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Guitar Amp Tone Controls

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Guitar Amp Tone Controls: Tone and Gain Sucking Leaches?

Guitar amps have tone controls. Always have, always will ... maybe.

More tone controls are better - treble, middle, bass - a tone stack for every channel! Always has been, always will be ... maybe not!

WHY?

Tradition is a powerful thing and change is hard to make. But, if you consider how tone controls affect an amp's signal chain, investigate what a guitar and amp sound like with minimal tone controls (or none!) and then decide if you REALLY need them, you might be surprised at your conclusion.

Tone controls change or modify the tone of an electric guitar signal as it passes through an amp. However, the primary determinant of how your electric guitar sounds is the instrument itself, the amp's overall design (gain stages, pre vs. power tube overdrive, etc.), its tubes, the speaker(s) and YOU the player. Tone controls are but one in a long line of factors strung between your brain, your gear and your ears.

We all have used tone controls to change the sound that our amp produces. Roll off the bass for a humbucker equipped guitar; trim the treble when you plug in that ice-pick Tele; peg the bass when playing your Strat; boost the mids to cut through the mix. All useful stuff. But, what would you sound like if you didn't have tone controls at all?

In my opinion, despite their tone tweaking usefulness, traditional tone controls can detract from the quality of the tone ... if you consider what your amp would sound like without them. Let's dive into the nature of tone controls to find out why I hold this wacky belief!

Virtually every tone control you'll run across, at least in a typical tube amp, is a ‘passive' device. That means that it cuts or reduces the volume of certain frequencies. A passive tone control cannot boost frequencies.

Terminology check: tone controls are often referred to as ‘tone stacks'. The passive components that comprise tone controls - resistors, capacitors and potentiometers - are connected in such a way that when they are drawn on a piece of paper - a schematic - the treble, middle and bass controls look like they are ‘stacked' on each other. That's where the term tone stack comes from.

Because tone stacks are constructed from passive components, even if you turn the knobs up to 10, each tone control still reduces certain frequencies.

Yes, that's right. With passive tone controls there is no such thing as a TRUE ‘flat' setting where the signal is not affected in any way - there is always some signal loss.

What the heck does all that mean?

Below is a graph that shows the frequency response of a typical treble, middle, bass (TMB) tone control often used by an amp company originally located in southern California. The graph depicts the level of frequencies with all the tone controls set to 10. As you can see the signal level at all frequencies is well below 0 dB -- that means that the signal level is being attenuated or reduced as it goes through the tone stack - even at a 10 setting (yes Nigel, the same would hold true at 11 too!).

Typical_Tone_Control_Response.jpg

What does this mean? Two things.

First, a tone stack reduces the overall level of your signal. That's why amps with traditional tone stacks need an extra gain stage to return the signal to its level before it got hosed down by the tone stack - more components, more cost, more complexity.

Second, even when all the knobs are on 10 the stack is changing the tone profile of your signal. The tone stack's frequency response as shown in the graph has a big dip centered on 300 Hz. That means that the volume level of those frequencies around 300 Hz is a lot less than the rest of the frequencies - a cut in the low mids.

Here's our tone stack's frequency response set to provide a flat frequency response. Note that although the tone controls are not shaping the tone - all frequencies are being passed at an equal level - the signal has been severely attenuated across the board.

Tone_Control_Flat.jpg

You'll likely be surprised to learn that to produce this ‘flat' response the controls have to be set as follows:

Bass = 1

Middle = 8

Treble = 0

I bet that's not where you set your tone controls!

There's a few things at play here. First, at this flat response point you have to really boost the volume to compensate for the gain loss through the tone stack. Second, it shows how much the typical tone stack scoops mids - bass and treble have to be severely attenuated to match the low mid-frequency response of the stack. Finally, this shows that the tone controls are highly interactive and changes in one dramatically affect the other - you have to dial in crazy settings to get a flat response.

So, if it takes this dramatic an alteration of your tone controls to get a true representation of what your guitar sounds like why bother?

Is all this ‘bad'? Not necessarily. The tone stack in question has been used in dozens of amp designs that produce great tone. Maybe you won't like the true sound of your guitar!

However, I want to plant a crazy idea in your brain: what would happen if you didn't have a tone stack or you had a very simple tone control that could make subtle tone changes, but would not suck nearly as much gain and would not dramatically alter the frequency response of your guitar?

Well, in my experience you can really ‘hear' your guitar(!) ... you'll hear a more balanced tone coming from your rig. Your tone will have more presence and, with an amp that has been designed with minimal or no tone controls, you will experience a more responsive, dynamic feel. If you like that sort of thing it's VERY cool!

Of course, it's impossible to properly convey the sound of a ‘tone-stackless' amp on a piece of paper ... you have to hear the difference!

So, when you see amps with minimal tone controls don't dismiss them. Play through them when you get the opportunity so you can see for yourself. You may be surprised at what you hear and feel!