MOSFET Distortion

[SlashLP97]

Has anyone ever done a high gain pedal with MOSFETs (not JFETs)?  I haven't seen much stuff out there that uses actual MOSFETs and I was thinking of trying to breadboard something up, I have a spice simulation that looks like some IRF530s could give some interesting results, any advice?

[dschwartz]

pfff lotsa them available..just do a  search.

[SlashLP97]

Everything I have seen labeled "MOSFET" is either JFET or depletion mode MOSFET, which really does not behave like a normal MOSFET, much more like a JFET

[cpm]

Everything I have seen labeled "MOSFET" is either JFET or depletion mode MOSFET, which really does not behave like a normal MOSFET, much more like a JFET

all the circuits i know with mosfet are to be used with the common 2n7000, bs170, etc, which are enhanced-mode MOSFETs

[SlashLP97]

I just looked through the entire schematics section and failed to see any designs, save for the poorly drawn "Mosfet overdrive" which looks minimalistic at best and the idea of putting a MOSFET into a Lava Rim, which from the schematic given and the concept of how to substitute would not work.  MOSFETs need to have a very high positive Gate-Drain bias (Very negative Source-Gate for P-Channel MOSFETs) to operate in a mode that is a full signal amplifier, aka one that does not chop off half or more of the signal because it is in the wrong operation region.  Anyone have any specific designs that use MOSFETs?

[aron]

High gain, MOSFETS??

Did you say Hi-Gain? My friend Joe Davisson is the king of hi-gain and MOSFETS and JFETS.

When I want hi-gain, I go to Joe :-)

http://www.diystompboxes.com/analogalchemy/sch/obsidian.html

[MikeH]

Zvex Box 'O Rock

[caspercody]

Isn't Soulsonics Freya a high gain Mosfet pedal? It is a pedal version of the Slo amp.

[kungpow79]

OCD uses 2n7000s, duh, I just made one 

[aron]

I really think that you guys don't know how good the Davisson stuff is. If you haven't built any of them, you cannot imagine how good it is.

[Renegadrian]

I built the VULCAN (jfet version) and it frekin' ROCKS!!!  I'd say go for the VULCAN (MOSFET version).

[mac]

I guess that for a single stage you could use a mosfet because it has a little more internal gain, but in a two or three cascaded circuit you can use fets.
I do not like mosfets because they tend to die in my hands.

mac

[WGTP]

http://www.aronnelson.com/gallery/main.php/v/WGTP/Mosfet_Incenerator.jpg.html?g2_imageViewsIndex=1

I have trouble getting Jfets to work and I like the "BLAZING" air ripping sound the Obsidian/BOR gets.

These are the type Mosfet stages typically used around here.  There is also the SHO, not shown.  Unlike Jfets, Op amps, etc., there are relatively few Mosfets that have found favor.  The 2N7000 and BS170 N Channel and the P channel BS250.  When I inquired about others being used, the answer was these are the ones that work, IIRC.  And the work very well as Aron pointed out.  Just be very careful about static electricity.  It's better to work with them in the summer.     I can't explain the depletion/enhanced mode business, if that is the concern.  

[bumblebee]

Zvex box of metal (5 super hard ons in series) is a high gain mosfet distortion.

[Gus]

FWIW  The MOSFET overdrive is something a little different.  Look at the drain and source resistor values.  The devices are power MOSFETs. 

Enhancement mod mosfets will start to turn on at a few volts and often have a max voltage between the gate and the drain and source.

You need to keep in mind the gate capacitance for things like miller and the low pass that can be formed when the gate is "feed" from higher resistance sources.

Type "mosfet amplifier" into google

http://my.ece.ucsb.edu/bobsclass/2C/Labs/Lab%202x%20MOS/Lab%202%20-%202C%202007.pdf

[shadowmaster]

Mos Rectifier by Ubaid88

http://www.diystompboxes.com/smfforum/index.php?topic=81411.0