Ok, just built it up. Very low output, almost non existent so I can’t tell if the other pots work. I have a hard time reading schematics using opamps so I can’t make too much sense of it. The voltages are as follows:
Voltages looks ok as far as I can see. Have you done all trouble shooting rituals, knifed the gaps, checked component placement etc? Been over the schematic and it seems to match the layout.
Double checked placement and values, all fine. Wiring is ok and tried other JFETs and opamps. Same result. I cranked the amp to test the pots, besides the volume pot, nothing else works. Just passing a low volume, clean signal.
Hmmm, that sucks. This could be one of those mysteriously problematic builds. Triple checked everything and it "should" work. The only thing that looks a bit odd is D5. I would have a coupling cap instead of a diode there. Worth a try?
A big one, maybe 1uF to make sure all frequencies comes through. Another thing that looks odd around the J FET....it acts like a buffer before the tonestack but it need a resistor across Gate and Ground to behave as it should. Usually a 1m or 2,2m resistor is used.
No change. I tried a 1uf and 2.2uf as well as adding the 2.2m. Maybe the schematic is flawed. I’m going to ask about it on FSB, maybe the creator can help. Thanks for all your help, you’re awesome. I’ll see if I can order some parts to try out the OTR if I can’t get anywhere with this. I’ll keep you posted.
Vitalka replied to my question on FSB. He said that the pins should all be half Vcc. It was also suggested to try different opamps, I tried one other one with the same results. Possibly just an error in my build then.
Ok, had a little time so I built it again. Works... almost. The gain pot doesn’t do anything and the depth doesn’t do much either. Voltages besides pins 4 and 8 are all 4.64v the demo doesn’t seem to have much of a variance with the gain control either, maybe that’s how it’s supposed to be? I’m going to see if Vitalka could lend a hand.
Great! Almost there. Very cool tricks from Vitalka regarding using a diode as capacitor between first op amp and the FET buffer which I guess is also biased via the diode? Nice with "outside the box" thinking and unknown tricks.
I don’t know, he said the gain pot should work but I have very, very little if anything and not even close to the amount of gain in the demo. I replaced the pot even took it out of the circuit and nothing changed. Vitalka added his perf layout on FSB but I’m gonna throw in the towel on this one. Thanks for all your help though. Maybe I’ll give the OTR120 a shot next.
Any more info on this
ReplyDeleteNot much except on FSB.
Deletehttps://www.freestompboxes.org/viewtopic.php?f=13&t=28914&p=269301&hilit=iguana#p269301
Ok, just built it up. Very low output, almost non existent so I can’t tell if the other pots work. I have a hard time reading schematics using opamps so I can’t make too much sense of it. The voltages are as follows:
ReplyDeleteJ201
G: 4.19v
S: 5.71v
D: 9.07v
TL072:
1: 4.54v
2:4.54v
3: 2.26v
4: 0
5: 4.49v
6: 1.59v
7: 8.48v
8: 9.07v
Any thoughts?
Voltages looks ok as far as I can see. Have you done all trouble shooting rituals, knifed the gaps, checked component placement etc? Been over the schematic and it seems to match the layout.
DeleteYeah, I usually knife the tracks before I even test it. I’ll check component values, it’s definitely possible I used a wrong resistor or two.
ReplyDeleteDouble checked placement and values, all fine. Wiring is ok and tried other JFETs and opamps. Same result. I cranked the amp to test the pots, besides the volume pot, nothing else works. Just passing a low volume, clean signal.
ReplyDeleteHmmm, that sucks. This could be one of those mysteriously problematic builds. Triple checked everything and it "should" work. The only thing that looks a bit odd is D5. I would have a coupling cap instead of a diode there. Worth a try?
DeleteI’ll give it a shot. How big?
ReplyDeleteA big one, maybe 1uF to make sure all frequencies comes through. Another thing that looks odd around the J FET....it acts like a buffer before the tonestack but it need a resistor across Gate and Ground to behave as it should. Usually a 1m or 2,2m resistor is used.
DeleteI can post a modified layout if you want to.
I can get a resistor from gate to ground but I’m out of non polarized 1uf so I guess use the same orientation as the diode?
DeleteYou could try a small value like 470nf but if using an electro negative leg should connect to Gate of the J FET just as the diode.
DeleteNo change. I tried a 1uf and 2.2uf as well as adding the 2.2m. Maybe the schematic is flawed. I’m going to ask about it on FSB, maybe the creator can help. Thanks for all your help, you’re awesome. I’ll see if I can order some parts to try out the OTR if I can’t get anywhere with this. I’ll keep you posted.
ReplyDeleteOh, bummer! Thanks for tackling this. Ok, let me know if you get more info on this.
ReplyDeleteI'll tag this "On Hold".
Since the voltages look OK, could one of the components be faulty? I did have to reuse the 47uf caps.
ReplyDeleteI don't know, the circuit should work except for the Deep control even wirhout those 47uF caps. I think there is a bug in the schematic:-/
DeleteVitalka replied to my question on FSB. He said that the pins should all be half Vcc. It was also suggested to try different opamps, I tried one other one with the same results. Possibly just an error in my build then.
ReplyDeleteOk, thanks for reaching out to him. Might just start on a new board?
DeleteYeah, gotta see what parts I have on hand and if I have time. Based on what I was told, could replacing the 1m and 22k resistors on pins 3 and 6 help?
ReplyDeleteOk, had a little time so I built it again. Works... almost. The gain pot doesn’t do anything and the depth doesn’t do much either. Voltages besides pins 4 and 8 are all 4.64v the demo doesn’t seem to have much of a variance with the gain control either, maybe that’s how it’s supposed to be? I’m going to see if Vitalka could lend a hand.
ReplyDeleteGreat! Almost there.
ReplyDeleteVery cool tricks from Vitalka regarding using a diode as capacitor between first op amp and the FET buffer which I guess is also biased via the diode? Nice with "outside the box" thinking and unknown tricks.
I don’t know, he said the gain pot should work but I have very, very little if anything and not even close to the amount of gain in the demo. I replaced the pot even took it out of the circuit and nothing changed. Vitalka added his perf layout on FSB but I’m gonna throw in the towel on this one. Thanks for all your help though. Maybe I’ll give the OTR120 a shot next.
ReplyDelete