Members Kazinator Posted January 26, 2013 Members Share Posted January 26, 2013 This is inspired by the recent tone cap thread. Instead of a tone knob on my main guitar, I installed a three way tone switch. In one position, there is no capacitance. In the two other positions, a capacitance is placed across the output: 1nF and 2nF, respectivelly. There is no series resistance at all. Though I do not have a continuously variable tone control this way, the use of a pure capacitance means the resonant peak in the response is retained. The pickup and the capacitor form an LC resonant tank. Without resistance in the circuit, the resonant tank is undamped. A regular tone control kills the resonant peak as you turn it down. A peak then reappears when the control is turned all the way down. I just recorded a quick little MP3 with my smartphone to demonstrate the switched cap setup. This guitar has only one pickup, a DiMarzio DP-156 "Humbucker from Hell" in the bridge. "Tone One" in the clip is with the 2nF capacitor across the pickup, the most rolled off tone. From there it progresses to "Tone Two", with the 1nF capacitor across the pickup, and then to "Tone Three" which is just the straight tone of the DP-156 without any shunt capacitance, other than that of the instrument cable and preamp's FET input. The effect is like having three pickups in one. (view in My Videos) Link to comment Share on other sites More sharing options...
Members WRGKMC Posted February 3, 2013 Members Share Posted February 3, 2013 Gibson used switched caps in a circuit called the varitone since 1959. The circuit also contained a 1 henry coil to make the circuit an actual passive EQ filter which you cant get with caps alone. Caps by themselves only with only cut or pass highs. With a coil added you can create notches with the midrange which is what most guitar players desire. The development of the solid body electric guitar in the 1950s initiatedradical innovation in pickups, switches, amplifiers, and accessories thatcontinues with ever greater technological sophistication. First there was asingle volume control, then tone control then three-way switches and onand on. The designer's goal was to enhance the players' control of theirsound. As each manufacturer rolled out a new feature, their competitorsresponded with their own.Gibson introduced the Varitone six-way tonecontrol in 1959 on the ES-345. Then in 1982 B.B.King and Gibson joined forces to create the oneand only Lucille featuring the Varitone with awide range of expressive sounds from a blazinghumbucker to a cutting single coil pickup. Andyes, there is a Varitone on the new Little Lucille.VARITONE CIRCUITThe Varitone circuit is a notch filter that utilizes a variety of capacitors toachieve a reduction in frequencies at set points within the overallbandwidth. As the varitone is rotated from Position 1 to Position 6 thecenter frequency of the filter shifts from higher to lower frequencies.Figure 1 demonstrates in general the type of frequency response that iscreated by the varitone.The specific characteristics are:Position 1: Bypass (no effect)Position 2: -8.5dB at 1875 HzPosition 3: -12dB at 1090 HzPosition 4: -15dB at 650 HzPosition 5: -16dB at 350 HzPosition 6: -20dB at 130 HzMono/Stereo Output JacksWhen using "Mono" Output Jack-1, both pickups are operational. If youwant "Stereo", you MUST use both "Mono" Output Jack-1 and "Stereo"Jack-2 together."Stereo" Output Jack-2When using output Jack-2 alone only the treble pickup is functional. Whenusing both jacks together Jack-2 carries the treble pickup signal."Mono" Output Jack-1When using output Jack-1 alone both pickups are functional. When usingboth jacks together Jack-1 carries the rhythm pickup signal.Gibson's former R&D Guru, J.T. Riboloff, who won an award fromthe Music Trades magazine in 1993 for his design of the Nighthawk, wenta step further by implementing a Varitone circuit in the Blueshawk. TheVaritone filters out specific, fundamental frequencies. Combined with twovolume, two push-pull tone, three-way switch frequencies in it's fivesettings, the Varitone gives the Blueshawk enough sounds to satisfy asession player. Click here to hear the Blueshawk sing."The Varitone opened up the spectrum of the tone paths of that instrumentquite a bit,"Riboloff said."The other nice thing with that Varitone is the push/pull tone pot whichbypasses the circuit. The Varitone selector is a rotary switch, andsomebody might want to change his tone in the middle of the song, buthe's also thinking about keeping his timing. He doesn't want to count howmany times he's clicked his Varitone knob. What this allows him to do is,for example, leave the circuit in bypass and preset his Varitone at thebeginning of the song. So if you want to locate position 5 on the Varitone,for example, preset the knob so that all you have to do is push that potdown."VARITONE CIRCUITThe Varitone circuit is a notch filter that utilizes a variety ofcapacitors to achieve a reduction in frequencies at set points within theoverall bandwidth. As the varitone is rotated from Position 1 to Position 6the center frequency(f0)of the filter shifts from higher to lowerfrequencies. Figure 1 demonstrates in general the type of frequencyresponse that is created by the varitone.*The specific characteristics are:Position 1: Bypass (no effect)Position 2: -5dB at 1875 HzPosition 3: -6dB at 1090 HzPosition 4: -7dB at 650 HzPosition 5: -10dB at 350 HzPosition 6: -14dB at 130 HzPush Pull Tone Control:- With the push pull tone control in the down position the varitone isoperational.- With the push pull tone control in the up position the varitone is removedfrom from the circuit.*Decibel levels based on 1000Hz : 1 Volt sinusoidal test signal Link to comment Share on other sites More sharing options...
Members Kazinator Posted February 7, 2013 Author Members Share Posted February 7, 2013 WRGKMC wrote: Gibson used switched caps in a circuit called the varitone since 1959. The Varitone is interesting, and really, the question is, why don't guitars ship with useful circuits like that. The circuit also contained a 1 henry coil to make the circuit an actual passive EQ filter which you cant get with caps alone. Caps by themselves only with only cut or pass highs. With a coil added you can create notches with the midrange which is what most guitar players desire. Capacitors and resistors can form a band-pass or band-stop filter, just not one with a very high Q (narrow frequency band).Any circuit built around a passive pickup does contain a coil: namely, the pickup!Also, there is already capacitance even if no capacitor component is present: the capacitance of the instrument cable. Together with the pickup, it forms a LC resonator: it has a peak at a particular frequency, and a -12db per octave rolloff (second order).Added capacitance (cap across the pickup) will lower the frequency of the resonant peak, and where the rolloff begins. The capacitor in parallel with the pickup does not simply cut high frequencies.If you simply want several tones which resemble the natural responses of various other guitar pickups, this is a nice approach which is also very easy to implement, with a minimal part count. The most basic implementation is a single cap in series with a switch, bypassing a pickup (or all of them: basically in parallel with the volume pot). I have the second least complicated thing which is to switch two capacitances or nothing.The Varitone circuit needs a coil because although there are pickup coils in the circuit, they are not there in a topology that allows notches to be created in the frequency response.It's hard to comment on what most guitarists want. If I were to guess, most guitarists want is to sound like So and So player, on such and such recording, and don't really have a clue how to get there. Probably the most common experimentation with guitar electronics is: replacement pickups. And that mostly shifts around the resonant peak. Link to comment Share on other sites More sharing options...
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