May Queen Issues

[guitonit]

Hey Guys,

I just put together the Runoff Groove May Queen, and all I am getting is splatt!!  Here are the measurements I am getting.......

Q1 2N5088
    B- .6v
    C- 6.89v
    E- 0

Q2 2N3904
    B- .65v
    C- 1.7v
    E- 0

Q3 J201
    B- 1.7v
    C- 2.43v
    E- 1.69v

Any thoughts??

Thanks
Scott A.

[B Tremblay]

Did you try to bias the drain of the FET to 5.5v?

[guitonit]

Pardon my ignorance, I'm still pretty new to all this.  How would I go about doing that?

SA

[Chris R]

adjust the 10k trim pot that is above the jfet on the schem.. untill it measures 5.5 volts between the trim pot and the jfet.

Chris

[B Tremblay]

The voltage reading should be taken with one DMM lead at the drain of the FET (the pin connected to the trimpot) and the other lead at ground.  As Chris said, then adjust the trimpot until your DMM measures 5.5v.

[guitonit]

I'll give it a shot.

SA

[guitonit]

Thanks guys for answering my newbie questions.  Adjusted the bias to 5.5V and now I have muddy sounding splatt

Any thoughts?

SA

[B Tremblay]

Are you sure of the transistors' orientation?  Did you use the PCB layout?

If you used the PCB (even just as a guide) for the Q3 orientation, the FET pinout is incorrect.  All the runoffgroove.com projects that use the J201 are developed with the DSG pinout (when viewing the flat side, pin towards floor).

If you did use the PCB layout, then you'll need to flip the FET and bend the source and gate pins so they are in each other's place.

I'm sorry for the error, I'll contact Will about correcting it.

[guitonit]

Yes I did use the PCB layout.  I will try flipping the FET

SA

[guitonit]

Ahhhh Success!!  Thanks for the info.  I am running into a noise issue though.  Seems very noisy when the guitar is turned down.

SA

[petemoore]

Jfets are tricky, and most probably different than BJT
 Referencing the particular Jfets pinout to the perfboard layout or schematic is recommended, since different Jfet types have different pinouts. I've had to twist two legs of jfets to connect them to the right socket pins.
 Getting different voltage readings will change the way a circuit works, some of the readings posted were either off enough to suspect a miswire, or misorientation...it's always a good idea to take a look at the pin voltages after fixing or changing anything that would affect bias, that they are within operating parameters.

[guitonit]

Pete,
here are the readings now.  Your thoughts would be appreciated.

Q1  B- .73V
     C- 6.85V
     E- .03V

Q2- B- .65V
     C- 1.77V
     E- 0

Q3- B- 1.77V
     C- 5.47V
     E- 1.72V

Scott A

Almost forgot, I swapped the source and the gate pins as suggested

[Impaler]

I'll get right on the fix guys, expect it by tomorrow mornin  :wink:

[guitonit]

Just wanted to say thanks again for everyone's help.  Good to know I can ask a "dumb"question and get the correct answer.

Scott A.

[Impaler]

Sent the fix off to Brian at runoffgroove a little bit ago. It's good to know that I can make a booboo and not be crucified for it =P

[petemoore]

These pinouts are very easy to miswire or misorientate
 When discussing voltages on Fet's it's best to stick to the technical terms for it's leads ... on Jfets and Mosfets the leads are source gate and drain...
 BJT              FET
Emitter ...     Source
 Base            Gate
Collector       Drain
 Also, please include battery voltage reading with Qpin voltages.
 OK heres my thoughts...Im gettig my head out there on this one...I assume someone will stop me if I'm messing you up:
  Q1 looks like it wont have much swing with the collector sittin high, the base emitter relationship looks like it could squeak by
  Q2 The Collector is sitting very low on this one, also there's just less than .7 volts between the Base/Emitter..not good
  The third one, being a JFet, should have it's source sitting above its gate...[I'll have to go look up the amount]
  There have been times when I can't check the pinouts enough, especially with Jfets. Take each pin, one at a time, reference the pinout, put drain on drain connection [reference the schematic, perfboard layout, or PCB layout youre using} use the schematic And layout for added debuggin fun etc.
  Anyway I would go over the wirings/pinouts, double check everything, resistor color codes, Check for grounds where grounds are should be, and shouldn't be,
 Ill just poke that DMM around in there [pick a point for the black probe] and put the red probe in different place [mostly near the black probes connection but elsewhere whynot] checking that I'm not getting a higher resistance across any in circuit resistor values [a lower reading could mean the current is flowing around the other way throughthe circuit]...follow the paths and 'considerate'...maybe use a magnifying glass and a close in bright light.

[B Tremblay]

A correct PCB layout for the May Queen is now available:  http://runoffgroove.com/mayqueen.html