twisted: .

:idea:  There is a very interesting article named "Tubes v/s transistors - Is there an audible difference?" by Russel Hamm available on the net. This guy shares his findings through many years as a studio sound engineer, and does a very interesting analysis on the harmonics produced by triodes, pentodes, transistors and op-amps when they distort.  :idea:

[Paul Perry (Frostwave)]

"intermodulation distortion" is what makes it sound like shit when you play a chord thru a fuzz. What happens is, whenever two different frequency signals go thru a non-linear circuit (that is, any circuit that distorts) ther is complex mathematics occurring & 'extra' frequencies are generated this is how a ring modulator works.
Unfortunately, unlkess you are Merzbow or KKNull or some other noize band, the intermodulation products aren't what you want, they are very intrusive and distressing  :x to most people (but not me, I have a tin ear)
http://computing-dictionary.thefreedictionary.com/Intermodulation%20distortion

[black mariah]

Unfortunately, unlkess you are Merzbow or KKNull or some other noize band, the intermodulation products aren't what you want,

Ohmygoodsweetlordinheaven, I never thought I'd see KK Null mentioned outside of the heavy metal forums I go to. :lol: Zeni Geva rules.

Speaking of IM distortion, I first ran into that after building my first Bazz Fuss the other day. I used some non-standard components and ended up with a rather odd octave-down sort of thing going on. Playing some power chords blended perfect, others were really funky sounding. Very cool, but not useful outside of a noise context.

BTW, the IRD from a remote control makes a Bazz Fuss sound really nice. :lol:

[Alpha579]

Oh yeh, i get ya...
Why is it that limiting bass response lessens IMD?

[R.G.]

Why is it that limiting bass response lessens IMD?

IMD is the product of any nonlinear process (clipping is one of those) on more than one frequency. Distorting a sine wave produces only harmonics of the sine wave, but distorting any two or more pure frequencies produces sum-and-difference IMD products. So lessening any frequency band lessens IMD.

IMD happens when more than one frequency is distorted. The less of any specific frequency that's there, the less IMD. Bass note distortion is often perceived as "muddy", so that's a good place to limit input frequencies to get less IMD and muddiness.

IMD at higher frequencies sounds harsh. This is specifically what Craig Anderton was aiming at when he designed the QuadraFuzz. The Quadrafuzz splits up the audio band into four separate bands, then distorts each separately and mixes the result back. This narrows how many frequencies are clipped together in any one clipper, and therefore lessens the amount of harsh IMD that's generated.

By the way, THD can be greater than the remaining signal content in the output of clippers and distorters.

[gez]

Out of interest, has anyone ever built (or played through) a quadrafuzz and, if so, what are they like?

[WGTP]

I guess our much beloved and emulated tube amps produce less IMD than most SS circuits and more of the lower ordered and desirable harmonics???  

[RickL]

I built one and wasn't overly impressed. It's not like it sounded bad or anything but it seemed like a lot of effort to get something that didn't sound a whole bunch different than any number of easier projects.

I was expecting it to be able to apply different amounts of distortion to different frequency bands but to me it just sounds like a distortion with a four band tone control.

Maybe I'm missing something.  :?:

BTW I built it using a hand drawn layout I found somewhere on the net (don't ask me where) using 4ms's CBCB construction method. Aside from one error on the layout (one of the regulators was wired incorrectly) it worked correctly from the start. I sound like a broken record when I advocate this construction method every couple of months but I think it combines the paint-by-numbers approach of PCB with the simplicity (no chemicals, cheap materials) of perf. (Cliff has now left the building)