I tend to jump into things blindly, especially when it comes to this hobby. Most of the amps, headphones, and speakers that I am interested in are not sold locally. Some of the best things in this hobby are made to order, and they often times don't have a 30 day trail. Needless to say, I have been burned many times when buying new gear. It is not the fault of the manufacturer or the dealer, just the fact of life in a hobby as subjective as audio. However, this is a very different story, this is the story of how a blind leap of faith lead me to the best amp I have ever heard. This is the story of how I came to own the first production model of the Suolo Monos from ampsandsound.
The Suolo Monos are not the first amps I purchased from ampsandsound. My first purchase was the Mogwai SE, which is an excellent amp in its own right, and the amp that introduced me to the craftsmanship and style that is ampsandsound. It also allowed me to meet and build a relationship with ampsandsound's owner Justin Weber. After owning the Mogwai SE for six months I reached out to Justin to discuss ordering a second amp from him. During our conversation he informed me that he had just begun designing a new set of mono block headphone amplifiers roughly based on his existing Kenzie amplifier. The amp would retain the 1626 output tube, but would add tube rectification, and replace the 12SL7 with a 5751 (which would also be compatible with a 12AU7, 12AT7, 12AX7 any any other interchangeable variants), giving the amp many more options for different tube combinations. He also increased the size of the output transformer to the same size as on my current Mogwai SE. When Justin was done describing his new creation to me I asked how much, he told me $5500, and I sent him the money via PayPal that evening.
While I waited for the new amp to be completed, Justin was nice enough to send me his Kenzie so that I could get a rough sense if the Suolo Monos would be the right amp for me. For those who have not heard Justin's original Kenzie, and are looking for a warm but balanced amplifier under $2000, I highly suggest you add it to the list of amps you are considering. Needless to say, after listening to the Kenzie, I decided that the sound of the amp matched what I was looking for. It was not perfect, but the Kenzie had tone and texture that I had really never heard from an amp before, and the Suolo Monos promised everything the Kenzie had, and so much more. So, I sent the Kenzie back and waited patiently for the Monos to be built and sent out to me.
The Suolo Monos arrived in two matching Peloton cases, and were extremely well packed. Each amp is quite small. I would describe them as cute, however they weigh much more than their size would suggest. Justin describes the finish of the amps as "jewel like," and I understand exactly what he means by that. The fit and finish are very impressive, and there is not a single thing out place. The amps feel incredibly solid.
Each amp has a stepped volume attenuator that has a nice smooth click to it. The volume knob is larger than on his other amps, and the results are slightly more ergonomic. At the front of the amp are three headphone jacks offering 8 ohm, 32 ohm, and 300 ohm impedances, allowing this amp to be used with virtually any type of reasonable efficient headphones. It also has an 8 ohm binding post on the back that allows the Monos to be connected to high efficiency speakers. Inside the amp, you will find point to point wiring and turret boards, with each element inside the amp carefully thought out.
The amp itself outputs around 400 mW from each output, with the 32 ohm output being the weakest at 350 mW. While the amp may sound light on power, don't let the specs fool you. I have successfully run the Abyss 1266 Phi CC from this amp, and while I would not necessarily say it is the perfect match, the result was very enjoyable and left me wanting for nothing.
What in the world is a 1626?
If you are like me, you may have never heard of a 1626 output tube. If you look at the tube, you might think to yourself, "aww it looks like a baby 300B," and you would be absolutely right. Justin describes the 1626 as a baby 300B, and while I have not spent a huge amount of time with 300B based amplifiers, I agree with that assessment. From what I have heard, the 1626 has an extremely similar tonal quality of a 300B, and with the right amp design can be quite linear, but still deliver that incredible liquid lifelike midrange. The Suolo Monos are designed right, and deliver not only a linear and extended experience, but also that amazing mid-range the 300B is known for.
The other thing that makes the 1626 an extremely interesting proposition is that you can buy NOS pairs for as little as $30. That means, depending on the tube selection, you can outfit these amps with a full NOS set for under $100. That is not only impossible with a 300B amp, but it quite hard with most tube amps in general.
The Review Setup
For this review I equipped the Suolo Monos with the following tubes from my collection:
The following cabling and source was used:
I have owned the amps and used them almost daily since around March 20th, so both the amps and the tubes are thoroughly broken in.
So how do they sound?
For those of you who have heard the Focal Utopia, you probably know that in the wrong system they can be overly clinical and the treble can get peaky. These headphones are also incredibly sensitive (104dB efficient) which means they will pick up on even the slightest noise from the amps or any other downstream equipment. I am happy confirm that the Utopia is silent on the 8 ohm and 32 ohm tap, and that any harshness that is sometimes associated with the Utopia is non-existent when using it with the Suolo Monos.
When using the Utopias with the Suolo Monos I get an extremely clear image, and it feels like I am sitting in the 10th row of the performance. I am pulled back just enough to get a complete view of the stage, but still close enough to feel the presence of the instruments and singers. For example Listening to Vampire Weekend's "How Long" I was able to feel both the presence of the performance, but also the space between the instruments and synth notes. In contrast with ampsandsounds Mogwai SE, I find myself feeling like I am sitting in the first row, I feel the passion of the performance, but I don't get the sense of space and depth that the Suolo Monos provide. Likewise with the original Kenzie, I felt like I was sitting about 20 rows back. Great image, great texture, but I didn't feel the performance. Not scientific by any means, but this is how I would describe the differences between the 3 amps.
Likewise anyone who thinks of tube amps or the Utopias of being bass shy or bass light need to give the Suolo Monos a listen. The bass this combo creates is clean, deep, and powerful, more so than the Mogwai SE (which is almost 16 times more powerful). To be frank this amp's ability to deliver good clean bass is unmatched by any other amp I have owned.
The other thing to point out is the excellent tonal qualities that this amp imparts on the headphones that are connected to it. Simply put, things just seem right. This may sound like a cop out, but it is the biggest compliment I can give the Suolo Monos. Everything that comes out of them, be it male or female vocals, guitars, violins, high hats, or snare drums, all sound incredibly realistic. The result is at times eerie, as spacial queues in the music will cause me to turn my head and wonder if someone else is in the room with me.
Trading out the Utopia for the Stellia offers a very similar experience. Everything I said before about the Suolo Monos and the Utopias are true when using the Focal Stellia as well. What the Stellia adds is a more liquid midrange, and deeper bass due to the design and tuning of the headphone. While the Utopia and Suolo Monos are neutral, the Stellia and the Suolo Monos are neutral warm. This is where the output impedance options are really useful. I usually listen to the Utopia on the 32 ohm output, which provides a bit more warmth and a little more bass, I listen to the Stellias on the 8 ohm tap, which provides a bit more air and space. The result is the right balance with either headphone, and the ability to customize the amount of warmth based on your preferences and needs, without having to do so using tubes.
So what matches well?
I think that the Focal line of headphones are a prefect match for the Suolo Monos; their high efficiency makes them a great match for the power output, and their brighter tendencies compliment the slightly warm leaning Suolo Monos well. While I have not listened to every type of headphones with this amp, I have heard and owned the ZMF Verite with this amp, and think it is an excellent combo. Likewise, to my surprise, the Abyss 1266 Phi CC also performs quite well. Is this the amp to drive a Susvara or an HE6? No it is not. But will this amp drive any moderately efficient headphone? Yes it will, and trust me you will likely be very happy with the results.
All that being said, if you are trying to create a neutral system or a neutral with a touch of warmth system, I would not pair the Suolo Monos with an extremely warm headphone or source. If you do so you will likely end up with something a little too syrupy. Maybe that is a win for some, but for me you can indeed have too much of a good thing.
Likewise, you do not need to spend $14k on source equipment to enjoy this amp. While the Schiit Gungnir Multibit, in my opinion, is bested in most every way by my AURALiC stack, it paired excellently with the Suolo Monos, and I happily spent the night listening to this DAC and amp combo. My point is, like many things, most need to make choices when buying their gear. For a long time I thought it was really important to have the gear in my system be of equal cost and performance. If I could go back in time, I would have probably bought a single statement piece (like an amp or headphone) and slowly upgraded my system around that statement piece. The Suolo Monos could easily be that first statement piece, and will scale well as the rest of your system evolves.
Perspective from the ampsandsound
In a conversation with ampsandsound's owner, Justin Weber, I asked him why he built the Suolo Monos, and who he thought the Suolo Monos were for? Justin responded by saying "The monos (referring both to the Suolo Monos and the Leeloo Monos) are not for everyone, they are for the person who wants hand built everything, and is into an old school design philosophy to avoid obsolescence."
The amps have no PCBs or silicon, and use just tubes, resistors, and capacitors which, Justin claims, means the amps will never be obsolete and will always be serviceable.
As the amps were being built I had asked Justin if he was willing to add an additional input, and a high / low gain switch, he declined. His explanation was "The Suolo Monos was a distilled design. Everything it needed, and no more. What remained will be executed at the highest level."
While at times I found Justin's purist approach frustrating, I find myself unable to argue with the results, and feel that he achieved all he set out to with the Suolo Monos.
I consider the Suolo Monos an end game amplifier. I like it so much, I invested in a life time supply of NOS 1626s, 5751s, and EZ81s. To me, the biggest sign of endorsement is spending your own hard earned money on a product. I bought this amp at its retail price. Not only that, but I trusted ampsandsound to deliver so much that I wrote the check without hearing or seeing the amp, and even before the specs were finalized. The resulting amplifier is stunning, a work of pure passion by the ampsandsound team, and comes with my highest recommendation. This easily could be the only headphone amp you will ever need to own. For me, it is one that will likely never leave my small collection. Thank you Justin Weber for a lifetime of audio joy. Now if you will excuse me, I am going to sit back down and turn up the volume.
Suolo Mono Amplifiers
Retail: $5500 a pair
All images by author or courtesy of ampsandsound