It’s been a while since I have been back on head-fi. During my absence work has been crazy, we moved, we re-emerged from the pandemic shell, and I got my hands on a new tube amp from ampsandsound. Yes like with many of Justin’s other amps I am one of the first to own the Rockwell. I have a longer more detailed review coming, however the Rockwell is simply so good, that I felt compelled to provide a preview.
In April Justin gave me a call and told me he was going to send me the Rockwell for review in mid May. I laughed and reminded Justin that I already owned the Nautilus and that I was not in the market for a new tube amplifier. He assured he just wanted my honest feedback and for me to write something for either head-fi or Postive Feedback. I gladly accepted and two days after moving in to my new home, the Rockwell arrived.
Sharing the same chassis as the Bigger Ben, the Rockwell is a medium sized amplifier. It will easily fit on more narrow shelves and while it is chunky it can be moved with only two hands (in comparison to the Nautilus which for me is a two person job). Like the Bigger Ben and Kenzie Ovation, it has one single ended input, a speaker/headphone switch, speaker binding posts, Jupiter capacitors (which are awesome), and a pair of input transformers. Input transformers isolate the ground of the amp and provide a quieter background. The power supply is tube rectified and is relatively simple in comparison to Justin’s other amps, with a big power transformer, and a small choke under the plate.
The Rockwell represents Justin’s re-entry into the world of direct heated triodes (DHT). The last DHT ampsandsound produced was the Agartha 2. A while back, I asked Justin if it was worth auditioning an Agartha. He told me that while he liked the sound of the Agartha, the noise floor was simply to high for my headphones (at the time I was running a Utopia and a Stellia). Ultimately when Justin retired the Agartha, one of the key reasons was the noise floor. To be clear DHTs will always have a higher noise floor just because a direct heated tube is noisier then a indirectly heated tube. The question is, could Justin deliver a DHT that provided a truly black background across the majority of headphones?
I am happy to say that when it comes to a low noise floor the Rockwell really delivers. With the Susvara and my 98db/watt speakers I had nothing but a black background. Sticking my head fully into the tweater and mid-range horn of my speakers I could hear nothing. Taking out my Hifiman HE1000SE (96db/mWatt) resulted in the same. I did ask Justin where he thought the headphone compatibility line was, as HE1000SE was the most efficient headphone I had on hand. He told me that anything north of 100 db/mWatt efficient will likely have slight background noise but things south of that should be fine. This means there should be no issues with the majority of high end headphones on the market today. Like the Bigger Ben, Nautilus, and Kenzie Ovation, the Rockwell has 5 impedance taps that are achieved through additional windings on the output transformers. These 5 taps are 8ohms, 16ohms, 32ohms, 100ohms, and 300ohms. With these 5 taps you can customize the sound and ensure that no matter the headphone you can always have the optimal voltage delivered. For me, I spend the vast majority of the time on the 8ohm tap, unless I am listening to HD600s or ZMF headphones in which case I am either on the 32ohm or 300ohm tap.
Moving to the Rockwell’s power output, this is easily the most powerful 3.5 watt amp that I have ever heard. The Hifiman Susvara is notoriously hard to drive, the Rockwell took control of the Susvara’s with ease. At no time did I feel like the amp was lacking in power. The same was true driving my horn loaded speaker, the 12 inch woofers were easily able to pressurize the room and there were no issues with volume.
Now that I covered some of the important but boring baseline stuff (power output, noise, compatibility) lets talk about how the Rockwell sounds. The Rockwell embodies the ampsandsound house sound. That means it is an amplifier that sits slightly to the right of neutral, that is dynamic, and fun. It is going to get your toe tapping. Comparing the Rockwell to the other high end amps and in the ampsandsound line (the Kenzie Ovation and the Bigger Ben/Nautilus) the Rockwell has its own unique take on the A&S house sound. While all of Justin’s amps are tonally dense, the Rockwell is tonally perfect. I tend to analyze the difference in the way music is presented on my headphones compared to how I would expect it to be presented live. Listening to the Rockwell I no longer found myself engaging in this game of comparison. It just sounded right. For me this was a revolution, and while every other amp in Justin’s line gets close to this, the Rockwell is simply better.
To give a comparison, for those who have listened to the Kenzie family of amps, the Rockwell maintains the rich presentation of the Kenzie, but with a lighter more open and simply faster. In comparison to the Bigger Ben and the Nautilus, the Rockwell is slightly more nuanced, and a little softer on the top and bottom. Do no read softer as rolled off, the Rockwell is just more focused on texture, where the Bigger Ben and Nautilus are more focused on slam. Listening to various artists including Mika, the Mountain Goats, and St Vincent, they all sounded exceptional. This proved that the Rockwell is not a one trick pony.
Where the Rockwell really excelled was in creating a 3D space. I found both listening with speakers and with the Susvara that sounds and instruments simply jumped off of the traditional 2D canvas. Recording quality did not seem to matter much, and while the Dave and M Scaler are exceptionally good at making even poor recordings sound great, the Rockwell really seemed to make lemonade from even the most sour of lemons.
You may be reading up to this point and you may say “ok this is clearly a love fest, but where is objectivity?” The Rockwell is not without its faults, but when put in context of cost and features those faults are relatively limited. I personally would have liked to have seen two inputs instead of one. I also would have liked to have an option to add an XLR input. To be fair there is not enough room for either of these additions, but it does not change the fact that I would like them. The other thing to note is that at the end of the day, the Rockwell does have a higher noise floor then a Kenzie Ovation or a Bigger Ben, so while you are fairly safe at <100 db/mW you have to carefully select your input tube to ensure your noise floor is as low as you can get. Luckily this is not hard to do, but still requires you to take the time to do it. Of course if you are < 96db/mW there is nothing to worry about. Other then the limited tube rolling options (we will talk about that in a moment), for my taste in my use, I have not found other faults.
Moving onto tubes
. For those of you who have read my previous reviews and comments in this forum, I think you may realize I love tubes. Direct Heated Triodes (DHT) are special. Some of the most legendary tubes in the audio world are DHTs (think 300Bs and 2A3s). Most people who own single ended DHTs will say that they sound holographic, emotional, and ooze nuance and detail (all of these things are true about the Rockwell). Once you go DHT, there is no going back. Of course people who own DHT amplifiers and re-tube them with NOS tubes also tend to have a lot of money. DHTs (especially NOS 2A3s and 300Bs) are expensive.
The Rockwell uses the familiar 6SL7 as an input tube. This is where familiar ends, it also uses the 6AX5 rectifier, and two 6B4G power tubes. Justin chose the 6AX5 for two reasons. The first is to make the entire amp run at 6 volts. This allowed for a simpler power supply and a quieter amp. The second reason was cost. You can buy NOS 6AX5 for between $5 and $30 a tube (for those who have been buying 5AR4s and more interesting 5U4Gs I am sure this sounds wonderful). The 6B4G is not overly common. There is only one new stock manufacturer which is Sovtec, and they make a very nice tube for this amp. However, if you buy this amp, you should be buying old stock, and you can likely afford it. NOS 6B4Gs can be bought for as little as $150 a pair. You have to look for them, but you can buy them for a very reasonable price (I know, because I bought 4 pairs for under $500). This is the kicker though, a 6B4G is a 6A3 but with a octal base instead of a 4 pin base. The 6A3 is a 2A3 but with a 6 volt heater current. By transitive property, the 6B4G is more or less a 2A3, but instead of paying north of $800 a pair, you are paying Less than $200. Justin says the Rockwell is “a thinking man’s DHT“, and I completely agree.
Wrapping this up, the Rockwell is another excellent amp from A&S. I have always loved Justin’s amps, especially his single ended amps that employ zero feedback, and the Rockwell is no exception. To the contrary it is easily my favorite of the bunch, and while my Nautilus is not going anywhere, neither is the Rockwell. The question becomes who is this amp for? I am not sure this amp should be your first tube amp. The Rockwell is really special and you need to have experienced other tube amps to understand what makes it special. Similarly, I think you are better served by the Mogwai SE/Bigger Ben if you are not interested in NOS tubes. However, if you want to own a really special and unique amplifier and are interested in that classic 1950s and 1960s sound you should order a Rockwell. When I went to box the Rockwell up for its return back to Justin, I simply could not do it. It really is that good.
More to come.
