Totaldac Reference D1

FrantzM

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Apr 20, 2010
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Hi

Learning much from this thread. This is the reason for frequenting this forum even as such ungodly hours (for me).. Lerning .. The Vivaldi thread drift toward technical discussions was most welcome and now this discussion about this extremely interesting DAC. I want to know more and eventually to audition...
More and more I see multi-amping as the ideal.

One question what about Analog with a system using no preamp? As seems to be the recommendation with the TotalDac D1?
 

AudioExplorations

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Apr 5, 2012
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-3.3Vrms max RCA, 6.6Vrms max XLR analog output

Is the gain of the analogue output stage adjustable or is it fixed at the above values?
 

opus111

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Feb 10, 2012
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An intriguing start to this thread...particularly given the Vivaldi discussions elsewhere...

Interesting irony here - I just found the following claim on dCS's website:

That's why (unlike every other high end audio manufacturer) we do not use commercial off-the-shelf DAC chips.


Seems they need to update this because Vincent's design doesn't use off the shelf DAC chips either, and there's no doubt its high-end.
 

totaldac

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Aug 17, 2012
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Hi

Learning much from this thread. This is the reason for frequenting this forum even as such ungodly hours (for me).. Lerning .. The Vivaldi thread drift toward technical discussions was most welcome and now this discussion about this extremely interesting DAC. I want to know more and eventually to audition...
More and more I see multi-amping as the ideal.

One question what about Analog with a system using no preamp? As seems to be the recommendation with the TotalDac D1?

Yes indeed the active crossover is a good solution, often used in the highest end studio and concert systems. The D1 DAC can be built as an active crossover, named D2 or D3, or can be a stack of D1 dual DAC. The input will be digital only. So if you have an analog source (LP....) you have several solutions:
-use an external 192KHz/24 Analog to Digital converter to convert all analog sources to digital. It will be limited by the quality of the D to A, you can have the best studio model or a low cost version, but then you can use all digital crossover functionalities, even the digital delay which is something very useful and which is almost impossible to do in analog audio. Also the 69bit digital crossover have almost no sound compared to analog components, active or passive, necessary to make an analog filter. You can also convert your LPs once and save them as a digital file.
-make a second active crossover, an analog type, which could be simplified compared to the digital one (for example without delay line), so you have two different system before the power amplifiers, one analog and one digital. Then use a big analog switch to switch from analog filter to digital filter to the power amplifiers.

The first solution is easy, the second is quite complex to do. Both give the best results for the digital sources.
 

totaldac

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-3.3Vrms max RCA, 6.6Vrms max XLR analog output

Is the gain of the analogue output stage adjustable or is it fixed at the above values?

This is the level for a 0dBFs signal (maximum possible in digital) with the volume set to max level (0dB). You can lower the output level using the volume control from the remote control, it will adjust the level in the FPGA. There is no switch to adjust the levels in the analog domain, I didn't want to add more analog circuitry, the analog stage is minimalist and optimised and can't be modified to keep the same sound quality. Also there is no mechanical switch, no relay, no silicon switch or anything else to switch in the analog signal patch.

It is still possible to attenuate externally if necessary, using resistor based attenuators or a transformer. Also in the dual DAC version there is no internal balanced to unbalanced conversion, if necessary it can be done externally using a transformer for example. All possible limitations must be outside of the DAC.
 

totaldac

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I've asked him before over on DIYA about his design, I don't recall getting an answer. But it wasn't this particular question just a general one about what he saw as the main flaws with IC-based R2R DACs I think. I know, I'm just too probing in my questioning...:p


Well, a quick and late answer, silicon DAC ICs can't embed VishayPG foil resistors which are far better than metal film resistors and silicon resistors.
 

opus111

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Feb 10, 2012
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I agree that those Vishay foil resistors have exemplary characteristics - superb stability over time and temperature, no question.

The designers of the TDA1545A though used another technique to ensure long term stability, continuous calibration, so there's more than one way to skin the cat. No metal film or silicon resistors needed that I can see (from reading the datasheet, not inspecting the die).
 

AudioExplorations

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This is the level for a 0dBFs signal (maximum possible in digital) with the volume set to max level (0dB). You can lower the output level using the volume control from the remote control, it will adjust the level in the FPGA. There is no switch to adjust the levels in the analog domain, I didn't want to add more analog circuitry, the analog stage is minimalist and optimised and can't be modified to keep the same sound quality. Also there is no mechanical switch, no relay, no silicon switch or anything else to switch in the analog signal patch.

It is still possible to attenuate externally if necessary, using resistor based attenuators or a transformer. Also in the dual DAC version there is no internal balanced to unbalanced conversion, if necessary it can be done externally using a transformer for example. All possible limitations must be outside of the DAC.

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.
 

totaldac

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I agree that those Vishay foil resistors have exemplary characteristics - superb stability over time and temperature, no question.

The designers of the TDA1545A though used another technique to ensure long term stability, continuous calibration, so there's more than one way to skin the cat. No metal film or silicon resistors needed that I can see (from reading the datasheet, not inspecting the die).

The long term stability is not really what makes the sound, the resistors must be a pure resistor (not self or capacitance effect) even in a fraction of a second, it must not depend on frequency (the DAC is switching high frequencies!), voltage, instantaneous temperature which is signal dependant, resistor noise, vibrations... A calibration can't solve that. Only one manufacturer build this resistor dies, then the rest of the system in the DAC becomes the limitation.
I tried to sort high quality metal film resistors to get a very high accuracy but the sound was behind VishayPG foil resistor although the nominal tolerance was higher. There was less resolution, less space, less life when listening.
The ohm tolerance is not the only quality for a resistance.
 

opus111

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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 I were you I'd get hold of some of Victor's Vishay resistors and build yourself a resistive attenuator (6.5V -> 0.5V is about 22dB). Put the attenuator inline with the cable between the DAC and your poweramp, nearest the poweramp. Vincent can tell us the minimum recommended load impedance and then we'll know the resistor values to use.
 

totaldac

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Yes indeed, the DAC is able to drive virtually any impedance, even a 32ohm headphone is ok, so the attenuator could have a 600ohm input impedance, and mathematically about 50ohm output impedance for 22dB attenuation, which is low as it should to drive a power amp.
 

AudioExplorations

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Would that result in higher quality attentuation than something that can be bought off the shelf, such as these Rothwell attenuators (available in 10dB and 20dB)? These are said to effect the transparency of the system.

smallbalatten2.jpg
 

opus111

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Better look inside to see what grade of resistors they're using ;) Are they expensive? If not buy them, try them and return them if not satisfied with an explanation for what sucks in the sound. Hopefully the manufacturer will appreciate the feedback. Then you can develop your own superior ones :D
 

AudioExplorations

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Interesting... if I purchased a pair of these (they are not much) and replaced the resistors with the highest available quality (vishnay?) resistors of appropriate resistance values would it be safe to say that this would give me the least detrimental gain reduction technically possible today?

I hate the thought of putting these into the playback chain however in a power amp direct configuration with my amp and speakers using only digital volume control my DAC options are just so limited as virtually all DACs (even on the lowest gain setting if applicable) put out way too much voltage.
 

totaldac

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I guess that they embed a transformer because most other product of this company are transformer based.
Transformer are not easy to do, not always transparent. It is possible to use resistor attenuators instead with the D1 DAC, even quite low value like 600ohm input impedance.
Also these adaptors are maybe filled with resin, so it might be impossible to remove the transformer and have resistor instead, maybe...
 
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opus111

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Interesting... if I purchased a pair of these (they are not much) and replaced the resistors with the highest available quality (vishnay?) resistors of appropriate resistance values would it be safe to say that this would give me the least detrimental gain reduction technically possible today?

Quite possibly though you'd need to check that the necessary resistors (you'd need 3 for balanced) could fit in the available space.

I hate the thought of putting these into the playback chain however in a power amp direct configuration with my amp and speakers using only digital volume control my DAC options are just so limited as virtually all DACs (even on the lowest gain setting if applicable) put out way too much voltage.

3 high quality resistors permanently soldered in is going to be way better than any pot or switched attenuator because there are no wiping contacts. Another thing - doing a true balanced volume control is very difficult. All in all the resistors seem a great solution.

Your only other superior solution is to get inside your poweramp and reduce its gain, Only recommended for experienced EEs who understand feedback very well though.:p
 

AudioExplorations

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Opus & Vincent thanks a lot for the information. I think I will check the feasibility of this, try to find out dimensions and build of these attenuators and see if it is possible to sandwich in the resistors. Could you let me know which exact resistors you would consider the SOTA/cost no object (ideally make and part #s') and which resistance values would be required to reduce by 5/10/15/20 dB. I will look into this and may start a seperate thread if I decide to move forward with the build process :).

Sorry for the thread drift... now back to the Total DAC!
 

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