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B.M.C. Announces PureDAC - Page 12

post #166 of 291

Thanks JCCI ,  for this great perspective, and for your active involvement in the forum - which I'm sure will provide you with insights for future product development.   I only heard and started reading about BMC a couple of days ago, but the more I find out, the more impressed I am.   

post #167 of 291
Quote:
Originally Posted by JCCI View Post

 

... The PureAmp is already inside our latest catalogue although we expect the product earliest in September. Specifically the use of the B.M.C. link with the shared DIGM and CI operation mode will be attractive for PureDAC owners. ...

 

 

ooohh... interesting.   I didn't see anything about the PureAmp on your website catalog. would love to hear more about it.  but can understand if you are not able to 'pre announce'. 

post #168 of 291
post #169 of 291
Quote:
Originally Posted by Audio Addict View Post
 

Go to page 13 of the catalog.

 

http://bmc-audio.de/tl_files/bmc_audio/pdfs/BMC-Catalogue_en-web.pdf

 

Got it !   thanks.   I must say, I'm very inspired to hear these components, including the speakers. 

post #170 of 291
I have no doubt the PureDAC's headamp is highly transparent, and this is why I use it perhaps 25% of the time for extended listening sessions.

My reasons for 'preferring' my tube amp are complicated. I tune neutral., i.e. I don't like syrupy, tubey sound. If there is a point of exaggeration, it may be that some tracks seem more dynamic, almost as if the Decware decompresses. Technically, it may be the response isn't quite linear and that rather than further compressing the dynamic range or faithfully reproducing the dynamics as mixed/mastered, the amp is expanding the range slightly. I'm no EE and this is sheer speculation; suffice it to say this is what it "sounds like" it's doing!

The other point is that without a doubt the amp adds even-order harmonics and puristically this is certainly coloration. However, all the music I listen to contains significant 2nd-order harmonics anyway. I don't listen to pure tones. I'm fairly sure my ability to distinguish the "pure Bosendorfer concert grand" from the "tube-augmented Bosendorfer" is pretty slim! The difference I think is likely to be subtle.

A third reason is the Decware Taboo sounded terrific before I bought the PureDAC. After, it sounded downright stunning.

The final reason: I tinkered with tubes a little when I was a teenager and I loved them. So, not surprisingly I actually like having a tube amp sitting in my room. Somehow, whether it is the ultimate in amplifier performance or not, the designer at Decware (and makers of other fine tube amps) succeeded in making something that sounds terrific. What's not to like? wink.gif

WRT my comment about the Meier SS amp (the Classic), it too just happens to be an excellent amp. At present it and the PureDAC headamp are my "reference" when I make tube changes to one of the Decwares.

One of these days I plan to compare the PureDAC and Meier and decide which is 'the best'. I suspect it may be the PureDAC because of the advantages of BMC's 'pure' topology. This comparison awaits time and opportunity.
Quote:
Originally Posted by KmanChu View Post

PureAmp? Very interesting.

In reference to the addition of tubes to the equation, I actually have just purchased a tube amp simply because I have always loved tubes and stumbled across a very good deal. I haven't received it yet, but I have wondered what it will add. I have always believed in "system synergy" and believed that proof was in the end sound. In the case of the PureDAC, however, it seems the headphone section isn't really a headphone amp, but rather the DAC output stage that can drive headphones. To those who find they prefer other amps, why is this? Do you feel it in some ways drives the headphones more appropriately? I don't see how there could be lower noise or lower distortion (especially in light of the tendency towards tubes.) Philosophically I want to believe in the "straight-wire-with-gain" philosophy even though I know system synergy is ultimately the most important aspect. My expectation (and hope) is that the new amp will enrich and color (in a good way) the listening experience, but I actually expect a slight loss of absolute resolution.

I guess the ultimate test would be to connect the PureDAC balanced outputs to the most reputable and transparent amp around (Headamp GS-X ii?) and see if it outperforms the balanced output. My guess is that it would be nearly indistinguishable. The GS-X certainly could outperform the PureDAC output, but it would require a better DAC to do it.
post #171 of 291

Some information about pre-announcements:

Generally we need a production schedule for offically announcing a product. Once a development is closed we prepare a pre-production and announce the product. The pre-production is actually a ready product simulating the mass production and also the last chance to collect some field responses and final corrections. This is also why the press can have some earlier samples and same is true for shows.

If the product is announced too early you can expect lots of bad comments.

 

In this very forum thread we do had this problem when deciding to implement some new features into the PureDAC and delay the release. Of course it was obvious that this product will be strong in it's price range. The larger range of comments was not frustration of inpatient customers but rather intends to damage it's reputation before even released.

As a brand we no choice but being as straight forward and reliable as possible, regardless specifications, release dates...

 

If anyone want's to know more about te PureAmp it might be good opening another thread.

The PureAmp is also interesting for very inefficient or low impedance headphones, i.e. AKG's classic K1000, HiFiman's HE6, Precides's AMT... LEF amplifier does not sound bad under unusually low load conditions, which is another advantage of this concept.

post #172 of 291
Quote:
Originally Posted by JCCI View Post

A little background about the headphone stage of the PureDAC:
First of all it delivers up to 13Vrms and a current not less than any other headphone amp. There is nothing a headphone amp is delivering differently, beside of course, individual sound flavours depending on the product. In addition the PureDAC headphone part delivers the signal voltage and the signal current from separate sources phase independent!

This is rather confusing, can you please clarify?
Thanks.
Signed,
Purely Confused.
post #173 of 291

Hi Chris,

Hopefully I can help clarifying.

I believe there are 2 points which should not be mixed up, to be clarified.

 

1. The mentioned output specification suggests there is an headphone amplifier, but then I mentioned not to need an amplifier is an achievement.

 

At the analog domain inside a "normal" DAC the following happens:

 

a. The DAC chip outputs an analog current which has noise from the sampling frequency

b. An operational amplifier (OPAMP is an amp concept based on very high feedback loop correction) converts the current to a voltage and filters some noise in the feedback loop. Inside the OPAMP, which in general is a chip, you can expect at least 2 gain and one driver stage.

c. A second OPAMP stage does the rest of the filtering and sometimes a little gain. This is then the DAC output.

For driving a headphone normally an additional amplifier and a volume control is needed.

d. The headphone amp applies a divider for volume control. This means a rather good signal is divided into a fraction of it's original magnitude.

e. This is done because a gain stage (in most cases again OPAMP) is applied which works with a fixed gain. So the signal is made bigger again.

f. The last stage is a current driver which is stronger for headphones compared to a line output.

 

The difference the PureDAC works looks as followed

 

a. Unchanged since this is just the starting point.

b. A "current injection" stage does the job b...e in a single stage inside the DAC using the original DAC current of the DAC chip and a variable current/voltage conversion ratio, losslessly replacing the volume control. It is so linear, it doesn't need a feedback loop at all, while delivering very low distortion. It also can convert to much higher voltages than a normal DAC, so any headphone (even speaker) level can be achieved.

Count the stages considering the internals of an OPAMP and the fact that each amplifier stage creates a "copy" of the input signal. The less lossy copies, the better.

c. The current driver is a LEF (Load Effect Free) stage which is very different to any other analog design and the topic of explanation #2.

 

2. The LEF Current Driver

 

Common point:

A normal amplifier output is a voltage source. The output delivers a stable signal voltage and the current depends on the impedance of the load - in our case a headphone. Impedance means the electrical resistance changes at every frequency in magnitude and phase and every headphone has a different impedance. So the amplifier is supposed to be universal in use.

 

Standard Amplifier:

Whenever the signal (music) voltage changes the current inside the voltage source has to change as well. But parts are not perfect regardless transistor, MOSFET or tubes. A change in current changes the behavior and causes distortion. Imagine you try to paint a painting and all the time somebody hangs different weights by a rubber band to your painting arm. You definitely will "distort" due to the non-linearity of your muscle.

The distortion is in general unacceptable, so a feedback loop is applied changing excess-gain to linearity. This idea works great in static and slow applications, but has it's limits for music reproduction: The feedback performance depends strongly on the phase fo the current related to the voltage. However, the phase situation is changing all the time not only by the load, but also by the output part itself. There are way more limitations, but this would be too much.

Feedback is the standard due to lack of better alternatives. Unfortunately true research on analog circuits has been stopped for very long time.

 

LEF Current Driver

Contains two parts:

a. The voltage source with a very low impedance output determines the signal at the headphone. But this voltage source should be protected from any movement in current, since it changes the ability to perform (distortion, "painter's arm with suspended weights). It should have a constant load and thus no load effects.

b. An independent current driver with a very high impedance output. "Independent" means also it "knows" nothing about the music source signal. Due to the high output impedance it can not alter the output voltage.

So how does it work? It is an electronic law that a change in voltage on an attached load causes a current. The current driver's task is to protect the sensible voltage source and monitor any current change inside it (so it watches the painter's muscle power change). Any current necessary to avoid a change is automatically delivered by the current sources, regardless of the phase.

Example with a speaker: Let's assume there is no music playing and somebody knocks on the woofer cone. The woofer would generate current and the LEF stage would supply the matching reversed current without any move in voltage! You don't have to knock a cone, since any speaker and headphone cone has enough inertia to do some unwanted movement.

 

Conclusion

- The LEF concept is clearly superior when controlling any kind of dynamic speaker.

- Since the voltage source has no load changes distortions never happer there and does not have to be corrected.

- Therefore a feedback loop is obsolete.

- LEF output stages are more linear than traditional class A

- The constant load of the voltage source makes pre-driver stages obsolete = shorter signal path

- Since there is no feedback loop, there is no need for excess gain; so one gain stage is enough = shorter signal path

 

Technology has to serve the music reproduction. Our task in engineering is to understand what happens while proceeding music signals and search for better solutions until the day we can't tell the difference to a natural performance. If the solution does what it should, you should have a better music listening experience. It is interesting to know how it works, but ultimately the music reproduction counts.

 

 

 

Sorry, I couldn't make is shorter; but hopefully understandable!


Edited by JCCI - 7/1/14 at 8:26pm
post #174 of 291

Hi Carlos,

Thanks for clarifying!

Maybe I should have pointed out that I am Electrical Engineer.

 

Anyway, your solution sounds quite elegant!

 

Chris

post #175 of 291

Wow.  thanks for the very impressive description , Carlos.  I'm very excited to hear your products.  I believe I have found a dealer here in Oregon.  If not, I will try to get to SF bay area to hear it. 

post #176 of 291

Didn't know that :rolleyes:, welcome to the club!

 

For you a slighty different explanation would have matched better of course, but I assume there are more readers around here. The analogy using something everybody understands really helps and it fits to the true problem. We used that many times for avoiding just to talk to ourselves.

 

However there are way more skilled people in explanation out there. The best I've ever heard was an argument why tubes are supposed to be better:

"Can you imagine how much better an electron feels when drifting freely through a vacuum instead of squeezing itself through a semiconductor?" This is unbeatable, but the guy sadly never published a book about the psychology of electrons. :wink_face:

post #177 of 291

In Portland it should be http://www.trueaudiophile.com.

A very nice guy and true music lover. I got badly sick at CES and he helped from the first day until the show cleanup!

post #178 of 291

ok...Puredac arriving next week!  :biggrin:

post #179 of 291
Quote:
Originally Posted by JCCI View Post
 

In Portland it should be http://www.trueaudiophile.com.

A very nice guy and true music lover. I got badly sick at CES and he helped from the first day until the show cleanup!

 

I did get a hold of TrueAudiophile in Portland, and look forward to meeting with him in a week or two when he has some more in stock ! 

post #180 of 291
Quote:
Originally Posted by JCCI View Post

Didn't know that rolleyes.gif , welcome to the club!

For you a slighty different explanation would have matched better of course, but I assume there are more readers around here. The analogy using something everybody understands really helps and it fits to the true problem. We used that many times for avoiding just to talk to ourselves.

However there are way more skilled people in explanation out there. The best I've ever heard was an argument why tubes are supposed to be better:
"Can you imagine how much better an electron feels when drifting freely through a vacuum instead of squeezing itself through a semiconductor?" This is unbeatable, but the guy sadly never published a book about the psychology of electrons. wink_face.gif

Hmmmm.....I had no idea that electrons had feelings! wink.gif
Is this how circuit breakers work? wink_face.gif
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