Aric Audio’s Jackpot tube Line-stage by Terry London

I started to realize that over the last twenty-five years, I had amassed a vast selection of the highest regarded NOS 12AU7-5814-12AX7-5751-12AT7 tubes ever manufactured. In my collection, I have legendary tubes from both American companies (RCA-TungSol-Sylvania-KenRad-Raytheon) and European companies (Telefunken-Valvo-Siemens-Mazda-Amperex-Mullard-Brimar). Besides, the most important factor is that each company’s tubes offer distinct tonal signatures; they all have different gain levels. I began contemplating whether it would be possible to have a tube-based preamplifier that, because of its circuit topology, could accommodate all the tube variances mentioned above.

I reached out to Aric Kimball, owner/designer of AricAudio, to see if he would be interested in building a custom line-stage with the following requests: 1) Could he design a circuit that would handle all the variances of my tube collection at an optimal level? 2) That it would be tube rectified, not solid state. I have found that tube rectification always sounds more natural and musical to my ears. 3) It would have balanced input/outputs. 4) A continuous vs. stepped volume control. I’m very choosy about the exact volume levels and find stepped controls either slightly too high or too low in dB when trying to reach the sweet spot for both dynamics and instrument size in my system. I consider Aric Kimball one of the finest artisan designers and builders of tube amplifiers and preamplifiers on the market today. I have professionally reviewed over seven of his pieces and have bought three for my different systems. Each piece was beautifully built, delivered reference-level performance, and was very reasonably priced compared to comparable gear from other manufacturers. AricAudio has a large and loyal following thanks to the attributes mentioned above, as well as its great customer service/support. These were the reasons I reached out to Aric first for this project.

I asked Aric to write an explanation about what he did in creating what he calls the Jackpot line-stage, based on my requests:

“Terry London had contacted me, stating that he had collected a plethora of small novel NOS signal tubes such as the 12AX7, 5751, 5814, 12AU7, and had asked if I would consider building him a personal line-stage that could use these tubes, along with balanced inputs and outputs. I said absolutely, as I used to build a 12AX7-based line-stage, and currently use the 6SN7 (which is very similar to the 12AU7 in many ways). What I decided to do was use both triodes of a single input tube and direct-couple them into a 12AU7 cathode follower so that we can drive real-world cable runs and low-impedance loads presented by some solid-state amps. This basically gives the line stage the ability to drive nearly any amplifier in real-world conditions. Setting the bias point for the input tube allows one to roll in a 12AU7, 5814, 12AT7, 5751, or 12AX7 into the front slot, thus allowing the user to not only change the sonic textures of the stage but also achieve various gains. This gives the user the ability to completely change the preamp’s character by rolling in a different input tube. You only need one tube because these are dual triodes- meaning a stereo signal is processed within one tube. Other benefits include better channel matching (as opposed to two tubes) and greater consistency, with the bonus of needing to purchase only a single tube per input and output, or buying pairs and having a backup tube for when the time comes.”

Regarding the signal inputs and outputs, this unit can be built as completely single-ended (RCA) or with balanced inputs and outputs. While the unit accepts and utilizes fully balanced connectivity, it is not considered “balanced from input to output” as this would mean a separate tube processes each of the positive and negative voltage swings, which essentially becomes similar to a “push pull” stage, and cancels the pleasant even order harmonics, making the sound more sterile or “solid state” sounding. By keeping the signal processing single-ended, you gain more of the natural tube harmonics, which most folks seek when purchasing tube-based products. How the signals are processed is that the balanced input signal connects to each end of a balanced input transformer, so that you get equal impedances, the full signal swing, and the benefits of noise rejection from the XLR cables. For the outputs, the single-ended tube signal connects to the primary side of an output transformer, which then gives you both positive and negative signals on its secondary side, allowing the connected amp to benefit from a fully balanced input signal.

There is also a 5-position output level controller, which allows the user to select from unity gain (gain = 1) to the full gain provided by the input signal tube. This can be as high as 40 dB with a 12AX7 or 10 dB with a 12AU7, and then provides 3 more equal steps in between to match the output signal to whatever amplifier you may be using. Nobody wants to run out of rotation with their volume control, or turn the volume knob up one notch and have it clip their amp, right? This fixes that issue nicely and makes my line-stages essentially “upgrade-proof”.

I’ve also incorporated my baseline standard of parts into The Jackpot to complement its performance, including a toroidal power transformer, all-film capacitors throughout the power supply, multiple chokes for ripple reduction, and more, resulting in a very robust, clean power supply. The signal path also features high-quality gold-plated Neutrik connectors, high-quality metal-film resistors, and robust film capacitors for the output stage, and, as always, it is completely hand-built and point-to-point wired. A Khozmo remote volume controller handles volume control duties and includes a high-quality aluminum block remote with a defeatable LED display on the front panel. The cost for a balanced Jackpot is $5,675.”

As I have stated in my other reviews, I believe a superlative tube-based line-stage should completely disappear, allowing the tubes to transmit their unique timbres/colors, spatiality, and liquidity into your system. The Jackpot surpassed any tube line-stage, in this critical attribute, that I have ever had in my system. I recently reviewed two excellent tube preamplifiers, the Linear Tube Audio Level 3 and the Backert Labs Rhythm 1.4, that allowed the tubes to shine through. However, the Jackpot offered a bit more “see-through” transparency, allowing the tube’s signature to come through in the music’s reproduction. Something I found surprising during my intensive auditioning of my collection of Jackpot line-stage tubes was how much the 12AU7 cathode/buffer tube affected the sound presentation. To be clear, the choice of the buffer tube was not as dramatic on the sonic effects as the selection of the signal tube. However, different pairings did create noticeable differences in color intensity, the width and depth of the sound-stage, and the layering of instruments on the sound-stage. In one way, the process of going through my numerous NOS tubes was laborious, but at the same time, it was quite fascinating. The conclusion, I finally came to regarding what tubes offered oil paint color intensity, the simmer of beautiful extended upper frequencies, the best spatiality regarding both the dimensions of the sound-stage and holographic imaging, dynamics and bass control in my present configuration of my reference system, were a NOS 12AU7 Amperex long plate D-getter as the buffer and a rare NOS 5751 Mazda silver plate 3 mica in the signal position.

With what I shared in this review, you can understand why I put the Jackpot line-stage on my list for STEREO TIMES 2025 MOST WANTED COMPONENTS LIST. The Jackpot is hand-built with superlative internal parts, allowing you to “tube roll” with total flexibility using any 12AU7/12AX7/12AT7 and their variants, thanks to its circuitry and variable output-gain control. Regardless of the music’s genre, I auditioned the Jackpot line-stage to evaluate its performance, and it presented an alluring musical experience that drew me into the music I was listening to. I want to be very clear about a very important characteristic of the Jackpot line-stage: its ability to vanish and allow the combination of the buffer/signal tubes to completely deliver their unique sonic qualities at a higher level of purity than other tube line-stages I have experienced. For many listeners, this could be your end-game preamplifier if you use 12AU7/12AX7 tubes, because you can match or adjust the synergy you want from your line-stage to shape your system’s total signature to your personal taste. If you then change other gear in your system (sources/amplifier/speakers), you could still “dial in” your rig’s ultimate sonic signature by changing tubes in the Jackpot.

Specifications
Price $5,675 Balanced version
Tube Rectified 5U4GB
Buffer & Signal tubes 12AU7/5814/12AX7/5751/12AT7
Adjustable gain 5 levels
Handcrafted wood chassis
Website: www.aricaudio.com/tube-gear/

Associated Equipment
Source:
Reimyo DAP-999EX Toku DAC
Pro-jet reference CD transport & LTA power supply
Amplification:
AricAudio Super SET 300B amplifier
AricAudio Jackpot balanced line-stage
Naiu Labs Ella MKIII amplifier
Plinius SA-50 amplifier
Loudspeakers:
NSMT System Two
Rosso Fiorentino Arno 40
Sonus Faber Auditor Elipsa
Accessories:
Vermouth Audio XLR Black Pearl MKIII IC’s
Vermouth Audio Reference speaker cable
Jena Labs reference AES/EBU digital cable
Krolo Design reference rack & footers
Puritan Audio power conditioner & grounding system
Vermouth Audio reference power cords