Woolly "James" Mammoth

Stompboxes circuits published in magazines, books or on DIY electronics websites.
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~arph
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Post by ~arph »

Hi,

I'm building some mammoths, with improved tonestacks.
Here's the schematic I'll be using. Kudo's to the creator of the James stack. I don't know who it is, but I think I first saw it in the James Muff and the SFT. It must go way back though..
The output buffer is also from the James muff.

Merry christmas!
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Post by soggybag »

Great idea, I had just been planning a Woolly Mammoth with a BMP tone control.

I'm guessing that R5,6 is a pot and R9 and R10 is another pot.

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Post by oldgravity »

~arph wrote:Here's the schematic I'll be using. Kudo's to the creator of the James stack. I don't know who it is, it must go way back though..
The James is the passive version of the Baxandall tone control - I believe it's so named because Peter J. Baxandall's middle name was James. So this would be from the 1950s.

Here's the original paper:

http://home.comcast.net/~stphkeri/Negat ... ckTone.pdf

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Post by ~arph »

Yes R5,6 and R9,10 are pots

also note that the "Wool" control is missing from the schematic. There should be a 2kB pot between the negative side of C3 and GND
Plus to tame the noise I got when built, I placed a 220pF between the base and collector of Q1
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Post by oldgravity »

oldgravity wrote: The James is the passive version of the Baxandall tone control - I believe it's so named because Peter J. Baxandall's middle name was James. So this would be from the 1950s.

Here's the original paper:

http://home.comcast.net/~stphkeri/Negat ... ckTone.pdf
Nope, I was wrong. The James is by E.J. James, and here's his original article:

http://home.comcast.net/~stphkeri/James ... ontrol.pdf

So the James tone stack actually dates to the 1940s!

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Post by ~arph »

Ha,

And that document has a correspondence in it that says it was designed by Michael Volkoff in July 1939

So perhaps it should be the Volkoff tonestack then.. :lol:
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Post by soggybag »

What should the pot values be for R5,6 and R9,10? Looks like you have two 1M resistors for R5,6 and two 500K resistors for R9,10.

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Post by ~arph »

Well, it's the james tonestack from the 21st century big muff.

Bass 1M lin, and treble 500k Lin or 1M lin. Both work fine.

It looks a bit funny since the schem is from LTSpice. I was simulating the circuit and decided to throw it out here as I had it drawn up already. That is also why the wool pot is missing. I have it at max gain here.

I was simulating the tone control settings, that is why you see no pots there but two resistors with a parameterized value.

One resistor has value {1meg * param}, the other {1meg - 1meg * param} If we step the param between .1 and .9 then the first resistor will go from 100k up to 900k and the latter from 900k to 100k, hence simulating a rotating pot. The point these two resistors connect is the wiper.

When I built it, it was too noisy with the wool maxed out, so I added the 220pF
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Post by soggybag »

I have this in the breadboard right now! I put it together a couple days ago. I hadn’t seen this post until just now!

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