Davisson’s JFET Vulcan

by gaussmarkov

Eagle3D POV-Ray Rendering of JFET Vulcan

I happened to notice a thread on diystompboxes.com started by Aron about Joe Davisson’s JFET Vulcan. You can listen to some mp3 clips that Aron posted in that thread. I had a layout for the BJT Vulcan from several years back so I decided to update it and convert it to the JFET version. This layout has not been verified yet, but I am confident that it is correct. If you do verify it, please let me know. You should be able to fit it into a Hammond 1590B enclosure.

Note that no power supply filter is included. Depending on your power source, you may want to add one. And the output comes from the middle lug of the LEVEL pot.

You may want to breadboard your build first in order to get the bias right for the JFETs. Choose values for the three 100K resistors that give you JFET drain voltages of 4.5V to 5V. Also, check out Joe’s notes about component values for higher gain.


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14 Responses to “Davisson’s JFET Vulcan”

  1. Kirby said:

    is that a render? if so, what did you use?

    Posted 12.06.2008 at 10:16 am

  2. gaussmarkov said:

    POV-Ray and Eagle3D. ūüėé

    Posted 12.06.2008 at 11:11 am

  3. bobby said:

    Posted 27.08.2008 at 5:35 am

  4. gaussmarkov said:

    nice!

    Posted 27.08.2008 at 7:35 am

  5. culturejam said:

    Verified!

    It sounds awesome. I forgot to check the 100k resistor values and just soldered everything. The result was good, but a little mis-biased sounding. So then I swapped out JFETs, and the closest I could get to “proper” bias is 4.7v, 4.2v, and 3.9v, respectively. Oh man, it sounds so damn good. Like a hot-rodded Muff crossed with a SLO.

    Great layout. Thanks!

    Posted 22.09.2008 at 9:03 pm

  6. Jim’s Personal Blog » Blog Archive » JFET Vulcan said:

    […] I did a breadboard of the ‘JFET Vulcan‘ after reading about it on the Gaussmarkov site. Here lately I’ve been just whipping […]

    Posted 09.10.2008 at 2:58 pm

  7. Jim said:

    That’s so weird that it automatically posted a weird link to my blog that I just did about this circuit…
    Anyways; go here if you wanna check it out.
    http://bandslink.com/wordpress/?p=33

    Love your site man!

    Posted 09.10.2008 at 3:00 pm

  8. culturejam said:

    Jim: I built the Vulcan from the PCB layout here, and it sounds much heavier than the sound clip that you posted on your blog. Mine is in Big Muff territory, but not as compressed.

    I went with 100k resistors, but then I swapped out JFETs till I got some that would bias properly.

    Posted 31.10.2008 at 10:33 am

  9. drushton2002 said:

    hey man i can’t wait to try this. are there any tweaks or switches to anything like that? different caps for boosts tone changes etc. i love switches LOL. cool site man thanks for having this stuff

    Posted 08.11.2008 at 3:28 pm

  10. Flyingz said:

    I rebiased, added BMP tone, removed R17, and changed R16 to 100K
    It has some fun in it but nothing special

    Posted 05.02.2009 at 7:06 pm

  11. Leo said:

    Hi Gauss.
    The circuit is excellent, the same the pcb, but has no tone control…What tone stack recommend?
    Thanx

    Posted 07.04.2010 at 2:35 pm

  12. sgRED said:

    Can anyone tell me, can I try to build it on a VeroBoard?! Would it be right, considering the noise and the shape of the leads on Gauss’s PCB which is great!? Here in Bosnia, it is hard to build pedals because it is hard to order chassis and much of the other stuff that is needed for the build. I have J201’s, but everything else is a bit harder to find…. Thanx anyone for an answer!

    Posted 13.03.2011 at 8:20 am

  13. Octavio said:

    Hola Gauss. Hace rato vengo siguiendo todos tus proyectos, y ya he hecho algunos. Me gustan muchos los dise√Īos de PCBs, est√°n muy bien ordenados y prolijos.
    Te cuento que recientemente arm√© este pedal… Reci√©n lo acabo de probar, y suena demasiado, tiene much√≠sima ganancia, yo dir√≠a que suena como Heavy Metal… cosa que no me gust√≥ mucho. Yo hab√≠a o√≠do los clips mp3 de ejemplo y me hab√≠a encantado como sonaba eso, pero esto nada que ver.

    Es una buena distorsión, pero es demasiado pesada (muy Heavy).

    Voy a ver de qué manera puedo modificar valores de componentes para aproximar el sonido a esto:
    http://diystompboxes.com/pedals/sounds/JFETVulcan5-7-08.mp3

    Posted 29.11.2011 at 12:32 pm

  14. jvc car audio said:

    Hi there, i read your blog from time to time and i own a similar one and i was just curious if you get a lot of spam comments? If so how do you reduce it, any plugin or anything you can recommend? I get so much lately it’s driving me insane so any help is very much appreciated.

    Posted 02.12.2012 at 2:04 pm