This Week on the Breadboard: The Voodoo Woman

[Chuck D. Bones]

I refer you to Bill's Law. You must have something out of place. Check the source voltage on Q2. Should be around 4.5 to 5V. What voltage do you have on U1-6?

With the GAIN all the way down, the MID control should definitely be noticeable. It only adds about 8dB at 750Hz, but you should hear it. If you use A250K, then wire it backwards, i.e. use pins 1 & 2. Or use a C100K, that's close enough.

The GAIN is humungous. With the stock circuit, I have no use for the top half of the GAIN control. When GAIN is cranked, it will completely swamp out the effect of the MID control.

 

[fig]

I reworked it as shown in the Voodoo Woman, with two minor alterations…an A250K @ VR1 and a 330nF @ C4.
I’ll give it a go tomorrow…

 

[Chuck D. Bones]

Need me to send you a 390nF and C250K?

But seriously folks, those are plenty close, as long as you wire the A250K backwards.

The Voodoo Woman is a much tamer beast. How would you describe the tone of the Voodoo-1 with the GAIN dimed?

Stephan asked me to add a switch to shift the mid freq from 500Hz to 750Hz to 1KHz. I'll post it tomorrow, I don't want to derail this trail.

 

[fig]

How would you describe the tone of the Voodoo-1 with the GAIN dimed?

Painful? It was fine up to ~3. Beyond that it saturated and just became clipped noise.

Need me to send you a 390nF and C250K?

I'd order some but they just end up at your place

 

[Chuck D. Bones]

Here's the lastest rev, with the MID-SHIFT switch. S2 is DPDT, shown in the 1KHz position. S2A to the left and S2B up is 750Hz, right & down is 500Hz. R6, R7, C2 & C3 (all 6 caps) are all part of the tuned circuit. We can pick any three mid frequencies we want by fiddling C2 - C3, R6 & R7. R7 also sets the max height of the mid freq hump. I also changed Q2 to a JFET for lower noise. The MOSFET wasn't that noisy, but this is better. Any JFET with a high Vp will do.

 

[cooder]

Here's a slight teaser then with the latest incarnation. By now called the 'Slight Return'...

 

[fig]

Here's the lastest rev, with the MID-SHIFT switch. S2 is DPDT, shown in the 1KHz position. S2A to the left and S2B up is 750Hz, right & down is 500Hz. R6, R7, C2 & C3 (all 6 caps) are all part of the tuned circuit. We can pick any three mid frequencies we want by fiddling C2 - C3, R6 & R7. R7 also sets the max height of the mid freq hump. I also changed Q2 to a JFET for lower noise. The MOSFET wasn't that noisy, but this is better. Any JFET with a high Vp will do. J111 is another good choice.

View attachment 27889

Dagnabbit, I just got the previous iteration working…

Which btw, is a fantastic circuit. It really expands the signal, opening up the dynamics with focus on MID / BASS shaping, without the GAIN overpowering whole thing. Plenty of volume over unity. Very nice indeedy.

Edit: I meant to add..the breakup is smooth and plays really well with guitar volume. With my ‘63 Tele into the blackface it was a nice growl when digging in.

 

[Chuck D. Bones]

Ooooh, 63 Tele. Chuck like!

Have you tried the subbing the MC3476 for the LM308 yet?

 

[fig]

Fig like too! It’s way more instrument than my skill level requires but it sounds so darned good.
I have a 3476 out and ready to go and hope to get back to it this evening. I’ve 2 or 3 BBs awaiting correction or in this case, substitution .

 

[fig]

I exchanged the LM308 for a MC3476, scuttled C6 for a 470KΩ from U1-8 to GND. I thought the MC3476 sounded a little more ‘mellow’ than the LM308, but TBH it could have also been a breadboard ghost.

What I do know, is this time I fed it various pedals (one at a time); A fuzz,phaser, and autowah. It handled them all very well IMO. It’s a definite keeper.

 

[Chuck D. Bones]

I thought the MC3476 sounded very similar to the LM308. It's good to have an alternative for the hard-to-get LM308.

I plan to try subbing it in other pedals.

 

[fig]

I thought the MC3476 sounded very similar to the LM308. It's good to have an alternative for the hard-to-get LM308.

I plan to try subbing it in other pedals.

A sound choice sir. Thanks!

 

[cooder]

Here it is in the flesh, thanks so much @Chuck D. Bones for seeing this through and nutting it out.
It rips and is pretty versatile with the mid shift, bass control and all. I dig it! Noice noice noice!

 

[Chuck D. Bones]

SWEET! Is that an LM308 or something else? I don't recognize the part no.

 

[cooder]

It's the Russian 'workalike' of LM308 (has I think an even slower slew rate). I don't have any legit LM308 here at the mo, and the Russian one didn't sound too bad in Rats that I did. I still would like to get a legit LM308 in there, one of those dayz, to hear and enjoy...

 

[cooder]

Any JFET with a high Vp will do. J111 is another good choice.

So does that mean I should consider one of my very hot J111 instead? Would that be better with a very high Vp or will J112 just be fine? Should I select J112 for a higher Vp from a few specimens?
Cheers

 

[Chuck D. Bones]

We already know that your J111s are too hot. J112 is recommended. Anything that gives a source voltage between 3V and 6V in that circuit will suffice.

 

[cooder]

Here my latest incarnation, it has a switchable buffer output which Dave conjured up for Warren and me, because he's that sorta nice genius guy. Called it vintage/modern.
Works noice, I did throw in a metal can Motorola LM308 and Mullard OA6 Germaniums for a bit of extra sauce.

This one is mine mine mine and stays on my board.

 

[Chuck D. Bones]

Beautiful!
Hey, where did you get that bitchen LM308H?
The Vintage/Modern switch, is that a gain switch on the output booster?

 

[cooder]

Hey, where did you get that bitchen LM308H?

Found it in the couch fold at my great aunties, must have dropped out of her hearing aid receiver device.



haha.
Yes the vintage modern is the gain switch. Also bitchin'.