Tell me about tone stacks and gain stages

[Eric]

For anybody who cares to comment...

What's a tone stack? What is gain staging?

My impression is that both of these terms refer to multiple opamps working in series in the path of your signal from the guitar to the speaker and the subsequent effect they have on your tone. Is that even close?

Reason I ask is I'm working on going DI to the house at church soon (with a T21 Sansamp GT2), and I usually play with a pretty good dose of OD/distortion. I want to know if this is something I'll have to take into consideration when fine-tuning my tone as far as how it'll sound in the house PA. I've been told that if you use too much gain on the guitar end, the tone stack in the house PA (maybe referring to the mixer EQ?) can make it sound thin and dumpy coming out of the house speakers.

Moreover though, I've just heard these terms for a long time and want to know what they mean.

 

[tunghaichuan]

I'll take a stab at this, but any of more savvy technical guys please feel free to chime in and correct me.

For anybody who cares to comment...

What's a tone stack?

This refers to the tone shaping circuitry, usually in the preamp. It is called a tone stack because on a schematic, two and three band tone controls are stacked one on top of the others.

What is gain staging?

A gain stage is simply what the name says, it adds gain to the signal. Gain stages in guitar amps take the relatively weak output from the guitar's pickup(s) and make it bigger (louder).

My impression is that both of these terms refer to multiple opamps working in series in the path of your signal from the guitar to the speaker and the subsequent effect they have on your tone. Is that even close?

That is pretty close. Gain stages add gain to the signal, and the tone stack shapes the sound of the signal. Some tone stacks eat up a lot of gain, so an extra gain stage is required to make up for the lost gain.

Reason I ask is I'm working on going DI to the house at church soon, and I usually play with a pretty good dose of OD/distortion. I want to know if this is something I'll have to take into consideration when fine-tuning my tone as far as how it'll sound in the house PA.

Tech 21 amps sound pretty good when using the DI, or so I'm told. I had one of their amp emulator pedals a while back, and I thought it sounded very good. So I don't think you need to take gain stages or the tone stack into consideration.

Moreover though, I've just heard these terms for a long time and want to know what they mean.

Hope my explanation was helpful.

 

[Eric]

Hope my explanation was helpful.

Indeed -- it at least gives me a foothold. Thanks!

 

[Eric]

That is pretty close. Gain stages add gain to the signal, and the tone stack shapes the sound of the signal. Some tone stacks eat up a lot of gain, so an extra gain stage is required to make up for the lost gain.

Couple of questions about this:

1. This is because the tone stack is comprised of capacitors and potentiometers, correct? In that same way that having a tone control in the circuit of your guitar will suck a little bit of bite off the top end, the tone stack can sometimes be a 'tone suck' and pull off not only gain, but also some subtleties of the tone. Is that accurate?
2. I imagine that what I described above is how passive tone controls work. For active tone controls, does each tone knob (treble, mid, bass) have a capacitor and then an opamp to kick the signal up for active control?
   
   OK, so I guess it was a 'few' questions...
3. What makes a tone stack eat up a lot of gain? Just the value of the capacitors in the circuit? I imagine it's probably more complicated than that.

 

[kiteman]

Passive tone stacks are usually a series of pots and caps where certain values of the caps affects certain bandwidths of freqs. They can only cut not add to the freqs.

The active tone stacks boosts as well cuts the freqs. You may notice that they have a "notch" midway on the knobs. This is neutral where it's not cutting nor boosting the freqs.

Gain stages is where the signal are multiplied to a bigger signal in stages. For example a preamp tube has two stages ( 2 triodes in one) it can do to amplified the signal. The signal may go through one or more preamp tubes before it hits the power tubes. Same thing with transistors, they also work in stages from small transistors to power transistors.