Kaj počne avtomobilski ojačevalnik? Edini vodnik, ki ga potrebujete

Vas zanima, kako delujejo avtomobilski ojačevalniki in za kaj se uporabljajo? Ste pripravljeni nadgraditi svoj avtomobilski avdio sistem, ki ga želite nadgraditi, vendar morate najprej vedeti več? Prišli ste na pravo mesto!

Pokril bom vse, kar morate vedeti:

- Kako deluje avtomobilski avdio ojačevalnik
- Kaj počnejo in zakaj so koristni za zvok

Razlike med različnimi razredi zvočnih ojačevalnikov

…in še veliko, veliko več!

Kaj počne avtomobilski ojačevalnik?

Avtomobilski ojačevalnik poveča zelo majhen električni zvočni signal iz glavne enote na višjo napetost. Lahko poganja zvočnike, povezane z zvočniško žico, z večjo močjo, glasnostjo in jasnim zvokom. Večina avtomobilskih avdio sistemov v armaturni plošči ima na voljo le približno 15 do 18 vatov in pri največji moči začnejo zelo močno popačiti.

Zunanji ojačevalnik ne samo da reši to težavo, ampak lahko tudi močno izboljša zvestobo reprodukcije glasbe, ki jo uživate.

Za močne nizke tone nizkotonci potrebujejo veliko moči, ki je nemogoče pridobiti samo z avtoradio. To je tudi težava, ko želite uporabiti 4 ohmske ali celo 2 Ω poprodajne zvočnike, ki potrebujejo več moči za maksimalno zmogljivost pri nadgradnji zvočnega sistema.

Zunanji ojačevalnik zagotavlja višjo kakovost zvoka, saj lahko nudi nižji šum in popačenje zaradi naprednejše elektronike, vključene v ta namen. Avtomobilski stereo sistemi pogosto uporabljajo bolj osnovno zasnovo in cenejše komponente, ki omejujejo, kaj lahko slišite.

Razložene ocene moči ojačevalnika

Neprekinjena ali RMS ocena v vatih opisuje izhodno moč, ki jo lahko ojačevalnik realno zanesljivo zagotavlja. Čeprav se sliši impresivno, je specifikacija "največje" ali "največje" moči bolj tehnična in ne tisto, kar boste dobili med običajno uporabo.

RMS moč se nanaša na povprečno kvadratno vrednost meritev, ki se uporablja v elektrotehniki za opis signalov izmeničnega toka (AC), kot so tisti, ki se uporabljajo v zvočni elektroniki. Ker se izmenična napetost razlikuje od enosmernega toka (DC), je matematika nekoliko drugačna. Meritve RMS to upoštevajo.

Za pomoč kupcem pri pridobivanju natančnejših informacij je bil ustvarjen standard Consumer Electronics Association (CEA) 2006, ki spodbuja zagotavljanje natančnih specifikacij. Prodani izdelki, ki vsebujejo specifikacije CEA-2006, so dokazali, da zagotavljajo tisto, kar proizvajalec oglašuje.

Kako deluje avtomobilski ojačevalnik?

Notranji napajalnik, ki ga napajata pozitivna in negativna napajalna napeljava baterije, ustvari višjo izhodno napetost – in večjo moč – kot je sicer mogoče iz 12-voltnega vira napajanja. Zaradi velike porabe amperov so debele napajalne žice in ozemljitvene žice v večini primerov izvedene neposredno na akumulator vozila in kovinsko podvozje.

Avtoradio pošlje zvočni signal prek kabla RCA ali druge povezave, kjer je okrepljen električni signal dostavljen do terminalov zvočnikov za uporabo z žico.

Skoraj vsi poprodajni avtomobilski avdio ojačevalniki imajo naslednje:

DC-DC (enosmerni tok) stopenjsko stikalno napajanje
Vezje za preprečevanje hrupa (»zemeljska zanka«)
Križno vezje zvočnikov
Premostitveno vezje
Dodatne priročne funkcije (npr.:vhodne stopnje na ravni zvočnikov ali ojačitev nizkih tonov)

Razloženi napajalniki za avtomobilski ojačevalnik

Zvok avtomobila predstavlja res težak izziv:z uporabo samo napajanja +12 V ne moremo neposredno ustvariti velike izhodne moči za tovarniške ali nadgrajene zvočnike.

Da bi to bolje razumeli, si lahko ogledamo Ohmov zakon, ki pravi, da je moč povezana z uporom bremena (impedanca zvočnika) in napajalno napetostjo. Obremenitveni upor se mora zmanjšati ali napetost povečati, da dobimo več moči.

Ohmov zakon je niz matematičnih formul, ki se uporabljajo za izračun moči, dovedene bremenu. Če želite pridobiti več energije, boste morali (1) zmanjšati obremenitev v ohmih (impedanca) ali (2) povečati razpoložljive volte.

Napajalnik s stikalnim načinom (SMPS) v notranjosti to omogoča, saj vzame napajanje +12 V baterije in ga večkrat poveča na približno 28 voltov do 32 voltov, na primer. Zagotovljene so tudi napajalne poti pozitivne in negativne polarnosti (imenovane tudi napajalne »tirnice«).

Čip preklopnega integriranega vezja (IC) tisočkrat na sekundo vklopi in izklopi visokotokovne tranzistorje, povezane s transformatorjem. Transformator, glede na število ovojev bakrene žice na njem, proizvaja višje napetosti na svojem izhodu. Ti so zglajeni in stabilizirani, da ustvarijo vir energije za kanale zvočnikov.

Posnetek alternativnih valovnih oblik (napetostni signali vklopa/izklopa), ki se uporabljajo za pogon tranzistorjev v napajalniku SMPS nekaj tisočkrat na sekundo.

Preklopni napajalniki DC-DC, kot so tisti v avtomobilskem ojačevalniku, se imenujejo step-up saj lahko vzamejo nižjo napetost in jo večkrat pomnožijo na višjo napetost. Step down napajalniki delujejo nasprotno.

Nekatere komponente, kot so preklopni tranzistorji visoke moči, so pritrjene na težko kovinsko ohišje ojačevalnika, da odstranijo in odvedejo odvečno ustvarjeno toploto. V nasprotnem primeru bi sčasoma odpovedali zaradi toplote, ki bi jih uničila.

Kako se ojačevalniki vklopijo in izklopijo

Signal nizkega toka (pogosto manj kot 0,025 amperov), imenovan "oddaljena" žica, se uporablja, da preprečimo, da bi ojačevalnik ostal vklopljen in izpraznil baterijo, ko ni v uporabi. Daljinska žica je povezana z izhodom na avtoradio ali napeljavo za vžig. Ko je signal +12 V odstranjen, se ojačevalnik izklopi in preneha črpati energijo iz baterije.

Vhodne stopnje, ojačevalni deli in izhodne stopnje

Prikazana sta dva dela, ki omogočata odličen avtomobilski zvok:razdelek ojačevalnika in izhoda ter vhodne stopnje. Plošča vhodne stopnje je sestavljena iz številnih manjših vezij, ki opravljajo stvari, kot je zagotavljanje funkcij križanja, omogočanje premostitve za večjo moč, zagotavljanje nadzora ojačanja in blokiranje šuma ozemljitvene zanke. Stopnje ojačevalnika sprejmejo zvočni signal s plošče vhodne stopnje, uporabijo izhod napajalnika in ga okrepijo, da ustvarijo močan izhod.

Vhodne stopnje

Vhodne stopnje morajo opraviti več opravil:

Omogočite, da se ojačevalnik poveže s stereo napravami brez priključkov RCA (vhodi na ravni zvočnikov, če so na voljo)
Preprečite, da bi hrup ozemljitvene zanke prišel v signalno pot
Zagotavlja funkcije križanja
Omogočanje prilagajanja stopnje ojačanja ojačevalnika

Vhodne stopnje uporabljajo izjemno vsestransko elektronsko komponento, imenovano operacijski ojačevalnik (operacijski ojačevalnik). Operacijski ojačevalniki so majhna ojačevalna vezja, vgrajena v miniaturne čipe, ki se uporabljajo za vse vrste zvočnih funkcij.

Preprečevanje hrupa

Hrup ozemljitvene zanke je pogosta in zelo moteča težava pri namestitvi avtomobilskega avdio sistema. Imenuje se tudisviljenje alternatorja , gre za vrsto nizke ravni električnega hrupa na poti zvočnega signala, ki se pojavi kot grozno cviljenje, ki se povečuje in zmanjšuje s hitrostjo motorja.

Ta vrsta hrupa je posledica električnih tokov, ki tečejo znotraj karoserije vozila in povezav zvočnih komponent. Ko obstaja razlika v električnem potencialu v 2 ali več točkah v sistemu, se ustvari majhna napetostna razlika, ki jo je mogoče povečati. To je videti kot visoko in nadležno cviljenje, ki ga slišite iz zvočnikov.

Zasnova filtra, imenovana diferencialni ojačevalnik vezje se uporablja na sprednjem koncu (vhodna stran) za učinkovito blokiranje in izničenje tega hrupa, preden lahko pride v poti glasbenega signala.

Križnice

Elektronske kretnice ponujajo način nadzora frekvenčnega območja, poslanega v avtomobilske zvočnike. Na primer, pri pogonu nizkotonskih zvočnikov nizkofrekvenčni filter blokira vse razen nizkih tonov, da zagotovi odličen nizkotonski zvok. Podobno lahko preprečite, da bi nizki toni popačili manjše zvočnike, kot so visokotonci ali vratni zvočniki, z uporabo visokofrekvenčne kretnice.

Ob pravilni uporabi kretnice vam omogočajo večjo glasnost, zaščito vaših zvočnikov in boljšo jasnost zvoka. Za naprednejše sisteme, kot so tisti, ki uporabljajo komponentne zvočnike, so še posebej koristni.

Elektronske kretnice v ojačevalnikih opravljajo enako funkcijo kot kretnice pasivnih zvočnikov, vendar brez obsežnih komponent, kot so induktorji in kondenzatorji, ki jih potrebujejo. Prav tako jih je enostavno nastaviti ali vklopiti/izklopiti s pritiskom na stikalo.

Ojačanje ojačevalnika

Kot pove že ime, ojačevalniki povečajo vhodni signal iz stereo. Ker ni standardne izhodne napetosti, ki jo uporabljajo različni avtomobilski stereo sistemi, je za najboljše rezultate potrebna nastavitev ojačanja, vključno s kakovostjo zvoka, zadostno močjo in preprečevanjem popačenja, imenovanega izrezovanje.

Prilagoditev ojačanja ojačevalnika omogoča nadzor izhodne ravni na podlagi ravni vhodnega signala. As some car stereos have stronger output signals the gain control can be reduced to better match it to the output level &volume.

The gain level affects the headroom which is the amount of amplification still available before the limit is reached. All types from car to home stereos and even home DJ equipment often include a gain adjustement.

It’s also a way to reduce noise. Because as all amps add some level of noise (like a “hiss” or similar) to their outputs, lowering the gain also reduces the noise produced and heard.

Amplifier sections and output stages

Simplified illustration of the amplification stages and output that most car amps use. Beefy output transistors capable of handling large amounts of current are connected to the switching power supply and drive the speaker. They’re controlled by some smaller components needed to split the audio signal into positive and negative halves needed to reproduce the musical signal.

Power amplifiers (as seen in the image above) have main sections dedicated to modify or manipulate audio signals as well as for delivering more current and voltage. The first sections contain small components like miniature transistors that divide the audio signal into two halves.

Next, after passing through the crossover filter and other stages, they’re directed to large high current transistors supplied with higher volts from the SMPS. The input signal is magnified to an identical but much larger waveform connect to the speaker outputs.

Car audio amplifier classes explained

The class listed by a car audio amplifier manufacturer is the type of technology used for the audio signal and to deliver power. Every audio amp uses a class A, class D, or class A/B design.

Class A: The most inefficient but provides audiophile quality sound. (Used in some past designs like from Rockford Fosgate)

Class A/B: Until recently the most popular because they offer reasonable cost and good sound quality. Class A/B amps work similar to class A but switch off when the signal reaches the zero voltage threshold, reducing power consumed slightly.
Class D: These amps are increasingly more common as they use newer technology to rapidly switch the power circuitry on and off, reducing waste and heat. Sometimes mistakenly called a “digital amplifier” although they don’t use digital technology for their basic functions.

Class D vs class A/B differences

Class A/B designs conduct, follow, and amplify the analog input signal most of the time, using some power even when nothing is being delivered to the speakers. This is because even when you’re not driving speakers some power is wasted as heat due to losses. That’s one reason this type gets fairly warm especially during hard use.

They have an efficiency somewhere around 65% meaning they draw about 35% higher amps from the battery than is delivered as power to speakers. This is wasted purely as heat!

By contrast, a class D amp uses pulse width modulation (PWM) technology that switches power components on only a portion of the time . Unlike class A/B amps they convert the input signal to square waves used to control the on/off timing. These are converted back to smooth audio signal waves before being delivered to speakers.

Class D amplifier models are about 85% efficient meaning they run cooler and can be much smaller than A/B designs. As they offer more power in less, they’re really common for very high power subwoofer amplifier (mono amp) models sold today.

Class A/B amps offer lower noise levels for less money, although today’s D models have caught up fairly well especially for brand name designs.

What are channels on an amp?

Channels are independent audio paths that are used to create a sound output from an amplifier. In stereo recordings, the left and right audio sources differ and provide left vs. right audio sound.

In car audio, left and right audio channels are separate outputs from a car stereo or an independent signal path with an amplified output. They’re used to give a fuller, more realistic sound when listening. Additionally, some stereos provide front and rear outputs pairs, although these are simply the same signals provided to drive an extra pair of speakers in the rear.

In many cases stereo amplifier channels can be “bridged.” This means that 2 channels can work together in a push-pull fashion to speakers with more power than one channel alone (usually about twice the power of a single speaker output).

Car audio amp connections, inputs, and controls

Most car amplifiers, whether expensive or budget-priced, are very similar in how they’re designed. Generally power connections are located on one end and audio inputs and controls are found on the other end.

In image above you can see adjustable crossover dials and the switches to enable them. The point after which sound frequencies are blocked, called the cutoff frequency , is adjustable by the user with a small dial in some cases. In other models, it’s a fixed setting operated with a switch and can’t be changed.

However, fixed crossover frequencies are normally set to the most commonly used values for convenience.

Power connections

Power and speaker connection terminals on a Pioneer GM-D9605 car amplifier.

Power connections are typically made using larger-gauge copper wire and connectors, often included in an amp wiring kit. RCA cables are used to connect the amplifier to the audio signal outputs of the head unit from which music is played.

Note that to bridge 2 channels on the amp and deliver more power as a single channel, they’re connected in a particular way. The bottom image above shows the polarity and wiring connections required. They’re marked as “Bridged” as you can see.

In bridged mode, one channel provides the positive speaker connection and the other provides the negative.

Speaker level inputs

A speaker level input wiring harness is shown. Speaker outputs from a factory stereo can be connected to the wiring then plugged into an amp to provide a signal when RCA jacks aren’t available.

Upgrading a factory installed car audio system can be challenging as RCA jacks aren’t usually available. In that case speaker-level (also called “high level”) inputs, if available, can be used to avoid buying additional parts.

These take the higher voltage speaker level signal directly from speaker wiring and reduce it to a smaller level the amplifier can use.

The other option is to use a speaker-level adapter to do the same thing.

How are car power amps installed?

A typical installation for a car amplifier. Large-gauge power wires are connected to the power terminals and fastened using screws. Speaker wiring is connected similarly. After installation, the sound system is tested and the amp’s gain control and crossovers are adjusted as needed.

In order to work properly, car amplifiers have to be installed with sufficient size and type of power wire. The most important reason for this is because a vehicle’s original wiring cannot handle the high-current demands of an amplifier.

For example, some may draw 50 to 80 amps or more or when driving subwoofers very hard. Factory wiring isn’t rated for these kinds of demands and a loss of voltage (and consequently, power) to the amplifier would occur. Therefore we route a large enough power cable to the battery and make sure a good, clean electrical connection is made.

A sufficiently rated fuse, held in a fuse holder, protects the positive power cable. If a problem like a short circuit occurs the fuse would blow and protect against causing a fire.

There are several wiring connections used on all car amplifiers:

A fused large-gauge power wire to the battery (+12V)
Negative connection to the “ground”:negative battery terminal or car’s metal body
Remote-on wire to switch the amp on and off with the stereo or ignition switch
Audio input signals:RCA cables or speaker-level inputs
Speaker wiring connections

Fortunately, this wiring is often easily found pre-packaged and ready for use by buying an amplifier wiring kit.

Car amplifier installation diagram

How are car amplifiers helpful?

Today’s amplifiers can power a whole car audio system with excellent sound quality and volume. Some are very compact and can be installed under a seat or even inside your dashboard! A good amplifier provides several times the power output of an average car stereo. Also, they’re much more clear and crisp sounding.

Car amplifiers have many benefits as well as being a necessity in some cases. Typical car stereos, even today, can only produce about 15 to 18 watts of power per channel at most.

At higher volumes and when attempting to drive speakers that need more power, the sound from a stereo becomes distorted and terrible. Driving speakers with higher volume is basically impossible with only a car stereo.

Car amps offer much better sound, especially for bass-heavy music. There are also some special situations where they’re the only option for upgrading the sound in a vehicle:

Factory stereo systems with no woofer
Factory-installed amplifiers that have died or are weak
The desire for powerful, clear sound when enjoying higher-quality music
Vehicle owners who want heavy volume
Boat and other outdoor vehicle owners (outdoor vehicles need extra power for better sound)

Additional benefits

As I mentioned earlier, many offer features like built-in crossovers that can prevent distortion and allow you to play speakers at higher volumes with enhanced clarity. Factory systems normally can’t do this and the sound will “break up” early when turned up to higher volumes.

Installing an aftermarket amplifier resolves this problem and allows more control over your audio system. Additionally, a system can easily be expanded to add a subwoofer for missing bass by either adding a 2nd amplifier or using 2 channels of a 4 channel amp to drive it.

2 channel vs 4 channel amps – what are the differences?

4 channel amplifiers are essentially a 2 channel amp with an additional stereo channel pair designed in. They offer several benefits:

You can drive front and rear speakers
Can drive front full-range speakers and use rear channels for a subwoofer
More compact than 2 separate stereo amps

Most 4 channel amplifiers today are bridgeable so they’re very flexible in how they can be used. However, be aware that a 2 or 4 channel amp normally requires a minimum of 4 ohms when bridged unlike stereo mode.