What are your Favourite ways to Distort?

[Alpha579]

Hey all,
Ive had some good experience with JFET's, but i want to see which method the majority favours...
Alpha

[Ansil]

i actually like overloading any thign into another amplification stage..  but diodes to ground is one of my favorites

[Peter Snowberg]

I think the answer you seek may be more in the filtering than the device that is creating the distortion to begin with. Here's a test you can use to widen your distorted horizons....

Get a 10 band stereo graphic EQ. Use a clean booster with low coloration to bring the guitar up to line level. Run that signal through 1/2 of the EQ. Next run that signal into your distortion creator be it JFET, MOSFET, BJT, or diode situation. Run the output of that into the 2nd half of the EQ, and finally run that into your amp.

Adjust everything so that you can hit the strings hard without the distorter and still get a clan tone (no clipping in the EQ or at the amp). Now engage your distortion and start playing with the knobs, being careful to not generate clipping in the EQ or amp.

You'll find that by adjusting the pre and post EQ you can get a huge variety of distortion tones and textures.

If you want the simple answer to your question though.... when it comes to generating smooth distortion I like a number of stages of creation without any of them being too extreme. JFETs and MOSFETs are my favorites.

Have fun!
-Peter

[freeradical24]

what are jfets and mosfets

[Peter Snowberg]

what are jfets and mosfets

JFETs and MOSFETs are types of transistors that are controlled by voltage. The standard NPN and PNP style transistors are also called BJTs and are controlled by current.

BJT = Bipolar Junction Transistor
FET = Field Effect Transistor
JFET = Junction FET
MOSFET = Metal Oxide Semiconductor FET

FET style devices work more like tubes do.

CMOS = Complementary MOSFET (using two MOSFETs of opposite polarity)

You will find more info here:
http://ourworld.compuserve.com/homepages/g_knott/

...and I'm sure others will add to the list of info sources. Almost any decent learning electronics site will give you more info than you can easily digest.

Take care,
-Peter

[smoguzbenjamin]

An FET is a Field Effect Transistor. Like transistors but they resemble tubes a bit more. Think of it as a voltage-controlled transistor.


edit: ah dang Peter beat me to it

[Gilles C]

I love FET distortion... because it's closer to tubes than transistors in the way they work.

And I love tubes, distorted or not, so...  

[Alpha579]

I was thinking, could you take the preamp of, say a marshall plexi, replace all the 12ax7's with JFET, and change the drain resistor to get 4.5v at the Fet drain. Do u think this would work, seeing as FETs work in a very similar way to tubes?

[Ansil]

I was thinking, could you take the preamp of, say a marshall plexi, replace all the 12ax7's with JFET, and change the drain resistor to get 4.5v at the Fet drain. Do u think this would work, seeing as FETs work in a very similar way to tubes?

do a perplexed its about as close as i have ever heard ss get

[Alpha579]

Sorry ansil, im not sure what you mean 'perplexed' :oops:

[Ansil]

its a clone of the marshall guvnor basically with some tweaks buy a guy who was a genius of tube circuits and well he pretty much nailed a tube amp in a box but is arrested from alst i heard

[Alpha579]

cool, where could i get the schematic  

[bwanasonic]

I notice *beating the snot out of a tube amp* isn't one of the choices. My favorite OD tone is the dirty channel of my amp with an assortment "kick in the pants" pedals (Orange Squeezer>AMZ Mosfet Boost, or Rangmaster usually). I plan on some sort of cascaded JFET build soon though.

Kerry M

[Alex C]

I was thinking, could you take the preamp of, say a marshall plexi, replace all the 12ax7's with JFET, and change the drain resistor to get 4.5v at the Fet drain. Do u think this would work, seeing as FETs work in a very similar way to tubes?

I believe Runoffgroove's Thunderchief does this.

http://runoffgroove.com/thunderchief.html


Alex

[Alpha579]

I think the Thundercheif recreates the sound, but i mean using almost an exact replica of the preamp, but replace 12ax7's with JFets.

[brett]

I'm no expert, but it seems to me that the sound of a hard-driven tube amp is often created by the power (not the preamp) tubes running out of juice.  So JFETs, CMOS, BJTs, whatever can be use in the pre-amp and you can still get that great overdriven tube sound.  

(My tube amp has a solid-state tone section, then a 12AX7 then 2 6CA7s(=El34)).  Overloading the input sounds bad, but turning up the master sounds awesome.  Can't speak for Marshals but it mighn't be the 12AX7(s) that are producing the cream).

cheers

[PaulC]

You could start off using pretty much an exact circuit from a tube amp (with the different drain/source resistors to make the fet work), but then you really do need to dink with the wave shapes and signal levels to get it close with FETs.

There's a few pedals on the market that are fet clones of circuits, but if you could scope things out you'd see the waves are pretty different stage to stage.  Some tube stages will be set to  sym clip while others will be set up to have a more  drastic asym clipping.  Looking at the cathodes of the tubes can sort of tell you what each stage is doing.  In a Soldano you've got a few sym clipping stages (for the most part) with a massive asym clipping from the stage with the 39k cathode resistor.   making the source resistors values the same as the tube stages, and then messing with the drain value wouldn't be the best way to do this.  You really need to scope it out and look at the waves of each stage to get them close.

Then there's the distortion "timing" from stage to stage.  The resistive dividers between the stages of the tube pre are set to allow a stage to distort a certian amount before/after another stage.  Headroom issues are very different from tubes and fets, so you might find that 470k/470k divider in a tube circuit will have a mild overdrive while slaming your fets much harder.  You may need to increase the divider ratio to drop the signal level into the next stages so they distortion with each other at the right ratios.  

Also there's something called Miller effect where the tube interacts with the circuit rolling off hi freqs.  Going back to the SLO you'll see a 470k grid resistor.  This reduces bias shift in the stage, and also rolls of the hi end a boat load due to the internal cap that the tube sort of has.  To get this same effect with a fet you'd need to hang something like a 100p to ground at the gate.

Other things would be in pwr supply sag.  The preamp voltages in a tube amp can change a good bit when the pwr amp is drawing alot of current.  Some kind of signal dependent voltage reduction would be cool to get some of this pwr supply compression going.

Last would be in the tone stack.  Copying a preamp tone stack is cool going into a pretty flat pwr amp.  Running them into another preamp  can give poor results because you're now stack EQ curves that are close to each other.  To me into things like a fender you always get a scooped out death metal tone.  One way to help alot is to add something like a Baxandell tone stack after the standard preamp stack.  That way the Marshall stack can put the "marshall" EQ curve onto the signal, and then you can use the Bax to tune it to the amp.


Later, PaulC

[bwanasonic]

I think the Thundercheif recreates the sound, but i mean using almost an exact replica of the preamp, but replace 12ax7's with JFets.

Unless I'm missing something, that's exactly what the TC is.

Kerry M

[Doug H]

I think the Thundercheif recreates the sound, but i mean using almost an exact replica of the preamp, but replace 12ax7's with JFets.

Unless I'm missing something, that's exactly what the TC is.

Kerry M

That's what the Meteor is too.  Both of these designs do a lo-fi emulation of the preamp and output stage.

Doug

[puretube]

tubes...