A visit with the Audio Research D-52B power amplifier

With the arrival of summer, a young man’s (*cough*) fancy turns to power amplifiers. Okay, maybe not. Lately I’ve been more interested in looking at wooded property to buy, walking on the beach and trying to remember what it actually feels like to be a young man. I’ve also been modernizing my 1948 Bungalow into something a little more tasteful. To my eyes, a good-looking stereo always helps and since my recently acquired Audio Research SP-7 needed a playmate, I decided to purchase a matching amplifier.

Trolling through Audiogon the past few months has been interesting because Audio Research gear certainly holds its value. You see, I wanted an amplifier for a future speaker upgrade - perhaps Magnepans – so I was holding out for something with a bit of power. After passing by several expensive amplifiers, I finally gave in and purchased an Audio Research D-52B for only $350.

The original D-52 was introduced in the heady days of 1978 – famous for disco, punk rock and Jimmy Carter. The D-52B revision came out in 1979 and originally sold for a then expensive $995, later increased to $1295 and then $1395. Rated at 50Ws per channel into 8-ohm and only 80Ws per channel into 4-ohms, the D-52B isn’t exactly a powerhouse. But under the lid, you can see a massive transformer flanked by a large number of power supply capacitors. This is one underrated amplifier that should be able to deliver a nice wallop of short-term peak power.

Early Audio Research solid-state gear was met with derision by the audiophile press at the time. That is hardly unexpected since ARC was one of the few carriers left of the mystic tube flame. The introduction of solid-state gear certainly made them few friends and based on the number of Audiogon ads, they have certainly sold less SS than tubes. When I bought my solid-state Audio Research SP-7, sound quality was actually second-tier in my decision. I just wanted something reliable with quality long-lasting controls. However to my surprise, the SP-7 not only worked well, it sounded great.

So how does the Audio Research D-52B sound? Let’s find out.

When I first received the D-52B from the FedEx, I was surprised by the weight. This amplifier weighs in at a nice 39 pounds but still has a relatively compact size. As usual with ARC gear, build quality is high. Removing the lid revealed the previously mentioned large power transformer and (in this case replaced) power-supply capacitors. There are also four output devices per channel, a quality circuit board, and the much-hated but mysterious Audio Research “Analog Modules.”

The first stop was my second system which is to be the eventual home of this amplifier. I removed the Mitsubishi DA-A10 and installed the Audio Research D-52B. Since neither of these amplifiers has a proper power-supply switch, I used the switchable powered AC jack from the Audio Research SP-7. The two ARC pieces with their silver-faces, black handles and high-quality lettering make for a handsome pair. Turning on the SP-7, I was greeted with a nice green LED glow from the D-52B.

The KEF Q-60s in my second system are remarkably forgiving . They aren't all that detailed and the treble has a nice roll-off which helps out the worst of recordings. But even through these limitations, I can tell that the D-52B has more treble detail and apparent speed than the Mitsubishi DA-A10. Dynamics through the 8" Uniq driver are very good as is the overall sound. Though not as "rich" and "full" as a vintage tube amplifier, the D-52B seems to be quite transparent and resolving. I won't mention soundstaging or depth since this second system setup is woefully inadequate for that type of listening because the speakers are too close to the wall and the source quality is too low. At this price level, I'm listening for frequency aberrations and general fidelity. Paired with Audio Research SP-7, this is a surprisingly good system for the money. I'm looking forward to replacing my KEFs with something even better, bringing the my second system even further along.

The second stop was my main stereo rig. The Magnepan 1.6QRs are notorious for their current-sucking demands, so I was interested in seeing how this little amplifier would fare. The last amplifier I tested here, the B&K ST-140 rated at 105WPC, was capable enough but was a notch below the Threshold in sound quality. As usual, removing the mighty Threshold S/500 from the rack was a chore. In comparison the D-52B looks like a pipsqueak but sometimes good things come in small packages.

This turned out to be an unfair comparison against the Threshold S/500 which has five times the amount of available power. At higher listening levels, I could tell the D-52B was running out of steam. Mind you, it never clipped harshly, but dynamics became squashed and the soundstage flattened. However, at moderate listening levels or with less dynamic material, the ARC amplifier turned out to be quite pleasant. Though detail and depth seemed less than the Threshold amplifier, the overall sound was still quite musical. An example of this is my original pressing of Neil Young - Tonight's the Night. Through the Threshold amplifier, I can really get a great sense of the room and it almost feels like you are there. With the Audio Research D-52B the lower resolution leads to less space and depth, minimizing the illusion. However, along the width of the soundstage, every instrument kept its proper place. Voices were very natural sounding as was the treble extension. From Blue Nile to Neil Young, the ARC was a competent amplifier that only suffered when asked for more power than it could deliver.

The Audio Research D-52B is by no means a perfect amplifier, but it is much better than I expected. Since this is a relatively ancient design, I'm also willing to cut it a little slack. With only 50Ws of power, it's really not up to the task of driving inefficient speakers unless you have a small room or prefer lower listening levels. It's also not a particularly resolving amplifier or one that captures the total possible depth from a recording. However, it certainly doesn't deserve the bad press it has received - at least from a sonic point of view - I will have to wait and see about the reliability. But nonetheless, for a second system or for one just built around musical enjoyment, the Audio Research D-52B is an excellent performer. Recommended but with caveats.

Second System:
Preamplifier: Audio Research SP-7
Amplifier: Mitsubishi DA-A10
Analog: Dual CS-5000 turntable - Audio-Technica AT95E cartridge
Digital: Pioneer DVD-V7400
Speakers: KEF Q60
Speaker cable: Canare 4S11 Quadlink
Interconnects: Cardas Crosslink

Main System:
Preamplifier: Threshold FET-10/HL
Phono Preamplifier: Audio Sector Phono Stage
Amplifier: Threshold S/500
analog: VPI HW19 MkIII with SDS - Rega RB300 with Incognito wiring - Denon DL-103R
Speakers: Magnepan 1.6/QR with Sound Anchor Stands
Speaker cable: Kimber 4PR/8PR Bi-wire with banana jacks
Interconnects: Cardas Cross and Cardas Quadlink 5C

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Fixing a Speed Issue with the Dual CS-5000 turntable

My Dual CS-5000 turntable has been having speed issues of late. The platter speed would start out slow and take time to get up to speed. Sometimes in the middle of an album, the platter speed would also minutely drop, effecting the tone of the music. A quick perusal of Google and I found that the power supply capacitors for the DC motor are known to go bad. Since electrolytic capacitors of this sort are inexpensive, I decided to go ahead and replace the originals.

To replace the power supply capacitors - first remove the lid, mat and turntable platter. Also remove the rubber belt at this time. Make sure the turntable is unplugged before proceeding.

The capacitor circled in GREEN is a 2200uF/25V unit. Polarity is indicated on the board, but as a note, the positive side is closest to the spindle. Removing it is easier with a solder-braid or sucker - if those tools aren't available, you can pull on the cap and slow ease it out by alternating your solder iron on each leads. Don't go too hot with your iron or you will risk damage to the PCB board.

The capacitor circled in RED is a 3300uf/35V unit. It's built different than the other unit - with three ground lugs on the edge, soldered onto the board. The positive lead is in the middle, soldered in the board. To remove, I cut out the top lugs and removed the solder on the bottom lug and positive lead. For replacement, I tied the negative lead to the topmost ground lug position closest to the spindle. The positive lead was obviously soldered to the original positive position.


I hate modifying or fixing gear that I really like, but any fears were laid to rest when I fired it up after reassembly. Now the turntable gets up to speed faster and doesn't have any tonal variance issues. Hurrah!


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A visit with the ATN95HE stylus

The Audio-Technica AT-95E cartridge is a budget best-buy. For only $49, it has a great sound that works well for entry-level turntables. With my Dual CS5000, I've put many hours on my AT-95E and enjoyed every moment. But (and there are always caveats at this price range), overall detail and treble extension is certainly lacking compared to more expensive offerings. The sound was very "midrangey" and a little muffled up on top. It is, however, a great tracker and does well with inner-groove distortion.

Since my cartridge was getting a little worn from use, I decided it was time for an upgrade. At only $59.95, I decided to just replace the stylus with LP Gear's AT95HE. The whole cartridge is also available. This "hyperelliptical diamond stylus mounted on a thin-wall Zualam tubular cantilever" was an easy swap since I just had to pull the old stylus out and replace it with the new one. The new cantilever/diamond is more delicate looking and should (in theory) track better too.

The great midrange character of the original is still evident, but treble extension is now much, much better. Perhaps it is just the effect of the treble extension, but detail and transparency has been bumped up a notch. There is an overall refinement to the sound that starts to knock on the door of true audiophile quality.

Overall, a great upgrade to an already great budget cartridge. Very recommended!


Second System:
Audio Research SP-7 preamplifier
Mitsubishi DA-A10 amplifier
Dual CS-5000 turntable with Audio-Technica AT95E cartridge
Pioneer DVD-V7400 DVD player
KEF Q60 speakers
various budget cables

A Visit with the Mitsubishi DA-A10

The Mitsubishi DA-A10 is a classic solid-state amplifier boasting some heavy industrial looks, dual mono power supply, input level controls and screw-type binding posts. Produced from the late 70s to the early 80s, the DA-A10 has a certain aesthetic appeal that I've always found desirable. Perhaps it is the McIntosh-like power transformers, black metalwork and the large can capacitors. Rated at 100WPC into 8 ohms and only 130WPC into 4 ohms, this amplifier isn't exactly a high-current powerhouse, but it certainly has more power than the other amplifiers in my second system setup.

With the recent addition of the Audio Research SP-7 preamplifier, I decided to buy another budget amplifier until I could score the right matching ARC amplifier. As soon as I saw the Mitsubishi amplifier on Audiogon, I pulled the trigger and had it in my sweaty paws within a few days. Unpacking the box revealed a heavy well-made amplifier that has a certain menace. Upon first seeing this beast, my mother-in-law even started asking questions about it. This is rare since my stereo hobby is mostly ignored by my in-laws.

So how does this amplifier sound? For the year, surprisingly good. Not to knock early solid-state, but the real golden era of SS amplification didn't really seem to take off until Krell, Levinson and Threshold started going. I won't even try to compare this amplifier to my Threshold S/500, but in my second system the Mitsubishi DA-A10 has a nice even-handed tone, great bass response and non-fatiguing treble. It's a great match with the Audio Research SP-7, getting more bass and dynamics out of my KEF Q60s than I ever imagined they could do. The sound is very smooth but not in old tubey way - just musical and engaging.

It runs really cool too with the heatsinks getting just barely warm at all. Of course these heatsinks are huge and I imagine there isn't much Class A power coming out of the output transistors.

Due to the age of this amplifier, I will at some point have to go through and replace some power supply capacitors. But right now I'm enjoying this little beast.



Second System:
Audio Research SP-7
Dynaco ST-80 refurbished or Adcom GFA-535
Dual CS-5000 turntable with Audio-Technica AT95E cartridge
Pioneer DVD-V7400 DVD player
KEF Q60 speakers
various budget cables
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A Visit with the Audio Research SP-7

Audio Research is a company that is known, along with Conrad-Johnson, for keeping the vacuum tube flame alive during the 70s and 80s. Back then there weren't many competitors in the lonely market of new audiophile tube gear - in the United States you had to go vintage, which many of my friends did, or spend the big money and buy an ARC or C-J piece. All of that has changed with the sudden rush of the Internet-90s and the increasing popularity of tube gear.

The Audio Research SP-7 was an odd duck - it's solid-state and is historically sandwiched between the famed SP-6 and SP-8 tubed preamplifiers. Audio Research was looking to expand their market share and offer something to the solid-state aficionado. But it would appear that this move did not have much success as their solid-state gear back then never sold in great numbers. And that is hardly surprising considering the near-religious mania of many vacuum tube listeners. It's either tubes or the highway - I know since I used to be in that camp myself. With Threshold and the Audio Sector phono stage, my views have softened in this matter since a good design is still good no matter what the technology is.

So how good is the Audio Research SP-7? Let's find out.

We've been remodeling our living room with a new, more modern look. I decided some different gear for my second system was in order - something that would fit the blond Ikea Expedit shelves I use to store my records. I selected an Audio Research SP-7 available on Audiogon almost solely on the looks and their renowned reliability. It didn't hurt that I've always admired my friend's SP-8.

The SP-7 is full-function preamplifier with a moving-magnet phono stage, tape outs, heavy duty case and controls that inspire confidence with their quality movement. Inside there are a bevy of capacitors and transistors on a thick PCB, all supporting the 'mysterious' potted Audio Research Analogue Modules. These are rumored to be op-amps made from discrete components, but I haven't found any conclusive evidence yet.

Hooking up the SP-7 to my second system, I found the sound to be much better than the Adcom GTP-400 or the Dynaco PAT-4. Bass with the KEF Q60s seemed to go lower and the overall sound was very clean, detailed and fast. Definitely not tubey at all but the sound was way less grainy than the other SS gear. It was a really good match with my Dual turntable.

On the main rig, I am using a low-output Denon DL-103R and was not able to check out the phono stage on the SP-7. That was handled by the Audio Sector phono stage while the SP-7 did linestage duties, temporarily replacing my beloved Threshold FET-10/HL. The FETs in the Threshold give a darker, almost tubey sound while the ARC had a brighter, more forward effect. The SP-7's treble was still good with no solid-state etchiness. The midrange was very detailed too. Depth and soundstaging was slightly more squashed than the Threshold while the bass for both was pretty much on par. In the end I was surprised how good the Audio Research SP-7 sounded considering the rather negative press these pieces get.

As far as looks and functionality goes, I couldn't ask for much more in this price segment. To further the looks of my second system, I'll be on the hunt for a matching Audio Research solid-state amplifier, so stay tuned.

Second System:
Dynaco PAT-4 refurbished or Adcom GTP-400 tuner preamplifier
Dynaco ST-80 refurbished or Adcom GFA-535
Dual CS-5000 turntable with Audio-Technica AT95E cartridge
Pioneer DVD-V7400 DVD player
KEF Q60 speakers
various budget cables

Main System:
Threshold FET-10HL linestage
Audio Sector Phono Stage
Threshold S500 amplifier
VPI HW19 MkIII turntable - Rega RB300 with Incognito wiring - Denon DL-103R
Magnepan 1.6/QR speakers with Sound Anchor Stands
Kimber 4PR/8PR Bi-wire with banana jacks
Cardas Cross and Cardas Quadlink 5C interconnects

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