CONTEST What? Another Contest?

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Question..could that distortion in the CH1 peak be parasitic oscillation....or is it just likely plain noise from the breadboard?
 
After going through a few ideas, I decided I wanted to keep my design as close to the original PCB as possible.
Hey, I always had big love for JFETs and Muffs - so, porque no los dos?

Wasn't sure what to expect, but this thing is Sofa King badass. The noise is also extraordinarily low - like eerily low, even at full gain.

Calling it the Fuzzduster for now. Will probably make a few tweaks, but it's already really close.

2SK880 JFETs with the source resistor trimmed to get 5.5V on the drain. Other 'high gain' JFETs should work just as well. The only deviations from the stock PCB are adding two extra caps - a source bypass on the input stage and a treble bleed on the gain pot.

IMG-1177.jpg



Fuzzduster-sch.png
 
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Well after two evenings of jacking around on the breadboard I managed to make a distortion (modified zonk into a bosstone) that will compress so hard at full volume on the neck humbucker of my LP that it will almost fart completely out 🙄 On the other hand depending where it’s at in the room you can listen to several radio stations 🤪 Back to the drawing board.
 
fig said:
Question..could that distortion in the CH1 peak be parasitic oscillation....or is it just likely plain noise from the breadboard?
Click to expand...
Speed up the horizontal sweep and let's get a closer look at the HF noise. Is this that MOSFET circuit you showed me on Sat?
 
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jubal81 said:
After going through a few ideas, I decided I wanted to keep my design as close to the original PCB as possible.
Hey, I always had big love for JFETs and Muffs - so, porque no los dos?

Wasn't sure what to expect, but this thing is Sofa King badass. The noise is also extraordinarily low - like eerily low, even at full gain.

Calling it the Fuzzduster for now. Will probably make a few tweaks, but it's already really close.

2SK880 JFETs with the source resistor trimmed to get 5.5V on the drain. Other 'high gain' JFETs should work just as well. The only deviations from the stock PCB are adding two extra caps - a source bypass on the input stage and a treble bleed on the gain pot.
Click to expand...
Interesting! Jubal81 loves him some JFETs! What resistances did you end up with on the trimmers?
 
Chuck D. Bones said:
Two more questions for BtR:
  1. What's the value of that mystery resistor connected to the high-side of the TONE pot?
  2. It's customary to put a capacitor between pin 2 of the TONE pot and the next transistor's bias network. Since your circuit doesn't have one, what happens to that transistor's bias when you turn the TONE pot?
Click to expand...
Chuck, was a little too eager (or perhaps lazy) to get this up before double checking everything. The resistor in question is 22k.

Secondly, you brought up something interesting regarding that missing coupling cap. At first I didn’t think it was necessary since there was a coupling cap before the tone control. I forgot that electricity goes BOTH ways. Turning the TONE pot does change the bias when looking at the transistors base voltage readings. Another little tidbit learned here. I have added the cap in the schematic and breadboard pic. See updated submission here.
 

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jubal81 said:
Hey, I always had big love for JFETs and Muffs - so, porque no los dos?
Click to expand...
That's sweet!
Blooze said:
Back to the drawing board.
Click to expand...
There's your problem....try a breadboard! :ROFLMAO:
BuddytheReow said:
I forgot that electricity goes BOTH ways.
Click to expand...
You just solved an issue on something else for me! 😘
Chuck D. Bones said:
Speed up the horizontal sweep and let's get a closer look at the HF noise. Is this that MOSFET circuit you showed me on Sat?
Click to expand...
Will do. No it's just a fetzer [but may end up with the MOSFET]. It seems I have a FETish as well.

btw, if anyone needs any odd bits for their entry, hit me up. I also have a few of the mini protoboards left if that is a barrier to someone's groovy entry. Free to good homes, and I'll throw in the hardware to build it. Solder it yourself though 🤪
 
fig said:
That's sweet!

There's your problem....try a breadboard! :ROFLMAO:

You just solved an issue on something else for me! 😘

Will do. No it's just a fetzer [but may end up with the MOSFET]. It seems I have a FETish as well.

btw, if anyone needs any odd bits for their entry, hit me up. I also have a few of the mini protoboards left if that is a barrier to someone's groovy entry. Free to good homes, and I'll throw in the hardware to build it. Solder it yourself though 🤪
Click to expand...
I could use some free time if you’ve got any laying around.
 
Chuck D. Bones said:
The scope pic says the CH2 signal is 1.67Ap-p. How can that be right?
Click to expand...

What scope pic? :sneaky:

Ohhhh...I guess I build a mean fetzer?

Hang on, I'll re-create the "" scene of the crime. I was going to turn it on anyway to zoom in on channel one for someone (me).
 
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Oh, LOL! I was putzing with the vertical on CH2, so that was @ 200mV...it reads p2p 1.20V @ 500mV, ampl 1V.
 
Zoom in more and measure the freq of the oscillation. Interesting that there are two regimes and the transition is pretty abrupt.

MOSFETs have a lotta bandwidth and make good RF oscillators, whether you're trying to build one or not. Does your circuit have a gate-stopper resistor? If not, try adding a 10K to 100K resistor in series with the gate. See if that kills the oscillations.
 
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