JFET Vulcan with Tone (Please Help)

[blindsjc]

Hi friends,
Just finished a JFET vulcan with Obsidian tone control
but I dont get any sound from it, I verified it a milion times
but dont find any error. The layout is based on gringo PCB
with tone and volume added at end. Please help to make
it work. The layout is this:

http://server6.pictiger.com/img/320187/picture-hosting/vulcan-jfet-.gif

Thanks

[soulsonic]

Where can you find the schematic for the Vulcan?

[blindsjc]

The schamtics are here:

http://diystompboxes.com/analogalchemy/sch/jfetvulcan.html

I hope you find some big error in my pcb. Thanks a lot.

Thanks

[blindsjc]

Gringo layouts for Joe Davisson's circuits
are here, just for a visual compare:

http://www.geocities.com/diygescorp/joedavisson.zip

Thanks again

[soulsonic]

Thanks! Hmm... that's an interesting circuit, I can see why it's a popular build. I wonder what the deal is with the diodes in series with the gates of the JFETs?
I'll take a look and compare everything and see if you're board design is off - but be patient, I'm kinda busy right now, so someone may beat me to it.

[blindsjc]

I think that these diodes are there
to control the fets saturation. So,
thanks a lot. If someone else have
any idea please post too.

Thanks

[PerroGrande]

I replied earlier, but it was lost as a result of the forum change/upgrade.

One of your resistors (lower left hand corner) has a connection to ground on one side, but to nothing on the other.  It should connect to the cathode of the diode.

[blindsjc]

Thanks friend,
But the connections for this resistor is ok at the pcb, I think I lost it
creating the image file to put in the web, so the real pcb I'm using
have this resistor correct connected, like this image:

http://server7.pictiger.com/img/335856/picture-hosting/vulcan-fet-.gif

I got some sound from circuit using a bypass over the 100pF cap,
but is a strange sound, appears to be a normal distortion but
dont have any sustain, it starts and ends fast. I used other J201s
to test, used inverted position too, but the result is the same.

Thanks

[blindsjc]

Somebody built a JFET Vulcan using gringo layout?
There is some secret on it or something else?

Please...

[petemoore]

  The 'gate' diodes limit signal input on one side of the waveform, 'compression occurs when input signal voltage exceeds a certain amount.
  Here's some things to try, see Debugging page also, replace the asterisk'd texts

• with the 'pertinent information about your circuit, the relevant information is much easier to read when  it is in one concisely written post//I've prepared this sample draft:
    Name and show link to circuit schematic.
    *Garfunkels accoustic pre-amp
    If you're using a layout or PCB post a link to that too.
    *GAPP layout
     Is there a connection between circuit power supply V+ and Gnd. under any of all power supply 'conditions' ie...is there shorting under and 'normal' switching conditions of input jack or DC jack or any other time?
    *YES   /    NO  [enter comments
    Measure battery voltage.
    *X.X2VDC
    Measure battery voltage with circuit loading
    *X.21VDC
  If using a power supply, what does it say on it about voltage rating?
    *Xvolt
    Also name power supply type
    *AC  or DC output
    test the voltage of the power supply.
    *9.2VDC
    Test votlage of power supply with circuit connected
    * .22vdc
    Is the circuit npn-negative ground?
    *Transistor type [npn/pnp...jfet, mosfet, Ge, etc.
    *Circuit polarity [neg gnd. or pos. ground?
    *Opamp type [Dual, single, OTA, CMOS...other
    connect DMM to ground, and test for continuity at every point in the schematic with a ground symbol, from the most 'distant' [test points should be beyond all connections and solder joints].
    Test the cables that are plugged if they can be plugged in, at the plug sleeves which connect to guitar and amp
    Is there continuity at all 'distant circuit ground points
    Stage 2
    Connect power supply, if there is a large current draw [ie voltage drops by 10% or more, disconnect power and post that result].
    Is there a >10% voltage drop in battery when circuit is connected?
    *Yes  /  No
    What voltages are measured [using ground as reference voltage =O.0V], using DMM at all active component pins?
    *Dual opamp
  *1  4.5v
  *2  4.5v
  *3  4,5v
  *4  0.0v
  *5  4.5v
  *6  4.5v
  *7  4.5v
  *8  9v
  -----
    *Single opamp
  *1  NC
  *2  4.5v
  *3  4.5v
  *4  0.0v
  *5  NC
  *6  4.5v
  *7  9v
  *8  NC
  -----
  *Transistor type
    *NPN
    *PNP
    *Jfet/mosfet/BJT/Ge?
    *Transistor part #
    *Data sheet pinout information
    Pin Voltage
    *D 9v         
    *G 2.2V
    *S  .21V
    Or substitue 'E/B/C if using bipolar transitor
    List any pertinent comments and questions.
    Stage 3
  Audio probe, and list results and comments.
    Test that all stages are 'separated' by DC blocking capacitors,
    Can you physically see that a capacitor is properly wired to the input and output of each active component stage? ie signal path must go through the cap to enter or exit the active stage.
    The circuit debugging may have limited results if the answers with * are not known or posted.
    BTW the opamp pins for most distorters [gain stages] are more than optimal, bias is 'centered' at 1/2 the power supply, except for the power supply pins [the 9v and 0.0v ones.
  
   

[blindsjc]

Thanks a lot Petemore, I will keep your post saved for future,
great work. I was so angry with the problem that forgot to say
details about the build, sorry. Thanks for all other frinds too.

Just found the problem: Gringo layout is wrong at R10 and
R15, his PDF file it says 1K for these resistors but they are 33K.
The effects is working now and the tone control from obsidian
appears to be a good choice.

I will send a message to Gringo, his work is great too.

Thanks