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:

Let me zoom-in to the tone control only:

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:

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:

And with the 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:

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).

Designators	Component	Notes
	Breadboard	Any breadboard will do, I used full size breadboard. You probably don’t want anything smaller than that.
	Jumpers and wires	As many as you need. I got some online, but 24 AWG solid core wire will do just fine.
	9V battery	I used 9V battery snap with Dupont wire.
IN	Switchcraft 12B	In – stereo jack (mono will do too)
OUT	Switchcraft J111	Out mono Jack
RV1, RV2, RV3	Alpha 16mm 100K linear pot	Any 100K linear pot will do, I used 16mm with PCB pins
C1	10n (0.01uF)	Metal film PET cap
C2, C13	220pF	Ceramic C0G cap
C3, C4, C7	220n (0.22uF)	Metal film PET cap
C5	470n (0.47uF)	Metal film PET cap
C6	4.7uF	Electrolytic cap 25V
C8	47uF	Electrolytic cap 25V
C10	100uF	Electrolytic cap 25V
C9	100n (0.1uF)	Ceramic X7R
C11	330nF	Metal film PET cap
C12	2.2nF	Metal film PET cap
D1-D6	1N4148	Small signal diode for clipping
R1, R3, R16	2.2M	1% 250mW metal film
R2, R5, R8	1K
R4, R10, R11	10K
R6, R12	470 ohm
R7	5.6K
R9	100 ohm
R13	47K
R14, R15	100K
U1	TL072	op-amp

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:

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).