SOLVED Windmill CB Mod

C

comradehoser

Well-known member
Hey folks,

It's been a frustrating week with pedal builds and mods. Finally measured all of my SMD J201s so I could implement the optimal OKKO Diablo/Deofol JFET cascade, and the crown jewel, the only 0.93 IDSS I have pinged off my chest and into the wilds of my basement when I was trying to adjust the alignment.

And then this little buddy, the Windmill with CB mods just didn't work at all. I had to fix the R1 and the R101-102/trimpot mods because I made some assumptions about the pads and connections that were incorrect when inspected with the DMM (I was being too excited/lazy, TBH).

Now I have some decent volume, but it sounds not.... good? Parpy, kinda gross distortion without a lot of "grain", even after biasing to the recommended 5.9 V on Q2 and Q3 Ds. Does not sound like the video demos of the WIIO, but who knows about how representative those are. This may be yet another case of "that's just how it sounds."

Did visual check. Double checked orientation, component values, and mod values. Don't really know what's up unless I misinterpreted the R1 "returns to GND" instruction and that's somehow affecting the J112 gain. I took the end of R1 that was tied to VREF and moved it to the ground pad going to the footswitch.

Provenance of the BS170 is either Stomp Box Parts or Mouser. J112 is Mouser.

9.38V in

Q1 J112 (0.45 IDSS)
D: 9.23v
S: 2.84
G: 0

Q2 BS170
D: 5.9
S: 2.95
G: 3.33

Q3 BS170
d: 5.89
s: 2.95 (variable)
g: 3.35

IMG_20251006_215452251.jpg

IMG_20251006_215524376.jpg

Anything jumping out at ye?
 
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Solution
Chuck D. Bones
Columbus was a dick. But he had a good PR guy.

Looks like you have R1 wired correctly. Remove D1, that should not be there and could be causing all of the trouble.
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I should have added the gain is not very apparent. Plenty of volume, not a lot of breakup.

I'm guessing it's something to do with the J112 seeing as the BS170s are biasing to target ranges? I don't really know what the source reading should be. I guess the drain looks okay ~9v coming off vcc, and the gate is coming off of the signal, so maybe it makes sense that it's zero, but then again there's that loop coming up off the source to the 100u cap and through the 9.1v zener, so maybe it should not be zero? More like maybe 9.1 v?

Sorry folks, I'm doing the best I can with my DMM divination sticks. The flux incense and ceremonial touching of component legs hasn't worked so far. I even sacrificed a J112.

Oops, schematic:
1759889442062.png
 
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Alright, here is maybe a slightly more productive direction to remedy my anemic build: what would I need to do to increase the gain of the circuit?

I am proceeding on the assumption that the issue is with Q1 since it's the most modified, and Q2 and Q3 seem to be responsive to the VREF trimpot mod and seem to be reading in target voltage ranges. I also assume I need to change R4, since Chuck mentions it as governing gain, but my drummer brain is unclear how R4 and the J112 source>diode>gate array with R4 and C3 would do that. I'm guessing that source>gate is a loop that amplifies the signal and R4/c3 govern the amount of the current pushing into the loop? Lower resistance = more current and JFET amplification?

I guess the other option is to breadboard the whole damn thing and fiddle everything until it sounds good.
 
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Mon Cher chat. Thank you so much for your help. It's always appreciated. Oddly enough, I did think of that and it was only functional in the non twisted position.

I will see what the transistor tester says, but maybe this indicates a funky j112 or something wrong in my circuit somehow. I do have a socket, but tested for continuity between pins, and it checks out
 
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Well, the j112 read DSG on ye olde tc1, so I tried twisting pin 2 for pin 3 again. It is functional.... Kind of. Whereas before I had volume and low clipping, now I have strangled clipping and low volume. Dimed volume and gain is giving me somewhat under unity.

Last time this happened to me I had majorly effed up resistor values, but I've been over the pedal 4 times and the values check out.

Most likely I am not implementing the mods in the correct way (?).

Vref is reading 5.21v at + of C101
VCC is 9.22v at R3

j112 with legs twisted is reading
D: 2.95 G: 2.25 S: 2.85

one side of R3 is reading 9.22v, the other side going into the drain of Q1 is 2.95v, which looks odd compared to what is going on in Q2 and 3. But I don't know. It's supposed to be that way? The Drain voltage into the J112 is the only thing that really isn't in the same ballpark as Q2 and Q3

q2 d: 6.22 g: 2.77 s: 2.99
q3 d: 6.21 g: 2.76 s: 3.01

(d voltages different because I messed about with the trimmer trying to improve signal)

Another view:

IMG_20251012_142649607.jpg
 
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comradehoser said:
...

Last time this happened to me I had majorly effed up resistor values, but I've been over the pedal 4 times and the values check out.

...
Click to expand...

Four times? Is that all? 😜

I've mentioned my 390Ω fiasco before, several times, but here 'tis again...
Shorty version:
I copied a schematic incorrectly, so even after literally at least a dozen times checking breadboard against *(incorrect) schematic, it all checked out correctly to me. My Amp-Sifu didn't even know what the circuit was when I behumbledly asked his assistance — I'd barely hit the return key when he replied back asking how I expected the transistor to turn on when the emitter was blocked by 390k — "Should be 390Ω". I replaced the 390k with 390Ω and was immediately fuzzed.


Chuck said "R1 now returns to GND", instead of VREF — which you mentioned, is there some other way to interpret that? R1 is going from the GATE of Q1 to ground — that's how I interpreted "returns".

Four times... maybe get a knowledgeable second-set of eyes on it instead of my dim four-eyes — les yeux de Chuck, peut-être.

Hmm, gotta go crawl around my roof some more. But...

200w.gif
 
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I decided to do some pedal therapy and regain confidence building the Aion Empyrean Deluxe/Darkglass Alpha-Omega.

Ripping circuit and functional off the bat. But no mods, so there's that.

And happy thanksgiving as well! Happy indigenous people's day to my 'murrican comrades.
 
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