Mini Boost debug

[jlullo]

Hey guys,
I perfed up a Mini Boost (roughly based on MarkM's Layout) and i'm getting no sound when the effect is engaged until i turn the pot all the way up... then, i'm getting a faint "farty" transistor sound.  I'm using two MPF102's

Q1
1 - 8.95
2 - 8.95
3 - 8.95

Q2
1 - 0
2 - 2.45
3 - 8.95

since i'm getting almost full voltage all the way through Q1, does that mean that it's blown?

thanks!

jonathan

[jlullo]

does anyone have the correct voltages?  i'm assuming Q1 is bad

[PerroGrande]

Can you post a link to the schematic + layout?

Obviously, the *voltages* on q1 are bad.  You *might* have a bad tranny (but you might not).  Always start by verifying physical stuff (solder bridges, cold solder joints, etc).

[amz-fx]

Most common problem is transistor orientation. Here is the pin config for most of the 2Nxxxx jfets.



Double-check your transistors. 

regards, Jack

[jlullo]

John,
I based my layout on this layout by markm:

i think it's an older version than the one he has posted now in his album, but it worked well for perf.  I've checked it out a lot, and i have no solder bridges or cold joints that I can find, it's bypassing well, so i'm figuring it must be a tranny issue.

Jack,
thank you very much!  by 1,2,3 i meant D,S,G... that would be the correct orientation for MPF102's as well, wouldn't it?

thanks guys, i appreciate it!

[dxm1]

by 1,2,3 i meant D,S,G... that would be the correct orientation for MPF102's as well, wouldn't it?

That would depend on the manufacturer, but Fairchild, On, and NTE all say DSG for the MPF102.

[benfox]

Maybe it's a reverse capacitor.
Verify again.
The transistor orientation use to be a problem.
Try to replace q1 with q2 and check the voltage again to see if it's the tranny or your soldering...
*good luck debugging !

[amz-fx]

I have seen MPF102 jfets that were D-G-S but not in a long time.  They were from Radio Shack.

To test your jfets, take your meter, set to read ohms,  and put the plus probe on the source, i.e. the center lead (2). Put the negative probe on the drain (1).  You should read a small resistance.  I tested a J113 and it was about 50 ohms but an MPF102 will be higher.   The drain to source resistance should be from 50 to a few hundred ohms with no connection on the gate. 

If the resistance is very high, try reading the ohms from 1 to 3 (put the plus lead on 3).  If the 1-to-3 resistance is low, then it may be a D-G-S pinout.

Be careful...  if you screw around with the jfet too much, you may store a charge on the g-s or g-d internal capacitances that can give a false reading. It won't hurt the jfet; just discharge with a piece of wire and try again.

regards, Jack

[jlullo]

thank you for the help guys!

Jack,
funny enough, one of the trannys is from radio shack (i was short one), and the packaging looked really old.... so i'll give that a shot!

thank you again!

[jlullo]

alright boys, i got a few spare fets (2n5952) and threw them in, and of course no sound.  I'm assuming it's a different pinout then j201's, and can't find the pinout on the datasheets that i downloaded.  anyone know this?

thanks!

edit:  nevermind.... found out they go in reverse compared to j201.  thanks guys!