Adding a tone control to Devi Ever's SM/VFM

[gonkulator_modulator]

Hi guys,

I want to add a simple tone control to my Devi Ever Soda Meiser/Vintage Fuzz Master (http://www.shoegazers.org/viewtopic.php?f=192&t=4191, something like Big Muff tone control. So where should I place it? Before the Volume pot instead of 10k resistor and 0.1uF cap? Or maybe before the third MPSA18? Sorry for the dumb question, I just want to understand the things better Any help will be appreciated.

[blooze_man]

Right at the end before the volume control usually works. I would build a tone control on a breadboard and plug your pedal into it and tweak before I commited to anything.

[familyortiz]

Gonk,
  I would concur with Blooze on placement before the volume pot. The 10k is a pullup resistor and the 0.1uF is a coupling cap to block DC from the output. Those should stay. I would actually use a higher value of cap myself for the coupling cap on the order of 1uF but you may try it as is. When I added a tone control like what you're doing, to the GGG Red Llama, I used a 10k tone pot and 0.1uF in series to ground.  It was right in the sweet spot, gave me a good tone range and made the pedal much more useable.

[gonkulator_modulator]

Thank you, blooze_man and familyortiz, for your replies Should it be smth like this?

[slacker]

That won't work R8 and C7 need to stay conencted to the collectors of Q3 and 4, like on the orignal schematic. The tonestack then goes between C7 and the volume pot. Like familyortiz said you might want to make C7 larger.

[gonkulator_modulator]

slacker, thanks OK, I've redrawn the schematic. Another stupid question: why should I make the coupling cap larger? What would it affect?

[familyortiz]

Capacitive reactance , essentially ac resistance, is inversely proportional to the cap value, i.e., more high frequencies will get thru with a higher value. If you like the frequency response with the current value, don't sweat it.

[gonkulator_modulator]

Thanks everyone for help I'll try different C7 values. I'll also breadboard the tone control as blooze_man advised. Maybe I should tweak some components values for the best tone

[bikini-inspector]

evening girls and guys

long time lurker's first post, so first of all: hello nice to be here


i built the soda meiser a couple of months ago and really like it for home use. However, in a band context, all i get is raised eyebrows from the bass player..

so i've been messing with a tonecontrol and different coupling caps. This is where i'm at right now:

- added .22uF (224) cap parallel to C7, not quite sure yet if it's going to be switchable (any thoughts?)
- c5 100nF (104)
- c6 100nF (104)
- R6 2.2K
- R7 4.7K

values were chosen by availability. When i checked with the tonestack calculator, this should give me a rather flat response, as don't want to lose the middle frequencies, maybe i'll even go for a TS-like slight mid hump.

also, I intend to insert a bypass switch for the tonestack.

what's interesting: increasing C7 doesn't seem to have any effect when the tonestack is bypassed, any idea why that is?

looking forward to learn about your findings...


edit:

more high frequencies will get thru with a higher value

really? I felt higher values give the thing more overall bass.....?

what i have always thought: caps can only pass high frequencies. The bigger the value, the lower the frequencies that can pass the cap.
So a cap in series (as in this case) is a kind of high pass filter, by increasing the value, more low end can pass through.
A cap to ground dumps the high freqs and only low freqs are left over. Increasing values determines how much of the high spectrum is "dumped"

have i always been wrong or has there been some kind of mixup? I dunno &%§! about ac resistance and capacitive reactance...all i had was this "explanation" ...

greets

[gonkulator_modulator]

bikini-inspector, hello and welcome I've just read the same 'bout caps. Increase of the cap value lets more bass through. BTW, very good idea to make the tonestack bypass.

[Ice-9]

Yes indeed, a bigger value of cap in this situation will let more bass pass.

If the cap is going to ground it would work in the opposite way . ie bleeding more bass to ground

[familyortiz]

"what i have always thought: caps can only pass high frequencies. The bigger the value, the lower the frequencies that can pass the cap.
So a cap in series (as in this case) is a kind of high pass filter, by increasing the value, more low end can pass through."

Good observations. Why is it that caps only pass high freqs and that a larger value of cap will let more bass thru? In reactance land, as I mentioned, this value is inversely proportional to the value, but what is just as important is that it is also inversely proportional to frequency:      Xc = 1 / (sC)     where C is cap value and s is frequency. As you can see, the Xc goes down for either higher cap value or higher frequency. You guys are exactly right... the bigger consideration here is improving bass response, but you can also see that there is an effect on high frequency response as well. I was thinking one dimensionally!

As to the filter comment, with a cap to ground, this statement, "A cap to ground dumps the high freqs and only low freqs are left over. Increasing values determines how much of the high spectrum is dumped" is more accurate than, "If the cap is going to ground it would work in the opposite way . ie bleeding more bass to ground."     That is why higher value tone caps, like a 0.1uF in a Strat are used for warmer, less trebly tones as opposed to a .033uF cap which will give more treble. In this case, the passing of the highs to ground is a greater consideration.