Review: The Audio Research SP-8 preamplifier

 

History: Audio Research has a long and, dare I say, storied past.  Back in the era when vacuum tubes where being consigned to the ash heap of history, they, and a just a handful of manufacturers were still making gear that used these ancient amplification devices.  Even in 1990 I remember being at a used electronics company in Colorado and receiving less-than-kind words when inquiring if they had any tubes or tube gear.  "Vacuum tubes?  Why would you want to use tubes?  Are you fixing an old piece of equipment?"

William Z. Johnson obviously didn't get the message,  Like so many afterwards, he started out modifying Dynaco gear, and branched out making his own equipment under the banner of Electronic Industries.  This latter became Audio Research which started with the SP-1 preamplifier and the Dual 50 amplifier.  They really didn't have a hit on their hands until the venerable SP-3A preamplifier, and D-70 plus D-115 amplifiers (and the various following iterations) came and made them serious contenders in the audiophile world.  They also dabbled - and still do! - with solid-state equipment but are, of course, really known for vacuum tubes.

The Audio Research SP-8, first introduced in 1981, went through several minor redesigns.  I tend to think of the circuitry as being the ultimate Dynaco PAS or Marantz 7. For example the phono amplification is done through a pair of 12AX7s with a 6DJ8+FET cathode follower, RIAA handled via the negative feedback loop.  The linestage is similar with a pair of 12AX7s and a 6DJ8+FET cathode follower with loop feedback.  Where Audio Research shines is the power supply.  In this case a solid-state regulator makes sure the phono state receives a dead quiet high voltage.  And, oddly enough, a combination of a 12BH7 and 12AT7 provide the regulated supply for the linestage.

Controls are fairly simple but with some older ideas that have gone out of fashion.  ie, of course there is a volume but there is also the increasingly rare balance control.  And something else - there is a stereo, mono, reverse, left, and right mode.  Add in the switchable AC outlets for that extra vintage feel.  There is, however, no tone controls or a loudness switch.  But one can mute, select the phono or four other line sources, and switch between tape out monitoring or input.

This particular SP-8 under review is a Mark II, Revision 5, and has only had three previous owners.  When my friend offered to sell me this well-known classic, I jumped at the chance even though it needed to be repaired.  It turned out, due to years of being in storage, the power supply section that handles the muting and 12AX7 filament voltage was no longer working.  Instead of troubleshooting it myself, I sent the unit out to the Audio Research service department, who still does repair work on this 30+ year old gear.  They not only repaired the power supply in question, but also cleaned the volume pot, replaced all of the electrolytic capacitors, put on new feet, and found an additional issue with the linestage that needed to be fixed.  Now this SP-8 is ready to provide service for many more years of service.

 

First Impressions: After unboxing the returned SP-8, I first had to figure out where to place the eight different tubes.  It isn't obvious since the circuit board is not marked.  Instead one has to look at the manual, figure out what version you have, and then double-check your work.  I'm glad I did because I had to swap the location of the 6DJ8 and 12AX7 in the phono preamplifier.  Luckily I did not power on the unit!  After switching the location of my two turntables, due to the interconnect lengths and phono input location, I was finally able to sit down and do some quick listening.

With new electrolytics and NOS tubes that needed to be broken in, I found the bass rather lightweight.  The top end was also bright and the midrange was a bit muddled.  Nonetheless I could tell there was an increase in detail over the replaced Classe Five.  I let the preamplifier cook for a few hours and things started to snap in place.  For example, Chet Baker's voice on the title song from the album She Was Too Good To Me, was very emotional; perhaps the closest one could get to the now deceased trumpet player.  Pink Floyd - The Wall had fantastic imaging without any blurring of the instrumental or voice outlines.  The Classe Five, in comparison, sounded a little darker and less forward.  The SP8, at least with the excitement that new gear brings, seemed to be a real step up in fidelity.

Listening Test: After a few days of background music duty, it was time to put the "new" Audio Research through its paces.  I could tell right from the get-go that the bass had become more extended and some of the forwardness had been reduced.  Note that tube selection will, of course, change the sound.  ie, a set of new production tubes may not be as satisfying as some original 1950s Mullard 12AX7s that I was lucky enough to have on hand.

I have an interest in electronic instrumental music, to the point where I have made my own albums.  For this review I didn't have the ego to listen to my own work but instead picked out the soundtrack Beyond the Black Rainbow by Sinoia Caves.  This has a heavy Tangerine Dream influenced album with one or two sequencers often going at once.  The SP8 did an extremely good job capturing the attack of the electronically produced notes, putting them into their shifting artificial space in the soundstage width.  Bass was also deep without any "classic tube" coloration or overhang.  This is no golden-hued Dynaco PAS experience but instead has a speed that, until now, I thought was impossible with the 12AX7 tube.

 

Neil Young's Tuscaloosa is a live album from his Ditch Trilogy days, starting with two acoustic numbers before the whole band takes the stage.  With the Audio Research his voice had a real presence, the body and the diapraghm can be heard projecting much like the "real thing".  I've done sound for a few live shows and this albums captures that experience quite well, also with the proper amount of hall/stage reverberation, along with the oddly recorded, cardboard sounding drums.  Likewise with the dynamic shifts, which were recorded in a honest way, capturing what it must have sounded like being there; provided you had access to the soundboard instead of being in the back row!

Imaging and soundstage depth was among the best I've heard in my system .  An example of this is the song Warm Ways on the self-titled Fleetwood Mac album.  This is a busy mix but the outlines of the instruments and voices weren't slightly blurred like lesser preamplifiers.  This led to more detail, or, as Audio Research would say, High Definition.  I've owned plenty of other preamps in my life but none have quite approached the sound of the SP8, which, given it's rather pedestrian signal circuitry, a real surprise.  It's neither dark nor bright (tube dependent, of course!) but seems to pass the sound from the Thorens TD309 turntable along in a refreshingly honest way.

Dead Can Dance albums, by some strange miracle, are usually very well-recorded.  My original 1994 UK pressing of Toward the Within is no exception, capturing the vibrancy and the crowd excitement of this live recording.  The song Sanvean, with Lisa Gerrard's voice taking center stage, is a beautiful tear-inducing song.  I was swept away by the emotion of her voice, proving that the Audio Research is no clinical piece of gear.  The depth and power of the music was, once again, presented very naturally without any undue added coloration that one would find in a vintage "warm" preamplifier, but neither did the overall sound swing the other way towards hyper-detailed iciness. 

Parting Thoughts:  Given the age of this preamplifier, it may be a surprise to many that I find it quite neutral.  However I look at this era, the late 1970s to the late 1980s, as a golden age of audio reproduction.  Yes there were fewer companies back then, but they were really pushing the envelope of technology.  There are many examples of this - Krell, Mark Levinson, Threshold, and, of course Audio Research.  The SP-8 is the sound of a classic 12AX7 feedback circuit taken to the extreme.  And it pays off - given the right tubes! - with a very neutral, high definition sound that is also transparent.  If you can find one, and have the patience to have it properly serviced, then the Audio Research SP8 is worth the trouble, especially if you are into vinyl reproduction.

I had to add the caveat about vinyl reproduction because of the high gain nature of the linestage.  The average CD player or DAC with a healthy 2V output will give one a very limited volume control range.  An example of this, with my second turntable, a Dual CS5000 and the Schiit Mani phono preamplifier.  I had to set the latter to its lowest gain setting - 42dB - otherwise the SP8 at the bottom of the detented pot mean I was only two click away before the music became too loud.  And this with an amplifier that is not particularly sensitive.

Review System:
Thorens TD-309 turntable with Ortofon 2M Bronze
First Watt Aleph J clone amplifier
Cardas Iridium interconnects
KEF R500 speakers with Cardas Twinlink speaker cable

The Most Important Amplifier In the World: The Dynaco 70

 

The Dynaco 70 is the most important tube amplifier ever made.  Sure, some may quibble at that characterization, but I can’t think of any other amplifier – at least within North America – that has turned on more audiophiles to the possibilities of tube amplification.  Like countless others, it was the amplifier that turned me on to an alternative way of listening to music. 

Back in the late 1950s, the stereo wars were heating up.  Many audiophiles had invested in the expensive monoblocks or stereo amplifiers from Marantz, McIntosh, and Fisher.  The smaller players – Heath, Dynaco, EICO, and Pilot were nipping on the heels of their more upscale brethren.   David Hafler made the right move at the right time by introducing a $99 stereo wonder – the Dynaco 70.

Sure, this little budget amplifier couldn’t compete with the big boys at a performance level, but it was such a bargain that no one seemed to mind.  The sales numbers certainly back this up.  Yes, the power transformer was woefully underrated for supplying the current to four EL34s, and yes, the 7199 tube is not an ideal driver/phase-splitter, but whatever failings the Dynaco 70 has is ameliorated by the warm forgiving sound that throws a big wide soundstage.  This is an amplifier made for playing music, and if paired with good tubes, the performance is damn well good enough to have made me a tube convert for life.

I bought my first Dynaco 70 at the tender age of nineteen.  I was heading off to college and needed a stereo system.  At the time I didn’t know anything about tube amplifiers but came enamored with them after hearing a McIntosh 240 over at a friend’s house.  I loved the black transformer and chrome chassis look and lusted after the glowing tubes.  When he asked if I wanted a tube amp, I readily agreed.  However, I will admit that I had to hide my disappointment when he brought out the brown caged Dynaco 70.  It certainly couldn’t compare to the McIntosh in the looks department.  But little did I know how this little tube amplifier would change my life.

The amplifier started stock with Siemens EL34s, a Mullard 5AR4, and RCA 7199s.  After a few weeks of that, the same friend suggested running an outboard tubed regulator to supply the front end.  With the shortage of 7199 tubes – this was before the Internet, mind you – I converted the PCB, through the use of a RCA manual and my first soldering iron, to use 6GH8As.  After that, it was modified to run the EL34s in triode.  After that, it was sadly sold to another friend who began his own audio journey with tubes.  At that point I was running modified Scott or EICO integrated amps, a small step before my DIY journey.

A few years ago, I exchanged emails with the fellow who bought the Dynaco 70.  He still had it!  We did a swap and I had my very first amplifier back in my possession.  The original circuit board was long gone, the tube sockets were shot, and the can cap had been replaced by a giant oil power supply capacitor.  This old amplifier was due for a rebuild.

In order to stay true with the spirit of the Dynaco house sound, my restoration was fairly limited in scope.  The input circuitry was replaced with a PCB from Triode Electronics that utilizes a pair of EF86 tubes and a single 12AU7.  The power supply can-cap was replaced with a SDS circuit board that fitted underneath one of the output transformers.  A bit of wire and solder, some new output tube sockets, and the amplifier was ready to sing again.  

For tube selection, I went with some budget Russian valves – EH EL34s, Sovtek EF86s and a 5AR4.  The sole American tube was a late production Phillips 12AU7.  The sound, as to be expected, was a little on the harsh side.  This was due to the “solid-state in a bottle sound” that afflicts many of the lower-end Russian tubes.  So it was time for a spate of rolling.  In the end, the amplifier finished with Matsushita EL34s, Dutch EF86s, a Hitachi 5AR4, and a 1950s-era RCA blackplate 12AU7.  This change made for a much smoother and cohesive amplifier that was quite enjoyable to listen to.

But, I’m not the sort of chap who wears rose-colored glasses.  The Dynaco, even with an improved power supply and new input circuit, suffers from several flaws that stop it from being a truly great amplifier.  

First of all, the power transformer is helpless underrated in the current department which will cause the voltage to sag at higher output powers.  Another issue is the use of a single 5AR4 rectifier to handle all four output tubes.  Sure, it’s within the specification of that tube, but still it is hitting the top of the envelope.  Of course these two problems can be rectified (ha! – editor) by an aftermarket power transformer and a different rectifier or even the use of solid-state diodes (which have their own issues).

However, even with those changes, I believe the fatal flaw of the Dynaco 70 rests with the A-470 output transformers.  Like many things Dynaco – especially on their budget gear – this output transformer was built to a price point.  At higher output levels, the amplifier sounds like the core is saturating, giving that pleasant “tube-like” compression.  It sounds like the images are on springs, causing the soundstage to shrink in size as large dynamic swings occur.  Why do I pin the blame on the output transformers?  I’ve heard the same effect on the Dynaco Mark IV, the monoblock version of the Dynaco 70 that have a much beefier supply that isn’t shared between two channels.

So yes, the Dynaco 70 – and all the new kit versions now available – is still a great introduction to the world of tubes, but it isn’t the end game.  There are much better - and admittedly more expensive – amplifiers that really lift the veil over the music and provide the sort of output that an audiophile wants to hear.

Review: Quicksilver full function preamplifier

Introduction
Quicksilver has been around for quite some time, but their products are often overlooked for the more flashy Conrad-Johnson, Audio Research, or whatnot.  However, much like VTL, Quicksilver instead concentrates on simple but solid tube circuitry, robust old-school construction, and moderate - at least for audiophile gear - prices.  The full function preamplifier in question is the earliest incarnation of the product having first hit the street in 1988.  Price back then was a princely $1995, making it roughly in the same price range as the famed Audio Research SP-8 or the slightly later Conrad-Johnson PV11.

I bought mine from a seller on Audiogon.  Shipping was prompt and I received a very heavy duty preamplifier that doesn't quite have the same ooze of quality that ARC or McIntosh has, but certainly is no slouch in fit 'n' finish.  Cracking open the top plate grills, you will see that the power supply and signal path are separated by a thick steel wall.  Very nice.  Component quality is also good though hardly esoteric.

Circuit and Controls
A quick look over the tube complement and circuitry:  Some of this is based on guesswork since no schematic could be found.  The power supply uses a large power transformer, a pair of 6X4s which are still widely available NOS, a small choke and a number of large Mallory capacitors to provide the DC smoothing, along with some regulation for what I assume are the tube filaments.  The line stage uses one 12AX7, one 12AU7, and one 12FQ7.  Since the reported output impedance is so low, I'm assuming the 12FQ7 is being used as a cathode-follower with some negative feedback wrapped around the entire circuit.  The last bit is the phono stage which only uses a single 12AX7 and a 12FQ7 with some sort of green LED biasing.  Coupling capacitor quality is in the meh range, but hardly out of place for the era.  The big 2uF capacitors on the output stage are some REL Polyesters (ughh).  The smaller signal caps are branded Quicksilver though also look to be REL made.

Front controls are fairly standard though a little dated: No remote here!  Lighted power, AC rear receptacle switch, and a mute button make up the left hand of the faceplate.  The right side has a tape monitor switches, a reduced (20dB) gain switch, a selector switch, and a stereo/mono/etc switch.  Volume control is dual mono with one stepped Blue Alps per channel.  These actually work better than expected - with the numbered volume steps it's very easy to match levels between channels.

Rear panel is the usual assortment of nice gold-plated RCA jacks and a grounding post for the phono stage.  Power cord is captive.  Fuse Holder holds a 1A unit.  AC receptacles are a nice throwback to the days when the user would power up his amp and sources with one flick of the on button.

The Sound
Okay, enough introductions - how does it sound?  Well, since this is an older unit, the stock tubes are long gone.  For the purposes of this review I used some really nice NOS tubes from my stash, so results will vary to a certain degree depending on what is plugged into the sockets.  In my case I used early 1960s short plate Mullard 12AX7s, a late 1940s black-plate RCA 12AU7, and 1960s-era side-getter RCA 12FQ7s.  Rectifier tubes were Tungsol 6X4s.  Some generic tube damping rings came with the unit, so I kept those in place.

It's been my experience that ultra-regulated, current-sourced, current-sinked, and whatnot circuits are very detailed, but also suffer from sounding slightly unnatural.  Note that tube regulators are usually better than solid-state, while shunt suffers from less sterile sound than series.  My own DIY experiments with a simple linestage showed that pulling regulation out of the circuit actually improved overall musicality and enjoyment.  Sure, some of the last bits of inner-detail are missing, but the music usually sounds more relaxed with a looser power supply.  This type of sound was very evident with the Quicksilver preamplifier which just uses chokes and caps to provide a clean source of DC.

Compared to my old Threshold FET-10/HL linestage and Audio Sector Phono Stage, the Quicksilver (with Cinemag step-up transformers) has a relaxed presentation that draws you into the deep soundstage.  It's almost like unclenching your teeth after a roller-coaster ride, or taking a good solid gulp of your favorite adult beverage: the muscles relax and you sit back with enjoyment, washed away by the sonic swirl of the music.  A good stereo should be a psychedelic experience - an unregulated and legal high - that lets you forget the troubles of the world.  With the Quicksilver preamplifier, I feel as if my entire audio experience has been improved.


Listening Notes:
I used my turntable exclusively for this review, but the linstage by itself is no slouch either.  The Audio Sector phono stage combined with the Quicksilver was a pleasant surprise, but the Cinemag and native phono section got the nod in sound quality.

The Who - Tommy (W. German Polydor):  The Quicksilver has very excellent detail and speed, keeping up with Keith Moon's manic drumming without breaking a sweat.  Small individual instruments - like a small bell - maintained their place in the soundstage while still being audible in the wash of thundering bass and guitars.  Depth was deeeeep, making my room seem bigger than reality.

The Beatles - Rubber Soul (Japanese Parlophone): This particular cut of this famed album has been described as bright and bass heavy compared to the original British pressings, but to my ears it sounds like it was eq'd flat.  With the Quicksilver, treble is extended and detailed with out any forwardness or grit.  There is lots of nice detail with John's wonderful voice cutting through the primitive stereo mix.  It's harder to get closer to the Beatles than this.

Tom Waits - Closing Time (80s Asylum): Perhaps I'm a sentimental slob, but I love this album.  However, the Quicksilver revealed the limitations of this later pressing.  Some detail, compared to some better versions, was missing, as if the music was hiding behind a thin gauze.  Tom Waits voice, however, was still wonderful, leading to some near tears while listening to the bittersweet song Martha.

Record after record revealed a preamplifier - and stereo system - that was very analog sounding.  Perhaps somewhat lacking in some of the hyperdetailed / transparency of more modern pieces, the Quicksilver was still no slouch.  When it came to musical enjoyment, I give it an extremely high ranking since it never sounds bleached out or unnatural, even with less-than-perfect recorded music.  If you want a preamplifier that speaks to the mind instead of the heart, you may want to look elsewhere.  I've gone down that road with my foray into solid-state gear, but I'll take naturalness over artificial effects any day of the week.


Overall:
Soundstaging:  Deep and Wide, imaging goes beyond the boundaries of the speakers and even the walls of my listening room.

Treble: Airy and extended, but also pure and detailed.  Compared to the darker Threshold/Audio Sector, it seems there is even more overall treble, but yet it never is harsh or unfaithful to the record.  A strange effect and not at all what I expected from tubes and a step-up transformer.

Midrange: Glorious, but not overly slow or "tubey" in the classic sense.  The Quicksilver certainly doesn't sound like a soggy Dynaco PAS.

Bass: The 12FQ7 output tubes can swing some current while delivering a low output impedance.  This translated into control.  I certainly didn't miss the solid-state drive of my last preamplifier combination.

Speed: (or PRAT) Good tube gear isn't supposed to be sloggy 'n' slow.  The Quicksilver preamplifier and Yaqin amplifier combination certainly doesn't sound like an aged tube integrated or a Dynaco 70 in need of a rebuild.  Instead, the music transients started and stopped on a dime with no overhang.  With the UREI loudspeakers, this led to a very dynamic, exciting, but yet unfatiguing sound.

Detail: As mentioned above, the Quicksilver is no king at wringing out the very last drop of detail from the music.  No, it isn't flat or uninvolving, but the very last bits of information are perhaps less apparent than some other units I've heard.  Some of this may be due to the large Polyster output capacitors.  An upgrade is due for some of the parts - notably some new polypropolene capacitors - so it will be interesting to see what effect this has on the sound.  But really, I'm not complaining because I'll take all of the positive attributes over hearing the squeaky chair of the violinist in the third row.of the orchestra pit.


Conclusion
For a going used price of $850-$1000, the Quicksilver full function preamplifier is highly recommended.  It's extremely well-made and is very natural sounding.  Errors - and I mean minor - are ones of omission with a high scale of musicality.  The simple circuitry will minimize future troubles since there are less "moving parts" once you get rid of the solid-state and regulation support circuitry often found in modern tube preamplifiers.  I expect to increase the audio grade of this unit with some coupling and electrolytic capacitor replacement, so stay tuned!


Main System:
VPI HW19 Mark III with SDS Power Supply
aluminum rebodied Denon DL-103R
Rega RB300 with Cardas wiring
Cinemag CMQEE-3440A in custom aluminum box
Cardas Cross 1M interconnects
Quicksilver preamplifier with (real) Mullard 12AX7s, RCA 12FQ7s, and a RCA 12AU7
Cardas Quadlink 5C 1M interconnects
Yaqin MC-10T amplifier with black-plate RCA 12AT7s and (real) Mullard XF2 EL34s
Cardas Hexlink 2M speaker cables
UREI 813A speakers
VTI BL503 equipment rack