DPA (Deltec) DSP200S & DPA200S

This article written by Malcolm Steward was first published in Audiophile magazine (UK),  1994.

dpa (Deltec Precision Audio)

DPA Digital’s 200S pre-amplifier is a line-level device optimised for digital sources. It uses a compound class A output stage described by the company as sophisticated and unique. This employs high speed class A drivers that operate permanently in class A to provide the amplifier’s output voltage, with current source power transistors boosting the stage’s gain. DPA claims this gives better than conventional class A performance because the output stage never switches off. It also avoids the “severe sonic degradations� of sliding bias circuits. The stage will drive headphones directly through a cable adapter.

Electronic switches operate the pre-amplifier’s balance control and input switching. DPA paid special attention to the power supply for the switch-gear and says this has enhanced the unit’s detail resolution and sound staging abilities. It also reckons that users can expect the switching to provide longer life and more consistent performance than conventional arrangements.

Surface mounted components are used throughout the pre-amplifier, again to provide improved detail resolution and a sweeter, smoother sound quality. The benefits are attributed to the absence of internal contacts in surface-mount devices and their lower radio frequency noise levels as a result of their physically smaller size.

DPA developed the 200S with the problems inherent in digital sources in mind – in particular radio frequency noise. All the inputs and outputs have been treated to counter RF interference and all the amplifier’s power supply lines are subject to filtering. The power supplies use low output impedance regulators with special attention paid to earthing and supply feed layouts. The claimed benefits are, again, a sweet, smooth natural sound quality with improved instrumental separation and focus.

The flick of a rear-panel mounted toggle switch converts the partnering 200S 50Watt stereo power amplifier into a 200Watt monoblock. Like the pre-amplifier it uses surface mount devices and thick film hybrid electronics. At the heart of the design is DPA’s thick film hybrid operational amplifier, the DHOA32. This device is similar to a regular, discrete component amplifier circuit in that it uses capacitors, resistors and semi-conductors. However, the components aren’t mounted on circuit boards: the resistors and conductors are built onto a ceramic base and surface mount transistors and diodes are silver soldered onto the conductors. The advantages claimed over conventional construction techniques include an avoidance of metal to metal contacts between resistors and conductors giving better low-level detail resolution, silver palladium conductors that are superior to oxide-prone copper contacts, and an overall reduction in circuit size giving better RF filtering and decoupling, which promotes smoother sound quality.

DPA describes the DHOA32′s circuit architecture as unique and claims that it gives a gain-bandwidth product in excess of 0.5 GHz, some one-hundred times better than conventional amplifiers. It further says that coupled with a highly linear open loop performance the design virtually eliminates high frequency distortion and gives exceptionally smooth treble. High power supply rejection improves instrumental separation and definition of timbre. In keeping with the design of the matching pre-amplifier, the power amplifier also employs a compound class A output stage.

The power amplifier’s power supply stage aims to counter the hardness and aggression found in digital sources. Again, DPA has included extensive RF filtering in the supply to give a smoother, warmer, more natural sound from CD. There are four power supply sections in the amplifier, one separate supply feeding each DHOA32 op-amp and another feeding each output stage. The supplies use two specially made toroidal transformers, which feature full electromagnetic screening and a unique inverted phase operation to cancel external flux. These measures reduce power supply noise pick up to give greater clarity and focus to the sound.

Both amplifiers use robust aluminium cases that are earthed – naturally – to reduce RF noise pick-up.

I have to admit that when DPA was Deltec I was never enamoured with the styling of the company’s amplifiers. The re-formed business’s range, however, although not radically altered, appeals much more to my aesthetic sensibilities. It looks tasteful, being neat, compact and visually quite understated. The clutch of bulbous, mushroom shaped knobs of the older pre-amplifiers has made way for a far tidier arrangement on the new DSP200S. This has a single rotary control for volume adjustment with source-switching, tape monitoring and balance functions controlled by four small push buttons. When first connected the unit defaults to the CD input but pushing the source button cycles through the other options, with discreet LED status indicators showing which input is selected. Similar buttons control fine adjustment of channel balance in 0.5dB increments. Fifteen different levels give maximum left-right shifts of 7dB. Pushing both left and right buttons simultaneously resets the balance to dead centre.

In the technical panel you will notice that DPA is a trifle keen about keeping its products free from radio frequency noise. To further quash RF, it suggests connecting the pre-amplifier to the mains supply by way of its The Power mains filter and Power Slink cable. DPA supplied one with the pre-amplifier and I used it throughout the review. I also followed the recommendation to leave the unit permanently powered, as is my normal practice with all solid-state components. I used a second The Power to filter the mains supply to the 200S power amplifier, again following DPA’s recommendations.

The rest of the system used to test the amplifiers was my Naim CDS CD player, supported by a Mana Acoustics seven-tier table, and a pair of Epos ES11 loudspeakers mounted on Slate Audio stands. Cabling was either Naim NAC A5 or Audio Note AN-SP. The pre-amplifier offers a disc input but this could more correctly be labelled “disc pre-pre-amplifier�. To use the 200S with a phono cartridge you need to connect the turntable through an optional RIAA unit available from DPA or a similar unit from another manufacturer. So I assessed this designed-for-digital amplifier solely with compact disc.

Driven by the Naim player, my initial reaction to the 200S system was that it presented a far friendlier, more easy-going character to the world than that of previous Deltec amplifiers. These, I always found, had a rather too clinical attitude where the search for detail took precedence over conveying the more emotional qualities present in music. The 200S amplifiers seemed to offer a more holistic, balanced view of performances, one that aroused my interest in the compositions and playing more successfully. So much so that I surprised myself by spending the first afternoon with these amplifiers listening exclusively to classical music and, even more surprisingly, enjoying the experience. The performance claims made by Robert Watts, DPA’s designer, for his amplifiers were all borne out in that first session. They did sound extraordinarily smooth and sweet. They were excellent retrievers of low-level detail. Their top end was refreshingly free from grain and harshness ,and they certainly did separate instruments well and realise their timbral qualities.

They were particularly forthcoming with Couperin’s Troisième livre de Clavecin – “La Superba ou la Forqueray�, which was, you might say, hardly astounding – the harpsichord was invented to make hi-fi equipment sound dazzling. However, the 200S amplifiers’ account of the music went beyond merely revelling in the instrument’s acute leading edges, capturing the subtly gradated dynamics and resonances that added depth and substance to its sound. They also highlighted the interplay between Rousset’s left and right hands bringing depth and harmonic shading to the performance itself. They brought similar colour and vitality to Vernon Handley and the Royal Liverpool Philharmonic’s playing of Arnold’s Sixth Symphony. The colour part of the equation was evident in the second movement where the piece develops from its brooding, slow opening with string washes and menacing, low percussion, of which the DPAs gave an explicit account, into a syncopated, jazzy swing, where horns, strings and timpani compete to whip up the tempo and dramatic quotient. The amplifiers relished this temporal, dynamic and timbral divergence, painting a picture in vivid musical hues that contrasted appropriately with the more delicate shades of the opening section. This they did with no recourse to pyrotechnics – they sounded almost restrained, in fact – making listening closely to whatever lay behind the dominant instruments remarkably easy.

My suspicion that these amplifiers had a partiality for modern music naturally led me to the Utah Symphony Orchestra’s recording of Varèse’ Amériques, which is loaded with motival playing, short of conventional melodic development, rhythmically stimulating and high in contrast with its “sound masses� and huge percussion armoury. The DPAs appreciated these qualities but fell short of fully realising the music’s awesome power in the most potent sections: there was a sense of the amplifiers not quite having the sheer muscle and grip necessary to hang on tightly enough to the most explosive playing. However, not many amplifiers have, so that’s not a damning criticism for a £1245 combination. I’d imagine that a brace of bridged 200S power amplifiers would breeze more confidently through this music.

The basic set-up had no problems with the thoroughly modern Pogues’ Waiting For Herb CD. This disc wasn’t released when I last listened to a Deltec system but I suspect that I wouldn’t have enjoyed it so much as I did through these newer models. Although the 200S combination made Sitting On Top Of The World appear a little more refined and polished than normal it didn’t diminish the music’s fundamental rhythmic swagger. It made a particularly impressive job of tracking Darryl Hunt’s bass playing throughout the disc, something that not every amplifier manages to do consistently. The only aspect of the amplifiers’ performance I would question, however, was that they made the band appear less Irish: the irrepressible fervour and abandoned feel that characterises their playing sometimes seemed to have been replaced by unseemly restraint and grace. The Pogues are accomplished musicians but they’re not a Celtic version of Steely Dan. Nonetheless, judging the amplifiers purely against the criteria with which they were designed, they were hard to fault. I wouldn’t argue that they offered a scrupulous view into the fabric of music and recordings, resolving information that less meticulous amplifiers regularly submerge.

That much was apparent with the CD single of Tim Simenon mixes of Björk and David Arnold’s Play Dead. The DPAs readily highlighted the differences in the five treatments of the song, showing how subtle and not-so-subtle alterations could change your reaction to the music. Ultimately, however, I found myself listening more to the arrangements than to the musical whole, even to the point of almost failing to be switched on by Björk’s sensual vocalising.

I’m not saying that the DPAs are cold shower amplifiers or unsympathetic to music’s emotional content but I would suggest that listeners to whom this aspect is vital should compare them to models recognised specifically for their “feel� and ability to capture the gestalt of performances. The 200S system doesn’t disregard this side of music but its depth of academic insight can overwhelm it – in my experience more so with rock than classical music. Whether that would affect your enjoyment of music, however, is something only listening will decide.

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