Cambridge Audio 851D excels at "budget" price point...

[JonMarsh]

OnTheBench.key by Jon Hancock, on Flickr



This came to my attention because of a flyer from Audio Advisor offering this unit for just $999.99 on April 1. (no fooling).



While the performance is not quite up to the standards of say, an AURALiC Vega, it is VERY close, according to JA's measurements- 19 bits of effective resolution, nice input filter options, and overall very good results in Stereophile's evaluation.

http://www.stereophile.com/content/cambridge-audio-azur-851d-da-processor-measurements#ReZhIsdujZqH3qE6.97

If an NAD M51 or AURALiC Vega are out of your price class for now, this bears serious investigation and consideration. It uses Analog Devices AD1955 in dual differential mode; this is the DAC used in the Berkeley Alpha DACs version 1 and 2. That price is up on Audio Advisor's web site as I write this.

The 851D is listed in Stereophile's April 2016 recommended components, and Art Dudley did wax rather poetic about the 851:

The Cambridge 851D was nothing short of shocking: It trounced the Halide and came close enough to the LP to scare if not actually bite it. The Cambridge allowed Heifetz's violin the same clear delicacy in its opening notes as the vinyl, and allowed the orchestra as great a sense of scale as heard from the LP. The sound through the Cambridge was open, yet with no lack of substance. Heifetz's tone, especially at the opening of the Finale: Allegro guerriero, was nothing short of exquisite. And the Cambridge made me realize that Sargent had, in this piece, a much more flexible sense of time than I'd ever before appreciated: More than once, a very subtle accelerando made itself apparent, especially in the plucked double basses during the introduction. Only in its conveyance of physicality—in the plucked strings of the harp, the breath behind the horn, the strike of the cymbal—and in its conveyance of the last iota of timbral saturation, did the LP win out.
Read more at http://www.stereophile.com/content/c...0f2GjvScDSd.99

Now, the interesting question from a marketing viewpoint is whether this is opportunism on Cambridge Audio's part or Audio Advisor or some combination of the two- perhaps this has been a slow moving product, (due to inept promotion?) and now they have some wind under the wings, so to speak, and are taking advantage. Or maybe there is even a newer version in the wings... who knows? But from everything I know about the market, I seriously doubt you'll find a better deal for this kind of money.

BTW, it includes balanced outputs and AES/EBU inputs, and according to JA even the TOSLINK worked at up to 192 kHz. (I don't do gear without balanced I/O these days)

Also, it appears that the 851D uses the same solid state volume control (with multiplying DAC as attenuator/gain control) as the 851A, NOT using a digital domain volume control, but that is not confirmed on the web site, but by presentation of some secondary details.

Since this is not the sort of thing I would want to speculate on and mis-represent, I just ordered a silver version to check out and evaluate. A full review will be forthcoming, including confirming the bench performance, and investigating the volume control behavior.

If this unit performs as expected, and reported by Stereophile, I will use it as my program source for the more budget system evaluations in the future. (CatZ and similar level projects).

Let's put this in perspective- the dynamic behavior and distortion appear to be very good, including power supply residual noise; the effective resolution is about 19 bits; the best measured digital sources right now are running about 21 bits, but it typically takes you $3K or more to get to that level.

My general recommendations right now are the AURALiC Vega at the $3.5K level and above for some distance; below that it's a tight race, with the NAD M51 being a long time favorite, but the Schiit Yggdrasil getting the nod these days at $2K (limited distribution; direct from Manufacturer only- in reality, it's a $3K class product).

I've looked now and then at items in the $1K class and haven't seen anything I could really get excited about. The $1599 851D at $999.00 changes that.

More later...

[wkhanna]

Great stuff, Jon!

your sense of value combined with your technical chops for weeding thru the chaff make your recommendations something everyone should pay close attention to.

thanks!

[knowledgebass]

I see it for $1,299CAD from a "authorized dealer" through the http://amazon.ca marketplace.
I'm not endorsing this Amazon seller, and have had no dealings with them, but there may be other ongoing discounts for this unit at all dealers.

[JonMarsh]

I've checked and seen it at discounted prices from a number of vendors. Checking tracking again on the one I ordered, it should arrive some time Thursday.

I have several things in mind I could do with it, but what most likely will happen is that it will go into a secondary simplified signal chain in the front end, along with a new Cambridge CD transport I ordered early this year, and that will be part of a simplified (to operate) setup for playing CD's in the family room to accommodate GF (too many things to turn on with the streamer and re-clocker and rubidium standard and DACs etc for GF, even though she's an ex IBM systems engineer... :W

[JonMarsh]

Getting setup for measurements and putting a plan together- should be able to figure out what kind of volume control it actually has, whether it's a multiplying DAC attenuator (desired) or a control truly in the digital domain (not as desirable)

In the meantime, why not a couple of pics?









Note, the rear panel is organized around the idea of "mundane" digital inputs using S/PDIF or TOSLINK available for several inputs, but there are several "premium" inputs, including an asynchronous USB input with ground lift options, a gold BNC S/PDIF, and an AES/EBU balanced input.

Available outputs are both single ended and Balanced.

Note, the 851D can be configured to work like a DAC with fixed full gain, or like a preamp with the variable gain volume control.

The cool thing about the latter is that for someone who has a system with only stereo digital inputs, this is all you need in front of a power amplifier. But it has all the connectivity for HT style system control built in, and has a an auto-power down feature to, in the absence of a signal for 40 minutes or so.

[JonMarsh]

Ladies and Gentlemen, let's look at some results...

OK- a bit of spare time available- so I've got some data on the APx555. My goal was not to duplicate all the measurements on Stereophile, but rather to investigate some specific issues, and perhaps reconfirm a few measurements that anyone can agree are significant, and which many competing units at higher prices don't necessarily do well on. Testing was done using the BNC S/PDIF input.


Volume Control- is it "digital" as some promo material states, or is the answer more nuanced and more useful?

Why is this important? It all comes down to bit depth and throwing away bit depth when you're using some significant attenuation- such as 20dB or more, and especially with a 16 bit signal (CD resolution) The volume control on the 851D can be enabled or disabled, so the unit can be used like a conventional DAC, or a DAC Preamp, in both cases with multiple inputs.

Ideally, I'd like to see a precision analog solution for the volume control - what this generally means is a rotary encoder control (or remote) as the input, and a counter that cycles the value fed to a relay switched precision resistor array OR a multiplying DAC chip, in which the internal R2R ladder is used to form an attenuator or gain control. What's often done, is running the digital input through a digital attenuator on board that attenuates the numeric value of the samples by a fixed amount before sending them to the actual DAC chip.

Well, with the right test there's a fairly easy way to tell what's happening. This is what we did:

The key is using a low level signal test for which attenuation is done in the digital domain, it will be spotted because of how thoroughly the waveform is mangled. Conversely, if the waveform is attenuated in the correct manner, we can safely surmise that the volume control is not a conventional digital attenuator, but acting in the analog domain, even if it is controlled digitally, say, by a BCD counter that indexes a multiplying DAC or relay set up and down the gain ramp.

What the test signal? Simply one of the classic demanding low level signals commonly used for evaluating DAC behavior- 1 kHz square wave at -90dBFS input level, which is basically just toggling the LSB (Least Size Bit) on the 16 bit PCM scale.

With the volume control bypassed, or with it turned up full, here's what you get from the 851D:


Figure 1
1kHz 16Bit_FS by Jon Hancock, on Flickr

Mind you, those are 200 uV steps around the zero volt level; with well defined steps and fairly visible Gibbs ringing. This level of clarity of the waveform at the low signal level places the 851D in the higher tier of DACs- I can show you many costing several times it's price that don't do as well.

So, the experiment is to crank the volume control down... if it is just adjusting the signal to the DAC, there's no where left to go below 1 LSB...

Figure 2
1kHz 16Bit_FS -6dB by Jon Hancock, on Flickr


But here at -6dB on the preamp (front panel readout for the 851D gives you the actual dB attenuation) it's dropped exactly where it should be, to half the voltage at 100uV peak, and otherwise there is no waveform distortion.

From this, I'm inclined to believe Cambridge Audio is using the same multiplying DAC based volume control as in the 851E analog preamp, though they don't say so in their literature. That's a good thing, if so, because it should result in very precise and predictable attenuation levels, AND very close channel tracking between right and left channel, something that's a bugaboo for analog pots.


How well does the volume control track the settings, and how closely do channels track each other?

To test this, I performed swept frequency response tests from 10Hz to 20kHz, checking both channels output, and looking at several attenuation levels, appending the test results to the same graph.


Figure 3
Frequency Response and volume tracking10Hz-20kHz by Jon Hancock, on Flickr


Now, this is the way volume control should work- tracking so tight you can't see any material difference in the channel balance.

One quick check- let's zoom in on that bottom trace with -30 dB attenuation-

Frequency Response and volume tracking10Hz-20kHz-17db by Jon Hancock, on Flickr

Here, we can see that there is about 0.1 dB of channel misbalance, and also about 0.1dB of roll off at the frequency extremes at 10Hz and 20 kHz. This is a very low value...



What's all this 24 bit versus 16 bit stuff, and under what conditions may it be fairly obvious, at least on the test bench?

OK, take a look back to the start with Figure 1...

Now, here's the 1 kHz sine wave at the same 90dBFS input level, but with 24 bits of data

Figure 4
1kHz 24Bit_FS by Jon Hancock, on Flickr

It's not hard to see that it's a better representation of the signal... though let's face it, it's a signal at a very low level.


Let's also look at some FFT's (Fast Fourier Transforms) - which show the harmonics and levels in relation to the fundamental...


Figure 5: -90 dBFS input level 1kHz, 16 bit data
1kHz_-90_16BitFFT by Jon Hancock, on Flickr


Figure 6: -90 dBFS input level 1kHz, 24 bit data
1kHz_-90_24BitFFT by Jon Hancock, on Flickr


As you can see from this, the Cambridge 851D is a quiet unit, and quite clean at 1kHz with low level signals.



I like my "boom and tinkle"- how does this unit stack up with regards to low frequency harmonic distortion and high frequency intermodulation distortion at high output levels?

First, a good test is to take it back up to 0dBFS at 1kHz, and see if there are any funny things going on BELOW 1 kHz; this will usually be due to power supply issues. Note that I've adjusted the volume control so that the output shown in the graph corresponds with the input level; in other words, we're running at net unity gain. This makes it easier to put a number on how far down noise and distortion components are from the main signal, when on the graph it is at 0dBFS.


Figure 7: 0 dBFS input level 1kHz, 24 bit data
1kHz 24Bit_0dBFS by Jon Hancock, on Flickr


This looks about is nice as I think we can hope for, so let's look at 50 Hz.

Figure 8: 0 dBFS input level 50Hz, 24 bit data
50Hz 24Bit_0dBFS by Jon Hancock, on Flickr

Gee, are you getting bored by all these clean results? Keep in mind I can show you units that retail for 4x the 851D's original price that don't do nearly as well...


For high frequency distortion, we can't really rely well on simple harmonic distortion FFT spectra, because it's mostly filtered out by the reconstruction filter, especially at lower sampling rates. A better way to evaluate is two tone HF CCIF Intermodulation distortion, and looking at the distribution of side bands of the difference frequency between the two tones, which using 18 and 19 kHz at the test frequencies, is at 1 kHz multiples.

This is what the test signal looks like, with a peak level of 0dBFS, the level of each individual tone is much lower, because they generate a beat pattern which reinforces and cancels depending on the specific phase alignment versus time.


Figure 9: 0 dBFS input level 18+19kHz CCIF test signal, 24 bit data
CCIF_18-19kHzOutputScope by Jon Hancock, on Flickr


And here, the FFT plot:

Figure 10: 0 dBFS input level 18+19kHz CCIF FFT, 24 bit data
CCIF_18-19kHz by Jon Hancock, on Flickr

This is a very nice result on this test, with none of the difference product being over the -120dB level.


BTW, I've looked on Cambridge Audio's web site, and I think the price drop is connected with them discontinuing this model. You can't navigate to the page for the 851D by their main menu, but you can find it via Google and get there.

Of course, it may be that they'll bring out an improved version... who knows? But if you have something around $1K altogether to spend on a DAC and preamp, and only need digital inputs, it's very hard for me to imagine doing much better than this.

As there is no headphone jack on this puppy, a listening test will have to wait until the weekend...

[wkhanna]

Jon, your explanations of such highly technical information are made so understandable that even i think i know what you are talking about!

well done, Maestro

[TEK]

Gee, are you getting bored by all these clean results? Keep in mind I can show you units that retail for 4x the 851D's original price that don't do nearly as well...

That would actually be quite interesting and educational. Would it be possible to take a couple of the most important graph and compere a "bad" unit to a good unit, and then do some explanations about what the differences are, as well as how you would expect that to affect the listening experience?
My problem, as a total novice, is that it is hard to evaluate what the different is and the meaning of it.

[5th element]

A digital volume control in a unit such as this should be fine.

The DAC used is 24 bit and when fed with 16 bit data it should fill in the missing bits with zeros. If the internal volume control of the AD1955 is used then there's plenty of room on the digital front end of the DAC to attenuate a 16 bit signal without any loss of data.

When using 24 bit data the LSB(s) is(are) going to be dominated by analogue noise either on the output stage of the DAC or simply noise inherent in the recording, so you'll still have a decent amount of range available on the digital volum control before you start throwing anything away.

Of course this is the reason why ESS use 32 bit digital front ends, as well as many others nowadays.

[JonMarsh]

that would be the case if DAC's routinely converted 16 bit to 24 bit data, but that often/usually doesn't happen. I believed this would be the case a number of years ago, but experience since then has changed my mind.

Let's look at one case- CD quality program material, which is probably 95% of what I listen to still. (always working on changing that, but...) And also compare against 16 bit if used with a SABER DAC realizing 132 dB (not a uniform situation by any means) and also how 24 bit data will likely do with the Saber - (taken from Six Moons review)


6moons audio reviews: AURALiC Vega by Jon Hancock, on Flickr


My own conclusions after doing a lot of listening tests, and getting similar feedback from my friend in Munich and his wife, is that it is better to use a high grade analog preamp than not, unless one doesn't have access to that- or must otherwise do things like pass through an HT processor signal path. I didn't used to think this way, but after listening in quite a few different situation with different components ( including original Berkely Alpha DAC, NAD M51, TotalDAC, and AURALiC Vega), I'm now on the wagon for a high grade preamp being the best way to go.

Of course, that qualifier is where the sticky wickets come in...

[5th element]

As far as I am aware all 24 bit dacs pad out the missing bits when fed with 16 bit data. Heck most work with a 64x bit clock which can clock in 32 bits per channel, so the front ends are certainly paying attention to how the data is packaged. For the internal 24 bit architecture to work the missing 8 bits have to be filled in with something otherwise things would stop working correctly.

The front end within 24 bit DACs will process at 24 bit, so if you feed it 16 bit data you can actually attenuate it by 48dB before the digital side of things starts to lose data. The trouble comes with the noise floor inherent within the conversion process. Even if the 48 dB attenuated 16 bit signal can be fully represented at the DACs digital volume control, the noise from the DAC is still going to come up and dominate giving you a real world S/N of 56dB rather than the full 96.

To this end the digitally represented volume control of the first table is indeed correct, but the issue I take with it, is with the analogue one. This is assuming a ridiculously low noise floor post DAC where one attenuates both the noise and the signal such that the S/R remains intact. The trouble with this assumption is that most analogue preamps, or any volume controlled stage, contains a signal buffer after the volume control element that limits the realistic noise floor of the entire system/source to around 122dB with respect to a 2Vrms signal - the usual standard for a single ended Hi-Fi signal.

With an analogue volume control, with a noise floor imposed of -122dB, you can only provide around 26dB of attenuation before you start throwing anything away.

Once you start using something like the AD1955, found within the DAC here, with 120dB of analogue resolution you're pushing the limits of both whatever the DAC unit can do and whatever preamp you may choose to put after it.

In these cases if you cannot hear the noise floor then you're certainly not going to be throwing away any data.

The only time when I have ever encountered audible issues with digital attenuation is with VST work, using both a digital attenuator as part of a processing pipe line and then a 24 bit digital volume control south of the VST plug-in. This was the worst of the worst in terms of what can happen, as the internal VST plugin would digitally turn down samples (amplitude) as part of the way the synthesizer worked, and I would then level match, digitally, after it. Not a good combination. In this situation the tail end decay of the VST plugins reverb was noticeably quantised, which gave me a right headache. Of course the system wasn't fully functional yet and I was toying with the digital level matching only as a stop gap method. That was quickly replaced with a CS3318 and the 30dB of digital attenuation that I was doing post VST, to level match drivers with considerably different sensitivities, went analogue.

You'll get no argument from me, where processing is required in multiway, DSP active systems, that you absolutely have to level match with an analogue volume control otherwise it's a recipe for, ultimate high fidelity, disaster. Of course the above example isn't likely to be encountered with properly mastered music (although I have got some CDs that audibly clip and that isn't pleasant) in two way systems. But those guys with the miniDSP?

[BobEllis]

I purchased an 851D based on this test and other comments. Initial impressions, WOW! It's still cold from sitting in the UPS truck and even though Christmas decorations have my Ardents up against the wall the clarity and realism of percussion is notably better than either my Schiit Modi MB or the Oppo BDP-103 analog outputs. I can't wait to pull my speakers out to a more proper listening position and see what this can really do.

I never read the dimensions, and given the connectivity I should have expected the size, but it still surprised me. Somehow in my mind's eye it was a 3/4 width 2.5" high box, not 17 x 4.2.

[JonMarsh]

Yeah, it is a full sized puppy- not like the AURALiC gear- but look at all the goes into and goes outa on the back panel- you've got to have some real estate for that!

[wkhanna]

Bob,

are you currently running the Pass A75 DIY amps?

[BobEllis]

Not yet, Bill. That's in storage, but will come out when the tree comes down. At the moment I'm listening with a Honey Badger that has way too much gain.

The DAC sound warmed up after reaching room temperature/breaking in for a few hours. Initially seemed a bit bass shy, but reached a lovely balance. Imaging is better than the Oppo by a long shot. Songs that I'd thought were center congested now throw an image wider than the speakers while locating instruments precisely. Still eager to get the speakers back to a more proper position.

[Jonasz]

So wich one is preferrable soundwise, Cambridge 851D or the NAD C510 (wich is supposed to be identical to the M51)?

[BobEllis]

I guess Ron and I will have to get together to do a DAC face off, since he has an M51 and I have an 851D. We are both very happy with our DACs and Ardents.

Jon's discussed the logic behind his preference for volume control in the analog realm. If your system resolution is high enough you'll miss the details thrown away to give higher attenuation values. Before my Ardents the impact of the Oppo BDP-103 digital volume control wasn't significant to me. This effect can be minimized if you can set up your system to need minimal attenuation. Although the 851D easily outclasses my Oppo, the difference is notably less with my low gain Aleph-J (volume setting 80 for normal listening) than when my Honey Badger (volume setting 20) is driving. Also worth noting is that the volume control system in the 851D

[Jonasz]

A face off would be very interesting indeed!
I have the NAD C510 and like it a lot. My system is in a transitional stage at the moment however and I can't hear it's true capabilities bc there's a Minidsp 2x8 acting as crossover with all the extra conversions and whatever contaminating the audiostream. Before acquiring the NAD I had my HT-receiver feeding the minidsp. The difference with the NAD is shocking despite the minidsp. The receiver will never get back into my music system again. The next step is to find a passive speaker design to build, don't trust myself with passive crossovers, and keep it simple with good audio components in the signal chain.

The 851D got the volume control in it's favour while the NAD has excellent HDMI connects for high quality 2 channel music video consumption. But wich one sounds best...? :P

[BobEllis]

Second hand reports are that unless the NAD is used at very high attenuation you'll be hard pressed to hear a difference.

If you just want to get the 2 channel signal out of an HDMI connection, then you need a device called and HDMI Audio Extractor like this https://www.amazon.com/Agptek-Premiu.../dp/B00TOBFSTE

[augerpro]

851D looks like it's been discontinued

[wkhanna]

wonder how that will effect the used market price?

[JonMarsh]

It was my expectation that was in process when the price cut came out...

That most likely means a replacement will be issued soon. (cross fingers- it's a great unit even at it's original price point).

[Jonasz]

Well, got one of each now and will decide wich one to keep after having compared them on a good pair of passive speakers.

[BobEllis]

I'm glad I got mine in time. Amazon listed 3 available when I bought it.

[BobEllis]

Now I've gone and done it! I just returned to the summer camp. While the Ardents stayed behind, I decided that 6 months was too long to go without my 851D since it is so easily transported. It just happens to be the perfect height for a monitor stand, too. At home my desktop system has been a set of Zaph designed Seas Excel based MTs. As Zaph isn't a believer in exotic caps, these use those GE surplus 4.7µF caps. I'd been using a Schiit Modi MB DAC and a Dayton T-Amp. Not terribly exciting sound, but it seemed satisfactory with the Ardents in the living room.

So now I am the 851D is driving a balanced Aleph J clone to the same speakers. The question is now what DAC am I going to drive the Ardents with come Fall? It's going to be next to impossible to downgrade the desktop system. As luck would have it, when building my Ardents I bought a pair of 4.7 µF Clarity Cap MRs before Jon changed to 3.9µF to accommodate the -02 woofers. These will shortly find their way into the tweeter circuit, and very likely the woofer shunts will become Jantzen Z-Superiors. That ought to make it that much harder to give up the Cambridge in the desktop system.

What next, keeping in mind by the rules I am one bicycle short of the appropriate number?

[wkhanna]

easy choice.......Soekris

see this thread

[BobEllis]

Thanks, Bill. Should leave me enough for a new bicycle and maybe even a decent set of wheels.

[wkhanna]

:roflmao:

maybe even a carbon fiber bottle holder, too!

[JonMarsh]

I'm still waiting for the "high end" Soekris, supposed to ship this month. It's a major part of my deferred gratification/vicarious living program to try to keep me sane with everything else going on.

BTW, though one friend at work took delivery some time ago of my first 851D, I decided I just couldn't do without having one, and did pick up another at an even nicer price. Sometimes you get lucky.


Like one of my best friends at work- he got lucky- his ideal job came out looking for him and found him. He announced his resignation the end of last week, and he'll be moving back to So. Cal the end of July- his wife is thrilled, because the community where his new job is located is quite close to her friends and family down there. It's a win all around, I'm very happy for him. Uh, well, maybe not a win all around, as it will leave a big gaping hole in our organization up here.

Now, I warned his previous boss, his current boss, and our VP of the potential for something likes this happening if they didn't do X and Y. Some time ago. Well, judgement day has come- they didn't do X and Y, and as a result, they had no golden shackles on him, hell, not even golden handcuffs. This is going to screw some things up seriously, including possibly me, as they may well come for me to bail out my boss by taking over his job. Basically, he was doing the work of someone two global grades higher than what they were paying him. Good value for them while it lasted, but now they're screwed and it will likely take six months to find someone comparable, if they can at all.

OTOH, I did get my vacation time in for next month, so I'll be doing some special projects here for GF, and also probably making a road trip up to Idaho with a friend to check some stuff out. Eventual relocation. A lot of Californians are doing that- for good reason, such as houses that cost about 1/4 what they do here. So whatever they do to try to cope with his departure, I won't be around to get ensnared in it. Hallelujah!

Tomorrow is chemo day- one more session, then an evaluation and probably starting radiation treatment. She's a trooper and fighter, but this has taken a lot out of her. You know those pictures of malnourished people they found in German concentration camps at the end of WWII? that's what this kind of cancer does to you... compare pictures of Steve Jobs in 2009 versus 10 years earlier.

[wkhanna]

it can be truly brutal at times.......

she apparently is one of the few with that extra-special will, strength & spirit to deal with this....
& i suspect your support has had some influence on that, too.....

you guys take care of each other, enjoy every possible moment....
we are getting along fine around here, but miss your grand knowledge, skill & motivational floggings...:smackbutt:

time to get some projects moving again, for me!

[csmielke]

Jon,
Lived in the Boise area for 8 years and it's a wonderful place. If you are into the outdoors it's like being in a candy store. Likely would have retired there (wife really wanted it) but middle daughter decided to go to the original USC in SC and oldest daughter was in grad school at U of Minn so it made no sense to go to the opposite end of the country. Besides I am a sailor and no place to sail, so SC it is. Sounds like you have some idea of where you are looking but if you need any input or help reach out. The Californians have been moving there in droves since the early 2000s driving up the housing market. I still get back there for weddings and to visit old friends. While I am there the fly fishing is great and I usually need a fix.
Chris

[Evil Twin]

I think you have nailed it on the head- once I was a pretty big outdoors guy, when I had the time. Spent a lot of time in Colorado.

One of our own here applied for positions at Idaho National Lab, Stephen Maning, and it brought me to thinking about up there, just to look and house and tease him a bit by sending him stuff. But that got me somewhat interested myself. More recently, I started looking at Western Idaho, as it's only about a 9 hour drive from the Bay Area. Lots of stuff going on there interesting- I've mainly been looking at the Boise Metro area, including Nampa, Meridian, Caldwell, and Kuna, and even a little further afield, like Mountain Home. I'd rather be a little closer to a metro area than Mountain Home is, but it's not much different from my commute to work here! But here there are several Starbucks in town, and none in Mountain Home! I suspect it might wind up being Nampa in the end.


The surprising (or not so surprising?) thing is friends that have friends that have moved there, or even running into old friends who are now looking close and hard- one wants to go up with me in July if I visit there.

I had my MacBook open to Zillow and one of the more recent attractive places, and a co-worker's comments (the one going back to So Cal) was that they'd left a 0 off the price (priced at $223K, out here, would be $2,230K.) I have my druthers, three car garage, 3-4 bedrooms, a nice master suite, around 2K sq ft, room for HT, music, and a guitar wall room, and there's a lot of good stuff out there... I'm starting to hear more and more about the ongoing "gentrification" of Idaho. Geez, hate to be just another one of the lemmings but I can't think of a better alternative...

Examples like this are quite typical... (the $223K example)



A lot of nice places in a range I should be able to pay cash for.

[csmielke]

Boise follow up

John,
Take a look at Eagle, we lived there and it has some great homes. We lived in a place called Island Woods on an island in the Boise river. Easy access to downtown and the university, though traffic is worcethan when I was there from 1999-2007. I have friends in the area who can us some updates on what is new. The towns you listed are a bit further west and more rural. You probably already know what a great easy to access airport is there with many connections through salt lake.let me know if I can be of help.
Chris

I think you have nailed it on the head- once I was a pretty big outdoors guy, when I had the time. Spent a lot of time in Colorado.

One of our own here applied for positions at Idaho National Lab, Stephen Maning, and it brought me to thinking about up there, just to look and house and tease him a bit by sending him stuff. But that got me somewhat interested myself. More recently, I started looking at Western Idaho, as it's only about a 9 hour drive from the Bay Area. Lots of stuff going on there interesting- I've mainly been looking at the Boise Metro area, including Nampa, Meridian, Caldwell, and Kuna, and even a little further afield, like Mountain Home. I'd rather be a little closer to a metro area than Mountain Home is, but it's not much different from my commute to work here! But here there are several Starbucks in town, and none in Mountain Home! I suspect it might wind up being Nampa in the end.


The surprising (or not so surprising?) thing is friends that have friends that have moved there, or even running into old friends who are now looking close and hard- one wants to go up with me in July if I visit there.

I had my MacBook open to Zillow and one of the more recent attractive places, and a co-worker's comments (the one going back to So Cal) was that they'd left a 0 off the price (priced at $223K, out here, would be $2,230K.) I have my druthers, three car garage, 3-4 bedrooms, a nice master suite, around 2K sq ft, room for HT, music, and a guitar wall room, and there's a lot of good stuff out there... I'm starting to hear more and more about the ongoing "gentrification" of Idaho. Geez, hate to be just another one of the lemmings but I can't think of a better alternative...

Examples like this are quite typical... (the $223K example)



A lot of nice places in a range I should be able to pay cash for.

[JonMarsh]

Appreciate your knowledge and hints, Chris. I've been looking there, too. In fact, yesterday I just signed the lease for a climate controlled storage unit in that area, I plan to take some things up in mid July and scout things out- have another friend interested in the area that may come along. There's a nice place up for sale at 1545 E Bishop Dr, Eagle, ID 83616 right now. I won't be seriously looking or ready to buy until the end of next year, if plans go as expected.

I have found some nice places in all of these communities, and have even been able to fulfill some of my, perhaps, more esoteric desires, at least on paper. How that will work out later, who knows? I'm a fan of high ceilings (better acoustics) and more European like styling- this place in Caldwell is an example attractive to me-



And I like modern kitchen designs...



And airy master suites.





And these things seem attainable in Idaho at an affordable budget.


For an even more eclectic esthetic, another place in Caldwell is very appealing to me...






Now imagine those rooms with a few pieces of teak or rosewood furniture, and how that would "pop" from the background..





My friends in California note that the main thing that is missing is another zero in the price...

[csmielke]

These homes look great

Jon,
These examples look great. Good luck with your search and let me know if I can be of any help. Another plus is that transducer labs is in Boise and perhaps a more direct connection is order?
Chris

Appreciate your knowledge and hints, Chris. I've been looking there, too. In fact, yesterday I just signed the lease for a climate controlled storage unit in that area, I plan to take some things up in mid July and scout things out- have another friend interested in the area that may come along. There's a nice place up for sale at 1545 E Bishop Dr, Eagle, ID 83616 right now. I won't be seriously looking or ready to buy until the end of next year, if plans go as expected.

I have found some nice places in all of these communities, and have even been able to fulfill some of my, perhaps, more esoteric desires, at least on paper. How that will work out later, who knows? I'm a fan of high ceilings (better acoustics) and more European like styling- this place in Caldwell is an example attractive to me-



And I like modern kitchen designs...



And airy master suites.





And these things seem attainable in Idaho at an affordable budget.


For an even more eclectic esthetic, another place in Caldwell is very appealing to me...






Now imagine those rooms with a few pieces of teak or rosewood furniture, and how that would "pop" from the background..





My friends in California note that the main thing that is missing is another zero in the price...

[JonMarsh]

Dang, I forgot about TL being in Boise. Who knows, maybe a visit?

[denesdr]

Hello! Any news on 851D vs NAD M51 (C510)? How they sound like each other?

[JonMarsh]

I've had no opportunity to do a direct comparison, as my M51 has been at Ron's for a while, it's his baby now. My Cambridge is with my friend who has my Wavecor Ardent's. Both measure quite well, and I'd describe them as leaders in their price class. If you have a sufficiently resolving system, I'd expect that there will be some differences; how much and of what nature would be hard to say.

In favor of the 851D, it does not do the volume control in the digital domain in the DAC, but runs the DAC full scale, and has a separate analog gain stage controlled by a digital encoder and using an R2R ladder style DAC as a precision variable resistor. I believe that is intrinsically better, I DO NOT use digital domain volume controls after a bit of experimentation with different kinds of program material and with high grade external preamps. This outlook has also been checked and reconfirmed with my close friend who lived in Munich but is now in Singapore, and also we are of that opinion even with high end DAC's like a TotalDAC-D1, in it's many variants. There is a solid theoretical basis for that, too, which I've discussed elsewhere, such as in the some of the DAC reviews.

That said, using the M51 in the digital domain as a volume control may likely out perform connecting it with a so-so preamp. YMMV, etc. etc.

By a higher end preamp, I mean something like the Auralic Taurus Pre or better- many preamps sadly don't have the dynamic range and ultra quiet input and low distortion to really do justice to digital inputs. The Audio Precision doesn't lie... The little Schitt Freya will do well, as long as you don't turn on the tubes... save that for providing some additional warmth for inputs without super wide dynamics, or just for fun now and then. :W

[allhifi]

Brilliant !

OK- a bit of spare time available- so I've got some data on the APx555. My goal was not to duplicate all the measurements on Stereophile, but rather to investigate some specific issues, and perhaps reconfirm a few measurements that anyone can agree are significant, and which many competing units at higher prices don't necessarily do well on. Testing was done using the BNC S/PDIF input.


Volume Control- is it "digital" as some promo material states, or is the answer more nuanced and more useful?

Why is this important? It all comes down to bit depth and throwing away bit depth when you're using some significant attenuation- such as 20dB or more, and especially with a 16 bit signal (CD resolution) The volume control on the 851D can be enabled or disabled, so the unit can be used like a conventional DAC, or a DAC Preamp, in both cases with multiple inputs.

Ideally, I'd like to see a precision analog solution for the volume control - what this generally means is a rotary encoder control (or remote) as the input, and a counter that cycles the value fed to a relay switched precision resistor array OR a multiplying DAC chip, in which the internal R2R ladder is used to form an attenuator or gain control. What's often done, is running the digital input through a digital attenuator on board that attenuates the numeric value of the samples by a fixed amount before sending them to the actual DAC chip.

Well, with the right test there's a fairly easy way to tell what's happening. This is what we did:

The key is using a low level signal test for which attenuation is done in the digital domain, it will be spotted because of how thoroughly the waveform is mangled. Conversely, if the waveform is attenuated in the correct manner, we can safely surmise that the volume control is not a conventional digital attenuator, but acting in the analog domain, even if it is controlled digitally, say, by a BCD counter that indexes a multiplying DAC or relay set up and down the gain ramp.

What the test signal? Simply one of the classic demanding low level signals commonly used for evaluating DAC behavior- 1 kHz square wave at -90dBFS input level, which is basically just toggling the LSB (Least Size Bit) on the 16 bit PCM scale.

With the volume control bypassed, or with it turned up full, here's what you get from the 851D:


Figure 1
1kHz 16Bit_FS by Jon Hancock, on Flickr

Mind you, those are 200 uV steps around the zero volt level; with well defined steps and fairly visible Gibbs ringing. This level of clarity of the waveform at the low signal level places the 851D in the higher tier of DACs- I can show you many costing several times it's price that don't do as well.

So, the experiment is to crank the volume control down... if it is just adjusting the signal to the DAC, there's no where left to go below 1 LSB...

Figure 2
1kHz 16Bit_FS -6dB by Jon Hancock, on Flickr


But here at -6dB on the preamp (front panel readout for the 851D gives you the actual dB attenuation) it's dropped exactly where it should be, to half the voltage at 100uV peak, and otherwise there is no waveform distortion.

From this, I'm inclined to believe Cambridge Audio is using the same multiplying DAC based volume control as in the 851E analog preamp, though they don't say so in their literature. That's a good thing, if so, because it should result in very precise and predictable attenuation levels, AND very close channel tracking between right and left channel, something that's a bugaboo for analog pots.


How well does the volume control track the settings, and how closely do channels track each other?

To test this, I performed swept frequency response tests from 10Hz to 20kHz, checking both channels output, and looking at several attenuation levels, appending the test results to the same graph.


Figure 3
Frequency Response and volume tracking10Hz-20kHz by Jon Hancock, on Flickr


Now, this is the way volume control should work- tracking so tight you can't see any material difference in the channel balance.

One quick check- let's zoom in on that bottom trace with -30 dB attenuation-

Frequency Response and volume tracking10Hz-20kHz-17db by Jon Hancock, on Flickr

Here, we can see that there is about 0.1 dB of channel misbalance, and also about 0.1dB of roll off at the frequency extremes at 10Hz and 20 kHz. This is a very low value...



What's all this 24 bit versus 16 bit stuff, and under what conditions may it be fairly obvious, at least on the test bench?

OK, take a look back to the start with Figure 1...

Now, here's the 1 kHz sine wave at the same 90dBFS input level, but with 24 bits of data

Figure 4
1kHz 24Bit_FS by Jon Hancock, on Flickr

It's not hard to see that it's a better representation of the signal... though let's face it, it's a signal at a very low level.


Let's also look at some FFT's (Fast Fourier Transforms) - which show the harmonics and levels in relation to the fundamental...


Figure 5: -90 dBFS input level 1kHz, 16 bit data
1kHz_-90_16BitFFT by Jon Hancock, on Flickr


Figure 6: -90 dBFS input level 1kHz, 24 bit data
1kHz_-90_24BitFFT by Jon Hancock, on Flickr


As you can see from this, the Cambridge 851D is a quiet unit, and quite clean at 1kHz with low level signals.



I like my "boom and tinkle"- how does this unit stack up with regards to low frequency harmonic distortion and high frequency intermodulation distortion at high output levels?

First, a good test is to take it back up to 0dBFS at 1kHz, and see if there are any funny things going on BELOW 1 kHz; this will usually be due to power supply issues. Note that I've adjusted the volume control so that the output shown in the graph corresponds with the input level; in other words, we're running at net unity gain. This makes it easier to put a number on how far down noise and distortion components are from the main signal, when on the graph it is at 0dBFS.


Figure 7: 0 dBFS input level 1kHz, 24 bit data
1kHz 24Bit_0dBFS by Jon Hancock, on Flickr


This looks about is nice as I think we can hope for, so let's look at 50 Hz.

Figure 8: 0 dBFS input level 50Hz, 24 bit data
50Hz 24Bit_0dBFS by Jon Hancock, on Flickr

Gee, are you getting bored by all these clean results? Keep in mind I can show you units that retail for 4x the 851D's original price that don't do nearly as well...


For high frequency distortion, we can't really rely well on simple harmonic distortion FFT spectra, because it's mostly filtered out by the reconstruction filter, especially at lower sampling rates. A better way to evaluate is two tone HF CCIF Intermodulation distortion, and looking at the distribution of side bands of the difference frequency between the two tones, which using 18 and 19 kHz at the test frequencies, is at 1 kHz multiples.

This is what the test signal looks like, with a peak level of 0dBFS, the level of each individual tone is much lower, because they generate a beat pattern which reinforces and cancels depending on the specific phase alignment versus time.


Figure 9: 0 dBFS input level 18+19kHz CCIF test signal, 24 bit data
CCIF_18-19kHzOutputScope by Jon Hancock, on Flickr


And here, the FFT plot:

Figure 10: 0 dBFS input level 18+19kHz CCIF FFT, 24 bit data
CCIF_18-19kHz by Jon Hancock, on Flickr

This is a very nice result on this test, with none of the difference product being over the -120dB level.


BTW, I've looked on Cambridge Audio's web site, and I think the price drop is connected with them discontinuing this model. You can't navigate to the page for the 851D by their main menu, but you can find it via Google and get there.

Of course, it may be that they'll bring out an improved version... who knows? But if you have something around $1K altogether to spend on a DAC and preamp, and only need digital inputs, it's very hard for me to imagine doing much better than this.

As there is no headphone jack on this puppy, a listening test will have to wait until the weekend...

Hi Jon: Such a fantastic 'review' ! Your detailed examination of the Cambridge Audio 851D (N?) and excellent, insightful writing skill annihilates 99% of what's out there in the "professional"-commercial field -across the globe no less.

What I found interesting is when you suggested perhaps a similar volume attenuation implementation used in the CA 851E (preamplifier).

(RE Quote: " ..:From this, I'm inclined to believe Cambridge Audio is using the same multiplying DAC based volume control as in the 851E analog preamp, though they don't say so in their literature. That's a good thing, if so, because it should result in very precise and predictable attenuation levels, AND very close channel tracking between right and left channel, something that's a bugaboo for analog pots").

I use CA's excellent (and highly under-rated 841E preamplfier. The 841E uses a resistor/relay volume circuit -with excellent results (except for high-attenuation settings tend to over-heat the resistors -causing volume "runaway" scenarios at times. This (excellent system), oddly enough, prompted CA to change volume implementation to a 'analog' volume control (CA's words) to the replacement/current 851E preamp.
When I sought clarification from CA -nothing was forthcoming. Leaving me to assume they opted for for the inferior/cheaper "pot" type (attenuation). A disappointing decision to my mind -no longer could I confidently recommend the 851E.

Yet, as I read your sensible observations, test results and comments (on the 851D), I wonder if indeed the 851E uses the clearly superior opto-coupling (to traditional, mechanical "pots) vol. attenuation ?
But if so, you'd think CA's Customer Service guys would confidently know about this very, very important preamplifier consideration -as it greatly influences SQ, as you correctly point out, and ensure customers are aware of this. I believe my inquiry went beyond to a technical representative -resulting in no further explanation other than 851E uses a "analog' controller. Such a shame.
For the 841E predecessor is truly a superb line-stage (and verifiable bargain) at the then $2K price point.

In any case, thanks for sharing this very insightful review into the 851D DAC. Perhaps you can offer mainstream 'Rag' writer's lessons in professional (and very insightful) writing/reviewing !

pj

[allhifi]

that would be the case if DAC's routinely converted 16 bit to 24 bit data, but that often/usually doesn't happen. I believed this would be the case a number of years ago, but experience since then has changed my mind.

Let's look at one case- CD quality program material, which is probably 95% of what I listen to still. (always working on changing that, but...) And also compare against 16 bit if used with a SABER DAC realizing 132 dB (not a uniform situation by any means) and also how 24 bit data will likely do with the Saber - (taken from Six Moons review)


6moons audio reviews: AURALiC Vega by Jon Hancock, on Flickr


My own conclusions after doing a lot of listening tests, and getting similar feedback from my friend in Munich and his wife, is that it is better to use a high grade analog preamp than not, unless one doesn't have access to that- or must otherwise do things like pass through an HT processor signal path. I didn't used to think this way, but after listening in quite a few different situation with different components ( including original Berkely Alpha DAC, NAD M51, TotalDAC, and AURALiC Vega), I'm now on the wagon for a high grade preamp being the best way to go.

Of course, that qualifier is where the sticky wickets come in...

Jon: Man, you know your stuff. And communicate (write) extremely well.

peter jasz
(P.S. I need to get a hold of you -PM)

[ergo]

In process of waiting for xover parts for getting my Ardents singing I discovered that one Estonian online shop was selling Azur 851D for 610EUR (20% vat included) and that with the Bluetooth dongle included. Seemed too good of a deal to pass by. I have a plan to build a pair of Hypex NC400 based power amps, so that will work well with those too.
Got it from post today and just listening to first tracks. First emotions do not disappoint, but we'll see once I get some hours and days of playing into it and listening.

[BobEllis]

I suspect that you will like it more as time goes by. I certainly do.

[Supernova]

My own conclusions after doing a lot of listening tests, and getting similar feedback from my friend in Munich and his wife, is that it is better to use a high grade analog preamp than not, unless one doesn't have access to that- or must otherwise do things like pass through an HT processor signal path. I didn't used to think this way, but after listening in quite a few different situation with different components ( including original Berkely Alpha DAC, NAD M51, TotalDAC, and AURALiC Vega), I'm now on the wagon for a high grade preamp being the best way to go.

Of course, that qualifier is where the sticky wickets come in...

Jon-

Have you looked into the Hegel P30? I know it's a lot more expensive than some of these units ($7000/$8000), but I've heard it's very neutral. I wouldn't mind seeing one tested and I've only seen limited subjective reviews on the unit and most focus on the H30.

-Peter

Here's a description by 6 moons. There's no data, but interesting after the first few paragraphs.

Description. P30. This preamplifier is relatively small and shallow but counters with a slightly bulging sculpted fascia. More surprising is its substantial weight. This derives from the hefty transformer and a very solid thick chassis of bolted aluminium panels. The review loaner was black and the whole affair stands on three aluminium footers with semi-spherical rubber bumpers. The metal wand is small but sports quality buttons. It would be nicer still to better distinguish the volume up/down controls since those aren’t completely intuitively located and need to be searched for each time. Beside volume and mute the remote will change inputs and double as controller for the matching CD player.

Front. Here we only get two knobs and a big central power button with an associated blue LED above. The right input selector is surrounded by medium-sized blue LEDs. This knob rotates endlessly to likely be a form of encoder that triggers relays. The volume control meanwhile rotates across a limited range to suggest a standard pot behind it. The entire affair looks very solid and elegantly understated.

Back. Looking at the back we see evidence of balanced circuitry. Besides 3/2 RCA i/o ports we get a matching pair of XLR inputs and outputs. Whilst the RCA sockets are medium class and spaced quite narrowly, the XLRs are superior Neutrik units. There’s also a pass-through input for AV processor/home theatre integration; two mini jacks to leash together Hegel components for complete system control; and the IEC power inlet.

Inside. The circuitry mounts on three PCBs. The motherboard occupies almost the entire chassis and then there are two smaller ones. Conceptually quite simple, the execution is very sophisticated and extends to a quite advanced power supply with control logic. The input signal encounters sealed Omron relays whereby the active source gets selected. The same relays at the outputs protect the power amps.

The signal path is ultra short. Hegel states that the signal in their preamplifier runs through only two transistors and between one to three resistors. First the signal enters one of the smaller PCBs mounted above the mother board for the volume control, a nice black Alps potentiometer that’s outside the signal path to merely control a resistor array triggered by transistors. This array is surface-mounted and powered from a discrete transformer secondary.

Post attenuation the signal meets the voltage gain section placed close to the rear panel. Here we find pair-matched mid-power transistors. Those promise significant current reserves. This circuit is based on Hegel’s proprietary SoundEngine concept and consists of two complimentary 2SK2013/2SJ313 Mosfet pairs in a balanced arrangement. Here we see traditional thru-hole construction to rely on premium parts like metalized precision resistors of ultra-tight tolerances. One of the RCA outputs has jumpers to select between variable/fixed output. This accommodates a recording device, external headphone amp or subwoofer.

As already stated, the power supply section is extremely sophisticated. It consists of many multi-stabilized and filtered stages powered by a Hegel-made triple-secondary toroid. Adjacent are many filter capacitors of varying sized including 6 x 10.000uF audio-grade Nover units and 14 smaller Rubycons. Polypropylene caps nicely decouple the power supply rectifier diodes. The overall construction is very solid and draws attention with its oversized power supply, discrete volume control circuit and Mosfet-based buffering and voltage gain. The RCA sockets aren’t gold-plated and the circuit itself is balanced to express the designers’ emphasis on fully symmetrical operation.

Technical data according to manufacturer:
Inputs: 2 x XLR, 3 x RCA plus home cinema bypass
Outputs: 1 x XLR, 2 x RCA
IR input: 3.5mm
Trigger: 12V output
S/N: >130 dB in balanced mode
Crosstalk: < -100dB
Distortion: < 0.005%
Intermodulation distortion: < 0.01%
Dimensions: 6 x 43 x 30cm HxWxD
Weight: 10kg