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Scythe Kama Bay Amp SDA-1000
16.10.2008.
    « Prev  : Stranica 1 od 3 :  Next »      By ::  Marin Kovačić 
- Uvod -
Danas ćemo se pozabaviti jednim interesantnim uređajem kakav se do sada nije još našao u našem labu. Radi se o Scythe Kama Bay Ampu, modelu SDA-1000, koji je zapravo PWM digitalno audio pojačalo. Da, dobro ste pročitali – ne radi se o hladnjaku (po čemu je Scythe dobro poznat) već o audio pojačalu kojeg smo imali prilike uživo vidjeti još na ovogodišnjem CeBIT-u.

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Šarena ali i informativna kutija

 

Kako se radi o prilično neuobičajenom gostu, malo ćemo pojasniti principe rada ovog uređaja, jer možda ima onih koji nisu upoznati sa ovom tematikom.
Scythe Kama Bay Amp je dvokanalno (stereo) audio pojačalo snage, koje ima deklariranu snagu od 10W po kanalu za osam ohmski zvučnički sustav.
Zadatak pojačala je naravno pojačati audio signal koji dolazi u njegove ulaze iz recimo CD playera, računala, MP3 playera; laički receno – pojačalo pojačava struju koja je potrebna za pokretanje zvučnih jedinica tj. drivera u našim zvučnicima.

Vjerojatno će se neki pitati gdje je pojačalo od npr. Logitechovih ili Geniusovih desktop zvučnika?

Ono je već ugrađeno u sam zvučnik, najvjerojatnije u onaj koji ima kontrole za glasnoću i kontrole za podešavanje tonova (bass, treble). Bitno je naglasiti kako je dodatno pojačalo snage poput Kama Bay Ampa suvišno i nepotrebno za takve zvučnike. Eksterna pojačala snage su namijenjena tzv. pasivnim zvučnicima, tj. onima koji nemaju već ugrađeno pojačalo i koji kao takvi ne mogu raditi samo priključeni na izvor zvuka bez prethodno pojačanja (ili mogu raditi ali vrlo tiho).
Kako bi još malo pojasnili stvari, objasniti ćemo još i pojam integriranog pojačala – izraz na koji su možda već neki naišli ali ne znaju što točno znači. Integrirano pojačalo je uređaj koji u sebi ima predpojačalo i pojačalo. S obzirom da smo objasnili čemu služi pojačalo, red je da objasnimo i čemu služi predpojačalo.
Predpojačalo je elektronsko pojačalo koje prethodi pojačalu snage. Zadatak predpojačala (preamp) je pripremiti signal za dodatno obrađivanje tj. pojačanje u pojačalu snage. Ono podiže napon od nekih 10 milivolta do 1 volta, ali ne vrši pojačanje struje. Bitno je podići napon na 1V jer pojačala imaju odreden prag osjetljivosti i najbolje rade sa signalom koji ima adekvatan napon.
Malo ćemo se i dotaknuti osnovnog principa rada Kama Bay pojačala. Proizvođač navodi kako se radi od PWM digitalnom pojačalu – što znači kako pojačalo ne radi u čistom digitalnom načinu rada (kao npr. pojačala marke NuForce) jer se analogni signal nikad ne prebaci u digitalni oblik.
Poveznica sa digitalnim pojačalima je u tome što se tijekom procesa pojačanja signal dijeli u male cjeline, od kojih svaka traje otprilike petstotisućiti djelić sekunde, i zatim se svaki taj nezavisni dio pojačava da bi se na kraju se svi dijelovi zajedno "zalijepili".
Ovakav princip rada je sličan 44.1 kHz uzorkovanju koji se koristi u CD-ima, također je sličan radu visokofrekventnih switching mode napajanja u računalima i PWM kontroliranim ventilatorima.



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