Simple Hobby Circuits For Guitar
We start with some basic volume and tone-control circuits easily implemented, with input and output jacks shown in case separate project-boxes are desired.
Volume controls can be used to make splitters and mixers.
Note that you could, but should not, use a splitter backwards to create a mixer. Rather, rewire the splitter circuit, as shown below, to keep the potentiometers oriented properly. In such cases the correct wiring of a potentiometer has the signal going in at one end of the resistive element with the other end grounded, while the signal is taken out from the wiper. That is how a potentiometer is meant to be used with audio signals. There are cases where the signal goes into the wiper, such as balance controls, but which means the ends of the element are two separate outputs, or where two signals are given at the element ends and their balance is taken from the wiper. But here, we want the element acting as a standard voltage-divider with the wiper providing the output signal.
Next is a simple tone-control with selectable high-end cutoff. Larger capacitor values affect highs more drastically. Comparisons between different switch settings will provide the best understanding of how different caps affect tonality as the Tone pot’s position is changed. This circuit is typical of on-board passive electric-guitar tone-controls except that the rotary switch allows for selecting different bleeder capacitors.
The most common and cheapest capacitors used in guitars are the ceramic disk types. However, they tend to impart a thin sound to the guitar signal. A better capacitor type is the polypropylene film-type capacitor, also called an “orange-drop” capacitor because of its looks. These always sound good and are of high quality, and are more reliable than other capacitor types, but do not cost much more than ceramic-disk types. The most expensive capacitors are the paper-in-oil electrolytic capacitors, and if you want vintage sound, especially if your guitar has humbucker pickups, these are often chosen for that purpose. There are even NOS paper-in-oil capacitors available online, but which often command extreme prices. Therefore, for the most bang or the buck, use polypropylene orange-drops instead. Electronics parts are available at www.stewmac.com , and metal project-boxes at www.parts-express.com . Other electronics sources include www.mouser.com, www.digikey.com, and www.newark.com.
For any project in this post, or effect or effects-line, here is a bypass circuit, if such a circuit is desired.
If you get an annoying 60 Hz line buzz from your guitar or effects device, the notch filter below will cut it out. This is called a “Twin-T” notch filter and cuts the frequency to be notched by -12 dB. The formula for part values is provided in case some other notched frequency is to be addressed with the same kind of circuit. I do not recommend using potentiometers to make this a variable notch filter, accepting experimentation.
The wah pedal involves a circuit where a single potentiometer sets the frequency of a notch filter, but the adjustable wah effect cannot be implemented passively. All wah-pedal circuits involve active circuitry using either transistors or op-amps, or both. Note, however, that wah-pedal circuits are easily looked up by searching the phrase "wah pedal circuits", or similar.
We start with some basic volume and tone-control circuits easily implemented, with input and output jacks shown in case separate project-boxes are desired.
Volume controls can be used to make splitters and mixers.
Note that you could, but should not, use a splitter backwards to create a mixer. Rather, rewire the splitter circuit, as shown below, to keep the potentiometers oriented properly. In such cases the correct wiring of a potentiometer has the signal going in at one end of the resistive element with the other end grounded, while the signal is taken out from the wiper. That is how a potentiometer is meant to be used with audio signals. There are cases where the signal goes into the wiper, such as balance controls, but which means the ends of the element are two separate outputs, or where two signals are given at the element ends and their balance is taken from the wiper. But here, we want the element acting as a standard voltage-divider with the wiper providing the output signal.
Next is a simple tone-control with selectable high-end cutoff. Larger capacitor values affect highs more drastically. Comparisons between different switch settings will provide the best understanding of how different caps affect tonality as the Tone pot’s position is changed. This circuit is typical of on-board passive electric-guitar tone-controls except that the rotary switch allows for selecting different bleeder capacitors.
The most common and cheapest capacitors used in guitars are the ceramic disk types. However, they tend to impart a thin sound to the guitar signal. A better capacitor type is the polypropylene film-type capacitor, also called an “orange-drop” capacitor because of its looks. These always sound good and are of high quality, and are more reliable than other capacitor types, but do not cost much more than ceramic-disk types. The most expensive capacitors are the paper-in-oil electrolytic capacitors, and if you want vintage sound, especially if your guitar has humbucker pickups, these are often chosen for that purpose. There are even NOS paper-in-oil capacitors available online, but which often command extreme prices. Therefore, for the most bang or the buck, use polypropylene orange-drops instead. Electronics parts are available at www.stewmac.com , and metal project-boxes at www.parts-express.com . Other electronics sources include www.mouser.com, www.digikey.com, and www.newark.com.
For any project in this post, or effect or effects-line, here is a bypass circuit, if such a circuit is desired.
If you get an annoying 60 Hz line buzz from your guitar or effects device, the notch filter below will cut it out. This is called a “Twin-T” notch filter and cuts the frequency to be notched by -12 dB. The formula for part values is provided in case some other notched frequency is to be addressed with the same kind of circuit. I do not recommend using potentiometers to make this a variable notch filter, accepting experimentation.
The wah pedal involves a circuit where a single potentiometer sets the frequency of a notch filter, but the adjustable wah effect cannot be implemented passively. All wah-pedal circuits involve active circuitry using either transistors or op-amps, or both. Note, however, that wah-pedal circuits are easily looked up by searching the phrase "wah pedal circuits", or similar.
What follows are two of the most common tone-control circuits used in guitar-amps and effects. The first is a 2-band “Passive Baxandall” type of tone control, and the second is a 3-band “Fender Tone-Stack”. Either type works great before or after any stomp-box.
Continuing the topic of tone-control circuits, we can consider basic passive filters using resistors and capacitors but no coils. A simple high-pass filter has a capacitor in the signal path but a resistor to ground, while a low-pass filter has just the opposite, as shown below. The formula for the corner frequency is the same for either filter, whether it is a high corner or low corner frequency. The formula is f = 1 / [(6.283)RC] where f is the corner frequency, R is the resistor value in ohms, and C is the capacitor value in farads (F). However, resistor values are typically large (e.g., kilohms) while capacitor values are always small (e.g., microfarads). It is assumed here that readers are already familiar with how to handle such part-values using a calculator.
With the low-pass filter, there is a resistor in the signal path so it is best to use a fairly low value to keep from attenuating the signal too much. But with a high-pass filter, the resistor is actually a shunt to ground and should thus be as large as practical. Since both filters use the same formula for capacitor and resistor values, the very same values will work for either filter, where the low-pass filter passes frequencies above the desired corner frequencies while the high-pass filter passes frequencies above it.
Here is a table of example values. Note, however, that it is best to use indicated values where R < 10k for the low-pass filter but R > 1k for the high-pass filter. The very same corner frequency works for either filter -- just interchange the placement of R and C to change from high-pass to low-pass or vice-versa.
RC Filter Formulas: f = 1 / [ (6.283)RC ] or C = 1 / [ (6.283)Rf ] ,
where f is frequency in Hertz, R is resistance in ohms, and C is capacitance in Farads.
Note: I did not determine all the above values using the formula myself but employed an online RC filter calculator that used the same formula.
Of course, you can put a low-pass in series with a high-pass to make a bandpass filter, where the low-pass corner is higher than the high-pass corner.
Note though that the filter only offers -3dB per octave of attenuation (slope) beyond a given corner frequency. So, for a -6dB slope, use two filters in series. However, don’t use more than two filters of any kind in series (low-pass, high-pass, or bandpass) since a slope that is too steep will make the filter sound like a frequency switch rather than a filter.
Apply a low-pass filter with a high corner to cut brittleness from a trebly guitar or effects device, or use a high-pass filter with a low corner to cut lows that are too boomy. Or use a band-pass filter to limit unwanted frequencies outside a desired range.
Alternatively, use passive filters to make line-level passive crossovers. Below we give 2-way and 3-way crossovers for the guitar. Use the 2-way for splitting the guitar signal to send it to two amplifiers or effects where one is for handling high frequencies while the other is for the lows. Or use the 3-way to split the guitar signal into three frequency ranges; highs, mids, and lows.
The first set of drawings does not provide a means of limiting extreme highs or lows, as most amplifiers and effects have built-in frequency-limiting circuitry. However, if upper and lower limits different from the standard 20 kHz high and 20 Hz low are desired, the high-pass and low-pass filters of a crossover can be changed to bandpass filters simply by adding a low-pass filter with a high corner in series to the high-pass filter, and a high-pass filter with a low corner in series with the low-pass filter. For example, there is little need to go above about 17 or 18 kHz, or below 30 Hz, for most audio work. However, with either kind of crossover topology, make sure to overlap the lows of the high-pass and highs of the low-pass within an octave of each middle bandpass filter limit.
Do not use these crossovers between speaker and amplifier. “Line-level” means low-level signals, from passive guitar output (a few hundred millivolts) up to 1 volt peak-to-peak from active guitar outputs or effects device outputs.
The guitar’s natural notes, on a 24-fret guitar, go from 82 Hz to 1.32 kHz. Usually, it is unnecessary to go below about 80 Hz for the lows, or the guitar can get too bassy, while it is unnecessary to go higher than about three octaves above the highest note, which means around 10 kHz. Highs above 10 kHz don’t sound like tones but are more like symbol sizzle and high-end hissing noise. In fact, the recommended EQ range for the 6-string electric guitar is generally from 80 Hz to about 8 kHz, including allowing for effects such as distortion overtones and/or higher-octave stomp-boxes.
The crossovers above are based on 700 Hz being the middle frequency in the guitar’s range, but allow for overlaps, so there will be no missing frequencies in either the 2-way or 3-way crossovers, while higher and lower frequency extremes are not limited since the built-in frequency limits of effects and amps already take the extremes into account.
Also, adding volume controls will help to set the frequency-bands at equal signal levels.
But while you’re at it, you can use bandpass filters with separate volume controls to make a 5-band equalizer, which provides a great deal of tonal control.
Frequency centers are; 14 kHz, 5.3 kHz, 1.6 kHz, 520 Hz, and 132 Hz.
For best results, put this circuit just before the amplifier, so it will allow for tailoring the overall sound of a guitar used with two or more effects devices. Most guitars only have a basic tone-control onboard, and most stomp-box effects only have bass and treble controls, at best. And even when a processor is used, they normally only provide three bands of tone control. Hence, the above circuit lets the user dial in just the right blend of frequencies according to personal preference. Of course, pair this circuit with the bypass circuit given earlier to use it selectively.
Continuing the topic of tone-control circuits, we can consider basic passive filters using resistors and capacitors but no coils. A simple high-pass filter has a capacitor in the signal path but a resistor to ground, while a low-pass filter has just the opposite, as shown below. The formula for the corner frequency is the same for either filter, whether it is a high corner or low corner frequency. The formula is f = 1 / [(6.283)RC] where f is the corner frequency, R is the resistor value in ohms, and C is the capacitor value in farads (F). However, resistor values are typically large (e.g., kilohms) while capacitor values are always small (e.g., microfarads). It is assumed here that readers are already familiar with how to handle such part-values using a calculator.
With the low-pass filter, there is a resistor in the signal path so it is best to use a fairly low value to keep from attenuating the signal too much. But with a high-pass filter, the resistor is actually a shunt to ground and should thus be as large as practical. Since both filters use the same formula for capacitor and resistor values, the very same values will work for either filter, where the low-pass filter passes frequencies above the desired corner frequencies while the high-pass filter passes frequencies above it.
Here is a table of example values. Note, however, that it is best to use indicated values where R < 10k for the low-pass filter but R > 1k for the high-pass filter. The very same corner frequency works for either filter -- just interchange the placement of R and C to change from high-pass to low-pass or vice-versa.
RC Filter Formulas: f = 1 / [ (6.283)RC ] or C = 1 / [ (6.283)Rf ] ,
where f is frequency in Hertz, R is resistance in ohms, and C is capacitance in Farads.
Note: I did not determine all the above values using the formula myself but employed an online RC filter calculator that used the same formula.
Of course, you can put a low-pass in series with a high-pass to make a bandpass filter, where the low-pass corner is higher than the high-pass corner.
Note though that the filter only offers -3dB per octave of attenuation (slope) beyond a given corner frequency. So, for a -6dB slope, use two filters in series. However, don’t use more than two filters of any kind in series (low-pass, high-pass, or bandpass) since a slope that is too steep will make the filter sound like a frequency switch rather than a filter.
Apply a low-pass filter with a high corner to cut brittleness from a trebly guitar or effects device, or use a high-pass filter with a low corner to cut lows that are too boomy. Or use a band-pass filter to limit unwanted frequencies outside a desired range.
Alternatively, use passive filters to make line-level passive crossovers. Below we give 2-way and 3-way crossovers for the guitar. Use the 2-way for splitting the guitar signal to send it to two amplifiers or effects where one is for handling high frequencies while the other is for the lows. Or use the 3-way to split the guitar signal into three frequency ranges; highs, mids, and lows.
The first set of drawings does not provide a means of limiting extreme highs or lows, as most amplifiers and effects have built-in frequency-limiting circuitry. However, if upper and lower limits different from the standard 20 kHz high and 20 Hz low are desired, the high-pass and low-pass filters of a crossover can be changed to bandpass filters simply by adding a low-pass filter with a high corner in series to the high-pass filter, and a high-pass filter with a low corner in series with the low-pass filter. For example, there is little need to go above about 17 or 18 kHz, or below 30 Hz, for most audio work. However, with either kind of crossover topology, make sure to overlap the lows of the high-pass and highs of the low-pass within an octave of each middle bandpass filter limit.
Do not use these crossovers between speaker and amplifier. “Line-level” means low-level signals, from passive guitar output (a few hundred millivolts) up to 1 volt peak-to-peak from active guitar outputs or effects device outputs.
The guitar’s natural notes, on a 24-fret guitar, go from 82 Hz to 1.32 kHz. Usually, it is unnecessary to go below about 80 Hz for the lows, or the guitar can get too bassy, while it is unnecessary to go higher than about three octaves above the highest note, which means around 10 kHz. Highs above 10 kHz don’t sound like tones but are more like symbol sizzle and high-end hissing noise. In fact, the recommended EQ range for the 6-string electric guitar is generally from 80 Hz to about 8 kHz, including allowing for effects such as distortion overtones and/or higher-octave stomp-boxes.
The crossovers above are based on 700 Hz being the middle frequency in the guitar’s range, but allow for overlaps, so there will be no missing frequencies in either the 2-way or 3-way crossovers, while higher and lower frequency extremes are not limited since the built-in frequency limits of effects and amps already take the extremes into account.
Also, adding volume controls will help to set the frequency-bands at equal signal levels.
But while you’re at it, you can use bandpass filters with separate volume controls to make a 5-band equalizer, which provides a great deal of tonal control.
Frequency centers are; 14 kHz, 5.3 kHz, 1.6 kHz, 520 Hz, and 132 Hz.
For best results, put this circuit just before the amplifier, so it will allow for tailoring the overall sound of a guitar used with two or more effects devices. Most guitars only have a basic tone-control onboard, and most stomp-box effects only have bass and treble controls, at best. And even when a processor is used, they normally only provide three bands of tone control. Hence, the above circuit lets the user dial in just the right blend of frequencies according to personal preference. Of course, pair this circuit with the bypass circuit given earlier to use it selectively.
Note that diodes provide clipping, instead of overdriving tubes, transistors, or op-amps. The principle is fairly simple. In the old days, the way to get distortion was to overdrive the tubes in an amp or the transistors in an amp or an effect. Later on, after op-amps became common, overdriving an op-amp would do the same thing, and certain types (JFETs) sounded better than others. The distortion was the result of an overdriven device chopping-off the tops and the bottoms of the signal, called “clipping”, because overdriving such devices makes them attempt to exceed design parameters. Doing so without going too far with an input signal allows clipping without destroying the device (tube, transistor, or op-amp). Thus was born the practice among many guitarists of using distortion to enhance solos and to get heavy and/or chunky rhythms, and so came the proliferation of stomp-box fuzz effects, overdrive boosters, and distortion units, and also the preference for tube-amps offering desirable overdriven tone. However, it was also discovered that diodes can be used to cause clipping without the need to overdrive electronic devices, but which also result in pleasing fuzz tones.
The following circuit is an example of how diodes can be used to impart distortion to any guitar signal. It is based on a project called the “Mod Box” that appeared in the May ’97 issue of Electronics Now magazine. And while that article is dated, the circuitry remains valid. The diagram below is based on the distortion subcircuit of the article’s circuit but requires a high-gain stomp-box of some kind between it’s input and the guitar.
The circuit below does not include a volume or tone control, but can still be used, as shown, between the guitar and a stomp-box providing gain, since the guitar and most effects have at least one tone-control and one volume-control of their own. Otherwise, use one of the volume or tone-control circuits given earlier at this circuit’s output.
The nature of the distortion caused by the different types of diodes is due to the material of the diodes. Silicone diodes give harsher sound than germanium diodes, while LEDs produce brighter sounds than either, but which is said to be better than sounds given by silicone diodes. Also, the symmetry of the diode arrangements makes a difference in the distortion produced, hence the symmetry switches, which allow the user to select different settings. Hint: Having one diode on one side of a group but two on the other side is said to emphasize even-order harmonics in the fuzz sound.
Additional Notes: Switching-out all the diodes in a group will not cause the signal to drop out, but will likely boost it, since the diodes each attenuate the signal a bit, so using all four diodes in a group attenuates the signal the most significantly; hence the need for a high-gain device between the guitar and any one of these circuits' inputs. The outputs, however, can go to any active or passive circuit, including other stomp-boxes or directly to an amplifier.
EOF
The following circuit is an example of how diodes can be used to impart distortion to any guitar signal. It is based on a project called the “Mod Box” that appeared in the May ’97 issue of Electronics Now magazine. And while that article is dated, the circuitry remains valid. The diagram below is based on the distortion subcircuit of the article’s circuit but requires a high-gain stomp-box of some kind between it’s input and the guitar.
The circuit below does not include a volume or tone control, but can still be used, as shown, between the guitar and a stomp-box providing gain, since the guitar and most effects have at least one tone-control and one volume-control of their own. Otherwise, use one of the volume or tone-control circuits given earlier at this circuit’s output.
The nature of the distortion caused by the different types of diodes is due to the material of the diodes. Silicone diodes give harsher sound than germanium diodes, while LEDs produce brighter sounds than either, but which is said to be better than sounds given by silicone diodes. Also, the symmetry of the diode arrangements makes a difference in the distortion produced, hence the symmetry switches, which allow the user to select different settings. Hint: Having one diode on one side of a group but two on the other side is said to emphasize even-order harmonics in the fuzz sound.
Additional Notes: Switching-out all the diodes in a group will not cause the signal to drop out, but will likely boost it, since the diodes each attenuate the signal a bit, so using all four diodes in a group attenuates the signal the most significantly; hence the need for a high-gain device between the guitar and any one of these circuits' inputs. The outputs, however, can go to any active or passive circuit, including other stomp-boxes or directly to an amplifier.
EOF
To keep external DC out of the pots and switches.
Of course, the capacitors should be bipolar types, since we don't know which polarity it will be.
Of course, the capacitors should be bipolar types, since we don't know which polarity it will be.
Nice passive circuits.
I will experiment with some. Looking to make some passive eq before headphone amp. Simple, just extreme highs and some lows. Nothing in the middle.
I dislike baxandall tone control because it starts in the middle. If your headphones neels just a help below 30Hz, adding baxandall creates midbass hump. Same applies for bookshelf.
Similarly if only correction needed in highs is above 10kHz, baxandall will create nasty shout around 2-3kHz.
Will experiment with cap values in circuit like this...
I will experiment with some. Looking to make some passive eq before headphone amp. Simple, just extreme highs and some lows. Nothing in the middle.
I dislike baxandall tone control because it starts in the middle. If your headphones neels just a help below 30Hz, adding baxandall creates midbass hump. Same applies for bookshelf.
Similarly if only correction needed in highs is above 10kHz, baxandall will create nasty shout around 2-3kHz.
Will experiment with cap values in circuit like this...
Attachments
Although most are intended as guitar circuits, I intend to use passive circuits between signal source (mp3 or cd player) and headphone amp.
Hello Kurtus,
About the "2 to 1 Mixer" and the "2 to 1 Mixer with Separate Tone Controls" in your first post:
I think that the volume controls will influence each other quite a lot. In the most extreme case, namely when the volume of one of the channels is set at zero, the other channel gets shorted to ground, so there will be no output.
To prevent this, two resistors have to be added between each wiper and the 10K resistor at the output. Since these mixers are supposed to work at guitar levels, the value of the two extra resistors has to be high (470K or even higher to ensure that the input impedance does not get too low when one volume control is set to zero). This will however cause quit insertion loss.
About the "Passive 5-band EQ" in your second post:
I think that the tone controls of the 5 bands will influence each other quite a lot. In the most extreme case, namely when the wiper of one of the bands is set at the down position, the other 4 bands get shorted to ground, so there will be no output.
Again resistors (now five in total) between each wiper and the 10K resistor will prevent this. But again, this will cause insertion loss.
About the "2 to 1 Mixer" and the "2 to 1 Mixer with Separate Tone Controls" in your first post:
I think that the volume controls will influence each other quite a lot. In the most extreme case, namely when the volume of one of the channels is set at zero, the other channel gets shorted to ground, so there will be no output.
To prevent this, two resistors have to be added between each wiper and the 10K resistor at the output. Since these mixers are supposed to work at guitar levels, the value of the two extra resistors has to be high (470K or even higher to ensure that the input impedance does not get too low when one volume control is set to zero). This will however cause quit insertion loss.
About the "Passive 5-band EQ" in your second post:
I think that the tone controls of the 5 bands will influence each other quite a lot. In the most extreme case, namely when the wiper of one of the bands is set at the down position, the other 4 bands get shorted to ground, so there will be no output.
Again resistors (now five in total) between each wiper and the 10K resistor will prevent this. But again, this will cause insertion loss.
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Good points all around, but I posted what I posted and I'm not changing things this time around.
Consider these all to be experimental circuits, and do with them what you will.
Also, readers can consider your comments and decide if they want to make changes before building a given circuit, then test and experiment accordingly.
Thanks.
Consider these all to be experimental circuits, and do with them what you will.
Also, readers can consider your comments and decide if they want to make changes before building a given circuit, then test and experiment accordingly.
Thanks.
That's disappointing. I'd be interested, but without knowing the allowed load and source requirements, it's a gamble.
Where did you find these circuits, maybe I can look it up myself.
Jan
Where did you find these circuits, maybe I can look it up myself.
Jan