Cujo/Rufus Fuzz Transistor choice

[mzy12]

Hey people

I'm perfboarding a Rufus fuzz and I'm just wondering what the transistor specs I should be looking at for the pedal. I'm guessing the BJTs should just have Fuzz Face HFEs, but what about the JFETs? Is there any particular VGS off and IDSS I should look for there?

Thanks in advance

 

[Cybercow]

Considering the build calls for J202 JFETs, I'd use those.

 

[mzy12]

Only thing is that there is a wide range of VGS off measurements that a J202 could have. Just curious if there's a more concrete number to aim for or if it should in the middle of the road or something

 

[Cybercow]

That's right. All JFETs have a wide range of Vgs(Off) values. But each has their own range. With that in mind, I'd still go with the J202s and socket them. If it doesn't sound right, check the Vgs(Off) value (by measurement) and look for another pair that have a more middle-of-the-road Vgs(Off) value. When you find a set with working Vgs(Off) values, try different JFETs that have near the same Vgs(off) value and see how those work.

 

[mzy12]

Gotcha. Will update this thread with any info I find.

 

[Robert]

I think I still have one of these somewhere. If I can find it I'll pull the JFETs and measure the specs.

 

[mzy12]

Thanks, that would be a great help.

 

[Chuck D. Bones]

Ping! Did the measurement ever happen? We know you have so much spare time, Robert.

 

[johnk_10]

i built one using all of the correct transistors and components that i ordered from Mouser, but for some reason it doesn't sound like any of the online demos of the original pedal at all. i had high hopes for it, but unfortunately, i find it to be unusable as a pedal.

 

[johnk_10]

the distortion in my build (which i've checked multiple times for errors and found none) just doesn't sound good at all to me. it really doesn't clean up well at all either.

 

[Chuck D. Bones]

Can you measure some voltages?
Q1 pin 1
Q3 pin 1
Q4 pin 2

 

[johnk_10]

Q1 pin 1 Drain: 1.016V
Q3 pin 1 Collector 2.678V
Q4 pin 1 Drain .734V
IMO, those seem really low for the Jfets.

 

[Chuck D. Bones]

Yes, very low for the JFETs and a bit low for Q3.

Are you sure you used J202 and not J201?

What is Vcc? Are you using a power supply or a battery?

This sounds like a job for the Troubleshooting forum.

 

[johnk_10]

Yes, very low for the JFETs and a bit low for Q3.

Are you sure you used J202 and not J201?

What is Vcc? Are you using a power supply or a battery?

This sounds like a job for the Troubleshooting forum.

they're definitely J202'S (from Mouser). I'm using a onespot power supply.

 

[johnk_10]

yes, they're definitely J202's from Mouser. VCC is 9.29V.

 

[Chuck D. Bones]

You have any spare J202's that you can measure Idss & Vp?

 

[darwin999]

You have any spare J202's that you can measure Idss & Vp?

Hopefully @johnk_10 bought them long ago when they were cheaper...
(or they're SMD...)



Ouch!

 

[Chuck D. Bones]

Ouch!
SMD are def cheaper.

 

[johnk_10]

i bought the non smd versions.

You have any spare J202's that you can measure Idss & Vp?

i'm out of them right now but just ordered some more of them.

 

[johnk_10]

just for experimentation, while waiting for the new J202's, i socketed the Jfets and installed J201's in their place, and it sounds exactly the same. Has anyone else built this circuit and is happy with the result? I certainly am not.