July 05, 2023 10 min read

Part-time Audio Arch Mono Block Review

by Sam Rosen


There are certain amplifiers that audiophiles know by name because of their legendary status–the McIntosh MC240 and the Harmon Kardon Citation V are two examples. But there is another amplifier that is even more well known, the Harmon Kardon Citation II, and today we will look at the rebirth of the this amplifier in the form of the ampsandsound Arch Monoblock amplifiers.

Words and Photos by Sam Rosen

Before I start the ampsandsound Arch Monoblock review, I want to provide a little history. The Citation II was original sold as a kit which included three legendary potted transformers spun by the Manhattan Transformer company, four KT88s in a push pull configuration, and a full pentode front end with three 12BY7A tubes per channel. Sporting nearly 40db of negative feedback, the amplifier was not only powerful but incredibly linear with variations being built as lab grade instruments. The circuit was complex, especially for a kit amplifier, and calibration meant setting the bias, DC, and AC balance. It ran tubes hot, right at the edge of their operating point, as it existed in a time where great tubes were plentiful.

The Citation II has always been a bit of a puzzle to me. For an amplifier as well-known as it is, and with a cult following as strong as it has, I had always wondered why no one made a modern kit remake or simply a new amplifier based on its circuit. It turns out the answer lies in the transformers, which are quite bespoke, and the inherent complexity of the circuit. Because of this, it looked like the Citation II would ride slowly and gracefully into the pages of history, forgotten and lost as the transformers failed and the repair expertise aged out of the business.


The ampsandsound Arch Monoblock Connection

Luckily for us, Justin Weber and the ampsandsound team had a different idea for the future of the Citation II. Justin always loved the Citation II and Citation V, and he has rebuilt and repaired them many times and always loved their sound. A few years ago Justin took his first step into a new world, rebuilding the Citation V as the Zion monoblocks with two primary goals: don’t change the circuit, and execute the build with no compromises. The resulting Zion monoblock amplifiers are the best amplifiers I have ever heard and are currently my reference amplifiers. Once the Zions were built, Justin then turned his attention of the Citation II.

The Citation II, as we discussed above, would be a much harder undertaking for ampandsound, but it was a passion project for Justin and several years later it is finally ready. Transformers were custom designed and custom wound by one of the best transformer companies in the business, and the original circuit was carefully studied, and optimized with the greatest care.

Like the Zion Monos, the Citation II remake–known as the ampsandsound Arch Monoblock–would not simply be a re-build. Instead, it was an undertaking to show respect to the hi-fi legend that was the Citation II. This meant separating the left and right channels into their own monoblock chassis, hand assembled with turret boards, with every part and piece over-spec’d by at least 100%. A lot had changed since the 1960s, and because of that Justin wanted to ensure that it not only ran KT88s like the original but also the now common but exceptional KT150.

I had been hearing about the development of these amps for quite some time, but finally a few weeks ago, ahead of AXPONA, two Seahorse hard cases arrived at my doo. As I popped open the top of the case, I saw the ampsandsound Arch Monoblock for the first time, and I witnessed the rebirth of a legend.


ampsandsound Arch Monoblock: First Impression and Build Quality

For those who have read other reviews that I have written, you know I have a soft spot for
ampsandsound. Justin is friend and has been for some time. I have owned or listened to nearly
every single amplifier he has built since 2018 and I have yet to hear a bad one.

However, I was not prepared for what to expect when I opened the Seahorse case. As I removed the packing foam, I went to pick up the first ampsandsound Arch Monoblock amplifiers and while my body tried to move it, the Arch had different plans and simply laughed at me. Each Arch weighs around 100 pounds, with the majority of its weight coming from the incredibly large custom wound transformers and the cold rolled steel chassis.

Once I got the help of my wife, I was able to remove one ampsandsound Arch Monoblock from its case and take a closer look at it. With every new amplifier in ampsandsound’s metal series, Justin continues to improve the finish quality. The first thing I noticed was the seaming of the metal chassis, which is more or less perfect. This is something I just do not expect from a hand-assembled product. The powder coating is also very well done and has a matte/satin finish to it that has just the right amount of texture.

The ampsandsound Arch Monoblock amplifiers are the first set of amplifiers that Justin has built with tube cages. I personally have never liked tube cages and normally immediately take them off and put them back into their shipping box. The tube cage ampandsound designed for the Arch is stunning, however, and it weights way more than you would expect, and the contrasting silver mesh and solid steel frame make it a sight to behold in person. I liked the cages so much that I decided to leave them on the amplifiers the entire time I had them.

Spinning the amp around, you will find RCA and XLR inputs. These are single-ended amps, but the
XLR input uses a balanced input transformer that properly sums the positive and negative legs
of the balanced signal, and in doing so retains much of the benefits that you normally achieve with fully balanced amps (noise rejection). The input transformer also isolates the amp from the source and helps prevent grounding issues and ground loops. There are three supported impedances, 4 ohms, 8 ohms, and 16 ohms, making this amplifier compatible with nearly very commercially available speaker. With output power exceeding 60 watts with KT88s, and 80 watts with KT150s, you will never be left wanting for more power.

There is a fixed bias selector switch on the back of the ampsandsound Arch Monoblock that lets you toggle between the KT88/6550 setting and the KT150 setting. Like the original, both settings run tubes hot, but the KT88 setting will show respect your vintage tubes if you choose to use them with his amplifier. On the other hand, the KT150 setting is meant to drive the 150 to its limits and makes the assumption that the added performance is worth the shorter tube life. This calculation in my opinion does make sense given the KT150s are a new production tube and readily available.

Removing the tube cage of the ampsandsound Arch Monoblock reveals five tube sockets, two for the KT88/KT150 and three 9 pin sockets for the 12BY7As. The 12BY7A is an awesome 9 pin pentode with extremely wide bandwidth (north of 40,000hz). Harmon Kardon chose this tube to be the input tube on the Citation V and the input/phase splitter tubes for the Citation II because of this incredibly wide bandwidth and the tubes’ linear nature. ampsandsound chose to keep the original front end in the Arch as removing it would be an insult to this great amp’s legacy.

The only negative is that there are no modern reproductions of the 12BY7A and you more or less need three matched pairs to run your ampsandsound Arch Monoblock amplifiers. The good news is that the tube itself is incredibly robust and will last a very, very long time, as there are even still Citation IIs with their original 12BY7As going strong. On top of that, it is still possible to buy replacements from eBay and reputable tube dealers. I myself own about 20 pairs for my Citation V and they are one of the least expensive tubes I collect.

Like everything else I have ever received from ampsandsound, the amplifier was incredibly well
packed and I always appreciate that they use Seahorse cases as it provides much better protection than an ordinary box, and it will stand up to the test of time and storage. The amplifiers were pre-calibrated, and each tube and socket was labeled, making setup a breeze. The hardest part of the setup experience was lifting the ampsandsound Arch Monoblock into my audio rack, but the results were well worth the effort.


Review System

Amplification: ampsandsound Zion Monos, ampsandsound Arch Monoblock amplifiers
Source/Pre: dCS Rossini
Power Conditioner: PS Audio P12
Speakers: Zu Audio Soul 6, Zu Submission MK II
Cabling: Wywires Platinum Interconnects, Wireworld Mini Eclipse Speaker Cable, Wireworld
and Wywires Power Cords

Listening Impressions

When I spoke with Justin prior to receiving the ampsandsound Arch Monoblock amplifiers, he told me that in his opinion the Arch Monos were more neutral than the Zions and that they were faster and provided and extra layer of resolution. So, as I sat down after letting the Arch Monos warm up, I was curious what I would hear.

In general, I think Justin got it right. The ampsandsound Arch Monoblock amplifiers are incredibly nimble, and they work more like surgeon with a scalpel or a foil fencer than a traditional sword fighter. Every detail was highlighted, and the nuances such as the rattling of the high hat stand could be heard in a way that simply was not as evident with the Zion Monos. Tonally, the amplifiers are cooler than the Zions, with the Zions providing a richer and more harmonic sound compared to a nearly solid state neutral tone that the Arch provides. Personally, I prefer the richer slightly warm tone of the Zion Monos but I was left amazed at the neutrality and details of the Arch. I was especially amazed four hours later when I realized I had no listening fatigue. In general, I am very sensitive to neutral or bright sounding equipment, and the ampsandsound Arch Monoblock amplifiers delivered all of the detail and clarity with none of the traditional fatigue that normally comes with it. Consider me stunned.

As I sat back and listened to Mika’s Live at Brooklyn Steel, which is one of my favorite albums, I found that I had a new appreciation for the drummer and bass player. In the past I had always noticed their presence but when Mika himself took center stage, and my attention was mostly fixed on him. With the ampsandsound Arch Monoblock, Mika’s presence was not reduced, but the details from the bass and drum player came forward. The stereo image drawn was significantly enhanced. This was true for every song on this album. Each one that played left me noticing new nuances that were never as obvious. “Love Today,” on that same album, easily produced one of my favorite renditions of that song, an engaging roller coaster from start to finish.

Listening to Yello’s The Eye, I really saw the speed of the ampsandsound Arch Monoblock amplifiers come to life. Each drum hit was clear, concise and exact. Sound seems to simply start and stop, and to continue with analogies I would compare it to a ballerina instead of break dancer. However, just imagine that the ballerina was as fun to watch as a break dancer. That is the thing with the Arch Monos–they were simply fun, and they were fun even when they were exacting and precise, and this is what makes them special. Listening to “Indigo Bay,” the Arch Monos painted a soundscape that enveloped the entire room. Each bass note reached low and the synth tracks had just the right amount of bite. It was enthralling.

Wrapping up my listening impressions, I listened to Cat Steven’s Teaser and the Firecat,
specifically the song “Moonshadow.” The bite of the guitar was palpable but never overbearing. I was able to turn the volume up to concert levels and at no point did the soundstage collapse nor did the detail ever change form pleasant to fatiguing. The final guitar round at the end of the song was especially impactful. The volume raises about 30% and the mic on the guitar becomes particularly hot. Normally I am reaching for the volume, but with the Arch Monos I simply sat back and let them do their thing, smiling the entire way.


Technical Impressions

The original Citation II was a technical marvel, and ampandsound Arch Monoblock amplifiers deliver on that legacy. With measured THD numbers of .028% at 5 watts and .051% at 60+ watts for KT88s, the distortion numbers are exceptional for a tube amplifier, and to be frank, for any type of amplifier. While I do not believe human hearing is that sensitive to THD (in comparison to other things) I am left wondering if the low distortion figures were the reason for the perceived clarity difference.

In either case, have no doubt that with the ampsandsound Arch Monoblock you are not only getting a beautifully built and incredible sounding amplifier, but also a technically proficient one as well. While I do not have the newest equipment, I do own a THD meter and use it to calibrate my
amplifiers, and I test all amplifiers that I review with it. I can confirm that my tests were in line with what ampandsound reported.


ampsandsound Arch Monoblock: Concluding Thoughts

ampsandsound has been busy over the last several years. They focused on personal audio, and then re-visited their roots with two channel audio. They have built out a line of reference amplifiers based on classic American designs executed at a level rarely seen in a purchasable product. The ampsandsound Arch Monoblock amplifiers are simply the latest success for the company, and those who are fortunate to listen to them will likely understand why I fell in love with the company’s products several years ago.

At $50,000, the ampsandsound Arch Monoblock represents their new flagship two channel amplifier. At a technical level it successfully delivers everything you would expect at this price point. There will be two pairs at AXPONA for the Arch’s first public debut. I think there will be more than a few people trying to figure out take a pair home with them. If you can afford them, you should listen to them. You are doing yourself a disservice if you don’t.

Thank you, Justin, and the ampandsound team, as always it has been a pleasure to listen to your products.


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