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Helm Audio Bolt Review (Portable DAC & Amp)

amirm

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#1
This is a review and detailed measurements of the Helm Audio Bolt portable headphone Amp and DAC "dongle" with MQA decoding. It is on kind loan from a member and costs US $99 on Amazon with Prime shipping.

The bold design seems a bit more substantial than some others:

Helm Bolt review headphone amplifier MQA DAC.jpg


Not much else to it than a 3.5 mm headphone socket:
Helm Bolt review headphone amplifier dongle MQA DAC.jpg


Interestingly, there is THX certification for this device. Didn't know there was such a program. This is the description:

Helm Bolt THX certification.png


Will be interesting to see how it measures!

There are no controls on the unit which is a miss. I like to see volume controls as a minimum.

Testing with Windows indicate there is an ADC in there so I imagine it could have microphone support but I am not sure.

Helm Bolt Measurements
Let's start with our usual dashboard:
Helm Bolt Measurements MQA DAC.png


Not bad! SINAD is dominated by second harmonic distortion. Definitely a competent design:
best stereo DAC review.png


While there is some source of jitter, overall response is by far cleaner than many other dongles:
Helm Bolt Measurements Jitter MQA DAC.png


So maybe THX certification means something.

Due to some interface issues regarding how I measure, I can't run other DAC tests so let's get into power starting with 300 ohm load:
Helm Bolt Measurements Power into 300 MQA DAC.png


Response is a bit nervous (noisy) but power is good for a dongle:
best headphone dongle 300 ohm.png


Same for 32 ohm load:

Helm Bolt Measurements Power into 32 MQA DAC.png

best headphone dongle 32 ohm.png


Sweep the load impedance we get:

Helm Bolt Measurements Power versus impedance.png


With both 300 and 600 ohm loads, we are voltage limited as is usually the case. As a result, there is no distortion even at full volume. Once we get down to 50 ohm, current limiting sets in causing clipping. To compute the available power for any of the output devices, find the corner before clipping occurs (graph shoots up) and use the formula on the graph. For example, for 12 ohm you have 0.83 * 0.83/12 = 0.057 or 57 milliwatts.

Helm Bolt Listening Tests
I was pleasantly surprised that it could drive my 25 ohm Ether CX headphone to reasonable level without distortion. Switching to Sennheiser HD650 produce good power and again, no sign of distortion. Quite adequate for on the go job.

Conclusions
Nice to see another high performance dongle DAC and amp. While performance is not the best we have seen, it is quite good indicating proper engineering.

I am going to put the Helm Bolt MQA on my recommended list.

EDIT: video review just posted:

------------
As always, questions, comments, recommendations, etc. are welcome.

Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 
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OP
amirm

amirm

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Thread Starter #3
The price has dropped a lot on S8. It was $129 I think when I first reviewed it.

On this, I think THX probably took a good cut.
 

PeteL

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#4
Thanks, that is quite decent performance. One day @amirm If it's a possibility, if it's something you're interested in. I would like to have a measurment if it does supply to the same specs with an average phone. And I believe you do one of these "un-self powered" dongles you do all, it's OS or phone related. A fair 50mW+ in 32 ohms, most of the time sounds far more autoritative and punchy on most Battery powered BT amps, than they seam to do to my ears on all the dongles I've listened to, when connected to a phone, which is the main use case. That lead me to think that Androis/Ios/phone manufacturers may limit the current pull from USB, but I don't have data to assess that, just my ears.

Edit: Or, I realise this is not simple, but I trust your ears too. While you are at your desk. Does it drives your 650s properly when you plug this thing in your phone?
 
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IVX

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#5
it seems this is es9281 based DAC, the same as Ztela and many others. One thing I wonder, if es9281 is a single-chip solution (USB-bridge+ADC+HPA combo), why such DACs always show measured specs much worse than ESS promised in the datasheet? -112dB THD+N, 2.0Vrms into 100k vs -100db measured above 4x times difference! -110dB THD+N, 1.0Vrms into 32ohm i.e. again 4.5x times worse. I believe, nobody goes to modify the reference design of es9281(IC+ a few passive parts surround), and you'll see exactly the same PCB inside of all such kind of DACs, so, what I should think about the specs mismatch? I think ESS does cheating regarding actual specs just to be comparable to Cirrus Logic DACs solutions ;)
 

JohnYang1997

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#7
it seems this is es9281 based DAC, the same as Ztela and many others. One thing I wonder, if es9281 is a single-chip solution (USB-bridge+ADC+HPA combo), why such DACs always show measured specs much worse than ESS promised in the datasheet? -112dB THD+N, 2.0Vrms into 100k vs -100db measured above 4x times difference! -110dB THD+N, 1.0Vrms into 32ohm i.e. again 4.5x times worse. I believe, nobody goes to modify the reference design of es9281(IC+ a few passive parts surround), and you'll see exactly the same PCB inside of all such kind of DACs, so, what I should think about the specs mismatch? I think ESS does cheating regarding actual specs just to be comparable to Cirrus Logic DACs solutions ;)
Not again....
 

soundwave76

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#10
I really like these video reviews! Have you ever done any videos of your AP analyzer and how you use it while doing measurements? You could mix short shots of these into the videos. Your initial listening reactions would also be a nice add :)
 
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#13
I bought a Hidizs 8 and it was very good, but the physical quality was poor. There was some kind of problem with the connection between the telephone and the dongle, sometimes it worked and sometimes it did not, and the supplied cables and connectors were lousy. I sent it back and ordered a Hidizs 9 instead. It has even better specifications, and it is better built, but too late I realized that it also drains the battery in a smartphone very quickly. Now I use Hidizs 9 only for my desktop computer, but am thinking of giving Hidizs 8 a second chance.
 

Sprint

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#14
@amirm Love your You Tube Videos.
 

Sprint

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#15
I bought a Hidizs 8 and it was very good, but the physical quality was poor. There was some kind of problem with the connection between the telephone and the dongle, sometimes it worked and sometimes it did not, and the supplied cables and connectors were lousy. I sent it back and ordered a Hidizs 9 instead. It has even better specifications, and it is better built, but too late I realized that it also drains the battery in a smartphone very quickly. Now I use Hidizs 9 only for my desktop computer, but am thinking of giving Hidizs 8 a second chance.
I had the same issue with both iPhone and iPAD. Are you using iOS or Android? I heard that for iOS, one needs the Apple Camera adapter. Then I tried with Fiio BTR5, the issue was same.
 
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#16
I had the same issue with both iPhone and iPAD. Are you using iOS or Android? I heard that for iOS, one needs the Apple Camera adapter. Then I tried with Fiio BTR5, the issue was same.
I am using iOS. Which of the issues did you experience? The battery drain or the Hidizs 8 poor quality?
 

AudioSceptic

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#17
This is a review and detailed measurements of the Helm Audio Bolt portable headphone Amp and DAC "dongle" with MQA decoding. It is on kind loan from a member and costs US $99 on Amazon with Prime shipping.

The bold design seems a bit more substantial than some others:

View attachment 112659

Not much else to it than a 3.5 mm headphone socket:
View attachment 112660

Interestingly, there is THX certification for this device. Didn't know there was such a program. This is the description:

View attachment 112661

Will be interesting to see how it measures!

There are no controls on the unit which is a miss. I like to see volume controls as a minimum.

Testing with Windows indicate there is an ADC in there so I imagine it could have microphone support but I am not sure.

Helm Bolt Measurements
Let's start with our usual dashboard:
View attachment 112662

Not bad! SINAD is dominated by second harmonic distortion. Definitely a competent design:
View attachment 112663

While there is some source of jitter, overall response is by far cleaner than many other dongles:
View attachment 112664

So maybe THX certification means something.

Due to some interface issues regarding how I measure, I can't run other DAC tests so let's get into power starting with 300 ohm load:
View attachment 112665

Response is a bit nervous (noisy) but power is good for a dongle:
View attachment 112666

Same for 32 ohm load:

View attachment 112667
View attachment 112668

Sweep the load impedance we get:

View attachment 112669

With both 300 and 600 ohm loads, we are voltage limited as is usually the case. As a result, there is no distortion even at full volume. Once we get down to 50 ohm, current limiting sets in causing clipping. To compute the available power for any of the output devices, find the corner before clipping occurs (graph shoots up) and use the formula on the graph. For example, for 12 ohm you have 0.83 * 0.83/12 = 0.057 or 57 milliwatts.

Helm Bolt Listening Tests
I was pleasantly surprised that it could drive my 25 ohm Ether CX headphone to reasonable level without distortion. Switching to Sennheiser HD650 produce good power and again, no sign of distortion. Quite adequate for on the go job.

Conclusions
Nice to see another high performance dongle DAC and amp. While performance is not the best we have seen, it is quite good indicating proper engineering.

I am going to put the Helm Bolt MQA on my recommended list.

EDIT: video review just posted:

------------
As always, questions, comments, recommendations, etc. are welcome.

Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
Yes, better than the Apple adapter, but for 11x the price. I wonder what Apple could do for $20-25 if they could be bothered?
 

AdamG247

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#18
Amir,

‘Excellent review. Thank you kindly for taking the time to do this for us! FYI.

NOTE: If you are a Veteran, Police, Fire or First Responder HELM offers a most amazing 50% Discount. I paid $50 USD for this Dongle. So if you can take advantage of this discount it’s a pretty great deal.
 

PeteL

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#19
I really liked to hear the statement in the video at 8:10. "Subjective testing is important for these things, The measurments we have are for continuous power, but some of them can do better for momentary peaks(...) I find that subjectively some of them sound better than others(...) Measurments is the baseline but listening is important"
-Amir
 
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