Chuck D. Bones
Circuit Wizard
With a mod or two...
This is a great-sounding pedal right outta the box, but of course there are always some opportunities for tweaks.
I replaced the BODY switch with a pot.
I powered Q5 from the 18V rail for more headroom. Probably not necessary.
I put the PRESENCE trimmer back in. I've been running it at 5 so far.
I replaced the BMP style Tone network with a BD-2 style Tone network and altered the values of C10-C11, C20-C21 & the TONE pot.
R18 never should have returned to GND, it's way better to return it to Vref. With R18 connected to GND, turning the TONE knob changes the bias on Q5, which could cause Q5 to saturate. I never want an input or output buffer to saturate.
I got lucky with the first group of J201s I installed. It's important that Q2 & Q4 have Idss higher than Q1 & Q3 and that Q5 has Idss >0.9mA.
You may have noticed that Q1-Q5 are "upside-down" in the PCB schematic. This is no big deal because in audio circuits, D & S are interchangeable. I'm a bit A/R (ok, a lot A/R) and I like my schematics to look a certain way. I could have wired the JFETs in accordance with the Build Docs and it would work and sound the same. Why did OKKO do it that way? Ich weiss nicht.
I'm only 90% satisfied with the Tone network, so I may do a little more tweaking there. One could put a James or FMV tone stack after Q3/Q4, but then Q5 would need to be a gain stage. It's all doable, but just because it could be done doesn't mean it should be. I might try it just for S&G.
LTSpice tells me that other JFETs could be used, provided we adjust R4 & R13 accordingly. I'll be trying 2N5457 next. They have a higher Vp and Idss compared to J201 and should produce a little more gain.
One could think of this as a Marshall-In-A-Box. There's a gain stage, a gain control, another gain stage and a tone control. The BODY switch (or pot) lets us select between a full Normal channel tone or a bright High Treble channel tone. Unless we turn DYNAMICS all the way down, or put a booster in front, the first stage runs clean. The FEED control is equivalent to a guitar's Volume knob, with a large treble bleed (C1). It lets us turn down some of the lows to compensate for fat Humbuckers.
This is a great-sounding pedal right outta the box, but of course there are always some opportunities for tweaks.
I replaced the BODY switch with a pot.
I powered Q5 from the 18V rail for more headroom. Probably not necessary.
I put the PRESENCE trimmer back in. I've been running it at 5 so far.
I replaced the BMP style Tone network with a BD-2 style Tone network and altered the values of C10-C11, C20-C21 & the TONE pot.
R18 never should have returned to GND, it's way better to return it to Vref. With R18 connected to GND, turning the TONE knob changes the bias on Q5, which could cause Q5 to saturate. I never want an input or output buffer to saturate.
I got lucky with the first group of J201s I installed. It's important that Q2 & Q4 have Idss higher than Q1 & Q3 and that Q5 has Idss >0.9mA.
You may have noticed that Q1-Q5 are "upside-down" in the PCB schematic. This is no big deal because in audio circuits, D & S are interchangeable. I'm a bit A/R (ok, a lot A/R) and I like my schematics to look a certain way. I could have wired the JFETs in accordance with the Build Docs and it would work and sound the same. Why did OKKO do it that way? Ich weiss nicht.
I'm only 90% satisfied with the Tone network, so I may do a little more tweaking there. One could put a James or FMV tone stack after Q3/Q4, but then Q5 would need to be a gain stage. It's all doable, but just because it could be done doesn't mean it should be. I might try it just for S&G.
LTSpice tells me that other JFETs could be used, provided we adjust R4 & R13 accordingly. I'll be trying 2N5457 next. They have a higher Vp and Idss compared to J201 and should produce a little more gain.
One could think of this as a Marshall-In-A-Box. There's a gain stage, a gain control, another gain stage and a tone control. The BODY switch (or pot) lets us select between a full Normal channel tone or a bright High Treble channel tone. Unless we turn DYNAMICS all the way down, or put a booster in front, the first stage runs clean. The FEED control is equivalent to a guitar's Volume knob, with a large treble bleed (C1). It lets us turn down some of the lows to compensate for fat Humbuckers.
