Framus Tone

[Muzzatron5000]

HI all!
I was wondering if anyone could help me with a small issue.

I made COT-50 and sounds great. I wanted to control the mids more so I added Framus style tone circuit after the volume pot.
So it goes from PCB > vol > mid control > output jack.

Is this the right place to put mid control pot?

Ive noticed that volume of the output changes as I rotate the mid control. Should I expect this or is there a better way to wire a tone after a vol pot?

Thanks,

[GibsonGM]

Typically one would find the tone control, and then the volume pot, Muzzatron (welcome, by the way).   Can you post a schematic of the COT-50?

Yes, they will interact...the value of the volume pot may matter too, so seeing the circuit would be helpful!

[Muzzatron5000]

HI - thanks for the welcome. I've been reading stuff on here for a while now. But still bit of a newbie.
The COT-50 is pretty simple I guess. Everything I mentioned above happens after the output stack of the board.

[antonis]

Framus Mid Control DOES behave as Volume pot

If you replace 1nF caps with their equivalent resistance for any given frequency, you result into a grounded (via 1nF and 100k resistor) pot lug 1..

Even for low frequencies, where caps impedance is larger than pot resistance, next effect input impedance is set in parallel with wiper + pot lower part + 1nF impedance + 100k, acting as lower part of a voltage divider configuration..

[FiveseveN]

That's not a schematic nor does it include a volume pot. The original only has the gain/"bias" control and so does any schematic I've found but if course it's trivial to tack one at the end like most takes on the Electra Distortion do.
Unless you add a buffer between the controls they will interact indeed. You could get away with scaling the tone control circuit by 10 so you have a 10K mids pot with a 100K volume pot, reducing the interaction. And definitely put the tone circuit before the volume pot.
It's a simple/primitive circuit from the '70s, you can't ask too much of it lest it stops being simple.

[Muzzatron5000]

Yep Ok thanks. Ill try reducing the size of the 1M pot. See how that goes. Thanks

[antonis]

Ill try reducing the size of the 1M pot.

You'll dractically alter filter's responce if you don't reduce 100k and increase 1nF caps valuew simultaneously..

[FiveseveN]

Oh dang, I read the mids pot as 100K, too early in the morning. Scale the values 100:1 then  .

[GibsonGM]

I simmed this for the fun of it, it works very well with 10k mid pot, 100n caps and 1k R to ground, ie., scaled.   

[Muzzatron5000]

Thanks GibsonGM

So is it possible to simulate the same set up using this?
https://www.guitarscience.net/tsc/framus.htm#RIN=1k&R1=100k&RM=1M&RL=1M&C1=1n&C2=1n&RM_pot=Linear

[GibsonGM]

It sure is, Muzz. Just hit the 'edit' button and enter your values, then 'apply'. 1K for R1, RM=10k, 100n for the 2 capacitors, and 100k for "RL", simulating the vol. fully up. 


I don't know the output impedance of the transistor stage...that is "Rin". You can leave it 1k and still see the general shape of what's going on.   If it is actually lower, that is better.     Close enough for gov't work! 

[antonis]

I don't know the output impedance of the transistor stage...that is "Rin".

3k3 for Collector signals of lower than 1N914 forward voltage drop..

3k3 // (0.026 / I_Diode) for signals of higher than 1N914 forward voltage drop..
(ridiculously low..)