Direct coupled, also known as "DC amp", refers to a type of amplifier

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...

. In this type of amplifier

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...

, the output

Output

Output is the term denoting either an exit or changes which exit a system and which activate/modify a process. It is an abstract concept, used in the modeling, system design and system exploitation.-In control theory:...

 of one stage of the amplifier is connected to the input of the next stage directly without using any reactive components like capacitors, inductor

Inductor

An inductor is a passive two-terminal electrical component used to store energy in a magnetic field. An inductor's ability to store magnetic energy is measured by its inductance, in units of henries...

s, transformer

Transformer

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...

s, and others. As a result, the frequency response

Frequency response

Frequency response is the quantitative measure of the output spectrum of a system or device in response to a stimulus, and is used to characterize the dynamics of the system. It is a measure of magnitude and phase of the output as a function of frequency, in comparison to the input...

 of this amplifier is quite flat all the way down to DC (0 Hz).

Current

The common use of the term "DC Amp" does not mean "direct current

Direct current

Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...

 amplifier", as this type can be used for both direct current

Direct current

Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...

 and alternating current

Alternating current

In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....

 signals. The amplification

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...

 of D/C (zero frequency

Frequency

Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...

) is possible only by this amplifier, hence it later becomes the building block for differential amplifier

Differential 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 operational amplifier. Unlike other multistage amplifiers

Multistage amplifiers

The performance obtainable from a single stage amplifier is often insufficient for many applications, hence several stages may be combined forming a multistage amplifier. These stages are connected in cascade, i.e...

, amplification of low frequency

Low frequency

Low frequency or low freq or LF refers to radio frequencies in the range of 30 kHz–300 kHz. In Europe, and parts of Northern Africa and of Asia, part of the LF spectrum is used for AM broadcasting as the longwave band. In the western hemisphere, its main use is for aircraft beacon,...

 (below 10 Hz) signals is only possible using direct coupling. This is because use of coupling and bypass capacitors is not possible as they provide very high capacitive reactance.

Advantages

There are several advantages of using this type of amplifier, including:

• Simple circuit arrangement as there are minimum number of components
• For above reason, also quite inexpensive
• Can be used to amplify zero and low frequency signals
• Provides uniform frequency response up to a high frequency
  High frequency
  High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...
  
  . Lower cut-off frequency
  Cutoff frequency
  In physics and electrical engineering, a cutoff frequency, corner frequency, or break frequency is a boundary in a system's frequency response at which energy flowing through the system begins to be reduced rather than passing through.Typically in electronic systems such as filters and...
  
   is zero and upper cut-off frequency is determined by values of components used.

Disadvantages

In addition to the advantages, there are also several known disadvantages. These include:

• Unwanted change in output voltage
  Voltage
  Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
  
   without any change in the input is often observed. This is caused by temperature
  Temperature
  Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
  
   variations, aging of components, etc and is referred to as 'drift'. This drawback
  Drawback
  Drawback, in law in commerce, paying back a duty previously paid on exporting excisable articles or on re-exporting foreign goods. The object of a drawback is to let commodities which are subject to taxation be exported and sold in a foreign country on the same terms as goods from countries where...
  
   can be removed using differential amplifier
  Differential 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....
  
  .
• At high frequencies gain decreases.
• Transistor parameters change with temperature, hence output is affected by temperature variations.
• Even if input is AC, some DC component
  DC coefficient
  When describing a periodic function in the frequency domain, the DC bias, DC component, DC offset, or DC coefficient is the mean value of the waveform...
  
   is present at output. This can be removed using differential amplifier
  Differential 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....
  
  .
• Any noise
  Noise
  In common use, the word noise means any unwanted sound. In both analog and digital electronics, noise is random unwanted perturbation to a wanted signal; it is called noise as a generalisation of the acoustic noise heard when listening to a weak radio transmission with significant electrical noise...
  
   or stray pickup appearing at the input is also present at the output in amplified form, due to high gain.

Application

Direct coupled is used in TV receiver

Receiver (radio)

A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...

s, computer

Computer

A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...

s, regulator

Regulator (automatic control)

In automatic control, a regulator is a device which has the function of maintaining a designated characteristic. It performs the activity of managing or maintaining a range of values in a machine. The measurable property of a device is managed closely by specified conditions or an advance set...

 circuits

Electronic circuit

An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow...

 and other electronic instruments

Electronic musical instrument

An electronic musical instrument is a musical instrument that produces its sounds using electronics. Such an instrument sounds by outputting an electrical audio signal that ultimately drives a loudspeaker....

. It also forms a building block for differential amplifier

Differential 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....

s and operational amplifier

Operational amplifier

An operational amplifier is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output...

s.

See also

• Direct coupling
  Direct coupling
  In electronics, direct coupling is a way of interconnecting two circuits such that, in addition to transferring the AC signal , the first stage also provides DC bias to the next...
  
  
• Capacitive coupling
  Capacitive coupling
  In electronics, capacitive coupling is the transfer of energy within an electrical network by means of the capacitance between circuit nodes. This coupling can have an intentional or accidental effect...
  
  
• Coupling (electronics)
  Coupling (electronics)
  In electronics and telecommunication, coupling is the desirable or undesirable transfer of energy from one medium, such as a metallic wire or an optical fiber, to another medium, including fortuitous transfer....