What component values affect.... website?

[donking2010]

I remember coming across some post somewhere stating there was a website or chart somewhere telling what different valued capacitors, diodes, resistors affected like Bass, Treble and so forth. Wondering if anyone had a link for that? Hopefully...

[WRGKMC]

There are thousands of pages on that topic. What you're dealing with is passive audio filters or RLC circuits. A coil, cap and resistor are at the heart of any equalizer except in a guitar you don't use additional op amps or transistors to boost the signal or make up for losses. A graphic equalizer for example uses finely tuned filters to boost or block frequencies. The formulas for doing this in a guitar are the same as building an EQ.

 

Most guitar circuits don't include a passive coil for a true audio filter. They instead use either a high pass circuit to cut bass or a low pass circuit to cut highs. The midrange comes from the pickup and instrument tones. When highs and/or lows are cut midrange is what's left over.

 

Gibson was one who used a circuit called a Varitone Circuit that included a 1 henry coil, and a rotary switch that had various caps to create a true passive filter that produced notch filters. All you need is amplification and you have an actual EQ circuit.

 

The problem with selecting components is cap values are manufactured in set values. .001uf, .005uf,.0075, .01uf, .035uf, .05uf, .075, .1uf, .35uf, .5uf .75uf etc are common values. Caps have tolerances that vary so the actual capacitance may not be dead on, plus their values drift as the caps age.

 

To get the in between values you use combinations of caps in series or parallel. Caps are added together using a mathematical formula like you do for resistors except caps additive in parallel and resistors are additive in series. This would make sense because resistors are designed to block voltage and caps are designed to pass voltage.

 

Caps in series use a formula using fractions 1/C eq = 1/C1 + 1/C2 If the cap values are equal the total fro the two caps in series is half the value of one of the two, the same way as resistors of like values in parallel is half.

 

Another method of varying the cap value is to pass or block some of the full audio signal using a resistor or potentiometer. The tone knob on a guitar does this giving you a variable amount or High or low pass filtering. Fixed resistors can also be used in the circuit so the caps effects on the signal are less drastic. A treble bleed (High pass circuit) often uses a fixed resistor so some of the lows are retained when the volume is turned down.

 

The real problem here is targeting the specific frequencies the guitar pickups and instrument itself produces. every pickup is different so you cant use the same values in every instrument. You can figure it out mathematically if you know what frequencies the pickup produces then use electronic formulas to target the specific frequencies you want to cut. Unfortunately this does take some education in electronics which involves using trigonometry and plugging in various component values to target the right frequencies.

 

This is what engineers do when designing circuits. They have a signal they want to change, then pick the right components to do the job, use the component values in formulas to get the proper outcome. If you know what's going in and what you want to come out of the circuit, the trigonomic formulas allow you to find the proper cap values.

 

From there it comes down to the easy part. You just build it and measure the input and output and confirm the math and quality of the components actually does the job. Math is always right so it comes down to the component quality and tolerances in getting results.

 

This is where most beginners get involved. They don't have the background in electronics and don't fully understand what the components do and even though they may have a basic understanding of what they do individually, they may not have a good enough picture in their minds eye to know what's happening with multiple components.

 

This is not that big a deal in simple passive circuits like you have in a guitar. I surely wouldn't expect someone to go out and get a technical degree just to manipulate a guitar circuit to get specific results. It would be much more simple to just buy a handful of components and swap them out till you find what you need under actual playing conditions using your guitar and amp. I do this myself. I do have a degree in electronics but its quicker for me to just swap a component then it is to crack out the test gear and calculator to compute what I would need to get specific results.

 

This is especially true on guitars because you aren't dealing with a single frequency like sine wave. A guitar produces all kinds of frequencies in a wide range including overtones, Open strings are going to produce different frequencies then your upper frets will so the tone shaping in the guitar is usually going to be very broad and basic. It wouldn't make sense to target a specific frequency unless all the strings can produce some fundamental tones within that frequency.

 

So by swapping a few different caps to target the offending frequencies you don't need usually gets the job done. Replacing the pickup is another way of changing the frequency range as well.

 

If you do allot of guitar work then there are some cool tools you can use to target the frequencies you want to block or pass. Soldering in 5 or 6 caps till you find the best value can be messy. It can be a pain in the butt on some guitars too. Pulling the pick guard off a Strat for example is very time consuming. What electronic techs use are called Decade boxes. You can buy or build one simple enough. Most have three rotary switches.

 

The first rotary switch has all the small cap values, .001, .0035, .005, 0075. If its a 6 or 10 position switch you can add the caps together and get a range of steps in between those values.

 

The second rotary switch in X10 and use values of .01, .035, .05, .075, etc. The third rotary uses X100 and uses values of .1, .35, .5, .75 and 1. Again in between values are obtained with caps in series or parallel.

 

From here you can have an input for your guitar and an output to the amp. Then you just select the cap values using the rotary switches using the multipliers to find the exact values that sound best. You can add a switch to put the caps across the signal to act as a low pass or in series with the signal for a high pass. The most you may need to do is clip the leg of the cap in the guitar to remove it from the circuit so it doesn't influence the signal. The rest can all be done outside of the guitar.

 

If you want to get real simple, You can take the end of the guitar cord and unscrew the metal cap so the hot wire is exposed and put a cap across the hot and shield to test different cap values. Or if you have an old cord, solder a couple of alligator clips so you can hook a cap across the hot and shield to act as a low pass or put a cap in series to act as a high pass. Then when you find the values and specific cap type that sounds the best you can then crack out the soldering iron and actually put the part in the guitar.

 

You can also build or buy decade boxes for coils and resistors the same way as you did for the caps. You can use all three and select the component values that produce custom filters for the guitar. Then you can either put the filter in the guitar or build it into a box you plug into.

 

Finally, reality kicks in here. Most values selected for instruments are already optimal and have a wide range of variance with most amps. The question comes down to what you specifically need. If a guitar needs a minor tweak swapping a cap can usually get the job done. If you want major tone shaping, its a "whole" lot easier to just buy an EQ pedal for $25 and be done with it. Reinventing the wheel to build your own filters is educational but not very economic, especially with the outrageous prices they charge for parts and shipping today. This is where scrounging old electronic gear and stripping the components can save allot of money.

 

 

[isaac42]

Why do you claim that only bandpass filters are "true filters"?

[WRGKMC]

I didn't. My point was if you want selective notch filter like you get with the sliders on a Graphic EQ you'd need a coil to have a full RLC circuit. Caps alone can only shelve high or low frequencies. They select a break above or below a point and pass or block the frequencies above or below a point.

 

Cap/resistor filters with a single resistor and capacitor are called one-pole filters. You can add a second cap and resistor to change the shape of the roll off but its simply multiplying the effect

 

If you use both series and parallel caps it can leaves the mids but you really cant shape the mids.

 

With a coil you can notch the mids with a sharp Q and leave the highs and lows. You cant do that with caps only. An RLC circuit can form a notch filter that only negates a narrow band of frequency. A Series RLC will attenuate a notch frequency and a Parallel RLC boost a notch.

 

This page does a good job in explaining many of the possible passive filter variations using these three components to create all kinds of filter shapes.

 

http://www.niu.edu/~mfortner/labelec/lect/p575_07a.pdf

 

Some are very cool. Many would need additional amplification to be heard well with the weak signal produced by a guitar pickup so you don't see many of these circuits in guitars. A coil for example is basically a long wire that can short most of the signal to ground when placed in parallel unless it has a resistor in series with it.

 

There are a few that will work fairly well without consuming too much of the source signal. A passive Varitone circuit for example leaves enough signal to be heard well through an amp if the pickups are strong enough. Given the cost of parts, switches, and the availability of low cost, high quality active circuits, you can do the same job much better with a low power consumption active circuit.

 

In a guitar like an ES335 you have plenty of room to install a 5 or 6 way rotary switch with all its caps. In a small cavity, your footprint needs to be very small and options are limited. Many of these miniature active filter circuits provide a 1:1 signal ratio with noise levels so low you don't know they are active. I use several of them in guitars and they do a superior job over passive components only. The battery life is in the 4000~5000 hour range on many of them so even if you put a battery in a hard to access place like under a pickguard you may only need to replace the battery once a year. I left one guitar plugged in for an entire week and it had no affect on the operation.

 

http://artecsound.com/pickups/electronics/index.html

 

Wiring them up is as easy as it gets so even an armature with minimal soldering skills should be able to get the job done. http://artecsound.com/pickups/electronics/wiringbook.html

 

Not sure if they sell direct but you can find plenty of resellers. http://www.ebay.com/itm/Guitar-Parts-Electronics-ACTIVE-CIRCUIT-ARTEC-EXP-ONBOARD-Tone-Expander-/191153601188

[donking2010]

Whoa WRGKMC a wealth of knowledge you have. I guess my question is meant to be much simpler than your answer.

 

1. If I have a....

.01uf cap and swap with a .0033um cap will my bass or treble increase?

also what about resistors...

ex. 6.7k resister swapped with a 3.9k resisitor will bass or treble increase?

 

I'm sure there's a simple way of explaining this like you decrease capacitor value to increase ____?

 

2. Also with resistors?

 

3. And what about diodes? (are diodes only for distorting the circuit? why would I choose a 1N4002 over a 1N914?

[WRGKMC]

Whoa WRGKMC a wealth of knowledge you have. I guess my question is meant to be much simpler than your answer.

 

1. If I have a.... .01uf cap and swap with a .0033um cap will my bass or treble increase?~~

 

If this is connected to your normal tone control its a lower value so you have a higher shelf and less treble roll off as you turn the knob down.

If the cap was in series with a pickup, you'd have less bass and more treble. In a treble bleed circuit across a volume you'd also have less bass and more treble when you turn the volume down.

 

~~

also what about resistors...

ex. 6.7k resister swapped with a 3.9k resisitor will bass or treble increase?~~

 

Resistors aren't normally tone shaping devices unless they are used with a cap or coil. Their basic function add or reduce the gain of the signal. The opposite of resistance is conductance, you can view a resistor as how well it conducts electricity. A pickup doesn't put out allot of voltage so you wouldn't normally use many resistors to reduce the signal gain. If they are in series or parallel with caps they can reduce the effects of those caps by splitting the signal path so you have some clean signal mixed with the colored signal of the cap.

 

An example might be that Treble bleed cap over the volume control. If the cap alone leaves the signal too bright when you turn the pot down, it can allow some normal signal through so the treble is less harsh. What specific value you'd use depends on the pickup type, amp type, pot type and the results you want to get.

 

 

~~

I'm sure there's a simple way of explaining this like you decrease capacitor value to increase ____?~~

 

Its better to understand what a cap does and then you can apply that understanding yourself to any circuit.

 

Caps pass AC and block DC. The higher the value, the more signal they pass. . In audio tone circuits, small values are usually used.

 

If you were to short the hot and ground in a guitar, you kill its output by sending all of the signal on the hot lead to ground. This is essentially what your volume pot does when its turned all the way down you have a dead short between the hot lead and ground. As you turn the pot up, its less conductive so its less shorted and more of the signal feeds out the hot lead to the amp. Turned all the way up the resistance is so great it barely affects the signal so you have the maximum signal output. This would be the same if you used fixed resistors. Pots are just variable. When you turn the pot you shorten or lengthen the percentage of carbon and thereby reduce how well it conducts electricity

 

Now apply that to a cap. If you put a cap across the hot lead and ground, you are shorting some of the voltage to ground. The trick to caps is, they are frequency dependent. High treble frequencies excite the cap more then slower, low frequencies.

 

As I said, caps block DC. Low frequencies conduct through a cap poorly, High frequencies conduct well. When the Frequency gets low enough the caps stops conducting those frequencies. If you have a very high capacitor it will conduct all frequencies. Very low it wont conduct any. This is one of the keys to filters. If you select the right capacitance, and that cap is high quality (high Q) its creates a sharp cutoff between the frequencies it passes and the frequencies it doesn't pass.

 

Whet you lower a cap value less low frequencies are shorted to ground, and only high frequencies are affected. If you use a medium value, you short both the high and mid frequencies to ground leaving only the bass frequencies to feed to the amp.

 

So a low value cap will only ground the high frequencies leaving darker tones. If you increase the capacitance, more and more treble is removed, then the midrange, then with a really high value, it removes all the signal just like a short or a pot turned all the way down.

 

This is with a cap in parallel. You can connect caps in series with the signal. In series, the opposite side of the frequency spectrum is affected, and you can start with a high value of say 1farad and it will pass all the signals like its a piece of wire.

 

As you decrease the value, the bass which conducts poorly doesn't get through the cap so you're left with mids and high frequencies, If you keep decreasing the value you get to the point where there's only treble. If you keep going down in value the frequencies that it passes will continue to rise to the point where its above your hearing and then there is no audible signal being heard till you essentially have an open circuit.

 

There are frequencies up there that pico farads can pass but those caps are mainly used in high frequency circuits like radio that tune in high frequencies in the higher kilo and mega hertz.

 

2. Also with resistors?

I basically explained that already. A conductor passes all of the signal. An insulator blocks all of the signal. A resistor (poor conductor) passes some of the signal The higher the resistance the less conductive it is, The lower the resistance, the more conductive it is.

 

 

Resistance only can appear to affect frequency, but its only with the way the signal appears to an amp. A guitar frequency isn't flat. Think of it as an island with a mountain. The left shore is your bass frequencies, the right shore which is your treble. The peak is the center is the midrange.

 

Adding resistance makes that island sink into the sea. What frequencies are lost first? The treble and bass shores. Then the peak gets narrower and smaller until only the top of the peak is left before it goes under. That's what the amplifier sees when you turn a volume control down so it appears like the tone is changing from the resistance. In truth there is less of the entire "island" of frequency making it to the amp. What gets boosted is mostly midrange.

 

You can reshape the midrange peak using caps and coils while leaving the treble and bass shores intact. This gives the sound a broader range of sound. you can even scoop the mids by digging a trench through the center of the mountain if you want, or only sink the treble or bass side. Its all in the component choices and values you use.

 

3. And what about diodes? (are diodes only for distorting the circuit? why would I choose a 1N4002 over a 1N914?

 

Diodes have many functions depending on the type. Their main function is to pass voltage in one direction only. If you put AC voltage which alternates its voltages from positive to negative, and the diode is hooked up to pass only positive voltage, you get half of the full AC sine wave. the negative cycle doesn't conduct so you have zero volts during the negative sweep of the cycle.

 

If you use 4 diodes wired properly and feed it with AC, you can convert both the positive and negative sides to pulses so there's no gap on the negative swing. Instead of looking like this n_n_n_n_ it has all both sides going nnnnnn Then if you pass that pulsed DC through caps, you get filtered DC.

 

Diodes as you can see can be used to convert AC voltage to DC by first making both waves pulse in the same direction - 0 to Max, and then you just smooth the bumps out with caps so you have smooth DC voltage.

 

Diodes can be used for many other things. Since they only pass voltage in one direction, you often find them on stomp boxes as protective devises. If you connect a wall wart with the proper polarity, they pass voltage to the circuit. If you have a wall wart with a bass ackwards polarity the Diode will block the voltage like a one way gate and prevent you from frying the circuit.

 

There are other things diodes can do. Some are made to operate in reverse. They are called Zenar diodes. They will conduct voltage in reverse but only up to a specific voltage then they prevent any higher voltage from passing. You often find these kinds of diodes in power supply circuits to regulate the DC voltage. When you hear the term, regulated power supply, chances are good a zenar diode is at work keeping the voltage at a specific amount so you don't get overvoltage to the rest of the circuit when the AC from the Power company fluctuates or someone in another room turns on a coffee pot.

 

You also have minimum voltage levels diodes can pass in a forward direction. A diode is made up of two material. One that has extra electrons and one that has a lack of electrons (or holes) to get the diode to conduct you need a minimal voltage to get electrons to jump across the physical barrier where the two materials are joined.

 

They are selected for not conducting at a specific low voltage and pass a signal when the voltage is high enough.

 

You also have low voltage diodes that have a maximum voltage they can conduct. You force more AC through them and the tops of the AC signal get flattened trying to force their way through a gate smaller then the signal is so the tops of the AC waves get flattened.