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Clíodhna My Designs Overdrive

Clíodhna – Tone Control

So far so good 😊. The first and the second part went pretty well. Let’s plough on. In this post I’ll cover tone control. The previous parts were dealing with clipping section – clipping and frequency response shaping. I conveniently omitted tone section. Now it’s time to add the tone stage.

You can jump to schematic, or breadboard diagram if you wish.

As usual, if you can’t be bothered to read, just skip to the video. You can always come back for more detail.

Tone Stage – Phase 3

In this part I’ll cover tone options. When I was breadboarding a Tube Screamer, I noted that it uses G taper potentiometer. This is to give better control over tone in the middle part of the rotation. Linear pots have poor control in that kind of a circuit.

I prefer using linear pots just because they are easier to source and I have a few of them. So my take is a slightly different circuit, but I tried to retain the sound signature of the TS.

Let’s look at the schematic:

Schematic showing my super Tube Screamer like pedal. The circuit has Tone Section now.
Clíodhna – schematic after adding Tone Control (click for full image)

Let me zoom-in to the tone control only:

Schematic of only tone section of the pedal
Tone Section only (click for full image)

Hold on …

That looks different!

Well, yes.

This is a slightly adapted Baxandall circuit and it only controls higher frequencies (let’s say treble). I chose it since it offers good control with a linear pot, and tone control of TS does just that, controls treble.

I modified the basic circuit to add a low pass filter (R12 & C11) before it to, so the frequency response is similar to the TS. I also added another low-pass filter (R14 & C13) mainly for my treble booster option.

The switch SW3, when ON, engages the low pass filter and gives us TS like response, and when OFF, it removes the filter and gives us a sort of a treble boost (like a Rangemaster – still different sound, but spiritually similar 😁).

That’ll sound different!

Well … not so much. I did a few attempts to get the sound just right, tweaked component values etc. The circuits are different and it’s tricky to get the sound exactly the same. Having said that, for the 90% of the pot rotation, it sounded the same as TS to me.

Frequency Responses

Here are frequency responses from SPICE:

Frequency response comparison

While it might look quite different on the first glance, the difference is really at the far end of rotation. The vast majority of the middle of the graph matches very closely.

If switching the treble boost on, we get quite a big difference in the output. So without treble boost:

Frequency response diagram of the tone control for our pedal when treble boost option is not switched on
“Normal”/TS option for tone control

And with the treble boost on:

Frequency response of the tone control when the treble boost option is ON
Treble Boost ON

Note that the diagram showing Treble Boost ON starts at 12dB. For treble boost OFF diagram it starts at 4dB.

Breadboard

Things are getting messy with breadboarding. Here’s the diagram:

Diagram of the pedal on a breadboard with tone control
Clíodhna – with tone control

I question the value of this diagram though. Without being able to follow schematic it’s really difficult to piece everything together. It’s just a reference point for video I suppose.

After a while, bigger builds, they look as just a big unyielding tangle of wires.

Bill of Material

Below is the BOM used for this demonstration. There’s a bunch of new components – well, 9. The Pot, 5 resistors and 3 caps (instead of the switch I used a wire, for now).

DesignatorsComponentNotes
BreadboardAny breadboard will do, I used full size breadboard. You probably don’t want anything smaller than that.
Jumpers and wiresAs many as you need. I got some online, but 24 AWG solid core wire will do just fine.
9V batteryI used 9V battery snap with Dupont wire.
INSwitchcraft 12BIn – stereo jack (mono will do too)
OUTSwitchcraft J111Out mono Jack
RV1, RV2, RV3Alpha 16mm 100K linear potAny 100K linear pot will do, I used 16mm with PCB pins
C110n (0.01uF) Metal film PET cap
C2, C13220pFCeramic C0G cap
C3, C4, C7220n (0.22uF) Metal film PET cap
C5470n (0.47uF)Metal film PET cap
C64.7uF Electrolytic cap 25V
C847uF Electrolytic cap 25V
C10100uF Electrolytic cap 25V
C9100n (0.1uF)Ceramic X7R
C11330nFMetal film PET cap
C122.2nFMetal film PET cap
D1-D61N4148Small signal diode for clipping
R1, R3, R162.2M1% 250mW metal film
R2, R5, R81K
R4, R10, R1110K
R6, R12470 ohm
R75.6K
R9100 ohm
R1347K
R14, R15100K
U1TL072op-amp
List of components for Clíodhna – phase 3 breadboarding

The Video

Here’s the video with me trying out some of the options covered in this post. I employed a looper for this so I can fiddle with tone control. With two extra options and 9 different sounds from the previous two posts – that’s 18 options 😮!

Hopefully I did a half decent job with this – check it out:

Trying the tone control out

More I listen to it, more I like the sound. I’m totally biased 🙄. Some settings suite more chord playing, some comping and some individual note soloing (and different settings on different parts of the neck sounds nicer).

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