Obsidian fet version

[zeta55]

I'm looking in on the version with 2N7000. Can the fets be substituited with some other fets :?

[petemoore]

Read GEO and find about biasing Jfets. Look at some Jfet biasing setups.
 Then look at the Obsidian schematic.
 If I were working with this I'd use a breadboard for 1rst transistor, get that going good, build it on a perf so it could be modded EZ if necessary, then work that into the rest of the circuit on the breadboard.
  There is a distant derivation of FF in the Obsidian IIRC.
  I never did get a Jfet to Bias in Q1 [or was it Q2..] of a FF..others have, ROG, and Tim Escebedo show Jfets in a FF setting.
 BTW The Transistor Obsidian Really Roxx.

[B Tremblay]

First off, the 2N7000 is a MOSFET, not a J-FET.

I've seen reference to a BS170 being used in place of a 2N7000.

[WGTP]

There are several versions of the Obsidian.  One is the FF type which used 2N5089's and the other is like a 3 gain/booster stages in a row that used 2N7000's or BS250's.  For the 3 in a row, it would be very similiar to use one of the Jfet circuits at ROG.  For the FF version, I don't know.  

Just a suggestion, but make a Vulcan and you won't be sorry.  

[zeta55]

There are several versions of the Obsidian.  One is the FF type which used 2N5089's and the other is like a 3 gain/booster stages in a row that used 2N7000's or BS250's.  For the 3 in a row, it would be very similiar to use one of the Jfet circuits at ROG.  For the FF version, I don't know.  

Just a suggestion, but make a Vulcan and you won't be sorry.  

I had a look at the Jfet cuircuits at ROG. I just might give it a shot with some J201 I've got resting in plastic bag.
So the Vulcan is that good, I guess I better build that one too. :twisted:

[RDV]

If that's the Revision D, it sounds really good and crunchy, but hisses like a stinkin' snake.

RDV

[zeta55]

If that's the Revision D, it sounds really good and crunchy, but hisses like a stinkin' snake.

RDV

I really don't know wich version it is. It says last revision 10.10.00 on the schematic and it has red leds across the gate and source of the fets.
I just got to try it.

[WGTP]

There is a newer version that uses P channel BS250's which Joe said were inherently quieter than the N channel 2N7000's (I think due to the manufacturing process or something???).  It did not have the LED's because he felt the BS250's were less prone to blowing.  I liked it and didn't notice anymore noise than other high gain stuff.

The Vulcan  has a nice squishy sound, but you may need to reduce some of the by-pass cap's if your using humbuckers.  Based on Joe's suggestion, I built a Jfet version that sounds pretty cool, but the 2N5089 is very close.  

[petemoore]

I think the thing is with the Obsidian is that Q2 is feedback looped and biased by Q3...anyway it's a complex wicket to me compared to a regular' linear design where you can tweek resistances and setup bias differently...
 See I like the subject, don't really know what the heck I'm typing about, but typing anyway...if someone WAnts to straighten me out...feel free...if not...that's cool too !!1
 Interesting concept I maybe partly understand, you understand...

[zeta55]

I did fire up a version of this circuit with J201:s today.

Sound?

Well not what I expected..I thought it would bee more metal type of sound with the gain knob way up.
I get more of a very overdriven valve sound type.  :twisted:

I now got do do something about the sharp edges that colours the sound, and maybe rebuild the tone control.  :?