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Pedal ("lotion», stomp-box) is designed to simulate the sound of a tube amp channels slaboperegruzhennogo Fender Twin Reverb and implementation effects «Clean» and «Crunch». A distinctive feature of this pedal is very plausible imitation tube sound, and low power consumption of the battery. («Clean» - sound with virtually no distortion, but with the corrected tone, usually bright, with a predominance of high frequencies. «Crunch» - sound on the verge of distortion and with a little overdrive). The article is intended not only for professionals, musicians, but also for beginners because some terms and concepts considered overly detailed, pro please treat this with understanding ...

A little history

In contemporary music, electric guitar takes about the same place as in the classical violin. Some styles of rock without electric possible at all ... For all that is in itself an electric guitar - an instrument with a rather weak capacity (to see this - turn it directly into a mixing console). Thats because electric sound is largely determined by the amplifier, or "gadgets" / preamp, in which it is included. Moreover, unlike the art audiophile distortion guitar sound play a key role. Traditionally considered the best sounding tube guitar amplifiers. In addition, there are both subjective and objective reasons - firstly, this sound familiar to most - because electric guitar was born at a time when other amps just was not in the second - that tube amplifiers have several very valued musicians properties rarely encountered in semiconductor chips: first of all the dynamics and readability. List the advantages of tube amplifiers can continue, but I have identified, in my opinion, the main thing.

Strictly speaking - "Lamp" is neither a guarantee of good sound (meet and lamp units with a hideous sound), nor the only possible way it was received. After all, despite all the advantages, disadvantages in lamp technology is also missing - this fragility lamps, and high cost, and weight / size. That is why since the advent of transistors, and later - chips, and large firms, and some enthusiasts do not stop trying to recreate the sound of a tube on the semiconductor elements. While it is still too early to say that this problem is solved completely and finally, I know some very striking examples of successful solutions, and single enthusiasts often ahead of even large companies - manufacturers of guitar equipment.

On receipt of the effect of "distortion" written hundreds of articles, there are thousands of schemes. But the sound, uncluttered, and weakly podgruzhenny amplifier is often overlooked, especially budding guitarists. But fate does not end with "metal", and it, darling, too, "wedge" will not spoil ... Another reason for the small number of such schemes - the relative difficulty of getting the right sound. It turns out - strong overdrive with a decent sound easier to obtain than a light bluesy crunch ... It is in the small-Heine particularly noticeable difference between the vacuum tube and semiconductor devices - light enters the restriction very smoothly, asymmetric, because the beginning of distortion and time-limited out of it almost unnoticeable. In addition - due to the nature Lamp restrictions - limited range of higher harmonics of the signal is poor, the sound does not cut the ear even on chords and excellent dynamics and allows to play loud and quiet, and to allocate the necessary notes and volume and tone ... The majority of the semiconductor pedal has a rather sharp threshold limit (usually done by limiting diodes or LEDs), causing distortions are very sharply above this threshold, and disappear when the attenuation of the signal below it, on hearing less pleasant than a smooth threshold lamp ... Dynamics semiconductor pedals usually much worse tube, after exceeding the threshold limits the tone and volume depend little on the tone and volume of the signal from the guitar. That in tube circuits obtained by "self-other" should be achieved in semiconductor artificial and often quite clever ways.

Among the classic tube amps kind of standard "wedge" is a Fender Twin Reverb, in fact, this scheme then used repeatedly in different amplifiers Fender, and in amplifiers and preamps other firms. Offered to your attention the scheme - one of the attempts to reproduce the sound of the legendary amplifier based on a semiconductor ...

Scheme pedal

Block diagram of the device copies the prototype: the sound is two cascades tembroblok in between. The resemblance to the prototype and ends ...

In the prototype, the first stage is built on the vacuum triode 12AX7 and has a gain (CG) of about 50. With a supply voltage of about 300V and cascade input signal levels, typical for electric guitar, the output stage is not limited to "focus" in the food.

The proposed device is powered by a 9V Crowns, same scale input voltage circuit may reach 4-5 V, depending on the type of guitar pickups and aggressiveness artist ... Because in the proposed scheme, the first stage is built repeater that provides normal operation with real signals. Repeater functions as a high output impedance matching guitar and relatively low input impedance TONE. With this input impedance corresponds to the standard pedal for guitar amps 1 Mohm.

Operational amplifier as a repeater chosen for several reasons: although this node could be done and FET real benefits such a decision would not bring. The fact that, although the FET and has a low noise level, the transmission coefficient of such a cascade is about 0.7-0.8 (1 for the OS), and it has more circuit parts, and most importantly - the relatively small gain of the second stage either it does not reveal the advantages of the cascade on Fri Also - in the applied chip TL072 includes two OS that makes use of one of the op-amp follower and economically justified, especially as the typical current consumption TL072 does not exceed 4 mA. But replacement by "next of kin» TL062 is not recommended - even though it consumes 10 times less noise properties it no longer satisfy the requirements of this scheme - in all its noise Heine appears noticeably audible hiss-...

Tone-in scheme similar to Fender pedal used, although it has a couple of differences - component values ​​are translated into downward resistance, as the signal swing is many times smaller than the prototype, and depth adjustment in each frequency band markedly increased (best ratings were picked up using in circuit simulation program simulator Micro-Cap 8 followed by thorough otslushivaniem and comparison with the prototype).

To reduce the audible noise level scheme, the controller gain is not worth after TONE, as in the prototype - and adjusts the gain of the second stage. Stock adjustment allows you to get sound from the wedge to the midgeyna (using guitars with pickups hambakernymi). The second feature of this switching regulator gain is that by increasing the gain changes the frequency response of the cascade - through capacitor C10 at high gains trimmed excess for this mode high frequency components from the input circuit.

Gain of the second stage at the minimum gain is about 11 - it is done to compensate for signal attenuation TONE. Amplification of the stage at the maximum gain - about 110.s Not very much, but enough to simulate load the V channel. Further increase gain no special meaning - the sound becomes less "tube" and loses the similarity to the prototype.

Actually, imitation Lamp restrictions combination gives TL072 op-amp with MOSFET transistor 2n7002. It therefore should not be changed to another type TL072 op-amp - not all types are suitable for the proper operation of this scheme. Diode VD3 does not allow internal reverse diode transistor VT1 open at negative half-wave output voltage.

Thats roughly the shape looks a limited output voltage DA1.2 sinusoidal input signal (shape depends on the signal frequency and the position gain and tone controls).

In its form, this waveform is very similar to the waveform of the tube stage, an inverted "upside down", here at the anode lamp waveform 12AX7:

Inclination of the upper shelves at DA1.2 limitations due to the fact that at the moment of the waveform capacitance C9 in the layout was par value of 0.1 microfarads, increasing it to 1 uF slope almost leveled. Actually slabogeynovy instrument was born almost by accident - "research" conducted for the production emulator haygeynovogo "red" channel amplifier Mesa Boogie Dual Rectifier. During the simulation form limited signal seemed strangely familiar and it was decided to use the stage for peaceful purposes slabogeynovyh ... It is because in the first layout was 0.1 microfarads capacitance - this heritage haygeynovoy scheme ...

Clearly that rounding signal at the start of limitations - rather smooth, which provides a relatively low level of higher harmonics. And with an increase in the amplitude of the input signal is a smooth rounding first upper half wave, then a more stringent limit bottom - the distortion increases smoothly as in the tube stage.

The second positive feature ligament TL072 op-amp with MOSFET transistor 2n7002 - this asymmetry restrictions. As in the case of the lamp first starts to confine one halfwave of the output signal (the lamp - the bottom, we have - the upper, which is absolutely essential, since the phase rotation of 180 degrees occurs repeatedly in the subsequent amplification). The shape restrictions caused MOSFETa properties that limit makes smoother than the diode. Then comes into play OS limitation on Nutrition (namely TL072, namely on the lower half-wave in this scheme gives a form of restriction attempts to make it otherwise lead to a much more acute angles at the entrance to the limit and noticeably worse sound). While still a shift output DC - similar tube stage that slightly changes the duty cycle of the output signal and a very positive effect on the dynamics of sound.

Tumbler «Bright» works like prototype - adds to the sound of "glass" when necessary. Capacitor C12 slightly softens tone output. In the case of voiced amplifiers to increase its worth, in the case of impaired hearing sound - remove.

Capacitor C7 together with button-effect switch is used to "kill" circuit emulator when the bypass - in izbezhanie penetration interference with the signal output of the circuit in bypass.

Bypass this pedal is a passive type, one of the varieties of true-bypass - the so-called split-bypass when the signal is not disconnected from the input circuit. That is why when the bypass is desirable "turn off" (from the word mute mute) the signal flow through the restrictor - otherwise possible penetration of harmonics limited output signal that is heard as unpleasant podzuzhivanie. Passive bypass this pedal is fully justified - because of low marginal gain pedal is not prone to self, and in co-operation with passive devices haygeynovymi bypass has lower noise and simplifies the pedal. If desired, it is easy to make active - follower DA1.1 in the scheme already, just add a capacitor and its output resistor to ground to eliminate clicks. Alternatively, the yield after nondisconnectable repeater can be used to connect the tuner (if the optional output jack, naturally) ...

Food scheme is carried out either by batteries "Crown" or an external power supply 9-12V via a standard connector block desirable stabilized.For reverse polarity protection diodes are VD4, VD5, through which automatically connects the power supply with a higher voltage, and if disconnected the power supply will automatically connect battery. Capacitor C11 eliminates the possible self-excitation circuit and increases battery life. It is possible to use only one diode, and switching power supply battery and carry in the power connector - most serial connector has an additional contact for the battery. Naturally - with this method when the battery is disconnected the power supply on the stage does not automatically connect, and more - will probably need to isolate the power connector from the body, it is not easy, if it is attached to the nut housing. Resistors R2, R3 and capacitor C2 create point "artificial ground" for normal OS from a single supply.

Warning: To Timer battery when unplugging from the input jack, negative cable from the battery is attached not to the ground (GND), and to the middle pin (ring) 

Connector Input. With the inclusion of a mono jack guitar cord this pin is shorted to ground and connect the battery.

Design and printed circuit boards

Many possible design options - it all depends on the imagination of the designer and opportunities. In the authors version dvuhplatnoy design - built on the same board tembroblok, on the other - all the rest, except the connectors and switches. At the same board soldered to the potentiometers, bolted to the body, and, thanks to its light weight, do not require additional bracing. Thus, the potentiometers are arranged in two rows, and perpendicular to the board and the housing cover parallel to each other. The disadvantage of this design - the need to connect the board to each other, as well as jacks and switches mounting wires. Same dignity - compactness and pedal boards in general. 

Points on the boards designated by single letters, interconnected (same points, of course) mounting wires. These same letters mark corresponding points on the concept.

The proposed fees are designed for installation of SMD components - this chip, transistors, diodes and resistors majority. An exception is made for capacitors "the pass" by the sound - there is recommended to use film capacitors, as the most suitable. It is not "snobbery tube", and the result is real auditions and measurements - Ceramic Capacitors noticeably louder, however, it becomes especially noticeable when lamp supply voltages and sweep signal in the circuit, because in the absence of the film can be at your own risk and put the ceramics, the more that the scheme itself and voiced slabogeynovaya.

In the absence of skill work with SMD quite possibly reroute fee under the usual details - though at the same time and will significantly increase its size, and the manual manufacturing (LUT) will repeatedly increase work drilling holes. Alternatively, the circuit can be assembled on a breadboard, completing installation scraps conclusions elements and isolated postings.

As the "main" button for effect On / Off switch used standard DP2T. 

As a body in the authors version used aluminum body ProsKit 203-125B. 

Perklyuchatel Bright - mikrotumbler 2 positions. Resistor R15 is soldered directly to his conclusions. 

LED display - ultra-bright 3 mm, color - to taste. Ultrabright LED current can reduce it to about 0.5 mA with sufficient brightness, which prolongs battery life. If applied LED with clear lens, its worth zamatirovat fine sandpaper-nulevkoy.

Making your body can be very different - from polishing body engraved with inscriptions, and to panel fabrication method METALLOGRAFIKA. 

In the authors version of the hull was painted with powder paint and lettering are made in the form of stickers on transparency film (booked in an advertising firm) - this method is well suited for small-scale or production unit.

Here is the finished device in the authors version:

Recommendations for use

Most standard will be the inclusion of pedal effects chain after device with an active bypass (such a device, it is desirable to have the first after the guitar in the effects chain, usually overdrive effect - "drive"). Pedal is designed for use in conjunction with guitar amps (and speakers, cabinets!), Therefore, has no filter comprising spikosimulyatora (device that simulates the frequency response guitar cabinet). This means that when you turn into a regular household power or mixing console for more gain sound can be frustrating, "sand." With this inclusion should not add a lot of gain and include mode «Bright». It is also possible to include the pedal before the main "drive" - ​​when this pedal can be used not only as a generator pedalborda channel, but also as a "warmer" for the main "drive".

Nourish pedal comprising pedalborda better from the power supply - usually this block is common to several effects. Current consumption pedal is about 4 mA, so it is without any complications and unintended consequences can be connected to an existing block (recommended stabilized power - or more gain on possible overtones and background). If it is possible - better to increase the supply voltage to 12V - with little noise and improved dynamic properties of the pedal. If the pedal is used separately - powered by Kroon is justified because of fresh alkaline batteries when the 5 hours a day with a pedal operated for approximately six months. Low battery indication is the dim glow of the LED for effect and degrade sound.

Glossary (dictionary of specific terms and slang)

" Wedge »(« ​​Clean ») - sound" clean "guitar (not to be confused with the bypass), with virtually no distortion, but with the corrected tone, usually bright, with a predominance of high frequencies.

" Crunch »(« Crunch ») - the sound to the point of distortion and overdrive with a small, typical for blues, rock and roll, hard rock, and some styles of" metal ". Very expressive, and allows execution bust chords.

" bells and whistles "- common slang name among guitarists effects pedals for guitar. Typically connected at the entrance of the guitar amplifier.

" Preamp "- guitar preamp, as a rule - 2 or 3 channel, usually not connected into the input of the guitar amplifier, and« Return »loop externalities - ie directly to the power amplifier.

" Dynamics "- property pedal / preamp allocate note played more vigorously from weaker music, sound volume and timbre. In the case of devices with more gain - its not as easy as it seems at first glance, because they have the property to align the volume of notes by limiting (and "extend" their duration).

" Readability "- property pedal / preamp do not" mess "sound when playing chords. Each note in the chord should be heard and not interfere with the rest. This gives the intelligibility of the sound at different riffs primarily and significantly improves the readability of the guitar in the mix.

" Gein »(« Gain ») - the ratio of the gain of the device to the threshold limit. More generally - the power amp overdrive.

" Haygeyn »(« Highgain ») - a kind of amps / preamps with an extended range of adjustment in the direction of maximum gain. Widely used in modern heavy music styles. Usually haygeynovye devices "incarcerated" under it more gain and small Heine sound unclear what causes such devices do multichannel - crunch channel usually contains less stages and has a different frequency response.

" Midgeyn »(« Midgain ») - a kind of amps / preamps with an average gain control range. Sound - from the wedge / crunch to sredneperegruzhennogo, typical for old-school rock, although widely used today.

" Bright "- underline mode for the treble range of electric guitars, adds brightness and sonority in the sound.

" Bypass »(« bypass ») - mode" bypass ", ie direct signal flow through the device without treatment.

" True-Bypass "- in terms of technology - passive bypass for mechanical contacts, without the use of electronic keys and active elements.From the perspective of some of the musicians - the only right kind of bypass ....

" humbucker »(« Humbacker ») - the type of pickup with two coils on a common magnetic system characterized by low sensitivity to interference and powerful output.

" Sand "- the high-frequency overtone flowing in the sound distorting pedals. When using the guitar speakers largely filtered out by the speaker.

" Drive »(« ​​Overdrive ») - channel preamp or lotion used to produce sound overdriven amplifier. Sometimes referred to as a soft overdrive overdrive, distortion - hard, but in fact - is the same thing ....

" Warmer "- pedal included between the guitar and amplifier / lotion / preamp for" heating "- increase the overall gain and changes in timbre.Typically uses a variety of boosters and overdrive with not much more gain.

" Spikosimulyator "- a device to simulate the sound through a guitar speaker / cabinet. Typically configured as a separate lotion, is sometimes included in the distorting preamps / lotions. Is a special filter, which roughly corresponds to the AFC AFC guitar cabinet.

" Cabinet "- guitar speaker, often on 4 speakers 12".

" AFC "- frequency response.

Original article sourse cxem.net