Despite the much reduced size of last March’s Audio World 2011 show at the Park Inn, Heathrow, London there were still new brands to be discovered and one such was StereoKnight, an American company based in Germantown,Tennessee where they make a comprehensive range of pre-amplifiers, one integrated amplifier (so far) the S40 and one mono power-amplifier in the form of the M-100. Not knowing anything about the brand I started a conversation with UK distributor Iain Borthwick of LW Audio, the UK distributor, who was very kind enough to give me a fairly detailed overview of StereoKnight as a company and the examples of their products that he was exhibiting. He told me that StereoKnight is owned and run by ‘James Zhang, a Chinese American with a manufacturing facility in China’ and that ‘James designs the units himself and they are not modified units or units used by any other manufacturers.’ Iain also told me that the ‘Transformers are wound to James design and are not copies of any other manufacturers. He also does not supply his transformers to competitors and as such are used exclusively in StereoKnight products’
As I had wandered into the room the thing that had attracted me to the StereoKnight products initially was their slight resemblance to Chapter Audio electronics. In fact I thought at first that they were from this British company but on closer examination they didn’t really look the same, except for the similar (possibly identical) volume and source control knobs; that both brands seem to use. I mentioned this to Iain who shrugged and agreed they did look similar and he suggested that perhaps Chapter Audio and StereoKnight used the same supplier for their knobs.
After chatting with Iain (a most affable chap) and hearing a detailed explanation of StereoKnight I sat down to listen and as I reported in my show report despite there being some room based negative issues with the sound I was still able to hear that these StereoKnight products were very much worth while exploring in more detail. So my curiosity well and truly piqued I was going to ask to review something from the range, when Iain beat me to it by offering to loan me a number of StereoKnight pre-amplifiers for formal review.
So in early May, over a period of a few weeks Iain sent me first a Silverstone ‘copper’ B&R Reference pre-amplifier and then an Enigma 1.0R pre-amplifier to review. As there was quite a lot to listen to and compare I will be presenting these reviews as a series, with the more affordable of the two pre-amplifiers, the Silverstone ‘copper’ B&R Reference pre-amplifier, up first.
However before digging into the review proper an overview of what exactly a passive magnetic pre-amplifier is I feel is in order.
Passive pre-amplifiers, the devils in the detail and the sting is in the tail.
Once upon a time passive pre-amplifiers were very much the hotly debated and desired item in terms of performance vs cost. (1) Twenty plus years ago companies like Mod Squad, Rothwell, and Audio Innovations, brought passives to the market that offered a lot but required very careful set up. These were resistive passive types which suffered easily from impedance mismatches and concomitant frequency response aberrations depending on volume setting and cable load. Since that time there have been a number of companies who have brought other designs to market, including LFD, Audio Synthesis, AudioZone, AVTAC, Bent Audio, DIYHiFi and Sonic Euphoria to name a few more and each has, in its own way, attempted to solve the issues that afflict the passive pre-amplifier as a breed.
However all of the designers of these products have decided to wrestle with the issues, knowing full well that an electronically silent and noise free environment is ultimately best for delicate easily corrupted musical signals and the passive pre not having a power supply or mains connection if designed right is a potentially excellent way to switch sources and adjust volume.
One British company had a good look at the problems surrounding passive pres and knowing that there was great potential in passives came up with one of the first to solve the volume gain issues. This company was Music First Design a spinoff company from Stephens and Billington who traditional made transformers and still do to this day. In recent times Music First have even been offering remote control functionality option with their products thus solving the biggest convienence issue many audiophiles have with adopting a passive pre.
Music First Audio’s solution to the previous passive designs flaws was to use transformers to deal with them as has StereoKnight. However before going into the ins and outs of these issues in more depth, it is, I feel very much worth asking a few salient questions before jumping into the review proper…..
What is a passive pre-amplifier exactly?
To put it simply a passive pre-amplifier is a pre-amp which has no powered components inside, therefore no potentially noisy power supply that can introduce interference to the delicate audio signals. As Stereo Knight put it a ‘Passive Preamp may represent a pure and simple pursuit of extreme High Fidelity. Simply to say, passive here means no active circuitry, i.e. no connection to AC wall power, in short, no power supply.’
While StereoKnight’s entry level pre the Silverstone Balanced is a true passive the Silverstone B&R has an on and off switch (2) and a single IEC mains input. If it’s a passive how and why does it have an On/Off switch and mains input? I will let StereoKnight answer that, ‘ But now days, the request of convenience, for example, the need for a remote control function has narrowed the concept of passive. Maybe no power on audio circuit is a more precise definition to the word “Passive”, these days.
The Silverstone B&R is no ‘hair-shirt’ design with a fully functional remote, which allows volume up and down, input selection (both Balanced and Single ended), output selection, left/right balance adjustment and display brightness adjustment. This level of armchair control is a far cry from what most past passive pre-amplifiers used to give you.
Why use a passive pre-amplifier?
Well put simply ‘less is more.’ The ideal in audio that was proposed by Peter Walker of Quad fame was that amplification should be like ‘a piece of wire with gain’, i.e no addition or subtraction to the audio signal and bar a cable with volume pot attached the passive pre-amplifier is as close to this ideal as is possible. However there are problems with this approach as many of the early passive pre-amplifier users discovered. They suffered from impedance mismatches and concomitant frequency response aberrations depending on volume control setting and cable loads. The art of system matching with a passive pre was almost a dark art and many systems that promised much failed to ultimately deliver and this is where the ‘passive magnetic’ design comes in as a solution to those problems.
What is a passive magnetic?
Put simply a Passive Magnetic refers to the use of a multi-tapped attenuation transformers instead of a resistive volume control device.
As mentioned above there were problems with the basic ‘resistive’ typed passive pre-amplifier designs of the past and these almost always suffered impedance mismatches and concomitant frequency response aberrations depending on setting and cable load. ’Traditional Passive Pre-amplifiers impose a large set of impedance values with additional resistance to accomplish attenuation. It requires the source to provide the power to drive the volume control’s resistance. By comparison, transformer-based attenuation with its electromagnetic coupling does not rely on the addition of resistance.
The transformer itself has very high impedance across the audio band. Accordingly, very little of the source’s output power is lost and only the very low winding resistance appears in series with the source prior to the pre-amplifier’s output. Thus the source only needs to drive the load and cables connecting to and from the Passive Pre-amplifier.
However, as the Passive Magnetic Pre-amplifier’s attenuation is increased (pre-amplifiers in most systems end up cutting the signal by 20dB or more at all times), the output impedance rapidly falls to very low values. This in turn translates into much improved ability to drive a load or cable. In fact, a transformer simply takes the drive ability of the source and passes it through with either a slight decrease over the source when any significant attenuation level is used.
The use of transformers dramatically improves on the ability of the Passive Pre-amplifier to drive cables (and loads) compared to traditional designs. In addition, the use of transformers will actually improve the ability of the source to drive its cables as well, which explains the experiences of senior audiophiles who found the use of the Passive Magnetic Pre-amplifier to be a substantial improvement over using no preamp at all.
The StereoKnight pre-amplifiers are equipped with true isolation transformers with separate primary and secondary windings. Gain in most preamps is redundant when the majority of amplifiers are driven to full output by the source voltage. Superior amplifiers don’t need assistance from preamps except for the bare functionality of attenuation and input switching.
However, design and manufacturing of this type of transformer is quite a complicated task but being a high end audio transformer supplier, StereoKnight has dedicated expertise in the research and manufacturing of audiophile grade transformers for many years.’ (quote StereoKnight)
Having looked at the ins and outs of what a passive pre and passive magnetic pre are we will now have a closer look at the pre-amplifier in for review.
Features and Functionality
The Silverstone B&R has three balanced XLR inputs and three RCA inputs, two variable RCA outs and two variable XLR outputs; these XLR inputs and outputs are available as a result of the StereoKnight Silverstone B&R reference pre-amplifier being a fully transformer-balanced input to output design.
All internal signals are transferred round the pre by silver cabling and as an option StereoKnight, did also offer a fully silver wired transformer version (3) The standard StereoKnight transformers (as in the unit reviewed) are wound with high quality copper. I asked Iain about what quality and type of copper was used in the transformers and he had this to say about that topic, ‘James will not divulge the type of copper except to say it the finest purity available.
Fit and finish of the sample I received and those I saw at the Audio World show were very high with a nice brushed aluminium finish and all fixing points are recessed. The back panel hardware is nicely fixed in place and all RCA and XLR inputs stayed nice and tight during review use. The back panel has nice clear legends to indentify ins from outs etc but one slightly unusual thing regarding the inputs orientation is that the left+ inputs are on the bottom and the right – ones are at the top. The pre-amplifier sits on four substantial, damped with a rubber O ring, aluminium feet.
Volume is adjustable via the right front Seiden dual mono ’33 step’ volume attenuator and via a rather nice metal remote, which allows you to also adjust left right balance, switching between the XLR and RCA inputs and dimming the display. This is done in progressive steps to full brightness or the other direction to be fully dimmed. There was no audible change in sound quality between the display on or off, so doing so would be only useful to reduce the amount of equipment generated light pollution in your listening room.
StereoKnight are keen to also point out the fact that the powered aspect of this design, solely for input selection and volume control, is kept totally isolated from the audio signal side, thus keeping to the spirit of the passive pre-amplifier design but providing the flexibility and functionality of traditional ‘active’ pre-amplifiers.
For myself as an analogue tape recording enthusiast the Silverstone has no fixed level output for hooking up to such a device. Such an omission for many is irrelevant these days but I for one feel the StereoKnight pre is missing a trick by not having such an output. One other omission that for some (though not I) would be seen as important is a Home Cinema processor Bi-pass. The lack of a phase switch(4), mono button or nameable inputs would be nice icing on the cake but their inclusion would push the cost of the pre to far upwards and not really add anything to the party as such from a sound quality point of view.
By saying the above re phase I am not belittling such a facility as I feel phase is both audible and important it is just that many XLR equipped sources have their own phase switches already fitted so the pre having the option, while nice is not absolutely necessary.
I tried the Telos RCA and XLR caps on this pre and its RFI rejection must be very good as fitting them resulted in no audible improvement in sound quality.
Swapping mains leads also resulted in no audible improvement in sound quality either. I did not really expect that it would but felt I should try this anyway as you just never know till you try.
After a month or so of trying the StereoKnight pre with various power-amplifiers both solid state and Valve (see the recent Air Tight review) I decided in the interests of consistency both in regards to my readers and my own reference system to re install the Meridian G02 pre and G56 power amplifier for the purpose of this review and the upcoming StereoKnight Enigma one (coming soon). The Silverstone was positioned on a set of M8 wood cones and also a SSC isolation platform and as I could hear no difference between either type of isolation platform I opted for the SSC platform as I plan on using one under the StereoKnight Enigma pre-amplifier during its own review.
Both items of Meridian electronics require a period of about a week to warm up so I set them up in their usual positions on my equipment rack and I positioned the StereoKnight pre-amplifier where my Bat Vk10SE phono stage normally resides. In order to give a fair hand to things I switched the StereoKnight pre off (remote control and source selection) and after 15 minutes or so powered the Meridian and StereoKnight kit on, in order to give all the items an equal period of warm up. In fairness while using the StereoKnight pre-amplifier beforehand I did not notice any benefit in leaving it power up or not but in the interest in being even handed I felt the afore mentioned course of action was best.
One thing worth mentioning at this stage is the choice of cabling I used. My normal reference cables are the well liked Atlas Mavros of which I use a complete loom: XLR to XLR, RCA to RCA interconnects and speaker cable and at the beginning of the review period I used them exclusively however at around the same time of the Stereo Knight items arriving with me I also received a complete cable loom from Tru SoundZ(5), a UK based cable manufacturer and as their cables are supplied run in I tried them with the Meridian pre – power combination and the Silverstone – Meridian G56 power- amplifier combination. I don’t want to divert attention away from this review or indeed pre-empt the Tru SoundZ review (coming soon) but the degree of synergy between the Tru SoundZ cables and both set ups really left me with a no brainer regarding conducting the review with the Revalation XLR to XLR cables I had been sent. I will say more about these cables in a forth coming review.
My normal source, the Moon Andromeda CD player was used and the speakers were my usual references the Anthony Gallo Reference 3.1’s. I did use my Marantz SA7 and Technics 1200 vinyl frontend, along with the BAT VK10Se phonostage during the review period but I will refer, only for simplicity sake, to my findings with the Moon Andromeda CD player. Equipment tables were my normal Clearlight Audio Aspeckt racks with mains being supplied to the two pre-amplifiers and power-amplifier via Audience Au 24 power cables and a single Analysis Plus Power Oval mains cable being used to power the Moon Andromeda CD player.
Thomas Dolby – Aliens Ate My Buick
The Dali Demo CD – Various Artists
Having used the StereoKnight for the last few months just for pure enjoyment and tentative exploratory purposes only a point came recently when serious comparisons and listening with my reviewers hat on was required and thus I girded my loins for the task ahead, which truth be told was no onorous task at all but a great pleasure.
Early on during my first few days with the StereoKnight I knew I was onto a winner with this particular pre-amplifier. It managed to be both open and detailed with very high levels of transparency but without having a forward or spotlit sound. Its presentation of musical information was very coherent across the bandwidths and it did PRAT well too. Above all though, it was musical with a lovely degree of clarity and insight but not clinical in its sonic signature. The StereoKnight sits just ever so slightly to the warmer side of neutral.
However there was one concern that niggled at me enough for me to have a chat with the distributor and that was in regard to the Silverstone having what seemed to me quite a high output voltage. With a number of items of equipment I tried it with there was at times just slightly too much gain, which reduced my ability to on occasions get past two on the volume control. My concern was am I getting full resolution at as low a level as two? The answer from Iain was yes and during my subsequent listening tests so far I have to conclude that he is correct, as I was unable to detect any lack of resolution between two and 14 (the maximum I took the pre too during normal review listening. Absolute volume adjustment depended on what ancillary equipment I was using at the time and the vintage of the recordings as well.
Modern compressed and loud CDs usually had the volume control hovering in and around the two to four point and older more dynamic CDs I was able to adjust up to fourteen. I should hasten to point out though that at no time even with this gain issue was there ever any distortion or overloading; just at times a slight lack of fine control of levels to be correct for my particular room. This was probably more of an issue in my normal system context as I run my system in fully balanced mode and that by its very nature gives more source output voltage to the pre and then onto the power-amplifier than a single ended RCA hooked up system would do.
I listened with to the Silverstone pre with a very varied program of different types of music during the time I had the pre. This included everything from Rock to Dance, to Jazz, a wide and varied selection of CDs and vinyl; including many of my regular test recordings, were spun. Frankly I think I would bore you if I outlined in detail what I heard from each recording so I will stick to sharing my findings with just a few of the recordings used during the period of the review.
Thomas Dolby’s album Aliens Ate My Buick is a long term favourite of mine and I have been using it for many, many years, in fact more than I feel entirely comfortable recalling, a growing awareness of old age is starting to creep in these days and as I sit down to listen to new equipment with recordings I have been using for almost all of my audiophile life, the ghosts of long ago listening sessions nip at my heels and remind me of how long I have been doing this both as a hobby, passion and job. Anyway I digress Aliens Ate My Buick is a great example of early digital recording (which may well be flawed compared to more modern recordings, that have higher bit rates but at least this one has a full dynamic range and no loudness issues; increasing problems with much of today’s modern music. Grumpy old man syndrome is kicking in I fear, as increasingly music is harder to sit back and enjoy as it is badly recorded.)which, while it is well known can sound a bit forward and brittle in some systems, also possess a wonderfully rich soundscape populated by very three dimensional instruments and one that has good depth to it. There is of course the infectious weird and whacky music too, reflecting Dolby’s quirky insight to life which manifests itself in quite humourous lyrics.
On the Meridian G02 pre-amplifier the tracks I played of the album had a cool, matter of fact presentation, with a good but slightly flat soundstage (flat in relative terms compared to more expensive pre-amplifiers). The music while very enjoyable lacked a truly three dimensional reality and in truth sounded, despite being fun to listen to, 2D, sat upon, less musical and just a bit lacking in life and air.
In contrast installing the Silverstone pre (achieved by swapping cables over, it sitting on the shelf above the Meridian G02) and listening to tracks like Budapest by Blimp, Ability to Swing (and I must confess others too as I found myself listening past the ends of my selected tracks regularly) had dimension, life, air and insight that the Meridian just failed to reproduce. I have always said the Meridian pre was about sins of omission not commission and the Silverstone in this system was all about injecting the life, detail, and musicality back into what had been flat. I hate using that word about the Meridian but to my ears that is how it reproduces recordings.
The Silverstone allowed the warmth and fullness of recordings, even the ever so slightly clean Thomas Dolby album to shine forth, revealing weight and scale as well as textural richness to to the mid band and upper bass, in this recording, that had been missing while using the Meridian pre-amplifier.
The Silverstone was also adept at digging out the pace, rhythm and timing in the music (something I have alluded to already) I was listening to. I would be very much inclined to say it excels at this but in a less obvious and more natural way than the usual suspects that are well know for this aspect of music reproduction. I was well aware of this aspect of the Silverstone’s performance when an old audio buddy had a listen one night to my system with the Silverstone in situ. In fact he said that he felt that even the Naim boys would quite like what the Silverstone was doing in that regard. I hasten to add thought that unlike Naim equipment (and I am thinking more Old Naim than New here) the Silverstone pre has no obvious tailoring to the frequencies, it is very much a full bandwidth design but manages to do what old Naim did and get you tapping your feet in time with the music. Something that was quite natural to do and not forced at all; those in the know will understand what I mean by that.
I think the best way of summing up the difference between the two pre-amplifiers was that the StereoKnight made music and the Meridian made sound. Now don’t get me wrong enjoyable sound but sound none the less. The Silverstone pre was more expansive in its music making ability and thus when wired in regardless of whether it was Atlas Mavros or the Tru Soundz cables it sounder, well frankly wonderful.
I had a listen to the Hugh Masekelia track Stimela (a review favourite of mine) a more recent recording than Aliens Ate My Buick, and in many ways this track, which in my opinion is an amazing live recording, really showed the difference up between the Meridian and the StereoKnight pre-amplifiers better than Aliens. The best way I can describe the differences between these two pre-amplifiers is to use this analogy. With the Meridian it was a good photo, with the SliverStone it was more like being there in the venue with Hugh and the boys. All the aspects that the Thomas Dolby album showed up was to be heard here too but the sheer dimensionality of the instruments and the texture was breathtaking. Frankly it was in many ways texturally like sticking valves into the system, with a sound quality very unlike what you normally would expect from a solid state system. There was no added warmth as such just more fleshed out reality.
Over the period of formal and less formal listening, no matter the source the Silverstone pre-amplifier delivered a musically engaging and rewarding sound no matter the music or even to a degree the quality of recording. It always managed to allow the music to shine forth and in a very enjoyable and informative way.
Well my initial thoughts that StereoKnight was a company worth checking out in more detail has very much been borne out by my experience with this pre-amplifier, as using it during the period of this review has been a real pleasure, both from a sound quality point of view and in a material way too.
Are there any negatives? Well apart from the lack of a fixed level output, the slightly tacky (just a personal opinion) logo on the top of the pre I would have to say no, not really. I would issue a very slight note of caution regarding the high output level for matching to power-amplifiers but in reality I never heard any real issue regarding this despite using the pre with a number of amplifiers, including a Music Reference RM 200, Copper Box 2A3 and an AirTight ATM300. I guess it’s just an inbuilt thing in me that I would quite like to see higher numbers, indicating volume level than what I sometimes had displayed on the pre-amp’s display.
Overall the Silvestone B&R Reference passive magnetic pre-amplifier represents excellent value for money and in my opinion punches well above the expected sound quality envelope for a pre-amplifier at its price-point, a not inconsiderable £2350, but considering what the end user gets for his or her money, in regard to build, fit and finish, flexibility of use and above all sound quality I think this is somewhat of a bargain at that retail price.
I am very impressed with this second up the range pre-amplifier and I am really looking forward to scaling the next level with the Enigma 1.0R pre-amplifier; the review of which, is coming very shortly.
Review product: StereoKnight Silverstone ‘copper’ B&R passive magnetic pre-amplifier
Current UK Retail Price: £2350
Source of review loan product: UK Distributor http://www.lwaudio.co.uk/
Manufacturer: StereoKnight 532 Bedlington drive, Germantown,Tennessee, United States of America. Website:http://www.stereoknight.com/index.html
- True balance input/output design with four transformers attenuation which isolates components, break ground loop problem and reduce noise
- Seiden 33 step volume attenuation with remote control based on 33 transformer output terminals
- 9V separate DC powered remote control function for source selection and volume control
- 3 single-ended or RCA input, 3 balanced or XLR input
- 2 single-ended or RCA output, 2 balanced or XLR output
- Point to point hand wiring with Teflon coated solid core copper wires.
- Full Heavy duty refined aluminium alloy body, faceplate and remote wand
- 6dB passive gain, so low gain amplifiers can be driven to their maximum efficiency by components that otherwise might require active boosting
- Dimensions: 18″ W x 12″ D x 7” H
- Weight: 25 lbs net; 30 lbs shipping weight
- Warranty: 2 years parts and labour
(1) Firstly they needed to be used with very short cabling and quite often this cabling needed to be shielded. Power-amplifiers needed to sited very close to the pre-amplifier and for many this caused problems as their particular system configuration might not lend its self easily to this sort of set up.
Secondly by their very nature having no power-supply meant they were usually very light and small and quite often heavy interconnect cables would pull them off the shelf they were sitting on and I recall in one particular occasion, seeing a Rothwell passive pre lifted into the air due to the springiness of the cables being used lifting it of the surface it should have been resting on.
Thirdly back in the early days of passive pre-amplifiers almost none came with a remote control. Perhaps this was less of a big deal back then (20 odd years ago) but certainly more of an issue into day’s market place, were ease of use from the comfort of one’s listening chair is a de-facto requirement, both expected and desired by the less masochistic audiophile.
Fourthly however these previous issues, as important as they are, pale into insignificance next to the fundamental flaw regarding changing performance as the volume control was turned further up the scale that beset almost all early passive pre-amplifiers. In most set ups the variables of equipment resistance and capacitance and that of cabling meant that as the volume went up the performance sound quality went down and quite often dramatically so. However despite that an ideally set up passive pre-amplifiers could sound amazing but for many this level of performance from a passive remained somewhat illussive.
(2) The On/Off switch is located underneath the pre-amplifies front fascia, about half the length of the average middle finger, just to the right side of the source selector; which is the control knob to the left side on the pre-amplifiers front panel.
(3)The silver version is not available at this time and will not be for a while due to shortages of the correct type of silver wire. The silver option also cannot be done retrospectively but must be chosen at the time of purchase.
(4) By saying the above re phase I am not belittling such a facility as I feel phase is both audible and important it is just that many XLR equipped sources have their own phase switches already fitted so the pre having the option, while nice is not absolutely necessary.
(5) I will be conducting a full evaluation of an entire cable loom of TruSoundz Revelation interconnects, speaker cable, power cables and mains distribution block in the not too distant future review currently under way. You can find more details on TruSoundZ here in the meantime http://www.trusoundz.com/indx.html
© Text and Photos Copyright 2011 Adventures in High Fidelity Audio…..except for StereoKnight product photos and album covers. Copyright belongs with their original publishers.
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