Buddy's Breadboard and Circuit Design Notes

[BuddytheReow]

The BMP tone stack was originally designed to drive a load around 80K. Play with the value of R4 in TSC and see what it does. We can design a BMP tone stack to drive just about any load, and it need to be tuned to the load to get the best sweep. I find good results when the TONE pot and load are the same value.

While we're talking about loading, what kind of load does the MOSFET booster present to the tone stack in the above schematic?

Any guesses?

I’m gonna guess 3.3m?

 

[Chuck D. Bones]

I’m gonna guess 3.3m?

BZZZZZZZZZZ!

Wrong answer, thanks for playing.

Anyone else?

 

[fig]

Does it depend on the control setting?

 

[Chuck D. Bones]

Mmmmmmaaaaaybeeeeee. To which control are you referring?

 

[fig]

The one that changes the load to the tone stack.

The VOLUME control sir.

 

[Chuck D. Bones]

The volume control is after the MOSFET in the schematic above, so...

BZZZZZZ

Thanks for playing.

 

[fig]

It’s quite a boost with just that bit.

 

[Robert]

It's basically a SHO at this point, right?

 

[fig]

Minus the U1-GS 1N4148?

 

[Robert]

Yep. I don't think the early SHO's had the protection diode.

 

[Robert]

If you like that circuit you should check out the Modus Operandi schematic and tack on that 2N2222A stage.

Maybe it's placebo (I never A/B'd them) but it seemed to add a little something. I could leave that pedal on all the time.

https://docs.pedalpcb.com/project/ModusOperandi-PedalPCB.pdf

 

[Betty Wont]

Yep. I don't think the early SHO's had the protection diode.

That's correct. Early SHO's had an extra bs170 taped to the inside lid for blowouts.

 

[Chuck D. Bones]

If you like that circuit you should check out the Modus Operandi schematic and tack on that 2N2222A stage.

Maybe it's placebo (I never A/B'd them) but it seemed to add a little something. I could leave that pedal on all the time.

I'd say that hanging Q2 there is a bit silly. Q1 can drive that 2-pole low-pass filter no problem. If one wanted to be clever, then Q2 could be configured as an active 2-pole low-pass and DC-coupled to Q1 since Q1-D and Q2-B are essentially the same voltage anyway.

 

[Robert]

I'd say that hanging Q2 there is a bit silly.

No, it was taped to the lid, I don't think they called it Q2.

Seriously though, you know I don't analyze these things.

If I go around "improving" things folks will raise hell. I leave the mods and upgrades to you guys.

 

[fig]

I did this..it’s a 2N4393 with a couple of clipping diodes…not 100% on the clipping level control, but still pretty cool.

 

[Chuck D. Bones]

Schematic please.

 

[fig]

It's the final two stages of the Voodoo Woman, with a 2N4393 tacked onto the OUT, and a 680Ω resistor to DRAIN, SOURCE to GND. DRAIN is OUT.

The clipping bit didn't actually do anything audibly.

 

[Chuck D. Bones]

That JFET is running on the edge of saturation. Id is idling at Idss.

 

[Chuck D. Bones]

Yeah, you really need a source resistor to get the biasing right. Or maybe it's doing exactly what you want, in which case forget what I just said.

 

[fig]

As cool as "running on the edge of saturation" sounds (and it sounds awfully cool....I may use it in some lyrics...royalties?)...I think I'll get myself one of them "source resistors" and run with the pack...thank you sirs!