Mosfets

[bulldogguitars]

I dont know if this has been brought up before, but was wondering, what are some good mosfets to use. Im wanting to try something different other than JFETS (love the sound of them). Im familiar with the 2n7000 and bs170, never used them though, but wanted other opinions. 

[bulldogguitars]

I guess Im looking for tonal characteristics. What do others think as far as how close to a tube feel do you get from them.

[Auke Haarsma]

I'd suggest a search on this topic. In my short time around here I've seen similar questions pretty often.

[petemoore]

  I've tried, I'm trying 2n7000's, someone says they may sound "hard', but of course..this one I biased thanks to all who help mosfets get that way..sounds great, or I hope it still does, it just got boxed.
  BS170..'famous' mosfet I'm about to try.
  I have an IRF 510 ..I think it is, a device I got from RS, it's a big thing with heat sink on it.

[markm]

I guess Im looking for tonal characteristics. What do others think as far as how close to a tube feel do you get from them.

One of the best things you could do is check out Jack Orman's site, there's a link at the top of this page "AMZ" which will take you right to it.
Lots of good info concerning MosFets there.
When you get done, head over to R.G.'s page GEOFEX link at the top of this page, there's a wealth of info there too.
Both of these fine gentlemen have taught me quite a bit about Mosfets and other effect related stuff and they don't even know it!
Read some of the info on their pages, Very informative and inspires loads of ideas! 

[bulldogguitars]

Thanks for the info, Ill check out their sites Thanks

[MartyMart]

Look out for the February FXX competition, I'll be unveiling a mosfet based distortion
which is coming along nicely  !!

Try playing with 2 or 3 mosfet boosts, with gain controls and filtering to tailor the sound.....
Jack @ AMZ has some superb info

MM

[JHS]

2N7000 and BS170P cannot be exchanged in a circuit, every one of them needs a different circuit layout.
Both vary in terms of specs a lot and biasing them correct for a booster w/o a trimpot is quite painful.

Both have an internal protection diode, other Mosfets don't have one,  but an additional 9,1-12V zener diode protection is furthermore needed to protect those Mosfet against higher static charge.

Good sample circuits for both are on the www, for other Mosfets you need to calculate the R-values acc. to the specs. from the data sheets.

Plugging the cable from some Mosfet circuits without switching them into bypass mode or removing the power supply can destroy the Mosfet(s) even if there's a additional protection diode.

JHS

[bulldogguitars]

Marty may I ask what type of mosfets your using for your distortion.

[MartyMart]

Marty may I ask what type of mosfets your using for your distortion.

Either all BS170's  or all 2N7000's per circuit as the pinout/specs are different.
You have to watch for noise as you add stages, Joe Davissons mosfet obsidian is a
total noise monster unless you use BS250 "P" channel mosfets  !!!
This does mean wiring as a positive ground circuit, ala PNP Fuzz
BS170/2N7000 are both "n" channel.
Three stages or five stages keeps the phase relationship correct for lower noise performance.
( dont ask me for the " EE " explanation ! )

MM.

[Jay Doyle]

Three stages or five stages keeps the phase relationship correct for lower noise performance.

Could you explain how having the output out of phase with the input reduces noise?

[MartyMart]

Three stages or five stages keeps the phase relationship correct for lower noise performance.

Could you explain how having the output out of phase with the input reduces noise?

Sorry, that should not have had "for lower noise performance" tacked on the end
it was part of another unfinished sentance !!
Too much going on today Jay !

MM.

[WGTP]

I have asked the question before and the response was that the 2N7000/BS170/BS250 had the characterestics that worked best for our typical applications.  Sort of like the J201 Jfet.  That doesn't mean others won't work.  Check out Gus' circuit for one to experiment with.  http://www.diystompboxes.com/pedals/mosfet.gif 

Might as well use the BS250's for less noise.

IIRC Joe D. uses 3 stages because 2 or 4 squeled when wired to a by-pass switch.

I thru some different designs together as a study on how a Mosfet Stage can be made here:  http://aronnelson.com/gallery/WGTP/Mosfet_Incenerator?full=1

Also check GEOFEX for a nice article.   

With ZVEX' new Box of Rock and Seymour Duncan's new LAVA ?  Mosfets are on the rise.   

[Jay Doyle]

Three stages or five stages keeps the phase relationship correct for lower noise performance.

Could you explain how having the output out of phase with the input reduces noise?

Sorry, that should not have had "for lower noise performance" tacked on the end
it was part of another unfinished sentance !!
Too much going on today Jay !

MM.

Oh, I see.

Having an odd number of stages means that the output will be out of phase with the input. This will greatly reduce squeeling because the two signals don't add, they subtract from each other, so local feedback is near impossible.

HOWEVER, this is not something you want to do if you plan on mixing this in parallel with other FX output that ARE in phase with the signal. They will cancel out for the same reasons as above and the sound will become thin.

[petemoore]

  Got one biased !! Pretty simple really, the last one must have had some mistake on it...best to try new stuff separately 'till it's going.
 A very nice tasting ingredient, mixes well with other ingredients amazingly well too. Mosfet tone like Jfet tone except more Mosfet-ey sounding..lol.

[MartyMart]

I see, so it's best to go for "even" stages and keep the gain down for avoiding squeal
while preserving the phase ....

MM

[WGTP]

I guess it depends on what your going to be running it in parallel with.

When the Blackfire first came out, folks were having problems with the squel when wiring true by-pass.  Notice latter versions have a 3rd stage added.  Being lazy and finding a nice little jewelry box, I didn't include a switch and it worked just fine, except it sounds like all Hell is breaking loose, in a good way.   

[Jay Doyle]

I see, so it's best to go for "even" stages and keep the gain down for avoiding squeal
while preserving the phase ....

MM

Well, theorhetically at least. If I were building for sale, I would be sure to design everything in phase because you don't know how it will be used. But I never mix signals so it doesn't matter to my own stuff.

MOSFETs are fairly easy to bias if you use a trim as a voltage divider and string a 1M resistor from the wiper to the gate. Then set your drain/source resistors for the gain you want and adjust the trim until you get it to bias in the area you want it to be biased.

MOSFETs, JFETs, Tubes, to me are all pretty easy to bias because they are voltage controlled, BJTs are more difficult to me.

[The Tone God]

Mosfets are on the rise.   

They are also part of this month's FX-X. hint hint.

Andrew

[Gus]

The Tone of a mosfet might have more to do with the cap from gate to source and gate to drain.

Look up miller cap also do some simple RC calculations using the source R "feeding" the gate of the mosfet.  If you use a power mosfet you can use the cap to your advantage the lowpass can get down in the audio range that takes some of the edge away.

Math can be your friend.  Look up the specs of different mosfets often the gate to drain and gate to source cap is shown. sometimes 1,000s of pf.

Also check passlabs.com DIY section

sitting in schematics for years
http://www.diystompboxes.com/pedals/mosfet.gif