Corduroy Fuzz Trimpots

Those set the bias for the J201 directly below each one of them.

Generally you're shooting for around 4.5V on the Drain of each J201.
 
Can someone point me to a video that shows how to bias the transistors. I have an analog multimeter. Do I need anything else?

Thanks.
 
Here's a quick lesson.
I'll assume you know how to use the multimeter.
Preset the trimpots to the middle of rotation.
Power up your pedal.
Connect black - probe to ground in your pedal. Usually the ground lug on the IN or OUT jack is most convenient.
Connect the + probe to the drain lead of one of the JFETs.
Slowly turn the trimpot closest to that JFET to get something close to +4.5V.
Repeat for the other two JFETs.
This is just a recommended starting point. Plug your guitar in and play for a while, see if you like the sound.
After that, you can tweak the trimmers by ear if you like. The sweet spot is probably somewhere between 3V and 6V and will vary by JFET and the user's preferences.
Corduroy is a cool pedal.
 
Chuck D. Bones said:
Here's a quick lesson.
I'll assume you know how to use the multimeter.
Preset the trimpots to the middle of rotation.
Power up your pedal.
Connect black - probe to ground in your pedal. Usually the ground lug on the IN or OUT jack is most convenient.
Connect the + probe to the drain lead of one of the JFETs.
Slowly turn the trimpot closest to that JFET to get something close to +4.5V.
Repeat for the other two JFETs.
This is just a recommended starting point. Plug your guitar in and play for a while, see if you like the sound.
After that, you can tweak the trimmers by ear if you like. The sweet spot is probably somewhere between 3V and 6V and will vary by JFET and the user's preferences.
Corduroy is a cool pedal.
Click to expand...

Hey @Chuck D. Bones,

I just build the Corduroy fuzz and after setting all J201 to 1,5v its too splatty on reduced volume/cleanup and low fuzz levels.
So after just using my ears and dialing in the trimpots without measuring I got it sounding close to how I hear it in the videos.
The drain voltages I got are: Q2 1,5v - Q3 3,25v and Q4 2V just by playing and checking how it reacts. Somewhere I remember reading that Brian biases the J201 cold?
Does anyone have the bias values from the original pedal? That part isn’t really documented.
So basically the big vs tight is a path through the LM386 and a path through the 2n5089 with different caps/resistors?
The 3 J201 work and both sides right? I first thought that tight and big had separate J201 to bias.

Only thing that I noticed that the bright pot isnt having much range? I measured the paths and the 15k resistors and 10n are all connected to the bright pot. It replaced the pot with a B25k and that didn’t fix it so maybe it’s not a large sweep?
 
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1.5V is way too low. I obtained good tone with the drains around 4.5V.
I don't know where you get your information on how Mr. Wampler biases the JFETs. 1.5V on the drain is HOT because it means higher drain current.
"Big" channel is thru the 2N5089. Gain of that stage is around 40dB, but then it's knocked down to about 25dB at Q2. Q1 makes distortion and is supposed to add a fuzzy tone.
"Tight" channel is thru the LM386. Gain of that stage is around 26dB, but then it's knocked down to about 18dB at Q2. IC1 makes very little, if any, distortion. It's job is to goose Q2.
The BRIGHT pot has the appropriate range on mine. It's supposed to be B25K, what did you have in there before? Verify R26 & R27 are both 15K, C18 is 2.2nF, C19 is 10nF. Do you want it to go darker or brighter?

Did you source the parts yourself or buy a kit?
 
Chuck D. Bones said:
1.5V is way too low. I obtained good tone with the drains around 4.5V.
I don't know where you get your information on how Mr. Wampler biases the JFETs. 1.5V on the drain is HOT because it means higher drain current.
"Big" channel is thru the 2N5089. Gain of that stage is around 40dB, but then it's knocked down to about 25dB at Q2. Q1 makes distortion and is supposed to add a fuzzy tone.
"Tight" channel is thru the LM386. Gain of that stage is around 26dB, but then it's knocked down to about 18dB at Q2. IC1 makes very little, if any, distortion. It's job is to goose Q2.
The BRIGHT pot has the appropriate range on mine. It's supposed to be B25K, what did you have in there before? Verify R26 & R27 are both 15K, C18 is 2.2nF, C19 is 10nF. Do you want it to go darker or brighter?

Did you source the parts yourself or buy a kit?
Click to expand...
I didn’t source the J201 myself, they were part of a kit from Musikding.
If I bias all J201 to around 4,5V it sounds completely off and very splatty, with the voltages I mentioned it sounds comparable to the real pedal.

I indeed double checked the resistors and caps which are correct. I had a B25k pot in there but tried a B50k to see if the pot was broken.
I’m not really using the bright pot and I almost always have it maxed. I don’t want it darker but replacing the caps C17-C19 with lower values or removing (2n2) didn’t work for me sound wise. So I kept it as the original.

I had the original pedal when demoing it: Velvet Fuzz demo - I’m only building them for fun.
 
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Hey, great demo!
If I had to venture a guess based on what you told me so far, I'd say the J201s you bought and the J201s Wampler used have different Vp & Idss. There is a lot of variation from lot-to-lot and I expect that Wampler tests and sorts his JFETs to ensure consistent sound and eliminate the need for trimpots. I doubt that Musikding tests their parts. Most (not all) of the J201s going around these days have low Vp and Idss. There are also a lot of fake J201s for sale and it's possible you ended up with some of those. If you want to explore this further, measure the source voltages on Q2 - Q4 with no signal. Leave the trimpots where you have them set. If your J201s are in-spec, then the source voltage will be between 0.3V and 1.5V.

On mine, the source voltages measured at the low end of the range, between 360mV and 370mV. I ended up with the drains at 3.13V, 3.23V and 5.00V. The trimmers ended up at 16K, 16K and 11K. I'm not saying that's the optimum setting, it's where it sounded good to me. I didn't have an original to compare. The trimpots all interact, so as you know it takes a lot of patience to get them dialed-in. To complicate matters, Q4's trimmer interacts with the output filter (R26, R27, C18, C19 & the BRIGHT pot).
 
Chuck D. Bones said:
Hey, great demo!
If I had to venture a guess based on what you told me so far, I'd say the J201s you bought and the J201s Wampler used have different Vp & Idss. There is a lot of variation from lot-to-lot and I expect that Wampler tests and sorts his JFETs to ensure consistent sound and eliminate the need for trimpots. I doubt that Musikding tests their parts. Most (not all) of the J201s going around these days have low Vp and Idss. There are also a lot of fake J201s for sale and it's possible you ended up with some of those. If you want to explore this further, measure the source voltages on Q2 - Q4 with no signal. Leave the trimpots where you have them set. If your J201s are in-spec, then the source voltage will be between 0.3V and 1.5V.

On mine, the source voltages measured at the low end of the range, between 360mV and 370mV. I ended up with the drains at 3.13V, 3.23V and 5.00V. The trimmers ended up at 16K, 16K and 11K. I'm not saying that's the optimum setting, it's where it sounded good to me. I didn't have an original to compare. The trimpots all interact, so as you know it takes a lot of patience to get them dialed-in. To complicate matters, Q4's trimmer interacts with the output filter (R26, R27, C18, C19 & the BRIGHT pot).
Click to expand...
Hey Chuck,

I measured the source values of the SMD J201s and they’re also all on the low side. Q2 - 0,31v, Q3 - 0,29v and Q4 - 0,32v.
I dialed them in by ear and came to the low volt values on the drain.
When setting the drains all to around 4,5v the Big side especially was splatty (broken) sounding and rolling down the volume didn’t clean up well.
So after fiddling around without measuring I ended up with a fuzz sound that works on a low setting like in my demo. And a fuzz sound that’s great halfway to a quarter. And a fuzz sound that becomes buzzy on max fuzz.

So checking your drain values should I try 3V, 3V and 5V to see how that works out? Why is the last one 5V?

Btw, the volume control here also seems to interact with the fuzz, to my ears it sounds like it adds more “amp” like sound to the fuzz when increasing and on low levels it’s like adding brightness to the fuzz.

Has anyone build the Cujo (Suhr) fuzz BTW?
Sourcing the J202 and BC546A can also be a pain right?
 
Last edited:
Just another question: If I want to try to get a better working bright pot I could solder the resistor pair and the 10n and 2n2 manually right directly on the pot?
Maybe this is also related to my bias settings and the influence each component has to each other? Like the influence on the bright pot which doesn’t seem to be working well for me?
 
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