Audio Research LS5 preamplifier & BL2 input controller

From the front, the LS5 looks identical to Audio Research's popular LS2: two knobs on either side of the Audio Research nameplate, and a row of toggle switches along the bottom. But that's where the similarities end; the LS5 is a completely different animal from the LS2, or even the balanced LS2B.

For starters, the LS5 is fully balanced from input to output. To understand the difference between a preamp with balanced inputs and outputs and a truly balanced preamp like the LS5, let's look at how most balanced input and output preamps process a balanced input, using the LS2B as an example.

Although the LS2B has balanced inputs and outputs, the input signal is converted to single-ended by a differential amplifier at the input. The preamp then handles the internal signal as single-ended, with one gain stage per channel and one volume-control element per channel. The single-ended signal is then converted back to balanced with a phase splitter just before the output jacks. This technique adds two active stages to the signal path.

By contrast, a fully balanced preamplifier like the LS5 handles the signal differentially from input to output—no differential amplifier or phase splitter. This method requires double the circuitry: a gain path for each phase of the balanced signal, and a four-element volume control (± left channel, ± right channel). Moreover, the noise, distortion, and gain must be identical between the two phases. Any difference between the phases will become part of the signal. 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.

The LS5 has six pairs of balanced inputs, two pairs of balanced main output jacks, and one balanced tape loop. The front panel has an input selector switch, volume control, and four toggle switches. A green LED indicates when the unit is turned on, dimming when the LS5 is muted by a front-panel toggle switch, or is in automatic mute when the unit is first turned on.

One of the toggle switches selects the amount of gain provided by the LS5—either 12dB or 30dB. If you're used to using the LS2, you could be in for a surprise when using the LS5; the LS5's gain selector switch is in the same location as the LS2's mute switch. It's easy to throw the LS5's gain switch thinking you're muting the signal. Instead, the switch adds another 18dB of gain. Yeeow.

My initial auditioning suggested that the LS5 sounded better in the 30dB position, so that's what I used for subsequent listening. This was a little too much gain for high-output source components. For example, the Sonic Frontiers SFD-2 digital processor's maximum output level of 6.65V (RMS with a full-scale digital signal, balanced) forced me to use the LS5's volume control around the 9 o'clock position.

Unlike all Audio Research preamps made in the past ten years, the LS5 is a pure tubed design. Though there are transistors and op-amps inside the LS5, these are not in the main audio signal path, apart from one FET in series with the audio signal, used as part of the gain switching.

The input stage consists of both halves of a Sovtek 6922 (a 6DJ8 dual triode), followed by both halves of a 12BH7A dual triode. The output driver is half of a 12BH7A, capacitively coupled (with high-quality MIT caps) to the output jack. This circuit is repeated for the other half of the balanced signal. In all, the LS5 uses ten tubes (four 6922s, six 12BH7As, footnote 1).

The impressive power supply fills the entire left-hand side of the chassis. A toroidal transformer is mounted vertically, supplying five bridge rectifiers from separate secondary windings. The 290V B+ supply uses discrete regulation, with Rel-Cap and Wonder Cap capacitors.

The LS5's build quality is excellent. Between the extensive power supply and circuitry using ten vacuum tubes, the LS5 is jampacked with components. As you might expect, it runs quite warm.

BL2 input controller
The fully balanced LS5 has no single-ended inputs. Audio Research believed that the LS5's fully balanced design would be compromised by including single-ended inputs in the same chassis. Consequently, they designed the companion BL2 balanced line driver to convert single-ended source signals to balanced. If your system has any single-ended source components, you'll need the BL2 as a companion to the LS5.

The BL2 is a slim chassis about half the height of Audio Research's preamps. The BL2 looks and functions just like a preamplifier, but with only 6dB of gain and no volume control. Seven pairs of single-ended inputs are provided, along with one balanced output and two unbalanced tape outputs.

Inside, the circuit uses JFETs at the input/phase-splitter stage, followed by an LT1223 op-amp for each phase of the balanced signal. The output line driver consists of a complementary pair of bipolar transistors, again one pair for each phase of the balanced signal. The circuit is direct-coupled, with DC offset trimmed out.

The power supply generates ±20V for the BL2's gain stages. A combination of IC and discrete regulation is employed, with FETs used as the series pass transistors on the ±20V rails. The power supply uses WIMA caps for the audio circuitry supply, and electrolytics for the timer, mute, and other housekeeping circuits. The circuit and power supply are quite simple and don't take up much real estate; the BL2 has a fairly simple task.

Listening to the LS5
I've used Audio Research preamps nearly continuously for the past three years and greatly enjoy their straightforward layout, ease of use, and quality feel of the controls. The LS5 continues this tradition.

When I put the LS5 in my system in place of the LS2B, I didn't expect much of a change in the sound; the LS2B is an excellent preamplifier. It was immediately obvious, however, that the LS5 was a significant step up over the LS2B.

First, the LS5 had a much warmer, richer, more full-bodied sound compared to the LS2B. The entire bottom end was bigger, with a tremendous sense of bloom in the bass. The LS2, by comparison, was leaner and drier, with less air. This isn't to say the LS5 was tubey or overly ripe; instead, the LS5 revealed more of the space and bloom in recordings (when called for), with a fuller rendering. Bass extension was also deeper, with a greater sense of weight and power.

The LS5's treble was a significant improvement over the LS2B's. The latter's slightly whitish grain was replaced by the LS5's liquidity and smoothness. The all-tubed LS5 was outstanding at presenting instrumental timbre without grain or etch. This contributed to the LS5's less analytical-sounding rendering. Despite being smoother, more relaxed, and less up-front in the treble, the LS5 revealed a full measure of musical detail.

I also liked the LS5's more laid-back perspective. The music was less forward—particularly in the mids—and set back behind the loudspeakers. The LS5 put more distance between listener and music, giving a feeling of ease and relaxation. Although the LS5's perspective was easygoing, music had a sense of palpability, life, and immediacy—a rare combination.

The LS5's soundstaging was spectacular—transparent, deep, layered, and infused with a beautiful sense of bloom. This is another quality that set the LS5 apart from the LS2B: the LS5 had a much greater sense of spaciousness, air, transparency, and bloom. The impression of individual instruments hanging in space was extraordinary. I heard none of the thickness and congestion sometimes heard from even high-priced preamps. Images were clearly delineated and focused, yet not in an analytical way. What made the LS5's soundstage truly special, however, was its sense of air surrounding instrumental outlines. This bloom infused the music with a feeling of realness; the LS5's presentation was the antithesis of sterile, canned, or "hi-fi"—the music had space to breathe and come to life.

Longer-term listening, particularly in comparison with the new $3495 Sonic Frontiers SFL-2 [currently under review by Russ Novak—Ed.] revealed the LS5 still to have a very slight whitish quality to the upper mids and treble. Nevertheless, I found the LS5's combination of qualities—liquid mids, smooth treble, warm bass, slightly laid-back perspective, and wonderful openness—musically addictive. The LS5 also excelled at preserving the differences in perspective on different recordings.

Listening to the BL2
Evaluating the BL2 was a challenge. Had I simply run the balanced outputs of a digital processor into the LS5, and the unbalanced outputs into the LS5 via the BL2, I'd have ended up comparing the processor's balanced and unbalanced outputs (and an additional run of interconnect) more than the BL2. To resolve this quandary, I compared the unbalanced outputs of the SFD-2 processor and the Vendetta, feeding the BL2/LS5 to the Sonic Frontiers SFL-2. (I used the ARC-supplied balanced interconnect between the BL2 and the LS5.) With a good feel for the differences between the LS5 and SFL-2 in balanced mode, this comparison would highlight the BL2's effect on the sound.

I found the BL2 fairly neutral, although it did add a slight brightness to the sound. The treble lost some of its purity, sounding more forward and a little coarse. The fine layer of grain was marginal, but audible when compared to the purity of the LS5 on its own. The sound was a little drier, and some of the bloom was gone. Some of the LS5's liquidity was diminished, and the presentation was more analytical and less relaxed. The BL2 made the LS5 sound a little more like the LS2B than the LS5 by itself—but still significantly better than the LS2B.

The Audio Research LS5 preamplifier is a superbly musical product. It provides the best of what tubes can do without the euphonic colorations of some tubed preamps. In relation to Audio Research's very successful LS2 and LS2B, the LS5 clearly operates at another level of performance (footnote 2).

Footnote 1: LS2 and LS2B owners can significantly improve the sound of these preamps by replacing the standard Chinese 6DJ8 with the excellent Sovtek 6922.

Footnote 2: As this issue went to press, we were informed by Audio Research that the LS5 has been upgraded. Robert Harley will be comparing the two generations of the LS5 in a Follow-Up.—John Atkinson

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.)