DIYstompboxes.com

DIY Stompboxes => Building your own stompbox => Topic started by: aron on May 07, 2008, 05:39:18 PM

Title: JFET Vulcan
Post by: aron on May 07, 2008, 05:39:18 PM
Since I have the mic out....

JFET Vulcan

http://diystompboxes.com/pedals/sounds/JFETVulcan5-7-08.mp3

JFET Vulcan with FX

http://diystompboxes.com/pedals/sounds/JFETVulcan5-7-08FX.mp3

Schematic:

http://diystompboxes.com/analogalchemy/
Title: Re: JFET Vulcan
Post by: WGTP on May 08, 2008, 10:05:40 AM
Do you like the Jfet or the regular Vulcan the best?  On the bread board I mix them.   We don't want Joe's cool stuff to get lost in all the distortions around hear.  :icon_cool:
Title: Re: JFET Vulcan
Post by: aron on May 08, 2008, 01:26:44 PM
I think I like the JFET one. It's one of the pedals I still have boxed. Yes, Joe's stuff is incredible.
Title: Re: JFET Vulcan
Post by: Marcos - Munky on May 08, 2008, 02:38:40 PM
Aron, do you have the layout you used?
Title: Re: JFET Vulcan
Post by: aron on May 08, 2008, 04:01:39 PM
I just wired by hand on perfboard like I always do.
Title: Re: JFET Vulcan
Post by: John Blund on May 08, 2008, 05:04:40 PM
Quite excellent! but I dont know if it's the guitar playing or the Vulcan that makes it sound good 8)
btw does the vulcan have any clean range?
Title: Re: JFET Vulcan
Post by: raulgrell on May 08, 2008, 06:25:51 PM
I find myself doing a lot of mixing of designs, mostly using different kinds of transistors within each circuit.

I have found 2 mods to Joe's designs that really made the sound for me:

For the vulcan, put a BJT in the middle stage, with the gain slightly decreased in the first stage and increased quite a bit in the second... Kinda like a hybrid of the JFET and the BJT design...

And the Blackfire, put a TransFET booster in the place of the second stage. I haven't had the opportunity to experiment with MOSFETs yet, but I think it could sound pretty damn good in the output stage of a blackfire.
Title: Re: JFET Vulcan
Post by: MartyMart on May 09, 2008, 05:10:12 AM
Great playing too aron !!
That's STILL one of my most treasured pedals :-)
A bit of an "unsung hero"  IMO 

Marty.
Title: Re: JFET Vulcan
Post by: cab42 on May 09, 2008, 09:02:05 AM
I'm very fond of mine as well.

I experimented with a few different tone controls and finally added a BMP tone control.

Regarding layouts. I used Martys vero layout for the BJT-version. Twisting the pins on the jfets and changing a few components made it work for the jfet version.

However, I remember seeing a more compact vero layout somewhere.

Great sound and great playing, Aron!

Regards

Carsten


Title: Re: JFET Vulcan
Post by: aron on May 09, 2008, 01:47:10 PM
The Vulcan does have clean range, although I use it for heavier sounds. It's a pretty darn good pedal. Mine fits easily in a 1590BB box. Raul, good ideas on mixing the two pedals!
Title: Re: JFET Vulcan
Post by: suprleed on May 09, 2008, 02:11:52 PM
Holy Crap! that sounded good!!! :o  What kind of amp are you running that into?

I've been looking for a good Vulcan sound clip for months.  Thx.  You have some toneful fingers my friend.  Love how it went from bluesy in the beginning to full on super lead in the middle to heavy chug at the end.  Nice, very nice.

[Me bowing in homage aka waynes world "we're not worthy."]  :)
Title: Re: JFET Vulcan
Post by: aron on May 09, 2008, 02:17:21 PM
This was my Traynor YRM-1. The cabinet is a 2x12 sealed back with greenbacks. I just close mic'ed it. I'm still looking for more clarity. I need to experiment more.
Title: Re: JFET Vulcan
Post by: aron on May 09, 2008, 02:20:37 PM
oh forgot to say, as with the BSIAB clip, no pedal changes. All the sounds are volume knob and pickup switch changes.
Title: Re: JFET Vulcan
Post by: jrc4558 on May 09, 2008, 03:02:02 PM
What will tighten the sound up and "clarify it" would be a 0.002 cap instead of 0.1 before the 1M gain control. In general - smaller caps throughout.
Title: Re: JFET Vulcan
Post by: aron on May 09, 2008, 04:11:07 PM
yes. When I was using it, I was playing through my champ. Now I should try more mods.
Title: Re: JFET Vulcan
Post by: gaussmarkov on June 11, 2008, 11:16:01 AM
fwiw, i made a project for this one.  i had a layout for the bjt version from years ago, so i updated it and posted it on gaussmarkov.net (http://gaussmarkov.net/wordpress/circuits/davissons-jfet-vulcan/).  here's an Eagle3D render of the build:

(http://i41.photobucket.com/albums/e270/gaussmarkov/Forum%20Posts/jvulcan-pov.jpg)

it isn't verified, but i am pretty sure it's all good.  if you do verify it, please post.
Title: Re: JFET Vulcan
Post by: Renegadrian on November 29, 2008, 10:33:23 AM
Well, some of you already know that I'm a metalhead and a "highgainer", so I started to buid this one back in may...
Then it was put on hold...I put the remaining components and wired with flying leads and no pots, just to try it...
Man, what a distortion!!! This will surely deserve a good box...
Title: Re: JFET Vulcan
Post by: corcia on December 08, 2011, 07:27:32 PM
I'm currently building a JFET Vulcan, could someone describe the procedure to bias the JFETs?
thanks a lot!!!!!!!!
Title: Re: JFET Vulcan
Post by: WGTP on December 08, 2011, 08:37:05 PM
Do you have a VOM? ;)
Title: Re: JFET Vulcan
Post by: corcia on December 09, 2011, 02:34:42 AM
Do you have a VOM? ;)

if you mean a Volt/Ohm Meter  :icon_redface:, yes i do have one.
Title: Re: JFET Vulcan
Post by: petemoore on December 09, 2011, 06:41:12 AM
 I"m no expert on Vulcan tech, but Jfets are not the same as other Jfets, even J201's.
   ...the Fetzer Valve article [and related Jfet measuring circuit] and GEO have good info on biasing Jfets.
   
Title: Re: JFET Vulcan
Post by: corcia on December 09, 2011, 08:30:40 AM
my question might be sillier than it seems....  ???
i'm starting from Gaussmarkov layout (and website), in his description, Gaussmarkov says "Choose values for the three 100K resistors that give you JFET drain voltages of 4.5V to 5V", my question is: where do I have to measure the drain voltage of each JFET? I don't know in which part of the circuit place the VOM probe to measure said voltage

PS: i apologize for my ignorance!!!!!!
Title: Re: JFET Vulcan
Post by: Suicufnoc on December 09, 2011, 08:34:15 AM
i'm starting from Gaussmarkov layout (and website), in his description, Gaussmarkov says "Choose values for the three 100K resistors that give you JFET drain voltages of 4.5V to 5V", my question is: where do I have to measure the drain voltage of each JFET? I don't know in which part of the circuit place the VOM probe to measure said voltage

Measure from ground to the drain of each JFET(the pin connected to the 100k resistor.)
Title: Re: JFET Vulcan
Post by: corcia on December 09, 2011, 09:31:07 AM
i'm starting from Gaussmarkov layout (and website), in his description, Gaussmarkov says "Choose values for the three 100K resistors that give you JFET drain voltages of 4.5V to 5V", my question is: where do I have to measure the drain voltage of each JFET? I don't know in which part of the circuit place the VOM probe to measure said voltage

Measure from ground to the drain of each JFET(the pin connected to the 100k resistor.)

ok, so I was right...my question was sillier than it seemed!!!

thanks a lot!!!
Title: Re: JFET Vulcan
Post by: WGTP on December 11, 2011, 01:04:36 PM
No, it's a good question.  Jfets are notoriously random.  ;)
Title: Re: JFET Vulcan
Post by: DDD on December 30, 2011, 09:44:09 AM
What will tighten the sound up and "clarify it" would be a 0.002 cap instead of 0.1 before the 1M gain control. In general - smaller caps throughout.
Well, 2.2 nF cap instead of the very first 0.1 uF cap would do the work a little bit better.