InCar Entertainment  - - AUDITION -

One of the orig­i­nal pil­lars of car au­dio world­wide, ris­ing pre­dom­i­nantly to fame dur­ing the 1980s and 1990s, Amer­i­can­born Cerwin Vega is a vastly ex­pe­ri­enced com­pany with an ex­ten­sive her­itage span­ning well over half a cen­tury. The com­pany has grown syn­ony­mous with good qual­ity but af­ford­able equip­ment, and al­though its am­pli­fier sta­ble in­cludes some of the might­i­est com­po­nents the car au­dio arena has ever seen, the Com­pany also pro­duces a range of smaller am­pli­fiers,which cater for those of us not want­ing or able to set ei­ther the world or their bank ac­count on fire.

Monoblocks don’t al­ways need to re­sem­ble of­fice blocks in or­der to achieve their goal. Of course there will be reaers keen to re­tort that smaller monoblocks in­evitably yield smaller power out­put and hence “less con­trol”.

But con­sider this. Just as a Hayabusa doesn’t re­quire the 7000hp mo­tor of an open­cut min­ing truck to get mov­ing, if you in­ject a lit­tle fore­thought into your subwoofer se­lec­tion you won’t re­quire quite so many thou­sands of watts in or­der to have its mo­tor struc­ture mov­ing flu­idly. I’ve learnt this from ex­pe­ri­ence and, clearly, so has Cerwin Vega.

And of course the flip­side of the equa­tion is space. Not ev­ery­one wants to sac­ri­fice half their boot in or­der to garner de­cent sub-bass. And with the rise of Class D am­pli­fi­ca­tion, this mind­set has borne wit­ness to the rise of a new genre of com­pact dig­i­tal am­pli­fiers, a genre that’s re­cently taken off like a ver­i­ta­ble rocket.


So, this B51 is the monoblock from the es­teemed new Stealth Bomber series from our Amer­i­can friends. It’s a high cur­rent dig­i­tal class-D de­sign, with the out­put chan­nel be­ing rated to pro­duce over 175 watts con­tin­u­ously when pre­sented with a four-ohm load, or 300 watts when faced with a two-ohm load. Load­ing it down fur­ther doesn’t com­pro­mise op­er­a­tions ei­ther; it just ups its power out­put to 500 watts con­tin­u­ous to face the chal­lenge and con­tin­ues right on its merry way. Com­pared with some, that might not sound too

the B51 rep­re­sents the epit­ome of what new-age mini power am­pli­fiers should be — smart-look­ing, and smart-sound­ing.”

strato­spheric, how­ever just look at its mer­its — an in­signif­i­cant foot­print of 195mm x 100mm, height of just 35mm, and weight of a mere couple of kilo­grams. So given its size its power out­put is quite sim­ply as­tound­ing.

The se­cret lies within the topol­ogy. Class-D am­pli­fiers utilise very pow­er­ful tran­sis­tors that are con­trolled dig­i­tally, switched be­tween ei­ther fully on or fully off, as op­posed to an ana­logue volt­age track­ing the in­put, as would be the case with a class AB de­sign. This sys­tem yields high ef­fi­ciency — leagues ahead of ana­logue coun­ter­parts. When the switches are open, all of the power supplied to them is de­liv­ered to the load and none con­verted into heat. On the other hand when they’re off they have full sup­ply volt­age stand­ing across them but no cur­rent flow­ing, so again zero heat is dis­si­pated. The darned laws of physics do get in­volved, sadly, so per­fec­tion re­mains an unattain­able state, but the Class-D de­sign can re­turn an ef­fi­ciency hov­er­ing around the 90% re­gion, with the re­main­ing en­ergy con­verted to heat (en­ergy can­not be erad­i­cated but only con­verted). Dis­tor­tion lev­els also re­main in­her­ently a lit­tle higher within this class of am­pli­fiers be­cause the out­put wave­form is built us­ing a square wave blocks. That said, the E51 does re­turn an im­pres­sive to­tal har­monic dis­tor­tion of 0.5%.

Fre­quency re­sponse is a suit­able 10Hz– 350Hz, and the sig­nal-to-noise ra­tio is 85dBA at 1 watt, or 101.1 dBA at full tilt. Along­side the dis­tor­tion, of course, is the other spec crit­i­cal to sub­woofers: damp­ing facto — in plain English the am­pli­fier’s abil­ity to con­trol the subwoofer’s mo­tor move­ment, both ac­cel­er­a­tion and the per­haps more cru­cial de­cel­er­a­tion to the zero point be­fore it be­gins the op­pos­ing side of the si­nu­soidal wave. This is of ut­most im­por­tance if you de­sire sharp and ac­cu­rate sub-bass re­pro­duc­tion. Cal­cu­lated nom­i­nally by di­vid­ing the subwoofer’s im­ped­ance by the out­put im­ped­ance of the am­pli­fier, the B51 boasts a damp­ing fac­tor of over 250.


Ap­pear­ance wise it’s fair to say Cerwin Vega am­pli­fiers have al­ways looked, well, typ­i­cally Amer­i­can. They’re of­ten large, bulky and cov­ered in heat-sinks (a look which I’ll con­fess I ac­tu­ally have no bones with). The Stealth Bomber units, though, are the antonym of this trend. They’re small, any­thing but bulky, and the de­sign­ers have spruced up the out­ward ap­pear­ance a lit­tle by com­bin­ing the over­all black case with some very stylish look­ing sil­ver end caps and side bars. This gives them the abil­ity to look right at home vir­tu­ally any­where, al­though given their size they’re likely to be un­seen any­way!

The outer case is pri­mar­ily alu­minium ex­tru­sion an­odised in black, while the bot­tom plate is stamped steel. The shock-re­sis­tant plas­tic end caps serve to pro­tect the con­trols and con­nec­tion blocks. Along one end re­side all the phys­i­cal power con­nec­tions, in­clud­ing 8AWG power and earth in­put ter­mi­nals, and dual speaker out­put ter­mi­nals so you can run mul­ti­ple sub­woofers if you so choose.

Along the other end are the re­maind­ing con­nec­tions, start­ing with high- or low-level in­puts. You sim­ply plumb ei­ther your RCA or speaker level into the plug pro­vided. Also here is a re­mote port for a bass level con­troller, while lo­cated ad­ja­cent are the au­ral con­trols. Aside from 10V–0.2V sen­si­tiv­ity th­ese in­clude a 10Hz–55Hz sub­sonic fil­ter, a 40Hz–400Hz low pass cross­over and a 0dB–12dB bass boost.

There’s no phase con­troller in­cluded. Ini­tially this ap­pears to be quite an over­sight be­cause the abil­ity to change phase can be crit­i­cal to get­ting the subwoofer blend­ing neatly with your front stage. How­ever Cerwin Vega has method in its mad­ness here, as swap­ping phase is as sim­ple as switch­ing the wires around — you’ll only do it once, dur­ing set-up. So to omit this is ac­tu­ally fis­cally wise; it al­lows for the man­u­fac­tur­ing costs to come down just that lit­tle bit more.

Dis­man­tling the unit for in­spec­tion is as straight­for­ward as re­mov­ing four cap screws and slid­ing the bot­tom plate off. Re­vealed thereby is a busy elec­tronic land­scape, in­tel­li­gently laid out, and qual­ity com­po­nents too, ap­pro­pri­ate for han­dling high cur­rent de­mands, all ro­bustly mounted upon a solid red glass cir­cuit board. A quadru­plet of 1000uF /25V Samwha stiff­en­ing ca­pac­i­tors smooth the cur­rent be­fore it’s trans­ferred across to a large air core trans­former for volt­age as­cen­sion. From here the higher volt­age is trans­ported to twelve 470uF/50V Samwha power ca­pac­i­tors for stor­age un­til needed, at which point it’s then dis­trib­uted across to ten au­dio­phi­le­grade MOSFETS. Th­ese tran­sis­tors de­liver power aplenty when called upon, and are lined strate­gi­cally along ei­ther side of the heatsink, care­fully placed to al­low for max­i­mum ther­mal dis­si­pa­tion when things start get­ting a lit­tle warm. Cerwin Vega has paid care­ful at­ten­tion to where the sig­nal han­dling com­po­nents re­side, for heat aside they must also be kept well clear of the cur­rent han­dling ar­eas lest they in­duce whine. Not as easy task with a phys­i­cal de­sign this small.


In­cluded in the box are mount­ing screws, tools, mul­ti­lin­gual in­struc­tions, a bass-level re­mote and an in­put plug with RCAs plumbed in.

Find­ing real es­tate for the unit is, of course, a non-event, with it fit­ting just about any­where larger than an ash tray. I had it in­stalled within 15 min­utes and be­gan by set­ting the gains against my os­cil­lo­scope. De­spite its diminu­tive pro­por­tions the out­put wave­form doesn’t re­veal sig­nif­i­cant signs of de­te­ri­o­ra­tion un­til well into the out­put range, which is a good sign for those a lit­tle con­cerned that the small unit might strug­gle.

As afore­men­tioned, subwoofer choice is an im­por­tant de­ci­sion when us­ing an am­pli­fier of this ilk; you’re don’t want to be hook­ing up a row of Cerwin Vega Stro­kers here... I set­tled on test­ing with a sin­gle highly ef­fi­cient 12-inch subwoofer run­ning in a sealed 35-litre test enclosure. Start­ing out with softer gen­res such as acous­tic, jazz and clas­si­cal the am­pli­fier proved clean and smooth, re­pro­duc­ing any and all low-end notes, with con­sis­tency to boot. Tak­ing it from there I stepped up the gen­res to the more dy­namic elec­tronic mu­sic be­fore fi­nally land­ing at the hard­est of gen­res for am­pli­fiers to re­pro­duce: rock and well-en­gi­neered heavy metal. When han­dling th­ese de­mands the B51 re­mained in im­pres­sively com­plete con­trol, even dur­ing the fast dou­ble-bass blast-beats of thrash and in­dus­trial-style metal, and to a sur­pris­ingly fright­en­ing vol­ume! That said I must also add the dis­claimer that you shouldn’t go har­bour­ing any un­re­al­is­tic ex­pec­ta­tions ei­ther. The B51 is not a ti­tanic-sized am­pli­fier, ergo there comes a point be­yond which you can­not push it. Nonethe­less it’ll pro­vide more than enough bass to sat­isfy those not aim­ing to bounce along the road in a wild SPL dis­play.

In con­clu­sion, then, the B51 rep­re­sents the epit­ome of what new-age mini power am­pli­fiers should en­com­pass. Its smart-look­ing, smart-sound­ing and given its mea­gre price tag of $449, it’s be­yond a bar­gain.

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