Gainclone
Encyclopedia
Amplifier
Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
made by do-it-yourselfers
Do it yourself
Do it yourself is a term used to describe building, modifying, or repairing of something without the aid of experts or professionals...
, or individuals interested in DIY audio
DIY audio
DIY Audio means "do it yourself" audio. Rather than buying a piece of possibly expensive audio equipment, such as a high-end audio amplifier or speaker, the person practicing DIY Audio will make it him/herself...
. It is a design based on high-power integrated circuits, particularly the National Semiconductor
National Semiconductor
National Semiconductor was an American semiconductor manufacturer, that specialized in analog devices and subsystems,formerly headquartered in Santa Clara, California, USA. The products of National Semiconductor included power management circuits, display drivers, audio and operational amplifiers,...
Overture series. The Gainclone is probably the most commonly built and well-known amplifier project amongst hobbyists. It is simple to build and involves only a few readily accessible, inexpensive parts. As an amplifier it is highly regarded by many in the DIY community.
Background
In 1999, 47 Labs introduced the Gaincard amplifierAmplifier
Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
. The Gaincard shook the audiophile
Audiophile
An audiophile is a person who enjoys listening to recorded music, usually in a home. Some audiophiles are more interested in collecting and listening to music, while others are more interested in collecting and listening to audio components, whose "sound quality" they consider as important as the...
community with its unconventional design. It had fewer parts, less capacitance
Capacitance
In electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...
and simpler construction than virtually anything preceding it, and relied for amplification on a chip, the National Semiconductor LM3875
LM3875
LM3875 is a 56 watt amplifier chip made by National Semiconductor that has become very popular in the DIY community for its low parts count and its high-end audio capabilities. It is the main chip inside the gainclone amplifier which surprised many high-end audio reviewers. - External links :*...
. These construction techniques went against the accepted wisdom of the time, which favored large power supplies and discrete component construction. This Gaincard was estimated to cost less than in parts, but it sold for with its small power supply
Power supply
A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy to electrical energy...
. Controversy ensued after a number of positive reviews.
Modern usage
The DIY community started building replicas or "clones" of the Gaincard using integrated circuits from National Semiconductor and other manufacturers in an attempt to see if good sound could be obtained, thereby the term: "gainclone". The name was first coined by a poster called "triodont" on the popular Audio Asylum board (ca. 1999;). Triodont (née Ray Salamat) tried to replicate the 47 Labs Gaincard amplifier (for his own personal use) and reported about it on the internet forum. Various modifications or improvements (depending on how you look at it) have been made to the original application circuit found in National's design notes since then. The simple circuits were easy to make and some started offering printed circuit boardPrinted circuit board
A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...
s and kits to make construction even easier.
The design concept has expanded and become rapidly more popular over the last few years as the simplicity of the design and availability of parts make it within reach of even a novice constructor. Now, the term "Gainclone" could apply to almost any amplifier based on a power integrated circuit
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
of some type, from any manufacturer. In fact, the more common term today for such amplifiers is "chipamp" rather than "Gainclone", as the desire to copy the Gaincard has given way to broader attempts at using IC amplifiers.
Controversy over these Gainclones still exists, and variations have spawned. There are hundreds of web sites with examples, kits, circuits, and descriptions of the Gainclone amplifier.
Typical characteristics
- A power opamp or audio opamp chip such as the National SemiconductorNational SemiconductorNational Semiconductor was an American semiconductor manufacturer, that specialized in analog devices and subsystems,formerly headquartered in Santa Clara, California, USA. The products of National Semiconductor included power management circuits, display drivers, audio and operational amplifiers,...
LM1875, LM3875LM3875LM3875 is a 56 watt amplifier chip made by National Semiconductor that has become very popular in the DIY community for its low parts count and its high-end audio capabilities. It is the main chip inside the gainclone amplifier which surprised many high-end audio reviewers. - External links :*...
, LM3886, or LM4780, which is a dual LM3886. - A physically very short feedback loop.
- Miniaturised construction with short path lengths throughout the circuit.
- Minimal extra components, usually of high quality.
- Small power supply filter capacitorFilter capacitorFilter capacitors are any capacitors used for filtering. Filter capacitors are common in electrical and electronic work, and cover a number of applications, such as:* Glitch removal on Direct current power rails...
s (often around 1000 µF). - Can be made using point-to-point construction rather than a PCBPrinted circuit boardA printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...
. - The power supply is often built in a separate chassis from the amplifier.
The National Semiconductor chips come in two versions. The "T" model is not insulated and has better heat transfer properties but it needs insulation when mounted on a heatsink. The "TF" model as in the picture is covered in plastic, and thus insulated, but it has less efficient heat transfer properties which means it can't run continuously at full power. The "T" model is recommended for heavy duty applications.
Sound
Most designs are very effective and produce high quality sound, even though some audiophiles consider chip-based amplifiers to be inferior to their discrete counterparts. Many others, however, are astonished by what these amplifiers are capable of. The chips have been carefully designed to incorporate a number of desirable features, including excellent power supply rejection ratioPower supply rejection ratio
In electronics, power supply rejection ratio or PSRR is a term widely used in the electronic amplifier or voltage regulator datasheets; used to describe the amount of noise from a power supply that a particular device can reject.-Definition:The PSRR is defined as the ratio of the change in supply...
, fast response, accurate bias current, over temperature protection and short circuit protection.
New generation chipamps
National Semiconductor new LME series offers very high performance driver chips for chip-based audio power amplifiers. They are LME49810, LME49811 and LME49830. Each of them consists of input differential amplifierDifferential amplifier
A differential amplifier is a type of electronic amplifier that amplifies the difference between two voltages but does not amplify the particular voltages.- Theory :Many electronic devices use differential amplifiers internally....
and voltage gain amplifier
Variable-gain amplifier
A variable-gain or voltage-controlled amplifier is an electronic amplifier that varies its gain depending on a control voltage .VCAs have many applications, including audio level compression, synthesizers and amplitude modulation....
(VGA). With the addition of discrete output transistors, a complete audio power amplifier is made. The LME49810 has a built-in output buffer and Baker clamp
Baker clamp
Baker clamp is a generic name for a class of electronic circuits that reduce the storage time of a switching bipolar junction transistor by applying a nonlinear negative feedback through various kinds of diodes. The reason for slow turn-off times of saturated BJTs is the stored charge in the base...
circuit. The LME49830 is designed for directly driving MOSFET
MOSFET
The metal–oxide–semiconductor field-effect transistor is a transistor used for amplifying or switching electronic signals. The basic principle of this kind of transistor was first patented by Julius Edgar Lilienfeld in 1925...
output.