# Variable-gain amplifier > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Variable-gain_amplifier > Markdown URL: https://mediated.wiki/source/Variable-gain_amplifier.md > Source: https://en.wikipedia.org/wiki/Variable-gain_amplifier > Source revision: 1352254013 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) {{Short description|Electronic amplifier that varies its gain depending on a control voltage}} A '''variable-gain''' ('''VGA''') or '''voltage-controlled amplifier''' ('''VCA''') is an [electronic amplifier](/source/electronic_amplifier) that varies its [gain](/source/Gain_(electronics)) depending on a control voltage (often abbreviated ''CV''). VCAs have many applications, including [audio level compression](/source/audio_level_compression), [synthesizers](/source/synthesizers) and [amplitude modulation](/source/amplitude_modulation). A voltage-controlled amplifier can be realised by first creating a [voltage-controlled resistor](/source/voltage-controlled_resistor) (VCR), which is used to set the amplifier gain. A simple example is a [typical inverting](/source/Op-amp) [op-amp](/source/op-amp) configuration with a [light-dependent resistor](/source/light-dependent_resistor) (LDR) in the feedback loop. The gain of the amplifier then depends on the light falling on the LDR, which can be provided by an [LED](/source/LED) (an [optocoupler](/source/optocoupler)). The gain of the amplifier is then controllable by the current through the LED. This is similar to the circuits used in optical [audio compressor](/source/audio_compressor)s. Another type of circuit uses [operational transconductance amplifier](/source/operational_transconductance_amplifier)s. In audio applications [logarithm](/source/logarithm)ic gain control is used to emulate how the ear hears [loudness](/source/loudness). [David E. Blackmer](/source/David_E._Blackmer)'s [dbx](/source/Dbx%2C_Inc.) 202 VCA, based on the [Blackmer gain cell](/source/Blackmer_gain_cell), was among the first successful implementations of a logarithmic VCA.{{cite web |url=http://www.thatcorp.com/History_of_VCAs.shtml |archive-url=https://web.archive.org/web/20200703115259/http://www.thatcorp.com/History_of_VCAs.shtml |archive-date=2020-07-03 |title=A Brief History of VCA Development}} [Analog multiplier](/source/Analog_multiplier)s are a type of VCA designed to have accurate linear characteristics; the two inputs are identical and often work with both positive and negative voltage inputs. == In sound mixing consoles == Some [mixing console](/source/mixing_console)s come equipped with VCAs in each channel for [console automation](/source/console_automation). The [fader](/source/Fade_(audio_engineering)), which traditionally controls the audio signal directly, becomes a DC control voltage for the VCA. The maximum voltage available to a fader can be controlled by one or more master faders called ''VCA groups''. A VCA master fader then controls the overall level of all of the channels assigned to the group.{{cite web |title=Allen & Heath ML3000 Block Diagram |url=http://www.allen-heath.com/media/ML3000-Block-Diagram.pdf|archive-url=https://web.archive.org/web/20221014092711/http://www.allen-heath.com/media/ML3000-Block-Diagram.pdf |archive-date=2022-10-14 }} Typically VCA groups are used to control various sections of the mix; [vocals](/source/Vocal_music), [guitar](/source/guitar)s, [drum](/source/drum)s or [percussion](/source/percussion). The VCA master fader allows that portion of a mix to be raised or lowered without affecting the blend of the instruments in that part of the mix. A benefit of the VCA sub-group is that since it directly affects the gain level of each channel, changes to a VCA sub-group level affect not only the channel level but also all of the levels sent to any post-fader mixes. With traditional audio sub-groups, the sub-group master fader only affects the level going into the main mix. Consider the case of an [instrument](/source/Musical_instrument) feeding a sub-group and a post-fader mix. If you completely lower the sub-group master fader, you would no longer hear the instrument itself, but you would still hear it as part of the post-fader mix, perhaps to a [reverb](/source/reverb) or [chorus effect](/source/chorus_effect).{{cite web |url=http://www.allen-heath.com/media/ML3000-USER-GUIDE.pdf |title=Allen & Heath ML3000 User Guide}} VCA mixers are known to last longer than non-VCA analog mixers. Because the VCA controls the audio level instead of the physical fader, wear in the fader mechanism over time does not cause a degradation in audio quality. VCAs were invented by [David E. Blackmer](/source/David_E._Blackmer), the founder of [dbx](/source/dbx_(company)), who used them to make [dynamic range compressor](/source/dynamic_range_compressor)s. The first console using VCAs was the Allison Research computer-automated recording system designed by [Paul C. Buff](/source/Paul_C._Buff) in 1973.{{cite book |author=Richard James Burgess |title=The History of Music Production |page=134 |url=https://books.google.com/books?id=8J6zAwAAQBAJ&pg=PT134 |date=2014 |publisher=Oxford University Press |isbn=9780199385010}} Another early VCA capability on a sound mixer was the series of [MCI](/source/Music_Center_Incorporated) JH500 studio recording desks introduced in 1975.{{cite book |last=Self |first=Douglas |title=Audio Engineering Explained |date=2012 |page=249 |publisher=Taylor & Francis |isbn=9781136121258 }} The first VCA mixer for live sound was the PM3000 introduced by [Yamaha](/source/Yamaha_Pro_Audio) in 1985.{{cn|date=December 2025}} == Digital variable-gain amplifier == A '''digitally controlled amplifier''' (DCA) is a variable-gain amplifier that is digitally controlled. The digitally controlled amplifier uses a stepped approach, giving the circuit graduated increments of gain selection. This can be done in several fashions, but certain elements remain in any design. At its most basic form, a toggle switch strapped across the feedback resistor can provide two discrete gain settings. With eight switches and eight resistors in the feedback loop, each switch can enable a particular resistor to control the amplifier's feedback. To minimize the number of switches and resistors, combinations of resistance values can be utilized by activating multiple switches. If each switch were converted to a relay, a microcontroller could be used to activate the relays to attain the desired amount of gain. Relays can be replaced with [field-effect transistor](/source/field-effect_transistor)s of an appropriate type to reduce the mechanical nature of the design. Other devices, such as the CD4053 bi-directional CMOS analog multiplexer integrated circuit and digital potentiometers (combined resistor string and [multiplexer](/source/multiplexer)s) can serve well as the switching function. == See also == *[Automixer](/source/Automixer) *[Mix automation](/source/Mix_automation) == References == {{reflist}} == External links == * [http://www.schmitzbits.de/vca.html Examples of non-optical VCAs] * [http://www5b.biglobe.ne.jp/~houshu/synth/ Some schematics for VCAs] * {{cite web |url=http://www.cgs.synth.net/tube/vca.html |title=Vacuum tube VCAs |archive-url=https://web.archive.org/web/20080513201131/http://www.cgs.synth.net/tube/vca.html |archive-date=2008-05-13}} * {{web archive |url=https://archive.today/20130221013802/http://glogger.mobi/v/31470/ |title=University of Toronto undergraduate lecture explaining how to implement a Voltage Controlled Amplifier using an operational amplifier and a photocell}} * {{web archive |url=https://web.archive.org/web/20081203003921/http://www.allen-heath.com/DL/vca_book.pdf |title=Allen & Heath's Guide to VCA Sound Desk Mixing}} {{DEFAULTSORT:Variable-Gain Amplifier}} Category:Frequency mixers Category:Electronic amplifiers Category:Dynamics processing Category:Synthesiser modules --- Adapted from the Wikipedia article [Variable-gain amplifier](https://en.wikipedia.org/wiki/Variable-gain_amplifier) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Variable-gain_amplifier?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.