Locrian99
Well-known member
More just documenting this one. As I figure it out. Next step is to replace the jfet again with one from a different batch.
So basically fully ccw the the pedal seemed to be working fine. As your turn the bias pot up it hits a volume jump then hit a volume drop and would get progressivelt more gated, def not correctly. Using smd mmbf201’s from mouser.
Measured voltages on Q3. Fully ccw the drain read 7.8, dropped as you rotated but before half way it was down to .8, going all the way to .3. Source and gate looked correct. So I measured the pot and it was reading max resistance of 4.7k, which I thought was a really odd number for it to be showing besides not being right. So I remove the pot measures 50k, I had resoldered the jfet already, then decided id also try a new jfet in there so I removed it. Grabbed another jfet but soldered the pot in first and measured it again. 50k (well like. 48). Soldered in the new jfet pot reads 4.7k again. So then i plugged it in and tested voltages. Still around. 7.8v ccw, turned fully cw i get a continuity beep. Now its grounding out part way through the rotation. I then unplug the pedal and I forget what the reading was but it wasnt continuity with ground without power.
So i double check that these are labeled j201’s (at least from the mouser packaging). Best i can cone up with is the 201 is so far out of spec it won’t work here, I’m not familiar enough with how jfets work but I know they turn on at some point and I’m assuming something like that is happening when it shouldnt. So at this point I have some j201’s from a different batch from digikey I think so I’ll try those here and see if that changes this.
Ive made three of these now and have never had trouble with the jfets. And they appear to he working in q1 and q2 position fine from this batch. Kind of interesting.
Open to any other ideas as to what it might be, may not be able to get back to it tonight.
So basically fully ccw the the pedal seemed to be working fine. As your turn the bias pot up it hits a volume jump then hit a volume drop and would get progressivelt more gated, def not correctly. Using smd mmbf201’s from mouser.
Measured voltages on Q3. Fully ccw the drain read 7.8, dropped as you rotated but before half way it was down to .8, going all the way to .3. Source and gate looked correct. So I measured the pot and it was reading max resistance of 4.7k, which I thought was a really odd number for it to be showing besides not being right. So I remove the pot measures 50k, I had resoldered the jfet already, then decided id also try a new jfet in there so I removed it. Grabbed another jfet but soldered the pot in first and measured it again. 50k (well like. 48). Soldered in the new jfet pot reads 4.7k again. So then i plugged it in and tested voltages. Still around. 7.8v ccw, turned fully cw i get a continuity beep. Now its grounding out part way through the rotation. I then unplug the pedal and I forget what the reading was but it wasnt continuity with ground without power.
So i double check that these are labeled j201’s (at least from the mouser packaging). Best i can cone up with is the 201 is so far out of spec it won’t work here, I’m not familiar enough with how jfets work but I know they turn on at some point and I’m assuming something like that is happening when it shouldnt. So at this point I have some j201’s from a different batch from digikey I think so I’ll try those here and see if that changes this.
Ive made three of these now and have never had trouble with the jfets. And they appear to he working in q1 and q2 position fine from this batch. Kind of interesting.
Open to any other ideas as to what it might be, may not be able to get back to it tonight.