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hollowman
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Need more info on Ayre Acoustics QB-9 USB DAC

One of my pet peeves about reviews/reviewers is inconsistency. For example, take Technical Descriptions, the part of a typical Stereophile review that usually comes before the "Subjective Sound Quality" section. Lack of details in Technical Descriptions really hurts the review and may prevent me from taking that reviewer seriously. Now they all can't be Robert Harleys (or at least RH during his Golden Years -- the 1990s, at Stereophile), but in his write-up for the Ayre QB-9, Phillips does not bother to mention the DAC chip or output components/topology this D/A processor uses. As a subscriber, an in-depth reader/analyzer, and a potential purchaser of reviewed products, I was/am/will always be expecting these details -- I like to know what I'm looking at or buying. If anyone knows these details about the Ayre DAC**, please reply to this message ... thx!

BTW: hats off to JA for the superb Measurements section of this review (tho' I'm a bit puzzled about the missing p-p jitter data). JA: I've seen you slip in Technical-Decryption details into your Measurements section (e.g. specific components) when the main reviewer may have "missed" them. But, frankly, I don't like to fish around for this info -- it should be standardized to the Technical-Description section. If a reviewer isn't "tech-savvy", a crash course in how to use a Torx wrench, a digital camera and basic PCB-component-identification is in order!

** Yes, I realize components, by themselves, are not the be-all/end-all of a product's ultimate performance ... implementation is equally (if not more) important: i.e., components must be encapulated in highly-effective and robust topology. That said, it's important that reviewers discribe both design/topology and components. Yes, there is a slight reverese-engineering risk here for the manuf. But that's what the USPATO is for!

hollowman
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Re: Need more info on Ayre Acoustics QB-9 USB DAC

Any takers on this query?
If neither the editor (JA) nor reviewer (WP) have anything to add, then perhaps an owner of the QB-9 can pop the hood for us. Of course, this would be pretty embarrassing to Stereophile, and rightly so. Don't get me wrong: I like the magazine; so having a review depart from norm (see orig post above) is disconcerting...especially for a product that was judged Stereophile's 2009 Overall Product of the Year! For a product to receive this kind of accolade, it needs to backed, IMO, by extensive topological description/discussion, part usage/choice, etc. JA's digital-processor reviews are a good (or, rather, "good enough for govt. work") example of what I was expecting for the QB-9 review.

Again, I'd like to see the following:
- Input receiver/decoder (other than the TI chip) and other components (e.g., use of pulse transformer, buffer)
- PCB: how many layers, build quality
- Clock (XO): what's the osc. freq.?, separate and regulated power
- More specifics on upsampling topology
- DAC IC (chip): brand/model
- Output components/topology: I/V, analog output reconstruct. filter and # of poles, brand/model of opamps (if used), etc.

Thx in advance for light anyone can shed.

BTW: Here's an example of a "review" of the QB-9 that, IMO, is pretty much useless.

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Re: Need more info on Ayre Acoustics QB-9 USB DAC


Quote:
Again, I'd like to see the following:
- Input receiver/decoder (other than the TI chip) and other components (e.g., use of pulse transformer, buffer)
- PCB: how many layers, build quality
- Clock (XO): what's the osc. freq.?, separate and regulated power
- More specifics on upsampling topology
- DAC IC (chip): brand/model
- Output components/topology: I/V, analog output filter, brand/model of opamps (if used), etc.

I am briefly borrowing a QB-9 for another purpose, so while I have the unit I will take a look inside.

John Atkinson
Editor, Stereophile

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Re: Need more info on Ayre Acoustics QB-9 USB DAC


Quote:
I am briefly borrowing a QB-9 for another purpose, so while I have the unit I will take a look inside.
John Atkinson
Editor, Stereophile

Very cool. I take it you're working on a Follow-Up for the mag? IAC, if the manuf. allows -- and in addition to the myriad requested description specifics I noted above -- more images (especially of internals) would be super cool.

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Re: Need more info on Ayre Acoustics QB-9 USB DAC


Quote:
I take it you're working on a Follow-Up for the mag?

I am doing some additional measurements, but Jon Iverson and Art Dudley will both be spilling some more ink on the QB-9 in the April or May issues.


Quote:
more images (especially of internals) would be super cool.

You can find one shot at http://www.stereophile.com/digitalprocessors/ayre_acoustics_qb-9_usb_dac/index2.html but I will capture a plan view of the main board when I get the unit from Art Dudley later this week.

John Atkinson
Editor, Stereophile

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Re: Need more info on Ayre Acoustics QB-9 USB DAC


Quote:
I am doing some additional measurements, but Jon Iverson and Art Dudley will both be spilling some more ink on the QB-9 in the April or May issues.

Cool. Hopefully, you can shed light on technical details noted above.

Quote:
You can find one shot at http://www.stereophile.com/digitalprocessors/ayre_acoustics_qb-9_usb_dac/index2.html

Yeah, saw this in the print mag, too. Looks like a stock shot. The one in the print version has two inset bubbles above it, attempting to show more details of certain SM components. But the parent image is so small, the microscopic child insets are valueless.

Quote:
...but I will capture a plan view of the main board when I get the unit from Art Dudley later this week.

Super! Looking forward to the images. Thx for all the leg-work.

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Re: Need more info on Ayre Acoustics QB-9 USB DAC


Quote:
I will capture a plan view of the main board when I get the unit from Art Dudley later this week.

Okay, I took the lid off while I was remeasuring the QB-9 today. It is pretty much as you describe: separate board with TAS1020B USB receiver, this powered from the USB bus.; data taken first to a Xilinx FPGA, which does all the necessary DSP, then to a Burr Brown DSD1796 DAC chip. Don't see any op-amps, so I assume I/V conversion is done with discrete devices or even with just resistors. Output stage is all-discrete, using surface-mount devices. Two crystals are used, 22.5792MHZ for 44.1k/88.2k data, 24.576MHz for 48k/96k. Quite a lot of onboard regulation apparent.

John Atkinson
Editor, Stereophile

hollowman
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Re: Need more info on Ayre Acoustics QB-9 USB DAC


Quote:
Okay, I took the lid off while I was remeasuring the QB-9 today. It is pretty much as you describe: separate board with TAS1020B USB receiver, this powered from the USB bus.; data taken first to a Xilinx FPGA, which does all the necessary DSP, then to a Burr Brown DSD1796 DAC chip.

Thx for the legwork...
What are ICs next to the white USB-to-main-board ribbon cable? Specifically:
- two ICs and op-amp(?) on USB board
- the small IC to the lower left of the Xilinx (main board)
Also, do you see star grounding anywhere?

Quote:
Don't see any op-amps, so I assume I/V conversion is done with discrete devices or even with just resistors. Output stage is all-discrete, using surface-mount devices. Two crystals are used, 22.5792MHZ for 44.1k/88.2k data, 24.576MHz for 48k/96k. Quite a lot of onboard regulation apparent.

Yeah, CH and company have done a good job on this one. Use of SMD and lots of regs keep leads short and -- among other things -- minimize parasitics. (Sorta reminds me of Naim digital topologies; and perhaps why the two companies score well in pace/rhythm/timing, bass slam, etc.)
To the QB-9, I would've added:
- Shielding around transformer
- Cu shielding on every digital IC (with Cu shunted to chassis gnd)
- the option of BNC or RCA SPDIF input.
- option for user to adjust/customize sampling and filter parameters via PC software

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Re: Need more info on Ayre Acoustics QB-9 USB DAC


Quote:
What are ICs next to the white USB-to-main-board ribbon cable? Specifically:
- two ICs and op-amp(?) on USB board

These appear to all be optocouplers/isolators, to keep the USB board, which is connected to the dirty PC ground, galvanically separate from the main board: one each NEC PS2801-4. IL 715-3, and IL 710-3, in order of pin count.


Quote:
- the small IC to the lower left of the Xilinx (main board)

This is the flash PROM storing the configuration data for the FPGA, part number Xilinx XCF025.


Quote:
Also, do you see star grounding anywhere?

Not superficially, but there may be ground tracks on the underside of the main board, which I didn't remove. What I found interesting is that there is no solder mask on the production boards whereas there was on the prototype shown in an earlier posting.

John Atkinson
Editor, Stereophile

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Re: Need more info on Ayre Acoustics QB-9 USB DAC


Quote:
Not superficially, but there may be ground tracks on the underside of the main board, which I didn't remove. What I found interesting is that there is no solder mask on the production boards whereas there was on the prototype shown in an earlier posting.

John Atkinson
Editor, Stereophile

Charles:

Very nicely done!

hollowman
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Were my threads (posts) edited and/or deleted?

Hi Stephen Mejias,

I created this thread but haven't checked in on it until just recently ...

http://blog.stereophile.com/content/need-more-info-ayre-acoustics-qb-9-u...

Disturbingly, there is quite a bit of content missing from the thread including a whole (complete) post (I think it was #6; I have some records as I composed it in Word before posting).

Can you please tell me what happened?

Thanks!

Best Regards,
-hm

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