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Review and Measurements of Fostex HP-A3 DAC and Amp

amirm

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#1
This is a review and detailed measurements of Fostex HP-A3 DAC and headphone amplifier. Even though the product is current and listed on both Amazon and Fostex websites, I also found reviews dating back to 2011. So unless there have been some revisions, this is an "older" unit. It is on kind loan from a member and lists for USD $299 with prime shipping from Amazon.

Any memory of Fostex's long history and Japanese lineage goes out the window the moment you gaze at the ordinary and DIY-like packaging of the HP-A3:

Fostex HP-A3 Dac and Headphone Amplifier Review and Measurements.jpg

What is the deal with the huge washer on the headphone jack showing?

Functionality is not bad with USB and Toslink inputs but is missing S/PDIF. I liked seeing the RCA/Phones switch allowing me to test the RCAs as the DAC output. Note that the volume control changes the RCA levels so you can use it to drive active speakers and such, avoiding a pre-amp.

No gain switch is included which I like to see as mandatory feature given the wild variation in headphone sensitivity and impedance.

No driver was needed as the unit only supports up to 96 kHz sampling and hence is UAC1 compliant.

Let's get into measurements and see how she does.

Measurements
As usual, I start with my Dashboard measurements using USB input:

Fostex HP-A3 USB Input Dashboard Measurements.png


You see what I am seeing? Two rather massive spikes at roughly 15 and 16 kHz severely degrade performance to a distortion that is at whopping 0.2%. SINAD (signal above power of noise and distortion) as a result takes a massive nosedive to very poor 54 dB.

I switched inputs to Toslink and they vanished:

Fostex HP-A3 Toslink Input Dashboard Measurements.png


While not great, at least nothing is badly broken as it is with USB.

I expect no-name companies to release such faulty products, not Fostex. Surely they have professional measurement gear to measure such obvious fault with the USB implementation.

Given how poor the performance of USB is, I am going to truncate the rest of the test and just show one power vs distortion curve using 300 ohm load:

Fostex HP-A3 Toslink Input distortion vs power at 300 ohm Measurements.png


Above was with Toslink by the way. Power is at 11 milliwatts which is OK.

Conclusions
I hate to bring bad news to members who loan me their equipment but there is no getting around the facts here. The USB implementation of Fostex HP-A3 is clearly broken. I don't know the source of that noise. It could be from within the unit, or bleeding from my computer's port in which case, the signature will be host dependent. With so many choices of DACs and amps out there, I see no reason to tolerate sub-par engineering as we see here.

This is a failing a product and I can't recommend its purchase.

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Jimster480

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#2
Short and sweet (or not so sweet for owners of this product) review.

With SINAD, what about your linearity test?

Since you got your new gear you haven't been doing your ENOB test (just showing the graph) and what about your old sine wave measurement where you had a colorful readout of the sine wave reconstruction?

I'm not nitpicking this review, I'm just wondering.
 

Veri

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#4
Short and sweet (or not so sweet for owners of this product) review.

With SINAD, what about your linearity test?

Since you got your new gear you haven't been doing your ENOB test (just showing the graph) and what about your old sine wave measurement where you had a colorful readout of the sine wave reconstruction?

I'm not nitpicking this review, I'm just wondering.
I think amir makes it short and simple if he comes upon big failing tests right away, since he (already) would no longer recommend the product.
 

helloworld

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#5
Is it possible to replace a XU208 xmos USB card for these broken usb input? A XU208 xmos USB cost about $20
 

Veri

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#6
Is it possible to replace a XU208 xmos USB card for these broken usb input? A XU208 xmos USB cost about $20
It's a mistake somewhere in the implementation, can't expect a chip dropped in will fix this.
 

amirm

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#7
I think amir makes it short and simple if he comes upon big failing tests right away, since he (already) would no longer recommend the product.
Exactly. If the owner asks for more tests I will run them but for others who may be interested in the product, there is no sense in showing more measurements.
 

Jimster480

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#8
Exactly. If the owner asks for more tests I will run them but for others who may be interested in the product, there is no sense in showing more measurements.
Yes but at the same time there are some other great products that you do recommend and still didn't do the tests the way I described.
This is all I am asking as your testing methodology has changed since you have received your new gear.
 

amirm

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#9
Yes but at the same time there are some other great products that you do recommend and still didn't do the tests the way I described.
This is all I am asking as your testing methodology has changed since you have received your new gear.
The new Audio Precision analyzer software is very different so yes, I have adjusted the testing to its capabilities and format.

That said, ENOB was not a measurement by itself. It was just a manual computation from the linearity test which I still conduct. You are correct that I have stopped computing that as it took so much of my time explaining it. :) The data is still on the graph and if there is a strong feeling, I can bring it back.

As before, when I have to perform "open-loop" tests where my analyzer cannot control the audio product such as in phones, networked DACs, etc., the tests will continue to be limited in range.
 

Jimster480

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#10
The new Audio Precision analyzer software is very different so yes, I have adjusted the testing to its capabilities and format.

That said, ENOB was not a measurement by itself. It was just a manual computation from the linearity test which I still conduct. You are correct that I have stopped computing that as it took so much of my time explaining it. :) The data is still on the graph and if there is a strong feeling, I can bring it back.

As before, when I have to perform "open-loop" tests where my analyzer cannot control the audio product such as in phones, networked DACs, etc., the tests will continue to be limited in range.
I understand, that's all I was wondering :)
 

urfaust

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#11
Thanks for the review, i almost ordered one a few weeks ago, there was a great deal on it from a local french retailer and i thought i would be good enough for one of my PC in USB (!), then i found it really ugly on the outside. In my mind Fostex was a serious brand in my teenage years, seems like just old memories now..
 
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