Over the past five years, we’ve resisted the temptation to dramatically change Atom Amp(+) due to its strong reputation and reliability–no need to change what works well. However, we believe there is always room for improvement, and we’re excited to introduce Atom Amp 2 and Atom DAC 2.
Atom Amp 2 is the best Atom you can own, built in an all metal chassis with an easier to grip knob, featuring both 4.4mm and 6.35mm SE outputs, DC protection, and stereo octo-buffers delivering 2.5x the power of Atom Amp+.
Atom DAC 2 is built in a matching metal chassis with USB Type C input, dedicated power switch, and a more efficient I/V stage that operates at cooler temperatures.
Standard Atom Amp+ and Atom DAC+ Remain
Before diving in, we have no immediate plans to retire Atom Amp+ or Atom DAC+. Each continues to set a high bar for transparency, value, and reliability. We found that half of new customers opt for the Standard Atom Amp+ over the more rugged HEVI edition. And thus, Standard Atom Amp+ and Atom DAC+ remain, while HEVI editions are being replaced by Atom Amp 2 and Atom DAC 2. In fact, we depleted inventory of Atom Amp+ in October and initiated a new production batch this month.
Why More Power?
We’ve held off on drastic changes to Atom Amp+ for two key reasons. First, power has not been a priority to most of our customers. Second, we’ve been hesitant to make changes that might impact Atom’s high reliability.
As often as we have advocated that most headphone listening requires below 1W of power, we continue to field questions and concerns over how much power headphones require. And after five years delivering the same 1W Atom Amps, perhaps our time is better spent, well, delivering more power? Some listen at extreme volumes with inefficient headphones. Or as one Youtuber commented:
“How much I need is not as important as how much I want, imo that’s how the market works.”
Point taken! His voice is not alone, and we’re happy to accommodate.
Failsafe DC Protection
With great power comes great responsibility: DC protection is standard in Atom Amp 2.
This is no off-the-shelf protection circuit. Common protection circuits are built for speakers, for which a volt may be considered safe. Protecting headphones requires detecting DC at 1/20th of this level without accidentally tripping during normal listening. Not exactly trivial.
Atom Amp 2’s protection circuit began in simulations. Real world prototypes were more sensitive than predicted, tripping at moderate volumes. Weeks of iterations later, the final sensing circuit relies on a precision rectifier built with a zero-drift opamp. Muting disengages only for safe audio output, and never accidentally mutes. The circuit has already protected us during development, muting output for minor assembly errors.
The original Atom Amp+ uses a single LME49600 buffer per channel. Adding parallel buffers increases power proportionally. However, LME49600s are large chips–not exactly optimal. Replacing the single, large buffer with numerous, less powerful buffers achieves the same goal in less space. Parallel buffers also happen to cancel out some common mode noise, pushing the noise floor even lower.
We evaluated several variations of paralleled output buffers. Atom Amp 2 was originally drafted with 4x OPA1692s per channel, due to their low quiescent current (cooler running). The setup achieved less output power than Atom Amp+, so doubling the number of buffers to 8x would improve the situation. By chance, OPA1692s were out of stock at the time of the octo-buffer prototype build. OPA1656s happened to be available, and the change stuck. Octo-OPA1656s deliver 75% more power than OPA1692s.
Atom Amp 2’s THD performance is exceptional and power is extreme. You can turn the volume knob to 100% with 32Ω headphones and hear perfectly clear music at 9.22VRMS = 26Vpp = 2.65W.
There is no incentive to move beyond octo-buffers, now that power is limited by voltage swing. Audio opamps are typically limited to +/- 18V rails before self-destructing, and it’s good practice to leave some safety margin. Redesigning around a differential output topology is the only way to push power dramatically higher in a solid state amp, but differential outputs have their own tradeoffs (more noise, higher THD).
Bit of trivia: Douglas Self built a speaker amp called OpAmplifier in 2010 using 32 pairs of NE5532s per channel. This amp may be even stronger with today’s OPA1656s.
Dual Headphone Outputs
On that note, some of you may ask, “Is the 4.4mm jack balanced or more powerful?”. This question refers to a differential bridged mode circuit, which doubles voltage swing, doubles noise, and raises THD–a mixed bag of results. We are pleased to report that both of Atom Amp 2’s headphone jacks deliver 26Vpp single-ended with a miniscule noise floor. If you want to see a differential output amp, let us know in the comments!
Making Atom in Metal
Yes, Atom Amp 2 and Atom DAC 2 are all metal! It’s been a long journey.
The injection molded enclosure simplified the original Atom Amp, allowing us to source and assemble Atoms rapidly. Injection molded designs came with a caveat: much higher tooling costs. The complex molds for a chassis like Atom Amp weigh a ton (difficult to transport), and cost a small fortune. So while each enclosure cost was low, the initial setup costs are prohibitive for lower volume designs. This is precisely why the Atom line has consisted of only an amplifier and a DAC. A phono preamp or equalizer may never have recouped its tooling costs.
We began the transition to an all aluminum version of Atom last year. The first engineering samples fit together unacceptably, so the production batch ran months behind schedule as we iterated. We concurrently prototyped HEVI editions, and given the manufacturing delay of the all metal chassis, we chose to share the surprisingly nice Atom Amp+ HEVI edition in the interim.
Those with OCD tendencies will appreciate that Atom Amp 2’s RCA Inputs now physically align with Atom DAC 2’s RCA Outputs:
Atom Amp 2 and Atom DAC 2 electronics evolved thanks to the extra mechanical development time.
Atom DAC 2 vs. Atom DAC+
Think of Atom DAC 2 as a refined build in an aluminum enclosure:
- The transimpedance stage now uses triple OPA1692s, reducing quiescent current and overall operating temperature by about 10F.
- The external rocker switch is now integrated on Atom DAC 2. Auto standby is still supported.
- The light ring now attaches firmly with screws, so it cannot be accidentally dislodged.
- The USB jack is now a modern Type C input.
Measurable performance is remarkably similar; Atom DAC 2 raises SINAD to 113 dB.
Atom Amp 2 vs. Atom Amp+
Atom Amp 2 is the pinnacle of the Atom line, at twice the weight and more than twice the power of Atom Amp+.
SINAD edges slightly higher to 120dB at 20-20k bandwidth, and the noise floor is lower than ever. More astounding is Atom Amp 2’s high gain performance, matching its low gain figure. These improvements are byproducts of the octo-buffer output stage–not intentional goals per se. The input stage and filter is unchanged given its high performance and excellent RF rejection; only the NJM5532 gain stage has been updated to OPA1656.
Output impedance increases slightly due to paralleled buffers, remaining well within acceptable territory. Minimum suggested headphone impedance is 6 Ω.
Regarding channel balance, the same custom, hand matched potentiometer is used in both Atom Amp+ and Atom Amp 2.
|Atom Amp 2
|Frequency Response, 20Hz-20kHz
|SINAD @ 2VRMS, 1kHz (Low Gain)
|SINAD @ 2VRMS, 1kHz (High Gain)
|SINAD @ 50mV, 1kHz
|Crosstalk @ 10kHz (RCA Out)
|Dynamic Range (AES17)
|< 0.7 Ω
|Max Continuous Power @ 600Ω
|143 mW (9.28VRMS)
|Max Continuous Power @ 32Ω
|1 Watt (5.66 VRMS)
|2.65 Watts (9.22VRMS)
Given the holidays, we expect most orders to ship early next week, Nov 27-28th. Please be patient–our team will be hand soldering thru-hole jacks on the first batch of Atom Amp 2 and Atom DAC 2s.
By the way, some lucky Atom Amp+ HEVI customers received free upgrades to pre-production “all metal” enclosures throughout summer and fall. These builds are correctly marked “Atom Amp+”, as they contain Atom Amp+ electronics. Atom Amp 2 is easily distinguishable at a glance by its dual headphone jacks.
21-Nov-2023: Atom Amp 2 has sold out within the first hour!
25-Nov-2023: More Atom Amp 2 circuit boards arrived yesterday, meaning we’re on track to resume shipping on Monday.
Reviews will be shared below as they appear:
- Home Studio Basics – JDS ATOM 2 REVIEW
- Z Reviews – Atom 2 will Redefine Affordable Audio in 2024