Something seems not quite right here. I've gone over my work a dozen times. I don't see any error. It works nicely but I'm getting a lot of fizzy noise and gaiting. It seems almost like a bias issue. I looked at the schematic but couldn't find any obvious cause. I'm stumped.
This is the last thing you'll want to hear, but... check again. I was having the exact same-sounding issue when I first built it. Gave up, came back months later, and voilà, turns out I was a dummy who forgot the 1k-to-v bias resistor off IC1 pin 6.
While you're poking around, try different values for the feedback resistor between pins 6&7 of IC1 to up the gain. I settled on 12k4 as sounding pretty close to a proper DR103. I also used BS170s for the FETs, for reasons I no longer remember.
I stuck a variable 25k resistor in place of the 3.3k and dialed back from the 12k a hair. But it really opened it up. I tried the BS170's and they sounded cool but I preferred the stock personally. But if someone can't find the JFET it's an option. I read somewhere that someone had trouble with a TL072 in a BAJA circuit so I swapped it for another and that seemed to eliminate the fuzz sound. Thanks for the help Sebastian. It really sounds better with a larger resistor on IC1. Also, I grabbed the first OD that I had handy and found that the Greer Lightspeed pairs quite nicely. Thanks again Sebastian and thanks for the layout Bajaman and of course Anders.
I remember there being a revision to the tonestack on this circuit by Baja. He posted it back in october 2022 and added a schematic update at the end of this thread:
Just finished this circuit and was getting no output signal at all so I traced the signal, and it appears that my Q1 is acting as a switch rather than an amplifier. As soon as I put a signal on the input, the voltage goes negative – from 4.8-ish to -1.8-ish – on the Gate of Q1 and the signal stops there. If I trace signal backwards from the output, everything seems peachy until I hit Q1. Otherwise, the voltages on all the I.C.s and Q2 seem OK. Any ideas about what I've done to make Q1 operate in this way? Thank You!!
Have you double checked the pinout of your FET? Are you using 2sk117? They have a DGS pinout instead of the more common DSG you see with J201, 2N5457 etc.
Thanks, Orion! I just now figured out what was going on– I had lug 1 of Gain connected to lug 1 of Master Vol. and then to the board. Once I wired both lugs to the same spot instead, everything worked great! Oops.
Got this one working, there were a couple of errors, one which I needed to bodge, but all is good now.
ReplyDeleteTo update the layout, Pin 6 of IC1 is not hitting the 1k to vbias, so I would move the cut from 17/13 to 16/16.
Secondly the 220nf cap coming from Pin 7 of IC2 is hitting D3 and D4, so I would add a cut at 11/22.
This is a really nice sounding circuit!
Thanks for verifying! The layout is updated and tagged.
DeleteSomething seems not quite right here. I've gone over my work a dozen times. I don't see any error. It works nicely but I'm getting a lot of fizzy noise and gaiting. It seems almost like a bias issue. I looked at the schematic but couldn't find any obvious cause. I'm stumped.
ReplyDeleteI'm getting close to nine volts on the drains.
DeleteJust to verify, are you using 2sk117s or another N channel FET? The sk117s have an unusual DGS pinout instead of the Isiah DSG
DeleteYeah, 2SK117's.
DeleteThis is the last thing you'll want to hear, but... check again. I was having the exact same-sounding issue when I first built it. Gave up, came back months later, and voilà, turns out I was a dummy who forgot the 1k-to-v bias resistor off IC1 pin 6.
DeleteWhile you're poking around, try different values for the feedback resistor between pins 6&7 of IC1 to up the gain. I settled on 12k4 as sounding pretty close to a proper DR103. I also used BS170s for the FETs, for reasons I no longer remember.
I'm eternally going over stuff that didn't work. Thanks for the help. I'll try the mosfet tip. And tinker with the feedback resistor value.
DeleteI stuck a variable 25k resistor in place of the 3.3k and dialed back from the 12k a hair. But it really opened it up. I tried the BS170's and they sounded cool but I preferred the stock personally. But if someone can't find the JFET it's an option. I read somewhere that someone had trouble with a TL072 in a BAJA circuit so I swapped it for another and that seemed to eliminate the fuzz sound. Thanks for the help Sebastian. It really sounds better with a larger resistor on IC1. Also, I grabbed the first OD that I had handy and found that the Greer Lightspeed pairs quite nicely. Thanks again Sebastian and thanks for the layout Bajaman and of course Anders.
DeleteSo glad you got it working! It really is a killer circuit. I've actually been enjoying it on bass even more than guitar.
DeleteI remember there being a revision to the tonestack on this circuit by Baja. He posted it back in october 2022 and added a schematic update at the end of this thread:
ReplyDeletehttps://www.freestompboxes.org/viewtopic.php?t=28926&start=20
Its an easy fix, just move the 2.2k resistor from A5/E5 to C5/E5. And extend the link at A6/C6 to A6/E6.
G1 is now connected to Bass 3,2 and Mid 1.
Thanks for the heads up! I had no idea the tonestack was updated. And now the layout is updated as well.
DeleteSounded great before and it might sound even better with the update. It takes a village. I can't stop playing this thing. Takk
ReplyDeleteJust finished this circuit and was getting no output signal at all so I traced the signal, and it appears that my Q1 is acting as a switch rather than an amplifier.
ReplyDeleteAs soon as I put a signal on the input, the voltage goes negative – from 4.8-ish to -1.8-ish – on the Gate of Q1 and the signal stops there. If I trace signal backwards from the output, everything seems peachy until I hit Q1. Otherwise, the voltages on all the I.C.s and Q2 seem OK. Any ideas about what I've done to make Q1 operate in this way?
Thank You!!
Have you double checked the pinout of your FET? Are you using 2sk117? They have a DGS pinout instead of the more common DSG you see with J201, 2N5457 etc.
DeleteThanks, Orion! I just now figured out what was going on– I had lug 1 of Gain connected to lug 1 of Master Vol. and then to the board. Once I wired both lugs to the same spot instead, everything worked great! Oops.
DeleteInteresting circuit. Low gain and *very* bright, but quite a nice character.
ReplyDelete