Post by StratLover on May 18, 2005 14:39:07 GMT -5
What type of guitar are we talking about ?
I had to ask. ;D
Anyway, here are some notes for you to take in, courtesy of John Atchley.
Tone Control Circuits: "First, understand that all "passive" controls, such as those used in Strats, are "cut" circuits. You are not "boosting" mid-range when you turn a tone control down -- you are "cutting" or throwing away high frequencies!
Capacitors have a very useful property, the impedance (total resistance) of a capacitor varies with frequency. At high frequencies the impedance is low, while at low frequencies the impedance is quite high. We combine capacitors and variable resistors (potentiometers) to make adjustable tone controls. There are several ways such controls could be wired, but we will look only at circuits as they appear in Stratocasters. Below is a simplified schematic showing a single tone control:
Simple Tone Control
Remember that the impedance of a capacitor varies with frequency? And that the impedance (resistance) of a resistor does not? In a nutshell, that is why the tone control works. As the variable resistor is cranked up to a very high value, the difference in the capacitive impedance for high and low frequencies becomes insignificant in comparison. Without getting heavily into the math let's use some easy numbers to see how it works. Let's say just for the sake of argument that the impedance of the capacitor is 25k ohms at 4khz, 12.5k at 8khz, and 50k at 2khz and that the pot is a 250k ohm pot:
When the pot is turned down there is 0k resistance (a short circuit) across it. Therefore, the impedance of the entire circuit will be 50k at 2khz and only 12.5k at 8khz. Thus, high frequencies have a much "shorter" or "easier" path to ground than low frequencies do. When the pot is turned up there is 250k resistance across it. Therefore, the impedance of the entire circuit will be 300k at 2khz and 262.5k at 8khz. The impedance is still lower for a high frequency signal -- but only by a very small ratio. Note that this circuit would not work in a "perfect" world! If the input signal were regulated such that the voltage never varied regardless of the load impedance and the amplifier on the output had infinite impedance and no padding -- this circuit would not vary the tone. However, magnetic pickups are not regulated and they are capable of delivering only a tiny amount of current. I'm trying to avoid complex math in these pages so I'll oversimplify a bit and simply say that as the load impedance (represented by the tone control) goes down, the voltage that is output by the pickup goes down too. Since the first gain stage of the amplifier is basically a voltage amplifier the final signal decreases with the voltage at the tone circuit.
In short, the tone control works because the impedance of the tone control is lower for high frequencies then it is for low frequencies -- which "pulls down" the high frequency output of the pickup.
I truly think that a TBX control is the most versatile of ALL tone pots. You get a real wide range tonally from great highs and harmonics all the way down to...........ummm smoky and semi muted, but still crystal clear and very distinguishable audibly."
When wiring caps in a series, experimentation is really the only way to find the tone and balance you are looking for. So you are definately doing the right thing by experimenting to find YOUR sound.
I myself LOVE a TBX with a 1meg. resistor and .010 cap. This tied in series to a .0223 on the second tone pot gives a pretty nice variance and mix of tone.
This setup is used in my Stratocasters(tm) and Telecaster's(tm) as well.
"Shoot for the MOON you just might miss and hit the STARS"
The mathematics of capacitors in series is similar to resistors in parallel. On my website, I have the formula and calculator to compute this: www.1728.com/resistrs.htm
An easier way (at least for calculations) is to combine capactors in parallel. In that case it is simple addition. For example, a .02 mfd capacitor in parallel with a .03 mfd capacitor makes a total capacitance of .05 mfd.
I was just reading a thread that mentioned wiring various caps in series to achieve new values;
That may have been me, relating to an idea to provide switching between tone cap values. The idea is that the lower the capacitor value, the higher is the frequency at which the tone control starts to roll off the treble. This is different to jsut not turning the tone pot so much.
As Wolf says, you can arrive at new cap values by adding them in series or parallel. With paralel, you just add them up, and the more you add the more capacitance you get. Putting them in series, the net result is less than that of the individuals. Wolf site has the math automated (clever chap that Wolf - ive no idea how he did that!)
For the idea of switching between tone caps, I have a hunch (untested) that it is better to do this with a chain in series, using switching to short some out, than by cutting between different disconnected capacitors. Im thinking there will be less switching 'pop' caused by static charges in the caps with the series arrangement, since they are always in circuit or drained.
Thanks to all of you guys for your responses; I got the layman's terms, the mathematical formula, and a summary by the the dude who's comments lead to me writing this thread!
I can tell you that all three of these responses are crucial to my happiness and well-being! ;D
Stratlover; It just so happens that we're talking about a '99 Jeff Beck Strat, though I've swapped the Laces for a Duncan PG+ in the bridge and SSL-2's N + M; I bought the set in a pre-wired pickguard, used. I can appreciate the TBX tone control (though I no longer have one), and it sounds like the way you have it set up is very useful. As I said, I've been doing some experimenting with wiring, but at the moment I haven't had time to get it back together, so I will elaborate more on this in the future. I'm actually considering trying a set of Bill Lawrence PU's (noiseless "single" coils).
Wolf; Thanks for the link. I've been looking at your diagrams for some time, and I'm actually starting to understand them! (I think).
John H; I believe that was your cap info that sparked my curiosity; always a good thing.
Again, thanks all; I'll post the results of my experiments when I get there...