Three passive one-knob tone controls

[dylan159]

This is more of a building block than a complete pedal, but I think it fits here.

I've been having fun with BMP-inspired tone controls lately, trying to make one-knob tone controls with different responses. Like any passive tone control, the original muff included, they are lossy and represent a noticeable load, so they work best with loud signals and decent impedances. I've modeled them in spice without much change with 1K output Z at the input and 500K input Z at the output, but 10K at the input already starts to take a toll. Like I said, that's true for the muff tone control as well. One could tweak the values to offer the same response with worse impedances by making them less of a load, but then they would work just with that impedance and offer less effect at more optimal impedances.

It wasn't until I was finished with these that I found out that AMZ had already done a lot with this kind of tone control, but unlike his presence control and double tone, these keep the one-knob nature while still offering a very different response, so they can be viewed as a simpler alternative. The Celeriac is a different thing instead.

Let's start with the Aubergine, a joke on being the opposite of a muff. All I did here was swapping the two capacitors around, and guess what? you end up with something similar, but with a slight mid hump at noon.

aubergineplot.png (5.99 KiB) Viewed 2445 times

The next step was to tweak some values so that the response was completely flat at noon, and here's the Starfruit. Of course the two filters end up having the same values, just one being lowpass and one highpass.

starfruitplot.png (5.34 KiB) Viewed 2445 times

Finally the Celeriac. This is still inspired by the big muff (which as AMZ told me it's actually been around from the 40s as tone control), but I thought "what if I have the two filters in series, controlled by the same knob, so that I can cut both bass and treble at the same time?" It got some time and tweaking of values but I finally got a tone control that goes from flat to all mids! Of course there's more tweaking that can be done to tailor the response in each case, but this one peaks at about 1KHz. Note the log pot.

celeriacplot.png (7.11 KiB) Viewed 2445 times

Here's some sound clips simulated with ltspice, so take them with a grain of... spice.
https://soundcloud.com/luciano-de-bened ... ntrol-demo


https://soundcloud.com/luciano-de-bened ... ntrol-demo


https://soundcloud.com/luciano-de-bened ... ntrol-demo

[Cub]

Hi Dylan,

That's some great stuff, especially the Celeriac ! Great to hear them all on a level playing field, that really makes the differences more audible.

Recently, my favourite recipe for a Muff control has become two 27k resistors, paired with two 4,7nF and two 10nF resistors on an on-on-on mid switch: dip-flat-bump, flat having the two 10nF caps engaged. It's almost identical to your Starfruit.
Some might like 39k in the low pass filter better (R1 in your Aubergine and Starfruit) for slightly more attenuated lows, but you'll still get ever such a slight dip in the flat position.

I thought about using a dual ganged blend bot instead of an on-on-on switch, but I'm not certain if there are enough useful sounds in between those three settings to make a pot necessary.

thanks for sharing this !

[dylan159]

Thank you for your appreciation. Of course anything has already been done to the muff stack in terms of values, and i should make clearer that my values are temptative and should be tweaked to taste. I had already done the cap mod in my muff a while ago, now I wanted to try and go a little further, but keeping it passive, small and one knob.

[Cub]

I should make clearer that my values are temptative and should be tweaked to taste.

Oh, but that goes without saying ! That celeriac should work great in a pedal that's more aimed at playing leads, I'm going to breadboard it the next time I'm building a Muff type pedal.

[dylan159]

Great! Somebody else trying them was just what i was hoping for! It should really change the character of the muff

[Cub]

Don't wait for me ! It might be quite a while before I can get to it. But it looks like a fun addition to an LPB-1 as well.

Speaking of which, I googled to see if a project of a LPB-1 with a BM tone control already exists and found the one attached below It's hosted as the "Simple Mid Booster" on Experimentalists Anonymous, but I can't seem to find who originally came up with it.
I don't have Spice, but it does look quite middy in Duncan's Tone Stack Calculator already.

[dylan159]

I don't have Spice, but it does look quite middy in Duncan's Tone Stack Calculator already.

Middy indeed! look at this! Altough duncan uses a different y scale, so it looks exaggerated there

Senza nome.png (4.76 KiB) Viewed 2368 times

This is a more extreme version of the Aubergine, which is just a fun experiment swapping the caps already in there, before i moved on. Basically you have a permanent bass cut and you can only cut treble with this.
Then I started wondering: you can remove the 11M because it's so ridiculously high it has just a small effect on the very low bass. What you end up with is this:

Cattura.PNG (5.61 KiB) Viewed 2368 times

Which is starting to look like the celeriac, but with a fixed bass cut. Same circuit as you posted, just moved some things around. It's an interesting variation that lets you keep more treble without boosting the bass back.

[dylan159]

Here's a real world demo of the celeriac I've just made. Sadly I can't add it to the main post anymore
https://soundcloud.com/luciano-de-bened ... tone-stack

[Cub]

Ooh, I like the sounding when the knob is at 5 and 7,5 ! It's great to not only see the graphs but also how these circuits actually sound.

Your way with a fixed bass cut is a lot better than it was done in that schemo I found. It's as good as fixed anyway with those massive 10M and 11M resistors.