How to choose and set up a stereo am­pli­fier: part one

What Hi-Fi (UK) - - Buyer's Guide Best Buys -

Whether you’ve al­ready cho­sen and bought am­pli­fi­ca­tion for your sys­tem or are yet to ex­er­cise your pur­chas­ing power, this guide will help you un­lock your stereo amp’s full po­ten­tial.

In­te­grated vs pre/power

Do you go for an in­te­grated am­pli­fier or sep­a­rate pre/power boxes? The for­mer is the most sim­ple and con­ve­nient – it packs both pre- and power am­pli­fi­ca­tion into one chas­sis. This means ev­ery­thing has been tuned to­gether, sav­ing you the work that goes into match­ing sep­a­rate am­pli­fiers.

Two-box am­pli­fiers in­volve split­ting pre-am­pli­fi­ca­tion (in­put se­lec­tion and vol­ume con­trol) from power am­pli­fi­ca­tion. The idea is to keep the sen­si­tive preamp cir­cuitry and the del­i­cate au­dio sig­nals flow­ing through it away from the elec­tri­cally noisy high-cur­rent power am­pli­fier sec­tion. Hav­ing sep­a­rate power sup­ply sec­tions helps to im­prove the sound too.

The most ob­vi­ous way of se­lect­ing pre­and power am­pli­fi­ca­tion is by stick­ing within one brand’s range. In­vari­ably they will have been tuned to work well to­gether. If you plan to mix-and-match, be aware some pair­ings will work bet­ter than oth­ers. The best way to find out is by trial and er­ror. And that’s true when it comes to match­ing source com­po­nents to your am­pli­fi­ca­tion. Sonic affin­ity can be de­ter­mined by com­mon sense to some ex­tent. If your source – a CD player, for ex­am­ple – sits on the bright side of neu­tral, it shouldn’t be part­nered with a stereo am­pli­fier with a sim­i­lar char­ac­ter.

Sys­tem match­ing

The speaker/amp part­ner­ship not only comes down to an am­pli­fier’s power out­put but also its im­ped­ance (mea­sured in ohms) and sen­si­tiv­ity (db). Im­ped­ance is a mea­sure of how dif­fi­cult the speaker is for the am­pli­fier to drive. The sen­si­tiv­ity of a speaker is a mea­sure of how loud a speaker will go for a given in­put. A good in­sight into an amp’s mus­cu­lar­ity is to com­pare its power out­put into eight ohms with that into four ohms. An ideal amp would dou­ble its out­put as im­ped­ance halves. Though most won’t achieve that, the closer it gets to it, the bet­ter. Though you may be tempted to go for the most pow­er­ful amp you can af­ford, you’ll do bet­ter by buy­ing a more sen­si­tive speaker.

That’s be­cause an am­pli­fier’s out­put has to dou­ble to match a 3db in­crease in speaker sen­si­tiv­ity. But num­bers can only tell you so much, and the best way of find­ing out if com­po­nents work well to­gether is to use your ears.

Place­ment

The sur­face your stereo amp sits on can make the world of dif­fer­ence. IKEA fur­ni­ture is not at the bot­tom of our list (that’s the floor), but we’d strongly sug­gest plac­ing it on a ded­i­cated hi-fi rack. Your choice shouldn’t be based on looks alone.

Dif­fer­ent ma­te­ri­als have dif­fer­ent acous­tic prop­er­ties. Gen­er­ally speak­ing, glass shelves tend to en­cour­age kit to sound for­ward, while wooden sup­ports tend to re­sult in a warmer and more rounded bal­ance. All that power can gen­er­ate quite a tem­per­a­ture, so it’s im­por­tant to give an amp a few inches of breath­ing space from a wall or rack to stop it run­ning too hot.

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