Totaldac Reference D1

dallasjustice

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Apr 12, 2011
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Well unfortunately then for myself (and a lot of others I imagine) running this DAC power amp direct is simply not an option due to the fixed gain of my power amp and sensitivity of my speakers. I have my current DAC set at 0.5V max output (gain of analogue stage) and I fine tune with digital volume. If I were to run your DAC power amp direct balanced at 6.6V! I would need to use enormous amounts of digital attenuation. I understand your logic for keeping the analogue output stage as simple as possible however for many (the majority?) of people running this DAC power amp direct would simply not be an option.

If this digital volume control were only 24 bits, then I would agree that it would have to chop bits off above the noise floor. OTOH, the TotalDac uses a 69 bit FPGA, so there are are plenty of bits to chop-off without getting into the noise floor even at very low volume. Vincent's design is a true lossless volume control at any level.
 

opus111

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Feb 10, 2012
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As a technical point, the volume control is only going to be as good noise-wise as the bit-width of the DAC its feeding. That's because no matter what the precision of the math, to get linear low-level performance, the result after multiplication has to be truncated or rounded and dithered at the 24bit level to feed into a 24bit DAC.
 

totaldac

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Aug 17, 2012
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If this digital volume control were only 24 bits, then I would agree that it would have to chop bits off above the noise floor. OTOH, the TotalDac uses a 69 bit FPGA, so there are are plenty of bits to chop-off without getting into the noise floor even at very low volume. Vincent's design is a true lossless volume control at any level.

Dallasjustice, what volume are you using most time on your Totaldac?
 

totaldac

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Aug 17, 2012
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As a technical point, the volume control is only going to be as good noise-wise as the bit-width of the DAC its feeding. That's because no matter what the precision of the math, to get linear low-level performance, the result after multiplication has to be truncated or rounded and dithered at the 24bit level to feed into a 24bit DAC.

The internal calculation are done on 69bits, and the dithering is also calculated on 69bits, the R2R ladder is 24bits, with the graphical noise floor on the 8K FFT at -153dBFs on average, which is sometimes/often a lower noise than an analog preamp. That is why it can sound as a transparent volume control. Very high performance dithering + low system noise are the key.
 

opus111

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Feb 10, 2012
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No, what you show on your FFT is not the noisefloor, its the noise in each FFT bin. That's a very common mistake to make.

An FFT is a histogram - not a graph. It represents discrete points so they strictly speaking should NOT be joined up to make it look like a graph. Rather it should really be displayed as a set of bars, each with a finite width. The height of each bar will vary according to how wide you make it. So if you want, say a -156dBfs figure rather than your current -153dBfs, just double the number of bins in your FFT. Doubling the number of bars halves their width. If you want to paint your DAC in an even better light, why not use 16X the number of bins. You'll then see a figure of -165dBfs.

You'll note in each case the actual noise coming from the DAC is unchanged. To get the true audio band (20-20kHz) noisefloor you need to add up the noise in each of your FFT bins.
 

FrantzM

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Apr 20, 2010
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The internal calculation are done on 69bits, and the dithering is also calculated on 69bits, the R2R ladder is 24bits, with the graphical noise floor on the 8K FFT at -153dBFs on average, which is sometimes/often a lower noise than an analog preamp. That is why it can sound as a transparent volume control. Very high performance dithering + low system noise are the key.


totaldac
This, to me, is pushing the envelope. From what I am reading here, extremely innovative approach. Question -153 dBF is lower than what anything analog can offer . So why the "often/sometimes' modifier? I would have thought : "Always"... Care to explain?
 

totaldac

Industry Expert
Aug 17, 2012
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-153dBFs is just a graphical reading of the FFT, indeed it is better to just look at the FFT graph. For sure this is not the THD+N nor the dynamic range.
Some preamp can have a better noise floor, but the active component of an analog preamp can also add a sound, there is no universal rule. The Totaldac D1 can also be used with an external preamp, in the case the D1 volume can be adjusted on 0dB, or less, -6dB for example.
 

jkeny

Industry Expert, Member Sponsor
Feb 9, 2012
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Vincent, have you tried RF MELF resistors & how do they compare? They seem to have all the characteristics you specify i.e mostly resistive into very high frequencies!

And could you say what is the "real" noise floor of the DAC?
 
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totaldac

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Aug 17, 2012
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Vincent, have you tried RF MELF resistors & how do they compare? They seem to have all the characteristics you specify i.e mostly resistive into very high frequencies!

And could you say what is the "real" noise floor of the DAC?

the tolerance (1%) and temperature of these resistor are not good for a R2R DAC.
I did not even measure the noise integration, I always prefer to watch a graph which shows the discrete spurious noise and the problems localisation, if there are. A graph tells more than one number.
 

jkeny

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Feb 9, 2012
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the tolerance (1%) and temperature of these resistor are not good for a R2R DAC.
I did not even measure the noise integration, I always prefer to watch a graph which shows the discrete spurious noise and the problems localisation, if there are. A graph tells more than one number.
Sure I understand the 1% tolerance but they could be matched by measurement to better than 0.1% (I presume you do this anyway?)
The spectrum analysis graphs are produced for these resistors as you would expect when technical superiority at RF is their selling point.

Maybe you can tell what is you FFT bin size then & the real noise floor can then be calculated?
 

totaldac

Industry Expert
Aug 17, 2012
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even 0.1% is not enough. I use 0.01%, and stable in time.

Next time I am making a measurement I will make the noise integration for a reliable value, till now I have just this graph, measured by a R&S audio analyser, can be compared to the bank of measurement from Stereophile. Note, the frequency scale is logarythmic so see also the hum noise, usually hidden at the top left of the graph.

fft_d1_dual_dac.jpg
 

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jkeny

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AudioExplorations

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Apr 5, 2012
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Yes I am looking for the best possible option available, I want to prove the concept and check the sonic impact. Is this the best available resistor for the job? Looking to attenuate both 10dB and 20dB. Thanks!
 

jkeny

Industry Expert, Member Sponsor
Feb 9, 2012
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Yes I am looking for the best possible option available, I want to prove the concept and check the sonic impact. Is this the best available resistor for the job? Looking to attenuate both 10dB and 20dB. Thanks!
Oh, I don't know if they are the best resisitor, I was just enquiring from him if he had compared them to the Vishay "Naked" foil resistors which seem to be the ones used in the DAC http://www.partsconnexion.com/resistors_vishay_var.html but Vincent can tell you if that is correct!
 

LL21

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Dec 26, 2010
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Hi TotalDAC,

Based on the reviews, your approach which is also getting some real, positive interest here amongst our 'resident experts'...i am very interested! I currently have a Zanden DAC which i enjoy very much...and as many people here are likely sick of hearing, i have long been debating about the Zanden Transport (which is coming down in price in the second hand market for obvious reasons).

However, I am very intrigued by your DAC. What Transport do you recommend one consider with it? I am not particularly focused on computer audio at the moment...but a SOTA transport with your DAC is very interesting!!! I have heard great transports and cheap dvd players...and they do make a difference. Since i am looking to 'finalize' my digital for the time being...i am either getting the Zanden Transport...or giving up Zanden altogether and going with another option. In your case, i would then need advice from you about some SOTA transport options to go with your DAC. Thank you!

If you wish to PM me, please feel free. Kind regards and congrats on all the positive feedback on your DAC.
 

totaldac

Industry Expert
Aug 17, 2012
567
701
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Hi TotalDAC,

Based on the reviews, your approach which is also getting some real, positive interest here amongst our 'resident experts'...i am very interested! I currently have a Zanden DAC which i enjoy very much...and as many people here are likely sick of hearing, i have long been debating about the Zanden Transport (which is coming down in price in the second hand market for obvious reasons).

However, I am very intrigued by your DAC. What Transport do you recommend one consider with it? I am not particularly focused on computer audio at the moment...but a SOTA transport with your DAC is very interesting!!! I have heard great transports and cheap dvd players...and they do make a difference. Since i am looking to 'finalize' my digital for the time being...i am either getting the Zanden Transport...or giving up Zanden altogether and going with another option. In your case, i would then need advice from you about some SOTA transport options to go with your DAC. Thank you!

If you wish to PM me, please feel free. Kind regards and congrats on all the positive feedback on your DAC.

Hi lloydelee21,
What does SOTA mean? The LP table manufacturer?
For PC users I recommend the D1 USB input. If you don't want to use a computer you can also use an audio server, like Aurender S10 among others, in this case I recommend to use the AES-EBU link for the best results. And if you want a CD drive yes indeed they make a difference. I have no specific recommendation but I recommend also to use the AES-EBU link which sounds better than coax with the D1.
 

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