QUESTYLE REF­ER­ENCE SYS­TEM GOLDEN EDI­TION

DAC / PRE-AMP / DUAL HEAD­PHONE AM­PLI­FIERS

Australian HIFI - - CONTENTS -

Though not with­out its quirks, this is the best desk­top au­dio sys­tem avail­able, or the ‘ne plus ul­tra’ ac­cord­ing to re­viewer Ernest Den­man.

Qestyle is a new­comer to high-end au­dio, hav­ing been es­tab­lished only five years ago in Shenzhen, China, to build prod­ucts based around a cur­rent mode cir­cuit its founder Ja­son Wang (Wang Feng­shuo) started de­vel­op­ing while he was an elec­tri­cal en­gi­neer­ing stu­dent at univer­sity and only com­pleted af­ter grad­u­a­tion. The first prod­uct to use this con­cept was the CMA800 head­phone am­pli­fier, the fore­run­ner of the CMA800Rs used in this Questyle Ref­er­ence Golden Edi­tion Sys­tem. Why two head­phone am­pli­fiers? Ac­cord­ing to Wang, his think­ing process was: ‘top power am­pli­fiers are of­ten de­signed as monoblocs to im­prove performance, so why not do the same for a head­phone am­pli­fier?’ Why not in­deed?

THE EQUIP­MENT

So, in ad­di­tion to fea­tur­ing two Questyle CMA800R head­phone am­pli­fiers (each of which has a re­tail price of $4,299), en­abling ‘dual mono’ op­er­a­tion, with the sig­nal from one head­phone am­pli­fier go­ing to the left ear­piece of a pair of head­phones and the sig­nal from the other head­phone am­pli­fier go­ing to the right ear­piece, the Questyle Ref­er­ence Golden Edi­tion Sys­tem also has a ‘Cur­rent Mode’ pream­pli­fier (CMA800P, re­tail­ing for $5,199) and a DAC (CAS192D, which re­tails for $4,299).

As you have no doubt al­ready re­alised, Questyle’s model num­bers are de­scrip­tive, so that the DAC is ca­pa­ble of 192kHz op­er­a­tion and also of pro­cess­ing DSD sig­nals.

The ‘CMA’ of course stands for ‘Cur­rent Mode Am­pli­fi­ca­tion’ and the ‘P’ is so ob­vi­ous as not to need ex­pla­na­tion at all.

How­ever, the ‘800R’ in the head­phone am­pli­fier stems from the fact that Sennheiser’s HD800s were Wang’s favourite head­phones, and he de­signed the CMA800R specif­i­cally for them, so he ‘bor­rowed’ the ‘800’ de­scrip­tor, as a ‘homage’ to the HD800.

(That said, the CMA800R can drive dy­namic head­phones from any man­u­fac­turer… it’s not just re­stricted to driv­ing HD800s!)

De­spite the em­pha­sis on the words ‘Cur­rent Mode Am­pli­fi­ca­tion’ in all Questyle’s lit­er­a­ture and model num­bers, Questyle’s prod­ucts are not ‘cur­rent source’ (a.k.a. transcon­duc­tance) am­pli­fiers—they are con­ven­tional volt­age source am­pli­fiers, but in­ter­nally use a cir­cuit con­cept sim­i­lar to that used by Krell in its ‘CAST’ (Cur­rent Au­dio Sig­nal Trans­mis­sion) am­pli­fiers, where af­ter a volt­age has been ap­plied to the in­put ter­mi­nals, it’s then am­pli­fied via cur­rent mode, then con­verted back to volt­age source be­fore be­ing de­liv­ered to the out­put ter­mi­nals. Or, to use Questyle’s own ter­mi­nol­ogy ex­actly: ‘ volt­age in­put and out­put, while the core am­pli­fi­ca­tion takes place in the cur­rent do­main oper­at­ing in a pure Class-A state, and al­low­ing the out­put stage to be ei­ther Class-A or Class-AB.’ Ac­cord­ing to Wang, the re­sult is ‘ ex­tremely wide band­width, ul­tra-low dis­tor­tion and a to­tal lack of tran­sient in­ter­mod­u­la­tion dis­tor­tion.’

Also, de­spite the fact that Questyle makes much of the fact it’s us­ing bal­anced am­pli­fiers to drive the head­phone out­puts, and claims this is su­pe­rior to us­ing un­bal­anced (sin­gle-ended) am­pli­fiers to drive head­phones, all head­phones are elec­tri­cally ‘bal­anced’ ir­re­spec­tive of whether they’re be­ing driven by a bal­anced am­pli­fier or an un­bal­anced am­pli­fier. The driv­ers in­side head­phones have only two wires and since the cur­rent into and out of any two-wire net­work is al­ways equal and op­po­site, this means head­phones can­not ‘tell’ whether the au­dio sig­nal comes from a sin­gle-ended volt­age source or a bal­anced volt­age source.

No­table on the ‘Golden Edi­tion’ series is Questyle’s use of Rogers 4350 ce­ramic printed cir­cuit boards (PCBs), which are only 0.8mm thick, yet have a di­elec­tric con­stant of 3.48 com­pared to just 2.55 for, say, Te­flon PCBs. Ce­ramic PCBs are used in high-in­su­la­tion, high-fre­quency, high-tem­per­a­ture ap­pli­ca­tions and are par­tic­u­larly suited for low-vol­ume elec­tronic prod­ucts. How­ever it’s im­por­tant to note that these ce­ramic PCBs are used only in the Ref­er­ence ‘Golden Edi­tion’ Series com­po­nents, not the ‘Sil­ver Edi­tion’ com­po­nents.

An­other point of difference is that whereas the PCBs of the ‘Sil­ver Edi­tion’ com­po­nents are pop­u­lated by high-quality elec­tri­cal com­po­nents, Questyle uses even-higher-quality hand-se­lected com­po­nents in its Golden Edi­tion com­po­nents.

Questyle’s CAS192D DAC is un­usual be­cause whereas most high-end DACs that of­fer DSD use a dig­i­tal-to-ana­logue con­ver­sion tech­nique known as DoP (DSD over PCM), the CAS192D pro­cesses the DSD bit-stream di­rectly—it even by­passes the CAS192D’s own on­board (and switch­able) dig­i­tal fil­ters to pro­vide true DSD. (Note that com­puter play­back via Win­dows—ev­ery­thing from XP up—re­quires in­stal­la­tion of driver soft­ware that Questyle pro­vides on an op­ti­cal disc pro­vided with the CAS192D.)

There is cer­tainly no short­age of dig­i­tal fil­ters se­lectable on the CAS192D, be­cause Questyle has ac­ti­vated all the op­tional fil­ters that are al­ready res­i­dent in­side the Cir­rus Logic Wolf­son Mi­cro­elec­tron­ics WM8741 DAC that it’s us­ing as its dig­i­tal ‘en­gine’. (The WM8741 na­tively also pro­vides the op­tions of di­rect DSD, or DSD via PCM.) The fil­ters avail­able for use vary de­pend­ing on the con­ver­sion mode you choose (that is, whether you choose to use over­sam­pling or no over­sam­pling) and the bit-rate of the dig­i­tal in­put sig­nal, but al­to­gether you can se­lect be­tween FIR Brick­wall, FIR Apo­dis­ing, FIR Soft-knee, FIR Half-band, IIR Apo­dis­ing, IIR Soft-knee and IIR Half-band. A full ex­pla­na­tion of the dif­fer­ences be­tween these fil­ters is be­yond the scope of this re­view, but there is a fun­da­men­tal difference be­tween an FIR (Fi­nite Impulse Re­sponse) and IIR (In­fi­nite Impulse Re­sponse) which is that an FIR fil­ter has time-re­versed ring­ing, whereas an IIR fil­ter doesn’t (a re­sult of hav­ing to have a higher Q than an IIR fil­ter to meet the same spec­i­fi­ca­tion re­gard­ing stop band, rip­ple, and roll-off.) This is best il­lus­trated vis­ually, as per the three shots from an os­cil­lo­scope that are shown on the fol­low­ing page. The first image shows an ana­logue pulse, the sec­ond is what that pulse looks like af­ter pass­ing through one of the Questyle’s FIR fil­ters, and the third af­ter it’s been passed through one of the Questyle’s IIR fil­ters. Al­though the IIR fil­ter has more ring­ing af­ter the pulse, there is no pre-ring­ing. (And, just in case you were won­der­ing, the rea­sons for the names are that a pulse pro­cessed by an IIR fil­ter re­sponse never falls to zero, but con­tin­ues in­def­i­nitely, whereas one pro­cessed via an FIR fil­ter even­tu­ally does.)

The fil­ters avail­able for use vary de­pend­ing on the con­ver­sion mode you choose (over­sam­pling or not) and the in­put sig­nal

Questyle cor­rectly points out in its man­ual that: ‘ Vi­brat­ing ob­jects in na­ture pro­duce a sound­wave which has sim­i­lar fea­tures to the IIR dig­i­tal fil­ter. There is no pre-ring be­fore the vi­bra­tion and the vi­bra­tion am­pli­tude de­creases grad­u­ally af­ter the vi­bra­tion’ … but fails to add that in na­ture, even­tu­ally to zero!

Questyle’s over­sam­pling cir­cuitry is very clever. To avoid re­peat­ing dec­i­mals and as­so­ci­ated round­ing er­rors, as well as jit­ter, it uses two clocks, rather than just a sin­gle clock, so that 44.1kHz and 48kHz sig­nals are only up­sam­pled four times (from 44.1kHz to 176.4kHz and from 48kHz to 192kHz), while 96kHz sig­nals will be up­sam­pled only twice… as­sum­ing you choose to up­sam­ple at all). For the sake of com­plete­ness, I should point out that the Questyle has a third clock, used for the USB in­put. The power sup­ply uses a cus­tom Pl­itron toroidal trans­former, Schot­tky rec­ti­fier, Nichicon 2200 F (×22) FG ca­pac­i­tors, and 22 power reg­u­la­tors.

The Questyle CAS192D DAC has three dig­i­tal in­puts: op­ti­cal (Toslink), SPDIF (RCA) and USB (Type B). The omis­sion of an AES/ EBU in­put is sur­pris­ing, par­tic­u­larly since there’s plenty of room on the rear panel, but not with­out prece­dent on a DAC in­tended for home use. There are two sets of ana­logue out­puts: bal­anced via XLR or un­bal­anced via RCA.

But whereas the DAC has am­ple in­puts and out­puts, the Questyle CMA800P pream­pli­fier is al­most bereft of them, with only two in­puts (one bal­anced, the other un­bal­anced) and only two out­puts, bal­anced (via XLR) and un­bal­anced (via RCA).

The CMA800R is also shy on in­puts, but this time there are three: bal­anced and un­bal­anced stereo in­puts, plus a sin­gle ‘full bal­anced mono’ in­put (used when us­ing the CMA800R as a monobloc) and two un­bal­anced out­puts (via RCA). On the front panel are two un­bal­anced 6.35mm ‘phone jacks, so you can drive two pairs of head­phones, plus a sin­gle bal­anced out­put for driv­ing one side of a pair of head­phones wired in dual-mono mode.

If you find your­self con­fused by the wiring in­struc­tions in the CMA800R man­ual, it’s be­cause Questyle has used the wrong rear panel di­a­gram. In­stead of be­ing a di­a­gram of the CMA800R, it’s one of the rear panel of the CAS192D. Questyle has also made an er­ror with the test re­port that ac­com­pa­nies each CMA800R. Whereas the com­pany says it tests ‘ over 30 fac­tors of spec­i­fi­ca­tions be­fore be­ing shipped out’, with a test re­port be­ing ‘ put into car­ton box’, the only thing in the car­ton is a generic, mass-pro­duced card that has two generic pre-printed graphs (THD vs. Volt­age and a Fre­quency Re­sponse) plus two QC stamps. That is, the test re­port en­closed in the box is not that of the spe­cific model you have pur­chased.

Al­though the com­po­nents look ‘full-size’ in the il­lus­tra­tions ac­com­pa­ny­ing this re­view, each one is only 330mm wide, 300mm deep and 55mm high. This siz­ing is be­cause Questyle re­gards these as ‘desk­top’ com­po­nents, and the sys­tem as a ‘Desk­top’ Ref­er­ence Sys­tem. Each com­po­nent is avail­able in ei­ther sil­ver or gold fin­ish but, as noted ear­lier, only com­po­nents with the gold fin­ish have the Rogers ce­ramic PCBs and the up­graded, hand-se­lected in­ter­nal com­po­nents. Due to the quality of these com­po­nents, and the price of each one, I was sur­prised at the brevity of the war­ranty pe­riod.

IN USE AND LIS­TEN­ING SES­SIONS

When I first un­packed the Questyle Ref­er­ence Sys­tem Golden Edi­tion sys­tem, it ap­peared to me that the CMA800P was ‘su­per­flu­ous to re­quire­ments’, be­cause since there is only one ‘source’ com­po­nent, it would make more sense to con­nect the CAS192D di­rectly to the two CMA800R head­phone am­pli­fiers, thus im­prov­ing the performance (elim­i­nat­ing su­per­flu­ous cir­cuitry, no mat­ter how good, will al­ways re­duce noise and dis­tor­tion) and si­mul­ta­ne­ously re­duc­ing the price of the combo and low­er­ing the height of the stack. This made even more sense to me be­cause whereas in other sys­tems re­mov­ing a pre-am­pli­fier would also pre­vent you switch­ing be­tween mul­ti­ple com­po­nents, us­ing pro­ces­sor loops, and maybe even al­low­ing con­trol over bass, tre­ble and bal­ance, none of these

niceties are avail­able on the CMA800R, so you’re essen­tially miss­ing out on noth­ing.

Alas, when I tried elim­i­nat­ing the CMA800P, I quickly dis­cov­ered why it’s an es­sen­tial part of Questyle’s Ref­er­ence Sys­tem. That rea­son is sim­ple: It’s the only com­po­nent that al­lows you to con­trol vol­ume level when you’re us­ing the CMA800Rs’ ‘Full Bal­ance Out­puts’ (which is the con­fig­u­ra­tion de­signer Ja­son Wang rec­om­mends). If you don’t use it, your head­phones will be run­ning ‘full bore’ all the time. This is be­cause al­though the CMA800R has a vol­ume con­trol, it only con­trols the vol­ume of the un­bal­anced out­puts, not that of the ‘Full Bal­ance Out­put’. And, of course, there is no vol­ume con­trol at all on the CAS192D!

My state­ment that the CAS192D does not have a vol­ume con­trol may seem con­tra­dic­tory for any­one who has looked at the ad­ver­tise­ments for it, many of which show a small plas­tic re­mote con­trol with two vol­ume but­tons. Sadly, these but­tons do not work at all (i.e., they’re in­op­er­a­tive) and this de­spite the fact that one of the fea­tures built into the WM8741 in­side the CAS192D is a dig­i­tal vol­ume con­trol. The mute but­ton on the re­mote does work though. While it’s not ex­actly dowdy, the build quality of the re­mote is nowhere near that of the main com­po­nents.

I first tried to de­ter­mine which of the many fil­ter op­tions I pre­ferred, which was com­pli­cated slightly by the fact that if I used 44.1kHz or 48kHz source ma­te­rial, I had three IIR and two FIR op­tions from which to choose, whereas at higher bit-rates, I had three FIR and only two IIR op­tions. (And when play­ing back DSD there are no fil­ter op­tions at all.) It didn’t take too long at all to find that I pre­ferred the IIR apo­dis­ing fil­ter, ex­cept that when do­ing the com­par­isons, I’d only been us­ing the same small sec­tion of clas­si­cal mu­sic, played over and over. Later, when I ac­ci­den­tally se­lected a dif­fer­ent fil­ter while play­ing some rock mu­sic, I found I pre­ferred the FIR apo­dis­ing fil­ter for rock. Re­view time con­straints meant I could not es­tab­lish if I pre­ferred dif­fer­ent fil­ters for other mu­si­cal gen­res, but I re­ally wouldn’t be sur­prised if I did. When switch­ing be­tween fil­ters, the vol­ume fades-out then fadesin, which I found an­noy­ing: I would have pre­ferred an in­stant switch, though I guess Questyle is do­ing the right thing by mak­ing sure that no switch­ing tran­sients can ever get near your loud­speak­ers.

When work­ing out my fil­ter op­tions I was us­ing my trusty Sennheiser HD800S head­phones, all set up for dual-mono, dual-bal­anced op­er­a­tion (via a four-pin to dual XLR adap­tor lead)… at which point I should men­tion that one huge ad­van­tage of us­ing Questyle’s ap­proach is that you get twice the volt­age swing and thus four times the power com­pared to us­ing just a sin­gle un­bal­anced am­pli­fier. And boy did the Questyles make the HD800Ss sing! As, I think, ev­ery re­viewer has noted of the HD800Ss, their ex­quis­ite clar­ity and the way they ren­der the finest de­tails of the mu­sic they re­pro­duce is be­yond ex­cep­tional. But with the Questyles driv­ing the HD800Ss, their al­ready state-of-the-art sound quality in these as­pects of performance was ratch­eted up a large notch—tak­ing them from be­yond ex­cep­tional and all the way out to fan­tas­tic. Lis­ten­ing to the in­tro to Never Give All the Heart (Brenda Fricker and Anuna, backed by The Chief­tains) was like a holy ex­pe­ri­ence… an au­di­tory ver­sion of the vis­ual cathar­sis one ex­pe­ri­ences when first look­ing up into the naves of An­toni Gaudi’s Sagrada Família. The crisp de­lin­eation of the vo­cal lines… the in­cred­i­ble feel­ing of har­monic uni­son from the merg­ing of the voices… there are few words that can de­scribe the ex­pe­ri­ence.

Also taken to yet an­other level was the bass de­liv­ery, which ac­cel­er­ated from be­ing just ‘fast’ to ‘light­ning fast’, such that for the very first time I completely ap­pre­ci­ated the com­plex­i­ties of the drum­ming on Dream The­atre’s Dance of Eter­nity. And not just the com­plex­i­ties of the drum­ming … I also fi­nally to­tally ap­pre­ci­ated the rhyth­mic in­ter­play be­tween the mu­si­cians, not sim­ply on a sonic level, but also on an in­tel­lec­tual level. The combo of the Questyles and the HD800Ss just peeled back the lay­ers of sound, re­veal­ing the white­ness of the bones be­low.

My only pre­vi­ous crit­i­cism of the Sennheiser HD800S’s might have been their midrange, which I’d have de­scribed as be­ing translu­cent, rather than to­tally trans­par­ent, but it ap­pears that I was ob­vi­ously not us­ing the cor­rect as­so­ci­ated elec­tron­ics to drive them when I made that assess­ment, be­cause when they were driven by the Questyles, the midrange of the HD800Ss went be­yond trans­par­ent to be­ing to­tally in­vis­i­ble. When lis­ten­ing to fe­male vo­cal­ists, the close­ness and re­al­ism— in­deed the hu­man­ity—of their voices was so un­canny it was al­most em­bar­rass­ing… as if I were in­trud­ing on their per­sonal space just by lis­ten­ing. I’ve heard noth­ing like it.

In or­der to in­sert a mod­icum of fis­cal re­al­ity into this re­view, I re-wired the HD800Ss back to a sin­gle 6.5mm phone jack, and re­con­nected the CAS192D di­rectly to a sin­gle CMA800R switched for nor­mal stereo op­er­a­tion, which ren­dered the vol­ume con­trol op­er­a­tional. A ret­ro­grade step? Well, yes… but whereas I was ex­pect­ing there to be a huge difference, I was more than a tad sur­prised to hear the HD800S’s were still oper­at­ing on a whole higher plane than I ex­pected. Per­haps not quite at the level I’d been ex­pe­ri­enc­ing with the dual CMA800Rs, but close… very, very close. So close that if I had to pull $4,299 out of my pocket in or­der to re­turn to the sonic nir­vana I’d been en­joy­ing only a few mo­ments ear­lier, I think I would hes­i­tate. But for how long? That I don’t know.

CON­CLU­SION

Through­out the time I was eval­u­at­ing this sys­tem I could not help but won­der why Questyle left out so many fa­cil­i­ties that many au­dio­philes might ex­pect, such as a vol­ume con­trol and a head­phone out­put on the DAC, ad­di­tional in­puts on the pre-am­pli­fier, and a cer­tainly a re­mote con­trol that could ac­tu­ally be used to ad­just vol­ume level! At least these omis­sions means that there’s a clear up­grade path should you wish to work your way up to own­ing a com­plete Questyle Ref­er­ence Sys­tem Golden Edi­tion Sys­tem by buy­ing one com­po­nent at a time. But whether you buy this sys­tem in­cre­men­tally, or take the plunge and do it all at once, you’ll end up the proud owner of what just has to be the ne plus ul­tra of desk­top head­phone au­dio. Ernest Den­man

An­other point of difference is that whereas the PCBs of the ‘Sil­ver Edi­tion’ com­po­nents are pop­u­lated by high-quality elec­tri­cal com­po­nents, Questyle uses even-higher-quality hand-se­lected com­po­nents in its Golden Edi­tion com­po­nents.

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