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Review and Measurements of Cypher Labs Theorem 720 and Fiio Q1 DAC and Headphone Amp

amirm

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#1
This is a detailed review, measurements and comparison two portable DAC and headphone amplifiers: the Cypher Labs Theorem 720 and Fiio Q1 DAC. The Theorem 720 is on kind loan from a member. It is a circa 2013 product and quick look on third-party sellers on Amazon shows a retail price of $1,000. I own the Fiio Q1 and it retails for just $69 (plus $8 for shipping on Amazon). Obviously this is not an even match from price point of view but the Q1 was the only portable DAC+headphone amp I had that includes a battery like the Theorem.

Physically, the Fiio Q1 is quite a bit more slick and pocketable than the Theorem 720:

Cypher Labs Theorem 720 DAC and Fiio Q1 Review.jpg

The Theorem 720 on the other hand looks like a hobby box. Definitely not for the pocket but portable nonetheless.

The Fiio Q1 does have a few faults of its own. Its volume control has no markings. The switch operation and LED lights are not easily decipherable from the poorly written manual.

Both products are plug-and-play from Windows driver point of view. I did have to install the ASIO drivers for the Q1 for some of my testing (see later) which was a disaster from the point of view of finding them. We are talking about dropbox links that don't let you download things to other drivers with Mandarin in file names and no instructions for help!

No doubt you are interested in how they measure. So let's get into that. As usual, if you are not familiar with what these graphs mean, refer to my tutorial on understanding audio measurements: https://www.audiosciencereview.com/forum/index.php?threads/understanding-audio-measurements.2351/.

Note: some of these measurements are made from the Audio Precision APx525 which is on kind loan from the company (you can see it in the above picture). You can tell them from the white background. I am still in the process of "porting over" my measurements to this new model. So the measurements may not be identical to same ones performed by my unit.

Measurements
For all the measurements I powered the units using USB from my computer. I did not attempt to measure them while operating on battery. I did do a quick test on Q1 and it seemed to have same performance either way.

Let's start with test of jitter and noise:
Cypher Labs 720 DAC and Fiio Q1 Jitter and Noise Measurement.png


Both of these outputs are from line out, i.e. treating them as DACs. The Theorem has some random low frequency jitter that is causing the broadening of the shoulders on our 12 kHz tone. The Q1 is much cleaner in this regard but has higher absolute noise floor.

Measuring THD+N using my analyzer, I saw an odd behavior in Theorem 720. Namely, even though the volume control does NOT change the level of line out, it serves to significantly degrade its performance if you turn up the level! You can see that in this output:

Cypher Labs 720 DAC and Fiio Q1 -90 THD+N Measurement.png


Using minimum volume control, the Theorem 720 produces distortion and noise that is 83 dB down from reference signal. The Q1 outperforms it by 3 dB at -86 dB. But as seen there is a sharp drop to just -67 dB when I turned up the level to max on Theorem 720. This is very odd and not proper.

Drilling into it using spectrum analysis the problem is very clear:
Cypher Labs 720 DAC Min Max Residual Noise and Distortion Measurement.png


We see massive increase in harmonic distortion at max volume. If you are going to use the Theorem 720 as a DAC, be sure to keep the volume control at minimum.

Looking at the same test but using headphone output with the output of Theorem 720 matched to the lower output of Q1 we see:

Cypher Labs 720 DAC and Fiio Q1 Line out Residual Noise and Distortion Measurement.png


The Theorem 720's distortion is dominated in the low order second and third harmonics which is perceptually more masked than later distortions.

Test of -90 dB sine wave shows this for each DAC:
Cypher Labs 720 DAC and Fiio Q1 -90 db linearity Measurement.png


The Fiio Q1 shows a pretty reasonable facsimile of a sine wave. The Theorem 720 though is a disaster with noisy output and sudden spikes.

Measuring the headphone output voltage and hence power (P = Voltage * Voltage/impedance) we get these sequence of graphs for Theorem 720:

Cypher Labs 720 DAC THD Distortion vs Output Level Measurement.png


Sadly this is nothing to write home about. Best case distortion is 0.02%. There is decent output power though with onset of clipping around 2.6 volt for 300 ohm load.

Here are the same results for Fiio Q1:
Fiio Q1 DAC THD Distortion vs Output Level Measurement.png


Distortion is an order of magnitude lower at 0.0026% beating the manufacturer's spec (0.005%). Just as well varying the output impedance made no difference in distortion profile! The only limitation is an output voltage that is limited to just 2 volts.

Let's look at intermodulation distortion which shows high frequency non-linearity better than THD:
Cypher Labs 720 DAC and Fiio Q1 Intermodulation Distortion Headphone Out 300 ohm.png



I have shown the headphone output of the RME ADI-2 Pro as reference. We see that the ADI-2 Pro easily beats both of these products and by good margin. The Fiio Q1 though, performs predictably and again with nice control of distortion at maximum level. As seen in other measurements the Theorem 720 starts to distort early and becomes highly distorted at max volume.

Here are the output impedance measurements and how they compare to all others I have measured in the past:

Cypher Labs 720 DAC and Fiio Q1 Output Impedance Measurement.png


The Fiio Q1 falls in the excellent category (although higher than the 0.3 ohm spec). The Cypher Labs is in the good category. So no real worry for either one in this front as far as changing the frequency response of the headphone in use.

Subjective Listening Tests
I matched the levels on both DACs at a loud but still comfortable level using the Sony MDRV6 headphone. There was a tiny amount of high frequency exaggeration on Theorem 720 but this was pretty slight. In non-critical listening this would not observable.

Unfortunately my AB switch causes ground loop noise and made the above comparison a bit more challenging. So I took the output of both DACs and fed them to my Stax SRM-007t headphone amp powering the Omega pro headphones. There, the Fiio Q1 was subtly cleaner. Again, this was a very small difference.

For the third test, I connected the Sennheiser HD650 using the AB box and cranked the volume up as much as needed. On some tracks with low average levels, the Theorem 720 managed to produce noticeably more output resulting in better fidelity compared to max volume on Fiio Q1. On other tracks such as Pop/Rock, max level was not needed and the two again were neck and neck. In my scan of my library, 90% of the tracks could be played with the HD650 and Q1 below its max volume.

Conclusions
The Cypher Labs Theorem 720 DAC measures like yet another "boutique" product. Anomalies such as headphone volume control changing its line out performance significantly, and poor low level linearity show that care was not used in the design of the unit. Its saving grace though is the higher headphone output which I needed 10% of the time with my library of music with the high-impedance and hence inefficient sennheiser HD-650. If I had both of these units for free, and the headphone I used was the HD-650, my vote would be for the Theorem 720. Otherwise there is little to hang your hat on at $1,000 retail price.

The Fiio Q1 on the other hand measures like a well-engineered and well-behaved device at a bargain price of just $69+ shipping. It is slick with nice industrial design and doesn't suffer from any obvious warts. I am listening to it using the HifiMan HE-400i and it sounds really nice. Wish it had a tad more output and then it would be perfect. As it is, the Fiio Q1 goes on my recommended list for an all-in-one budget headphone amp and DAC.

As always, questions, comments, corrections, etc. are all welcome.

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mindbomb

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#3
@amirm can you check how low you can set the volume pots on these before there is channel imbalance? I'm concerned about the q1, since it doesn't use an alps pot
 

Timbo2

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#6
Yes, as I was finishing the review I realized I had not post that.
Thanks Amir! Did you measure output impedance? That might be especially useful for the Fiio and IEMs.
 
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#8
He's saying you can't predict voltage at low impedance from voltage at high impedance, but the graphs have the actual measured voltages with various loads.
You're right. I didn't read the graphs properly and assumed they were regular output power graphs that had been converted from voltage :confused:
What has been said does apply to the Speaka USB DAC/amp though. Amir only made a single voltage measurement with a 33 ohm load. Hopefully he'll get back to it and measure it more thoroughly.
 

amirm

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#9
Been reading too much head-fi lately? ;)
No, it is a matter of simple formula for power. The HD-650 has 300 ohm impedance which means that the amp is severely disadvantaged from power point of view. Since power = voltage^2/R, you get 10 times less power delivered from the same amp driving a 30 ohm impedance headphone.

I have half a dozen headphones for testing and the HD-650 is the only one that causes the amp to max out before my ears do!

This is why I carefully said because of its high impedance it is less efficient on the amplifier. Not because the headphone itself is inherently inefficient.
 

amirm

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#10
Thanks Amir! Did you measure output impedance? That might be especially useful for the Fiio and IEMs.
I did. I even had the graph prepared but forgot to post it. I just updated the original post with it. As you see, the Fiio is excellent in that regard.
 
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#11
No, it is a matter of simple formula for power. The HD-650 has 300 ohm impedance which means that the amp is severely disadvantaged from power point of view. Since power = voltage^2/R, you get 10 times less power delivered from the same amp driving a 30 ohm impedance headphone.

I have half a dozen headphones for testing and the HD-650 is the only one that causes the amp to max out before my ears do!
How much the amp outputs alone isn't enough to determine how loud the headphones will play. Of the headphones I recall that you own (MDR-V6, HD 650, HE-400i), HD 650 have the lowest voltage sensitivity, needing more than 0.2 Vrms to reach 90 dB, so that would be the explanation for the fact that they're the hardest to drive.
HE-400i are actually less power sensitive than HD 650, which means power sensitivity isn't a very good indicator of overall headphone sensitivity/efficiency/call it what you want.
https://www.innerfidelity.com/images/SennheiserHD650.pdf
https://www.innerfidelity.com/images/HiFiMANHE4002014.pdf
See bottom right corners.

This is why I carefully said because of its high impedance it is less efficient on the amplifier. Not because the headphone itself is inherently inefficient.
I struggle to read what you said as anything else than calling the headphones inefficient (because of their high impedance).
 

amirm

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#12
@amirm can you check how low you can set the volume pots on these before there is channel imbalance? I'm concerned about the q1, since it doesn't use an alps pot
So I have been struggling to find a good way to present this data. In the past I have shown frequency response at a handful of volume settings. Problem with that is that you may be interested in a different level than the ones I tested.

So I created a new test where I measure the output "gain" (relative level) of both channels and the difference in them as I turn the volume control manually. Here is what that output looks like for Fiio Q1:

Fiio Q1 Channel Imbalance vs Volume Measurement.png


The key line is the one in navy blue with its scale to the right. The faint graphs show the levels as I adjusted the volume manually. So you can use that to decide what level you may be listening at and then look at the corresponding graph in navy blue and look to the right for its dB differential.

One line summary here is that worst case differential occurred at about -44 dB versus full volume which was 0.55 dB (putting aside the extreme attenuation at the end of the scale). Otherwise, the error seems pretty small to me.

The theorem 720 by the way had errors as high as 10 dB!!!

Anyway, what do you think of this type of measurement? It is quick for me to run other than having to be somewhat methodical about how I turn the volume control.
 

amirm

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#13
I struggle to read what you said as anything else than calling the headphones inefficient (because of their high impedance).
Not sure what the struggle is about. I have said subjectively and explained objectively that it is the headphone I have which requires maximum amount of power to achieve the desired loudness. This is not a headphone review but amplifier and in that regard, it is a matter of simple math that the amplifier power is hugely reduced due to headphone impedance.
 
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#14
I have said subjectively and explained objectively that it is the headphone I have which requires maximum amount of power to achieve the desired loudness.
As the measurements I posted show, this is simply not the case. HD 650 need 0.13 mW to reach 90 dB. HE-400i need 0.59 mW to reach 90 dB.
While your subjective experience is correct, your technical explanation didn't account for the sensitivity of the headphones. Even headphones with identical impedance can have different sensitivities.

This is not a headphone review but amplifier
Let's get back on track then. Can we expect to see linearity measurements for these devices?
 

RayDunzl

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#15
Anyway, what do you think of this type of measurement?
I like the presentation.

Suddenly I wonder if the imbalance is also frequency dependent.

For grins, try a sweep at a few different volume levels... See how the error stacks up...
 

amirm

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What has been said does apply to the Speaka USB DAC/amp though. Amir only made a single voltage measurement with a 33 ohm load. Hopefully he'll get back to it and measure it more thoroughly.
Testing USB only devices has been difficult/labor intensive with my Audio Precision Analyzer. With the new unit though, it is much simpler if the device comes with ASIO drivers (or I can use ASIO4ALL). To wit, here is a quick test of Speaka at different loads as compared to Fiio Q1 which I just ran:

Speaka vs Fiio Q1 DAC THD Distortion vs Output Level Measurement.png


The Fiio Q1 definitely outperforms it with higher max output and lower noise/distortion along the way. So if one can afford the larger unit and double the price, better performance can be had.

Back to speaka, once I have all of my tests ported to the new Audio Precision, I can run a more complete set of tests against it and its clone.
 

amirm

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#18

Timbo2

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Yeh, seems like a similar story. Here is a quick shot of the Theorem 720. Note that the scales are different from Q1:

View attachment 12886
Just to make sure I'm reading these correctly, since you are making a manual sweep the time is going to vary. But assuming you are doing your best to keep your speed consistent cutting the time in half should roughly correspond to the volume at 50%?
 

amirm

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Suddenly I wonder if the imbalance is also frequency dependent.

For grins, try a sweep at a few different volume levels... See how the error stacks up...
Are you trying to create work for me Ray??? :D

I ran a test where I changed the volume until I registered 0.3 dB error or so. Then did a frequency sweep:

1527361585488.png


As you see, it doesn't vary at all at this scale. If I zoom the heck in, we get this:

1527361646989.png


So there is tiniest amount of variability with frequency but not a material thing.

Now I have to go and do some gardening. My seedlings need to be transplanted and it is way past the time I should have done it!!! :)
 
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