Hi all. I built a Grapevine by Madbean, on a self etched board. The previous one came out perfect. This one seems to be in almost working order, but the output is very weak and muddy. Turning the pots (gain, tone and level) works and also switching between Rock and Rawk mode has a noticable difference, but like I said very low output (close to unity).
Q1
G = 0V
S = 1.37 V
D = 5.5 V
Q2
G = 4.1 V
S = 5.5 V
D = 8.8 V
Q3
G = 5.5 V
S = 6.1 V
D = 5.5 V
Q4
G = 0 V
S = 0V
D = 1.5V
Q5
G = 1.65 V
S = 8.8 V
D = 8.8 V
Q6
G = 1.5V
S = 1.65V
D =8.8 V
Any clues?
Something's up with Q6 the gate should be about 4.5 volts, so check the stuff connected to the gate. The voltages on Q4 and Q6 should be about the same as Q1 and Q2.
Schemo to save anyone else looking for it ;)
http://www.madbeanpedals.com/projects/Grapevine/docs/Grapevine_ver.2.pdf (http://www.madbeanpedals.com/projects/Grapevine/docs/Grapevine_ver.2.pdf)
Quote from: slacker on September 21, 2011, 01:52:24 PM
Schemo to save anyone else looking for it ;)
http://www.madbeanpedals.com/projects/Grapevine/docs/Grapevine_ver.2.pdf (http://www.madbeanpedals.com/projects/Grapevine/docs/Grapevine_ver.2.pdf)
oops, sorry. I have to go gigging now, I'll check it later tonight.
Sorry for the delay, it just got really busy over the past weeks and couldn't find enough time to sit down with the effect. There was a short on the gate of Q6, as suggested, so I fixed that. New voltage readings (significant changes marked with an asterisk):
Q1
G = 0V
S = 1.37 V
D = 5.7 V
Q2
G = 4.1 V
S = 5.5 V
D = 9.2 V
Q3
G = 5.7 V
S = 6.3 V
* D = 9.2 V *
Q4
G = 0 V
S = 0V
* D = 4.6V *
Q5
* G = 4.6 V *
S = 9.2 V
D = 9.2 V
Q6
* G = 4.3V *
* S = 4.6V *
D = 9.2 V
As far as I can judge, voltages look peachy...but now, there's no sound from the effect at all! Not even the muffled stuff from before, it's dead quiet. New suggestions? (maybe fried one of the JFETs?)
FIXED! Audioprobed it, found another short on the source of Q5.