A Full Review of HELM Audio's Dynamic BOLT DAC/AMP

Manufacturer & Model
HELM Audio BOLT DAC/AMP
MSRP
$99.00
Link
https://helmaudio.com/products/boltdac
Highlights
Lightweight and bendable form-factor, USB-A and USB-C connectivity, THX and MQA certification, Auto-sensing power output, crystal-clear and natural sound.
Summary
HELM Audio's BOLT DAC/AMP is THX certified and capable of MQA rendering, unlocking incredible Hi-Res audio playback from computers and smartphones. The device is highly portable and delivers plug-and-play performance, making it easy to move from source to source. Output is balanced and natural, rendering MQA tracks with breathtaking realism and clarity.
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In its fourth year of existence, HELM Audio is a British-American audio firm that caters to enthusiasts seeking high-quality, affordable audio gear. It recently began shipping a new portable DAC/AMP called BOLT ($99), a dongle device that assumes control of digital-to-analog conversion duties when connected to a computer or smartphone. Boasting THX and MQA certifications and a quartet of CES Innovation awards, BOLT packs a tech-heavy punch with a form-factor that can easily slip into a pocket.


Overview
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BOLT currently resides as HELM's only portable DAC/AMP solution, shipping in a handsome box clad with Hi-Res images and graphics. Internally, a foam insert houses the device along with a faux-leather carry pouch, a USB to Type-C adapter, and a fold-out instruction manual. It's an attractive package containing just about everything you need to enjoy high-quality audio.

BOLT's three-piece construction is robust, with a flexible 2.25" shielded silver cable accounting for half of its overall length (4.4"). Beyond offering flexibility when connected, HELM says the cable creates a performance-enhancing separation between BOLT's USB-C connector and headphone output/DAC. Both ends of the cable terminate into rigid rubber sleeves; durability does not appear to be an issue.

The headphone output is a rectangular chassis measuring roughly 1.25" long and 0.50" wide, housing a 3.5mm TRRS female connector, a multi-color LED indicator, and both the brains and brawn of the operation. HELM highlights its use of a three oscillator design for jitter-free precision and a TRSS connector that's soldered directly to the DAC's PCB. The DAC, which conducts digital-to-analog conversion, is shielded for EMI isolation and reduction of crosstalk.

HELM doesn't reveal specific information about BOLT's DAC chip on its website, but privately confirmed it’s an ESS Sabre 9281Pro. Most importantly, the chip is compatible with PCM audio up to 384kHz, DSD up to 5.6MHz, and Hi-Res formats such as FLAC, AIFF, and WAV. It's also capable of MQA rendering, which means it can fully unfold MQA tracks streamed by services like TIDAL or Nugs. While most devices can use a core decoder to playback MQA at CD-quality resolutions, BOLT's rendering capabilities take matters a step further, unlocking the finest levels of detail and best possible sound quality.

The icing on the cake is THX's stamp of approval, which certifies that BOLT delivers a flat frequency response, low noise and distortion, and high output.


Set-Up
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BOLT ships with Android, iOS, macOS, and Windows 10 compatibility, allowing for plug-and-play use with computers and smartphones offering USB-A or USB-C connectivity. If you intend to use BOLT with an iPhone, you'll need Apple's Lightning to USB Camera Adapter and the included USB-A adapter. Apple's camera adapter will set you back roughly $30 and adds some extra bulk to the arrangement, stretching its overall length to 9.25", which is a consideration if you're looking to pair BOLT with an iPhone for tunes on the go.

Thanks to built-in headphone impedance auto-sensing, BOLT automatically adjusts its power output based on the type of headphones or IEM connected to the device. An output of 1V is selected for impedances less than 150 ohms, while 2V is selected for 150 ohms or greater.


Playback
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Listening evaluations employed a MacBook Pro (USB-C connection) and iPhone 11 Pro (requiring Apple's USB Camera Adapter), along with OPPO's closed-back PM-3 and Acoustic Research's open-back AR-H1 planar magnetic headphones.

Connection points, both USB and 3.5mm, remained wiggle-free and physically solid throughout demo sessions.

Recruiting the extensive Hi-Res audio libraries of TIDAL, BOLT's onboard LED indicator accurately identified audio resolutions. Blue indicated resolutions up to 48kHz, red marked 48kHz or greater, while magenta was reserved for MQA rendering. It might seem relatively inconsequential, but there's a certain satisfaction to selecting an MQA track and seeing that magenta light smile in your direction.

BOLT had more than enough oomph to drive both the PM-3 and AR-H1 to volume levels that sounded elevated and powerful. In fact, the top-end hit levels that were too loud for my personal tastes. More importantly, output was dazzling and sonically delightful, even when pushed to the highest volume limits.

Taylor Swift's newly recorded "Love Story - Taylor's Version" (MQA) was jaw-dropping, exploding with crystal clear definition and emotional dynamics. With zero hints of fuzz or coarseness, the song effortlessly flowed with Swift's vocals leading the charge. "Willow" (MQA) was another mesmerizing listen with lyrics and stringed instruments etched with insane levels of detail and realism.

BOLT wasn't shy about delivering bass, either, fueling one of my favorite demo tracks, Whethan's "Good Nights" (MQA), with plenty of balanced low-end presence. This song also has ultra-fine echoey details that can be lost on a lesser system, and BOLT recreated them with revealing accuracy.

When connected to a Mac (macOS Big Sur), BOLT accepted every file I threw its way, never flinching or stumbling. The only misstep of inconvenience came while using TIDAL’s desktop app, as volume control was only available within the app, not the computer's global volume controls.


Conclusion
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HELM's BOLT DAC/AMP is a nifty device capable of driving a squeaky-clean headphone listening experience that's naked, neutral, and devoid of added noise. It makes you wonder: how much higher-end can sound become? And while I'd like to experience the ultimate – definitive – sonic limits, BOLT suggests you needn't search further.

BOLT's biggest drawback is its inability to connect directly to an iPhone. While the incorporation of Apple's USB camera adapter is inconvenient, it's not a deal-breaker. Yes, it adds physical length to the arrangement, but it's more than manageable for desktop duty and isn't too cumbersome when a phone is carried in a back pocket.

Priced at $99, HELM Audio's BOLT DAC/AMP is easy to recommend and affordable enough for the masses to enjoy. Pair it with a quality set of headphones and Hi-Res tunes, and I guarantee you won't be disappointed. Solid Buy.

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HELM Audio's BOLT DAC/AMP Specifications
  • Output: 1.1 Vrms at <150 Ohms, 2 Vrms at >150 Ohms
  • Format compatibility: PCM, MQA, DSD DoP
  • PCM Sample Rates: 44.1 kHz, 48 kHz, 88.2 kHz, 96 kHz, 176.4 kHz, 192 kHz, 352.8 kHz, 384 kHz
  • Connectivity: USB-C INPUT, 3.5MM OUTPUT, USB 2.0 High-Speed
  • SNR: 120 dB
  • THD+N%: 0.0008 at <150 Ohms, 0.0013 at >150 Ohms
  • FR 20Hz-20kHz: +/- 0.06 dB
  • Dimensions: 4.4" long x .5" wide
  • Weight: .25oz
 
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Sonnie

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Amazing what they can do in such little space.
 

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Mind-blowing, really. Just the concept of 1s and 0s, racing into that complex machine, only to emerge as crystal-clear analog audio. Crazy.
 

mlknez

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Another "me too" device delivered a full year after most others. The review doesn't show what the justification of the product or the cost is.
 

Todd Anderson

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Another "me too" device delivered a full year after most others. The review doesn't show what the justification of the product or the cost is.
The cost is $99. Justification? Not sure what you mean...
 

mlknez

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Why is it $99? It is more expensive than the competition that has been in the marketplace for over a year. Why do we need THIS particular product when there are 9 similar products already on the market? What ios, android, windows, macosx, linux players is it compatible with? Why doesn't it also include balanced output? What is the max and min load that is recommended for use with it? Does it have adaptive amplification? Can you combine to get SACD/DSD/DVD-Audio multichannel output?
 

Todd Anderson

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You're going to need to re-read the details and you'll find some of your answers... and the technical questions you have that aren't answered, I can confirm with HELM. This is not a multi-channel device, that's rather evident. And no manufacturer is going to publicly reveal their BOM and design costs. That's information that's occasionally shared, but not for public dissemination. Obviously the price will be driven by THX and MQA licensing.
 

Priit Varik

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To solve the problem with bulky Apple lightning-to-camera adapter, chinese came to rescue:
Screenshot 2021-04-12 at 21.07.22.png
Someone mentioned that those cheap chinese OTG adapters can fail fast, I think at this price point it will not be a big problem.
Plus it is a good deal smaller, than the Apple solution.
IMG_0453.jpeg
 

Todd Anderson

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To solve the problem with bulky Apple lighting-to-camera adapter, chinese came to rescue:
View attachment 41162
Someone mentioned that those cheap chinese adapters can fail fast, I think at this price point it will not be a big problem.
Plus it is a good deal smaller, than the Apple solution.
View attachment 41161
I wonder how it performs... THX sent me an Apple lightning to USB adapter and said that the alternative (Lightning to USB/USB-C adapter) didn't perform as well for audio. Would be interesting to see if something like this OTG adapter degrades overall quality...
 

Priit Varik

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I wonder how it performs... THX sent me an Apple lightning to USB adapter and said that the alternative (Lightning to USB/USB-C adapter) didn't perform as well for audio. Would be interesting to see if something like this OTG adapter degrades overall quality...
Well, to my ears, and my taste of music, I can not tell any difference between it and the Apple USB3.0 camera adapter (with external power). But the bulkyness of the latter totally negates the nice portability features of the Bolt.
Also a nice feature - listening at max volume on my 32-ohm and 106dB/mW headphones, it draws "only" 75mA of current. I have the feeling that iOS warning "this accessory draws too much current" is set at 100mA.
IMG_1043.jpgIMG_1023.jpg
 
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Todd Anderson

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That's the dongle I'm referencing. Hang tight... let me see if I can get some clarification from THX's engineers.
 

Todd Anderson

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Carada Cine-White 0 gain
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LG Electronics 65-inch B6 OLED, Sony 65-inch X900F
Ok. THX says that the large adapter (which you have in that photo) doesn't supply enough power to their DAC/Amp when it's plugged into a computer or phone.... depending on the owners headphone impedance (and volume level) it could cause Onyx to shutdown.

So, that might not be the case with BOLT. But, good information, nonetheless. Your mileage will vary.

Thanks, @Priit Varik, for sharing the workaround you've found. I think a lot of folks will find it useful!
 
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"there's a certain satisfaction to selecting an MQA track and seeing that magenta light smile in your direction"

+1 :T
 
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