Audio Research LS5 preamplifier & BL2 input controller Robert Harley, Steven Stone Return

Robert Harley returned to the LS5 in November 1994 (Vol.17 No.11):
While I was auditioning the $4495 Audio Research LS5 Mk.I preamplifier that I reviewed in August, I took possession of the $3495 Sonic Frontiers SFL-2. As much as I liked the Audio Research, it was clear that the Sonic Frontiers was serious competition. In some respects, the SFL-2 was the winner. The Sonic Frontiers had a cleaner treble, with less grain. In fact, it was the SFL-2's lack of treble grain that pointed out the LS5's trace of edge on instrumental textures. The SFL-2 revealed that the LS5 had a very slight whitish quality to the upper mids and treble. I wouldn't have thought it possible—the LS5 was extremely clean and pure in the treble, but the SFL-2 took treble purity one step further.

The SFL-2 also excelled at soundstage transparency—that "hear-through" quality that makes the music come to life. Soundstage size was bigger through the SFL-2, but the LS5 had a greater ability to change the spatial perspective depending on the recording. On small-scale music—Gary Schocker, Flutist (Chesky CD46), for example—the LS5 presented a tighter, smaller, more intimate perspective. Although the LS5's sense of size on large-scale music was smaller than that portrayed by the SFL-2, the LS5 seemed to have a wider range of spatial perspective. In addition, the LS5 had a greater feeling of bloom. This was perhaps partially the result of the SFL-2's more forward and slightly drier midrange. In the context of my system, the LS5's less forward presentation better suited my taste.

Although the LS5 could be described as warm, full, and rich in the bass, the SFL-2 had a slightly weightier character. The region below about 60Hz was better defined through the SFL-2, with tighter pitch definition. The Sonic Frontiers also had a bit more extension and dynamic impact in the lowermost octaves. In the bass and midbass, however, the LS5 was more articulate, better revealing detail and nuance.

With single-ended sources, the all-balanced LS5 has to be used with Audio Research's $1495 BL2 input converter. I preferred the SFL-2 to the LS5/BL2 combination when using single-ended sources; the BL2 added a slight brightness and dryness to the sound. The SFL-2 clearly excelled in treble smoothness and overall liquidity.

Overall, I was very impressed by both preamplifiers, but if you have single-ended sources, the $3495 SFL-2 is a terrific bargain.—Robert Harley

Robert Harley wrote about the LS5 Mk.II in December 1994 (Vol.17 No.12):
My review of the Audio Research LS5 fully balanced tube preamplifier in the August 1994 Stereophile (Vol.17 No.8), along with my comparisons with the Sonic Frontiers SFL-2 in the November issue (Vol.17 No.11), conveyed my belief that the LS5 is a superb preamplifier, but perhaps not a contender for the State of the Art. At $4495—plus $1495 for the ARC BL2, needed to accept single-ended signals—the LS5's price raises the standards by which it must be judged. There are a lot of great preamps out there for six grand.

As much as I liked the LS5, I had a few reservations about its sound. My primary criticism concerned the preamplifier's treble, which lacked the liquidity I so enjoyed from the SFL-2, instead sounding a touch grainy. The LS5's treble had a somewhat whitish, almost metallic quality compared to the SFL-2.

Other than that shortcoming, I greatly enjoyed the LS5's spectacular ability to present a recording's space, depth, air, and detail. The LS5 threw before me a huge, deep, transparent soundstage. Moreover, the LS5 excelled at presenting a sense of space between the images, rather than fusing them together. It was as though there was a bloom of air around instrumental outlines that made the music more lifelike, less synthetic.

Audio Research apparently felt the original LS5 didn't live up to its potential: the preamplifier was replaced almost immediately after its introduction by the LS5 Mk.II, a fairly serious redesign of the product costing $4995. The LS5's 12BH7 tubes were replaced by Sovtek 6922 (6DJ8) types—the 12BH7s apparently became overly microphonic during shipment. Moreover, the Sovtek 6922 sounds great, and is available in quantity.

Next, the entire gain structure was overhauled. In the LS5, a solid-state switch put an 18dB pad in the signal path when in the 12dB gain setting. This switch remained in-circuit no matter what the gain setting. The Mk.II handles the two gain modes by a completely different method. ARC has eliminated both the solid-state switch and the pad, instead changing the open- and closed-loop gains simultaneously in the same ratio for both gain settings. This resulted in lower noise and more transparent sound. Indeed, making the LS5 quieter was a motivation for the redesign—some customers with very sensitive loudspeakers complained of noise. In addition, the op-amp–based DC servo was replaced by a DC feedback loop.

The LS5's Alps detented potentiometer has been scrapped in favor of a continuous-rotation, motorized Alps pot now used in all ARC preamps except the LS7. ARC claims the new pot not only sounds better, but also offers the ability to be remote-controlled. Remote volume control is a $500 option, either at time of purchase or as a retrofit. Although the pot is intrinsically motorized, the circuitry to drive the pot and the remote itself are what add $500 to the price.

A few other changes were made—power-supply tweaks and different capacitor brands—but the main differences are the new gain topology, different tubes, and elimination of the solid-state switching.

Sound: The LS5 Mk.II is clearly an improvement over the LS5. Although both preamplifiers have a close family resemblance, the Mk.II was more musical, the biggest difference being in the treble. The Mk.II's treble was smoother, cleaner, more refined, and better integrated with the rest of the spectrum, rather than sounding slightly separate from the music. In addition, the treble was less forward and incisive in the new design—a quality that better complemented the preamp's overall spaciousness. I also heard less grain, manifested as less spittiness on vocal sibilants, a more velvety violin sound, and a cymbal sound that was more like burnished brass and less like chromium.

The mids were also better portrayed in the Mk.II, sounding warmer and richer, with less forwardness. A slight edginess to brass instruments was ameliorated. Overall, the Mk.II was more harmonically coherent. The music had a greater sense of ease and flow through the Mk.II.

Nonetheless, I still wouldn't characterize the LS5 Mk.II as sweet, laid-back, or tubey. The preamp still has a trace of forwardness in the treble, and may not be quite as smooth and clean as the Sonic Frontiers SFL-2's high-frequency reproduction.

I also heard a marginal increase in transparency and soundstage focus—already the LS5's strong suits. Finally, there was less sonic disparity between the two gain modes. The original LS5 sounded so much better in the 30dB position that the 12dB mode wasn't worth using; the Mk.II made the 12dB gain mode sound as good as the 30dB mode.

The LS5 Mk.II made a synergistic match with Audio Research's VT150 power amplifiers. The VT150s' ultra-liquid mids and treble were a perfect complement to the Mk.II's highly detailed rendering. System matching is therefore vital in achieving a musically satisfying result; listen to the LS5 Mk.II in your system before making a final decision.

Conclusion: With the Mk.II revision of the LS5 preamplifier, Audio Research has taken an excellent preamp and made it truly world-class. The Mk.II expands on the LS5's strengths, and corrects the product's musical shortcomings. The more liquid mids, cleaner treble, and less incisive sound were all welcome changes. Fortunately, the Mk.II retained the LS5's ability to portray great space and depth, and, particularly, to reveal a wonderful sense of bloom around image outlines.

Overall, the LS5 Mk.II is a reference-quality preamplifier, and one with which I've spent many an enjoyable hour.—Robert Harley

Steven Stone listened to the LS5 Mk.II in July 1995 (Vol.18 No.7):
The Threshold T2 handled frequency extremes well. Highs lacked any etched quality, while low-frequency information was clean and well-defined. Only when I compared the T2 directly to the Audio Research LS5 Mk.II could I hear a very slight amount of additional high-frequency grain through the former. Low frequencies were slightly tighter on the T2 compared to the LS5, but the LS5 did have slightly more bass authority and bloom. Compared to the LS5, the T2's midrange was ever so slightly leaner, with the LS5 having a hair more lower-midrange energy.

The question is, of course, whether the T2 is subtracting harmonic information or the LS5 is adding extra harmonics. After much listening and thought, I concluded that the T2 did subtract a smidgen of harmonic juice from the midrange and bass, and added a hair of grain to the upper frequencies. The LS5 also had a more three-dimensional soundstage presentation. Both instruments and soloists had a certain dimensional palpability with the LS5 that was missing through the T2. The front of the soundstage through the LS5 began several feet behind the front of the speakers instead of at the speaker grilles, as with the T2.

A final difference between the LS5 and the T2 was that I was better able to hear into dense musical passages with the Audio Research. This was surprising, since transparency is a strong suit of the T2. Remarkably, the LS5 consistently surpassed it in rendition of inner details. Bear in mind that the LS5 is a purist design, lacking even a channel-balance control or any sort of display. The LS5 does have a remote, but it sports only Volume Up, Volume Down, and Mute. In terms of ergonomic ease, comparing the T2 to the LS5 is like comparing a modern Lamborghini to a vintage Bugatti.—Steven Stone

Steven Stone returned to the LS5 Mk.II in February 1996 (Vol.19 No.2):
Compared to other preamplifiers I've used recently, the Carver Research Lightstar Direct acquitted itself very well. The Carver had less personality than the Threshold T-2, lacking that robust midbass "slam" and ever-so-slight bit of top-end grain. The Carver also had somewhat better low-level detail, and a more neutral overall harmonic balance. Both preamplifiers were emotionally involving, and both did an excellent job of conveying the music's feeling. The Threshold reminded me of the Wheaton Triplanar Ultimate tonearm, with a more dynamic, even Rabelaisian, presentation. The Carver was more like a Clearaudio/Souther arm, with better low-level detail and more precise imaging, but less dynamic bravado.

Compared to the Audio Research LS5 Mk.II, the Carver had a slightly smaller soundstage coupled with a somewhat less holographic rendition of dimensionality. The Audio Research sounds a bit larger than life, and has a warmer, richer harmonic balance, especially in the lower midrange. The high-gain Audio Research has a much higher noise floor than did the Carver, which was silent as a grave. But the Audio Research's amazing dimensionality, liquid midrange, and explosive dynamic abilities give it an unforgettable sonic signature that may not be entirely neutral (as I discovered in my bypass tests), but is so musically satisfying that one is inclined to overlook its quirks while reveling in its sonic glories.

In some systems, the Audio Research's 33dB of maximum gain will make it indispensable. Anyone who is scared away from the LS5 II because of its lack of single-ended inputs should know that I've used it with a wide variety of single-ended sources via Neutrik and Boulder RCA/XLR adapters, with excellent results. It's still my favorite active preamplifier despite its low-level noise, lack of balance control, primitive remote, and excessive gain. Gorgeous sound has to count for something.—Steven Stone

Audio Research Corporation
6655 Wedgwood Road N., Suite 115
Maple Grove, MN 55311
(763) 577-9700

JRT's picture

(edited to clarify)

More properly noise sums as RMS sums of the contributions of the various sources of noise.

Random noise separately generated on different signal paths does not correlate in a downstream difference sum, so does not cancel.

Within an amplifier you get linear distortion and nonlinear distortion and inherent noise (also a nonlinearity), and in the many ways that these are modulated and shaped and combined.

This inherent noise is the noise that I am referring to. I am not referring to external interference.

Jim Austin's picture

Is your argument semantic? Are you questioning the use of the word "noise?" Whatever you want to call it, noise or something else, if an unwanted signal is induced--eg, due to changing e/m fields in the vicinity of a cable--is the same or very similar in the two wires, then the noise--or the portion of it that is the same--will cancel.

This is a well-established, widely accepted advantage of balanced connections. It is why balanced connections and circuits are ubiquitous in the pro-audio world, where longer interconnections are often needed.

Jim Austin, Editor

JRT's picture

To contend with EMI... Using balanced interconnection, a differential pair of conductors with impedance balanced (very similar) with respect to ground is designed such that the varying electromagnetic field through which the interconnection cable passes will induce similar currents on the pair, and those currents passing through those two similar impedances will cause similar change in signal voltage on the pair. In this case, being similar is a combination of one fraction of that change in signal being exactly the same on both conductors, and the remaining fraction of the change in signal being different on both conductors. The fraction of the similar change that is exactly the same is in the common mode and the remaining fraction is in the differential mode. The balanced interconnection terminates downstream into a differential input, which largely cancels the common mode, rejecting it, and passes the differential mode though the input of the amplifier.

Key in that balanced interconnection is in managing the unwanted change by getting most of it into the common mode, equal, same, so that the differential input can reject most of that common mode. The balanced interconnection most usually utilizes STP, shielded twisted pair. That is a pair of insulated wires twisted and wrapped with a shield covered by an outer jacket. The grounded shield reduces the EMI entering the pair of wires. The The EMF carrying the EMI induces current on the pair of wires, and the twist and the balanced impedance causes the induced currents to be more nearly equal. That EMI current through the balanced impedance causes the related change in signal voltages to be nearly equal on both wires, places most of the unwanted change in the common mode. The differential input passes the difference and blocks most of the common mode.

That described above is not the largely random inherent noise that I was referring to.

The inherent noise generated within the amplifier is largely a random nonlinearity. A differential pair of paths through a bridged dual mono pair of amplifiers will generate different random noise on each of the pair. Take the difference at the output and the random noise does not cancel, because it is random, without coherent phase, uncorrelated in the difference sum.

It is very much more complicated than this gross simplification. There are a lot of different types of noise, and any of it can be further modulated and shaped and combined. It is a big subject suitable for graduate level coursework, and I am not suitably qualified to author those textbooks.

Somebody more like Bruno Putzeys could teach all of us much.

Bogolu Haranath's picture

Speaking about Bruno Putzeys ....... The new NAD M33 integrated amp being shown in CES 2020, uses the new Purifi's 'Ultraquiet Amplification Technology' ....... M33 is scheduled to be available this spring 2020 ......... Jim Austin could review it :-) ......

John Atkinson's picture
JRT wrote:
A differential pair of paths through a bridged dual mono pair of amplifiers will generate different random noise on each of the pair. Take the difference at the output and the random noise does not cancel, because it is random, without coherent phase, uncorrelated in the difference sum.

If the noise in the two signal paths is uncorrelated but truly random, you still get some noise reduction in the differential output signal. This is because the sum of the uncorrelated random noise is 3dB greater than the individual noise signals compared with the 6dB increase in the audio signal level. In effect, therefore, you get a 3dB reduction in the noise level.

John Atkinson
Technical Editor, Stereophile

Jim Austin's picture
that you were disagreeing with something Harley wrote in the review. As far as I can tell, what you and Harley wrote are consistent. Jim Austin, Editor Stereophile
JRT's picture
Jim_Austin wrote:

I assumed that you were disagreeing with something Harley wrote in the review. As far as I can tell, what you and Harley wrote are consistent.

I took issue with something Harley had included in that article, which I thought was unintentionally misleading, and was feeding what I perceive to be a common misperception.

A dual mono system bridged to differential will cancel what is shared in common, but that will be mostly some of the 2nd order harmonic distortion, and almost none of the inherent noise generated within those separate gain stages. In reaction to his comment quoted below, I was only trying to point out that the inherent noise is not shared similarly in common, so does not really cancel.

Robert_Harley wrote:

The advantages of a preamplifier being truly balanced are the elimination of two active stages (the differential amplifier at the input and the phase splitter at the output) and the fact that any noise or distortion common to both phases of the balanced signal will cancel when combined.

It is true what he said that any noise shared in common will cancel, but it is also misleading because the vast majority of the inherent noise is not shared in common, not enough to matter much, because those two sets of inherent noise are randomly generated inside two separated amplifier functions prior to the differential sum at the end.

Bogolu Haranath's picture

According to Benchmark blog (see, balance connections), common mode noise is 3rd harmonic (odd-order) :-) .......

JRT's picture
Bogolu_Haranath wrote:

According to Benchmark blog (see, balance connections), common mode noise is 3rd harmonic (odd-order)

Do you have a link to that reference? I would like to read it.

I suspect that Benchmark, in referring to "3rd order" or "odd order", likely used the word "distortion" and did not use the word "noise", as nonlinear distortion and noise are two different categories of nonlinearities, and they very well understand that. Nonlinear distortion can also ride the common mode, not just noise.

Bogolu Haranath's picture

Jim Austin posted a link to Benchmark's blog in one of his replies on Benchmark LA4 pre-amp review web page :-) .......

Bogolu Haranath's picture

According to many audiophiles 2nd order harmonic distortion is quite pleasing to the ear :-) .......

Bogolu Haranath's picture

If you are talking about 'active noise cancellation' (ANC) technology used in some headphones ....... they use small microphones to pick up noise and send a 180 degree opposite phase signal to cancel the noise :-) .......

JRT's picture

in this.

Bogolu Haranath's picture

Your initial comment did not clearly specify ...... So, I posted my comments about ANC in headphones :-) .......

Bogolu Haranath's picture

BTW, as an additional note ..... Some automobiles are also using somewhat similar ANC technology to cancel the noise :-) .......

Bogolu Haranath's picture

Most of the headphone audiophiles don't like potential ANC interference for the FR of music anyway .......... They prefer 'passive noise isolation' instead, if needed :-) .......

tonykaz's picture

Hmm, I wonder.

If this thing is as good as the reviewer's adjectives it'll still be in his music system today. Is it?


does ARC gear go off as easily and quickly as it's tubes performance.

Reading stuff like this has me pondering who wrote it, probably an aspiring Marketing Exec.

I've taken in a wide range of ARC gear in Trade, none of it was anywhere near as good as the Product Reviewer's claims.

ARC is nice gear, I could easily live with an SP6 B thru E. but it's not as lovely as an Audible Illusion Modulus.

Tony heading for Home and a nice 83F swim in the pool.

ps. even so, I wish that William Z was still around.

spivechild's picture


JRT's picture

I find that the print editions of magazines are very compatible with the system that I use for reading those, which is me. I prefer to read and turn real pages rather than virtual pages. And if I hang onto some print magazines for a few decades, I don't have to be concerned about future incompatibility with reader software and future operating systems, only the space claim of the print magazines (which for me is admittedly considerable). If I cannot read the print edition, then I probably cannot read the computer screen.

Bogolu Haranath's picture

Is your computer screen 8k ultra, ultra hi-res, Dolby vision, IMAX enhanced? ....... Just kidding :-) ........

spivechild's picture

Says the guy responding in the comment section on a webpage.

New decade, new Stereophile. Let’s concentrate on.....print media! The only way to make sure Stereophile is flat line once all the baby boomers are dead or have cataracts which shouldn’t be long.

Jim Austin's picture
Your message has been received, loud and clear, by the editor and the publisher of the magazine--mainly because of the email you sent. The rest is spam, so please refrain from multiple postings in future. Jim Austin, Editor Stereophile
Ortofan's picture

... truly necessary, in that same era alternatively one could have purchased the $1200 Onkyo P-388F.
The P-388F also had unbalanced inputs (and outputs) - without the need for a separate box - as well as separate phono sections for MM and MC cartridges. For the price of the ARC unit, one could have afforded to include the M-388F power amp plus the DX-788F CD player.

OTOH, if you needed to spend the entire amount on a line stage with balanced inputs and outputs, then there was the Accuphase C-250.

Bogolu Haranath's picture

LS5 has just a touch of 3rd harmonic distortion ........ See, Fig.7, measurements ....... Do the Onkyo and Accuphase have that? :-) ........

Jason Victor Serinus's picture

Is everyone aware that this review is 26 years old?

Bogolu Haranath's picture

"The more things change, the more they remain the same" ........ Alphonse Karr :-) ........

JHL's picture

Surely everybody knows that musical pleasure derives directly from beating digital Stereophile about the head, neck, shoulders, head, face, and neck; that Bogu never, ever logs out; and that pedantry itself was invented in these comments threads.

Whatever joy an Audio Research component gave 26 years ago is completely irrelevant to the world in general, my good man.

Why, just ask us.

Ortofan's picture

.. joy?
Having owned the ARC preamp for the past quarter century or having opted for the far less expensive Onkyo unit and having invested the $5K price difference in an S&P 500 index fund, where that $5K would have grown to about $25K today?

Bogolu Haranath's picture

Money alone can't always bring happiness ....... OTOH, that $25K could buy the new ARC Ref. 160S ..... Not a bad idea :-) ........

JHL's picture

speculating on hindsight beats hifi hands down. Vaguely reminds me of the guy hectoring others with the wholly superior sound of the loudspeaker he's never built, the rubes.

Never change, digital S'phile commentariat, never change.

Ortofan's picture

... none of the above.

The stereotypical audiophile would never be satisfied with the less expensive piece of equipment (and letting the excess funds accrue interest in some account), nor would they have kept the ARC unit(s) for several decades.

Instead, they would have continually failed to summon up the courage to step off the perpetual trade-in/trade-up merry-go-round for fear of possibly missing out on something better.

Bogolu Haranath's picture

If we humans stopped looking (and making) for 'something better', we would still be living in caves (not wine caves) :-) ......

JHL's picture

As if it's still somehow not clear, digital S'phile commentariat are the only thing standing between order in the universe *and people doing what they want with their money*.

Oh the humanity.

Jim Austin's picture

>>As if it's still somehow not clear, digital S'phile commentariat are the only thing standing between order in the universe *and people doing what they want with their money.

So you think that if it were not for the commentariat, people would not do what they want with their money?

Jim Austin, Editor

JHL's picture

I doubt the chronic second-guessing contingent sees far enough past its black and white preoccupation with perceived sins and ills to realize normal people aren't listening. To it, I mean.

Glotz's picture

They still rock!

I've heard these ARC power amps several times, and they are completely musical and throw a pretty convincing illusion. They may have possessed a slightly whitish character with some noticeable noise vs. more modern equipment, but they are testament to the ARC lineage and it seems like splitting hairs for arguments' sake.

They were fantastic for it's time, even more so with the Ref600's! I heard this alongside the MP-1 prototype around the same time (the no display/switch-only version in '95/'96). I can't remember the exact name of it, but I think JGH reviewed it? (Searching for that is a 'pita', btw.)