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Henry Engineering Matchbox II USB DAC/ADC Review, Measurements & Tear Down

amirm

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#1
The Henry Engineering Matchbox II was loaned to me by a member for measurements and hardware teardown/review. I am not sure how well known this DAC is. It is targeted toward television broadcast world. It unusually has both ADC and DAC plus professional AES/EBU output (balanced version of S/PDIF). In that regard, it appropriately only has balanced inputs and outputs.

upload_2017-10-4_18-9-42.png

Retail price is fairly high for consumer market but appropriate for professional use at $479.

Specs are rather modest, stopping at just 48 Khz sampling and bit depth of 16 bits. Again, this is fine for video applications where 48 Khz sampling is standard and 16 bits sufficient.

Measurements
As always, my go-to measurement is 24-bit, 48 Khz J-test signal. I had not noticed that this device is limited to 16 bits when I did the testing so the 24-bit depth of the signal is lost on it. Indeed, that shows up in the measurements:

Henry Engingeering vs Behringer.png


The Matchbox II is shown in red and in yellow, I have the Behringer UMC204 HD USB ADC/DAC ($79) using its balanced output just the same. Immediately we see a much lower noise floor for the UMC204. However that is offset by its anemic output resulting in 123 db differential between the noise floor and peak signal (NOTE: this is not the true signal to noise ratio).

The Matchbox II has far stronger output. It initially put out some +20 db of output. Using its adjustments I brought it down to minimum which was still higher than Behringer. Using the same measurement as above (not shown) the Matchbox II achieves 120 db. So fairly comparable to Behringer UMC204 HD.

Not so comparable is good bit of spurious spikes at many frequencies shown with red arrows. Some of these rise up as much as 20 db from noise floor showing less than ideal engineering. Compare that with the super clean output of the Behringer UMC204HD (yellow) and you see that much better can be done.

For another comparison, I fired up my newly acquired Exasound e32 DAC ($3,500) and compared it to the Matchbox II:

Henry Engingeering vs Exasound.png


The Exasound runs circles around it, producing 140 db differential between its measurement noise floor and peak output (again, don't confuse this with signal to noise ratio). It is also much freer of spurious responses than Matchbox II.

Conclusion
From measurements point of view and specifications, there is little to recommend the Henry Engineering Matchbox II. It is limited to 16 bits and 48 Khz which in this day and age, is simply not acceptable. Its measured performance lags much cheaper DACs like the Behringer UMC204HD.

Its high output level though is nice as is the option of having AES/EBU output and full balanced input and output. I did not test its headphone output but it comes with one too.

In the next post, I will do a teardown of its hardware.
 

amirm

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#2
Hardware Teardown
The Henry Engineering Matchbox II comes in typical, low-volume, DIY level enclosure. It is rather heavy duty though. Only four screws hold the top and it was easy to take the top off:

Full inside 20171004_173839.jpg


Immediately we see that despite being a small box, it includes a linear supply. Not a fan of the AC wire going across the whole unit to get to the primary inputs of the power supply. +- 15 volts are produced to driver the output op-amps which explains their high output level capability. The op-amps are socketed so the tweakers can go to town messing with them.

The capacitors are Lylon brand which do not warm the heart of any engineer as far as quality brand is concerned. Since this is a linear power supply and caps are running at very low voltages (as compared to running at peak DC mains voltage in switching power supplies), reliability should not be a major concern.

There is a nice routed slot separating high voltage from low voltage part of the PC board.

The DAC/ADC is in the daughtercard on the right. It popped off easily. For a professional application I would have liked to see a screw holding it down.

DAC module 20171004_173933.jpg


We see an integrated USB ADC/DAC silicon from BurBrown/TI (PCM2906C). 1000 piece budgetary pricing is $5. I suspect this ADC/DAC silicon is designed for embedded and PC solutions, not for dedicated high-end external DACs.

Strangely -- in a good way -- the capacitors here are high-quality Nichicon and at 105 degree rating no less. See no need for the latter as the unit runs pretty cool. But put in a rack with poor cooling and other sources of heat may have motivated this choice but then again, the main board did not sport such quality.

As we see, construction is modern surface mount with the exception of the Nichicon caps and connector.

Speaking of those parts, let's look at the back of the board:

flux residue 20171004_173921.jpg


We see flux residue from soldering which has not been cleaned.

Worse yet we see solder splatter on some of the parts:

Solder splatter 20171004_173957.jpg


That bit could fall off and cause a short elsewhere. I saw other solder bits on other components.

Similar less than stellar soldering quality exists on the main board which is entirely through-hole construction.

Conclusion
Overall, there are no safety issues here which is good. But otherwise, for a nearly $500 device, I expect better quality of construction. Combined with less than ideal measured performance, this DAC leaves me grumpy and anxious to run and find something better to review and measure! :)
 
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