ampage Tube Amps / Music Electronics	For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

debugging sweet thing (jfets)

:

5/11/2000 12:07 PM

debugging sweet thing (jfets)

I etched a new board, the old board looked kind of "iffy" where I had to scratch out traces that shouldn't have been.
Swapped the components over and....nothing.
Looked it over thoroughly, looked fine.
However, the voltages were definitely not right. When the plug is in and the ground connection is made, nearly all of the points on q1-q4 have continuity with the meter. In addition, R3 is developing some heat. That can't be right....
Here's some voltages again, maybe someone can figure it out.
The voltages are listed in order of gate, source, drain.

Q1: 4.83v 4.73v 5.73v
Q2: 5.76v 5.70v 6.68v
Q3: 4.73v 4.64v 5.66v
Q4: 5.71v 5.66v 6.63v
Q5: 2.82v 3.29v 6.59v

Now, I buzzed around with the meter without the plug grounding out the battery. Everything seemed to be okay, no shorts anywhere, the source of Q1 did buzz to ground, and the source of Q3 buzzed to ground (only when drive pot was maxed) Which seems to make sense, there's only 100 ohms resistance to ground at those spots.

5/11/2000 1:13 PM

Minibooster voltage readings are typically as follows (powered by 9v):

Upper jfet: Drain 9v, gate 4.5v, source slightly over 4.5v

Lower jfet: drain 4.5v+, Gate 0v, source a few volts (depends on source resistor)

Your readings are way off so maybe the jfets are in wrong (there's no 9v anywhere)... drain-source-gate is the typical pin designation for many common jfets (looking at the flat side with the pins pointed down)

-JACK

5/11/2000 4:25 PM

Another thing, Ed. Don't mean to nitpick here, but perhaps I didn't explain it good enough the first time. You should buzz out the board -before- you install the components. Just simply check that pads that should be connected are connected, and ones that shouldn't, aren't. You should check any questionable looking traces, especially ground traces that may be edged up against some pads where they shouldn't, etc...

Doug

5/11/2000 4:41 PM

I checked everything out pretty good with the meter, at least any questionable traces that might lie kind of close to another trace or pad. I'm pretty sure I got that covered, I believe that I put the jfets, at least q1 - q4 back in wrong. I was sure I had it right, and I don't have the pedal in front of me to check, but that has got to be the problem.
If anything, i'm getting experience in doing this sort of thing, making all my mistakes now ;-)

;-)

5/11/2000 6:32 PM
Doug	>If anything, i'm getting experience in doing this sort of thing, making all my mistakes now Oh is that what it's called? I get "experience" every time I build a pedal! Doug

5/11/2000 7:12 PM
R.G.	Experience? Experience is what you've got left after you've forgotten their names.

5/11/2000 9:42 PM
Ed Guidry	Experience is what you've got left after you've forgotten their names. I just might put that in a sig line (with correct attribution, of course)

Page 1 of 1