Samuel Johnson Audio

Abrand new company, Samuel Johnson was founded by a group of enthusiasts, most of whom had met through their work with a Scottish-based manufacturer of control systems for industrial applications and who discovered further common ground in a consuming interest in hi-fi.

With an established background in the design and manufacture of precision electronics, the team has enjoyed something of a headstart in the new venture. Much of the groundwork had already been done, proven either through those aspects it has in common with sophisticated control circuitry (power supplies, for example) or through gradual development over the years on the designer's private workbench. An immeasurable additional advantage was that so many of the component sourcing, board and fabrication issues were already resolved.

Samuel Johnson Audio is based in Prestwick, Scotland. The company, like its name, displays healthy cross-border links since its designer, Norman Johnson, is English, like his 18th-century namesake, while many of his colleagues are Scots, like the great lexicographer's friend and biographer, James Boswell. But one shouldn't make too much of these things! SJ needs no historical prop.

Curve Ball
Certainly if looks and build quality are arbiters of success, SJ should find itself stretched to meet demand, for the styling and attention to detail evident here is exceptional. There are three products initially in what is termed the Premium range: a pre/power amplifier combination and a DAC, while a CD transport is said to be nearing completion. Here we look at the pre/power coupling.

The 360mm midi-width cabinets are available in a choice of finishes. The review samples, pictured here, were in a light champagne gold, but chrome-like polished aluminium, black and graphite are other current options. The covers have a textured paint coating while the fascias present a striking combination of anodised aluminium and real wood – a choice of rosewood, ash, American walnut, cherry, mahogany or walnut.

These fascias must have presented a major challenge in their precision marrying of curved sections of such dissimilar materials. Points of subtle detail abound. For example, the control buttons sit in recesses whose curved profile is a miniature concave echo of the palm-sized handset's elliptical profile. The company logo is subtle too, set only within the large standby button.

Lid-off shot of the ppa100 power amplifier shows the two screened, custom-wound 300VA toroidal transformers, one per channel

pca100 Preamplifier
The pca100 preamplifier, or control amplifier as SJ terms it, is unashamedly minimalist in its function, offering no balance or tone controls or filters, despite its unusually high component count, much of which concerns the highly elaborate power supply arrangements. As standard there are six unbalanced line-level inputs, all electrically identical, presenting a 47kohm input impedance and a sensitivity of 360mV for 1V output at full gain.

An optional phono input will be available, but at the time of writing this was not yet finalised. It seems likely that there will be a choice of modules to suit MC or MM and high-output MC cartridges. The line inputs are labelled CD, Tuner, Aux 1 and 2 and Tape 1 and 2, and there are separate recording outputs to allow active off-tape monitoring and/or dubbing with three-head recorders. Separate 'listen' and 'record-out' selectors allow one source to be recorded while another is heard.

Original pages from the Apr '00 issue of HFN in which Ivor Humphreys took stock of the first two products from the newly formed Samuel Johnson Audio company

The SJ components are normally left powered on and brought in and out of standby by the large button on the fascia. An adjacent small LED glows orange in standby, and green when the circuit is ready. Five small buttons activate logic circuitry to control input and record output selection, volume up/down and mute. Input/record output status is indicated by two labelled rows of six blue LEDs and the mute condition by a single red LED. All these functions (apart from standby) are also available on the remote control handset [see p131], which manages with just four buttons.

On The Boards
The rear panel of the pca100 sports a fused three-pin IEC mains socket with an integral rocker switch (that is normally left on), 13 pairs of gold-plated RCA phono sockets and a 6.35mm headphones output. Why so many phonos? Well, two are in place ready for the optional RIAA board, but there are four more pairs connected in parallel and allocated to the main preamp output, facilitating bi-, tri or even quad-amplification should this be required.

As mentioned, the component count is high. The circuit is built on three printed circuit boards, one each for the power supply, front panel switching/logic/display, and for the main audio circuit. I don't recall seeing such an elaborate power supply in a preamplifier. An EMC filter follows the IEC input to minimise mains-borne interference and this is followed by no fewer than six (wonderfully silent) transformers. Four of these are custom-wound, canned/screened toroids, providing independent supplies for the input and output stages of each channel.

The preamp (top) has five recessed buttons for volume up/down, mute and selecting Listen or Record functions. Both the pre and power amp (below) sport large standby buttons to the far right of the fascia bearing the company's logo

Extreme Measures
Each transformer feeds its own bridge rectifier, a pair of 6800pF reservoir capacitors and monolithic voltage regulators to provide the ±15V DC feed to the audio board, with local decoupling around each active device. The fifth transformer feeds the control logic, display board and motorised volume control, while the sixth, smaller one, is devoted to the signal switching relays.

Many would consider this an altogether extreme set-up for a preamp, but Johnson is convinced that signal integrity depends upon maximum stability of the low-voltage DC supply lines, on near-zero crosstalk between stages and channels, and on the lowest possible noise floor throughout.

Another key aspect is a short signal path and to this end all the relevant circuitry is located adjacent to the rear panel, with the switching handled locally by an array of 12 Meisei encapsulated relays. Separate amplifier stages are employed for the main and headphones outputs and the tape output is properly buffered (for once).

The audio circuit is based on extremely high-quality IC devices from Linear Technology: the low- noise LT1007 and ultra-low-noise LT1028 high-speed operational amplifiers, the latter used for the CD input and for Input 3 that the RIAA module will occupy. Discrete bipolar devices supplement the output ICs to provide a low-impedance Class A drive, the main output defined at 100ohm (which can drive long pre/power interconnects) while the headphone output – a separate circuit – is less than 1ohm and thus suitable for pretty well any moving-coil headset. The main board, meanwhile, is a four-layer type with an integral ground plane to help maintain a low noise floor and inhibit interference.

ppa100 Power Amplifier
The power amp takes the reduction of residual noise and interchannel crosstalk to near obsessive lengths. The former is encouraged by the use of star grounding and the latter given a headstart by the simple expedient of constructing the units as two completely separate power amplifiers in the one cabinet.

This division extends even to the use of two large screened, custom-wound 300VA toroidal mains transformers, one per channel. The two amplifier circuits are, of course, identical, each built on a single PCB that runs the length of the cabinet and is mounted on standoffs behind its associated heatsink. Each channel has 40,000pF of reservoir capacitance in the form of four BHC Aerovox electrolytics with incoming mains subjected to an EMC filter.

Mains input is via a switched, fused three-pin IEC socket and the signal inputs are on gold-plated phonos. Loudspeaker outputs employ Speakon connectors. Although well-known in professional circles, these are still rare on domestic products. The locking plug-to-socket fitting is obviously very secure but I have to say that the actual cable-grips are nothing to write home about, the wire retained by side-entry grub screws in familiar 4mm plug fashion. Bi-wiring is readily achieved, though, because the grips are doubled-up within the plug.

Quality Control
The amplifier is fully protected against DC offset, short-circuit and over-temperature. As with the preamplifier, it is normally left powered on and brought in and out of standby from a push-button located on the fascia. Again this has a bi-colour LED tell-tale. Two other LEDs, one per channel, show red at switch-on and turn green after a couple of seconds once the supply has settled and the amplifier's relays un-mute.

The power amplifier provides a gain of 32dB and is rated at 50W per channel into 8ohm, providing a doubling into 4ohm. With its massive power supplies, it is clearly capable of delivering very high instantaneous current levels and it takes but a short period of listening to establish that it exerts phenomenal control.

Invisible Touch
Used in tandem, or individually in the context of other systems, these two units proved to be truly outstanding, virtually transparent to the signal. Employed together between a 508 24 CD player from Meridian and a pair of Quad ESL-63 speakers the combination provided extraordinary definition, conveying an astonishing amount of detail – every strand in the musical fabric, every subtlety of timing in complex textures in perfect order.

Canned toroids provide independent supplies for the pca100 preamp's input and output circuitry. A key aspect of the design is the short signal path, with core circuits being located close to the rear panel

It's rude to point, but there's a precision of focus here which has one singling out individual performers in a complex score simply because they are now so tangible – perfectly integrated yet also discrete. There's a special delicacy in the tonal balance too, which is both silky-smooth and wide open at the frequency extremes. A key factor is the exceptionally quiet, 'black' background; low-level detail is perceived that much more clearly when there's not even the vaguest hint of a blemish on the canvas.

Criticisms? Well nothing's perfect, of course, and though I can find nothing to fault in the sonic performance, ergonomically the preamp is a little idiosyncratic in the way its Listen and Record selectors simply cycle through the six source options.

One Love
What this means is a single jab if you are going from CD (Input 1) to Tuner (Input 2), but if you then want to go back to CD you need to press the button five more times. As there is no delay in the actual switching, other sources which happen to be active will be heard momentarily in passing, which can certainly be irritating.

Where the preamp's fascia offers separate buttons for Listen and Record selection, the delightful little solid aluminium handset has just one, cleverly combining both functions in conjunction with its Mute button. With the mute off the Selector button cycles through the Listen inputs in the normal way; when muted it cycles through the Record output sequence. This means that you cannot change the Record settings via the handset without interrupting a source you are auditioning, not, perhaps, that it matters very much at all!

Shaped like an egg, the remote handset is small enough to fit in the palm and offers all the functions found on the preamp's fascia – apart from standby – using just four buttons

The only other limitations, to my way of thinking, are the lack of any visual indication of the volume setting along with the preamplifier's insistence on returning to CD for both Listen and Record at switch-on, regardless of the last-used choice. Oh, and because the input names are printed on the display window and the LED indicators are set a little way back, viewing the unit from an angle can line up the right LED with the wrong legend. But now I'm being too pernickety, for on the whole I've rarely been so impressed with an amplifier combination, so confident that in all key aspects it performs flawlessly.

Conclusion
I had less time than usual to prepare this review but have nevertheless spent a disproportionately large amount of it simply listening to disc after disc, drawn in by sheer involvement in a wide range of music and musical types. My primary interest is in classical music but I found myself trawling through my idiosyncratic collection of non-classical favourites as well, fascinated by myriad small details that had scarcely registered before but which were now plain to hear.

'No compromise – just music', the Samuel Johnson company motto goes, a lofty aspiration but to my mind reached by these truly excellent units. If there is any justice, they should surely fare well.

Ivor Humphreys

Source: www.hifinews.com