DAC Output Voltage

[sandyk]

24 minutes ago, mansr said:

Right, those graphs show that THD+N is better with an even higher supply voltage and correspondingly higher output voltage.

 

 Which is why in my DIY DAC I use ±16.5 V supply rails which is close to optimum for these opamps.  

[mansr]

4 minutes ago, sandyk said:

 Which is why in my DIY DAC I use ±16.5 V supply rails which is close to optimum for these opamps.  

What output voltage are you using?

[sandyk]

50 minutes ago, mansr said:

What output voltage are you using?

 

Standard. But that is not the point here , as I am not about to redesign my >15W/Ch. Class A amplifier to use even higher input voltages .Some opamps in the series such as the LME49860 use even higher supply rails which can be an advantage in a high quality preamp where they often sound considerably better at + and - 20V (or higher) supply rails

LME49860.pdf

[mansr]

2 minutes ago, sandyk said:

Standard. But that is not the point here .Some opamps in the series use even higher supply rails which can be an advantage in a high quality preamp where they often sound considerably better at + and - 20V (or higher) supply rails

According to those graphs, for a given output voltage, THD+N stays constant once the supply voltage is sufficiently high (distortion breaks down as the rails are approached). Raising the supply voltage further only causes increased power draw.

[sandyk]

11 minutes ago, mansr said:

According to those graphs, for a given output voltage, THD+N stays constant once the supply voltage is sufficiently high (distortion breaks down as the rails are approached). Raising the supply voltage further only causes increased power draw.

 That's why I suggested + and -20V which is what I use in my discrete Class A preamp.

 Just because they can go to + and -22V, does not mean that they should be used that close to maximum for the reasons that you have stated.

[mansr]

12 minutes ago, sandyk said:

 That's why I suggested + and -20V which is what I use in my discrete Class A preamp.

 Just because they can go to + and -22V, does not mean that they should be used that close to maximum for the reasons that you have stated.

Still going by the graphs you posted, for 2 V output, ±12 V supply is enough to reach minimum distortion. A higher supply voltage increases power consumption. This raises the temperature and with it the noise level. Not good.

[sandyk]

The closest they show is 3V output into a 10K load, which will be similar to (or a little lower than) that of many Preamps and Power Amplifiers,  and the LME49720 graphs show that + and -15V is better than + and -12V, with + and -17V a hair width better than + and -15V.
 

We are now getting into the Nit Picking area!

LME49720.pdf

[mansr]

Let's overlay those THD+N graphs from the datasheet and give them some colour:

 

Blue is ±12 V, red ±15 V, and green ±17 V supply. Notice how the three curves overlap almost perfectly up to the 2 V mark. In this region, THD+N decreases linearly with increased output voltage, suggesting that it is dominated by a constant noise level. At some output level, distortion starts rising and overtakes noise as the dominant THD+N contributor. The level at which this happens increases with increasing supply voltage.

 

This tells us that to minimise THD+N, we should use the highest allowed supply voltage (±17 V) and set the gain such that we get the output voltage at the bottom of the corresponding curve. If design requirements call for a lower output voltage, the lowest possible THD+N at that output level can still be obtained with a lower supply voltage. It need only be high enough that the chosen output voltage puts us somewhere on the linear part of the THD+N curve. A higher than necessary supply voltage only wastes power.

[Ralf11]

this thread makes me feel good about having pre-amps

[mansr]

1 minute ago, Ralf11 said:

this thread makes me feel good about having pre-amps

How come? You could change the title to "Preamp Output Voltage" and the discussion would be just as relevant.

[sandyk]

In my case,  I found that my DAC sounded a little better with + and -16.5V supply rails to the analogue area instead of the original + and -15V rails.

Yes, I did try going back again as I had trimpots on the PSU PCB.

.

[mansr]

Alex, since you "disagree" with the datasheet, perhaps you could present your own measurements along with a description of the test setup you used to obtain them. There's also a form on the TI website for reporting errors in datasheets.

[sandyk]

2 hours ago, mansr said:

Alex, since you "disagree" with the datasheet, perhaps you could present your own measurements along with a description of the test setup you used to obtain them. There's also a form on the TI website for reporting errors in datasheets.

 I am not claiming that there is something wrong with their data, but your superimposing leaves a bit to be desired at the 2V level which is what I am using. I checked this again in Photoshop at 600dpi.

As I said previously you are nit picking. Neither are your freezing games practical, as in opamps and transistors etc. the HFE increases with temperature. The tiny measured  improvements you make in one area ,are likely to cause minor degradation in some other areas, and to most people will not be noticed as an audible improveemnt.

 

We are now well and truly off topic and I have no further interest in wasting my time arguing with the self proclaimed Troll, and will not be doing so in this thread.

[mansr]

10 hours ago, sandyk said:

I am not claiming that there is something wrong with their data, but your superimposing leaves a bit to be desired at the 2V level which is what I am using. I checked this again in Photoshop at 600dpi.

The graphs are done with vectors in the PDF, so it's easy to make the lines a bit thinner. Here's a higher resolution image with that change:

 

The curves still track perfectly up to the 2 V mark.

[kumakuma]

4 hours ago, mansr said:

The graphs are done with vectors in the PDF, so it's easy to make the lines a bit thinner.

 

Raster images sound better on my system. 

[sandyk]

9 hours ago, mansr said:

The graphs are done with vectors in the PDF, so it's easy to make the lines a bit thinner. Here's a higher resolution image with that change:

 

The curves still track perfectly up to the 2 V mark.

You can't let it go can you, even though the differences are very trivial  ?

 I didn't want to have to post this, but saved it just in  case. The only change was the addition of 2V at the bottom of the diagram and the highlighting of the .00003 % line in  red.

 I use the LME49710HA in my DIY DAC

 Feel free to continue talking to yourself in this thread.

 

[mansr]

12 minutes ago, sandyk said:

You can't let it go can you, even though the differences are very trivial  ?

 I didn't want to have to post this, but saved it just in  case. The only change was the addition of 2V at the bottom of the diagram. I use the LME49710HA in my DIY DAC

 Feel free to continue talking to yourself in this thread.

 

Yes, a higher supply voltage enables a higher output voltage without distortion. If you're not making use of that, the higher supply voltage is not doing you any favours. A supply of ±12 V is just barely enough for a 2 V output. To be on the safe side, I'd go with ±14-15 V. Anything beyond that will only generate additional heat that nobody wants.

[MattFinish]

On 12/13/2019 at 3:08 PM, The Computer Audiophile said:

Hi Guys, I get many DACs in for review every year and many have different output voltages. Some have 2Vrms, 4Vrms, 6Vrms, and I have one now with 7Vrms...
 

 

I have just upgraded my DAC and the resulting volume seems much lower (nothing else has changed). So i'm keen to put my scope across the balanced output and see what the voltage out is. I am presuming you would measure HOT to GND and COLD to GND? Would the traditional voltages there be 4V pp if I use a sin as an input? Do I need any dummy load or do you do it open circuit? Really appreciate you advice as I have checked everything else and I am stumped as to why the level has dropped. I want to make the check before I go back to the manufacturer.

Regards, Matt

[cjf]

.

[cjf]

On 11/20/2022 at 12:27 AM, MattFinish said:

I have just upgraded my DAC and the resulting volume seems much lower (nothing else has changed). So i'm keen to put my scope across the balanced output and see what the voltage out is. I am presuming you would measure HOT to GND and COLD to GND? Would the traditional voltages there be 4V pp if I use a sin as an input? Do I need any dummy load or do you do it open circuit? Really appreciate you advice as I have checked everything else and I am stumped as to why the level has dropped. I want to make the check before I go back to the manufacturer.

Regards, Matt

It may be easier to just look at what the Spec sheets claim from both DAC's. If the older one has higher output voltage listed then you have your answer without any additional leg work needed on your end.

 

On the other hand, if the newer DAC claims higher output voltage than the older one, you could try to use that approach without doing any measurements. If they fight you on it then you could break out the meters to see if what they claim in the spec sheet is true or not.

[MattFinish]

59 minutes ago, cjf said:

It may be easier to just look at what the Spec sheets claim from both DAC's. If the older one has higher output voltage listed then you have your answer without any additional leg work needed on your end.

 

On the other hand, if the newer DAC claims higher output voltage than the older one, you could try to use that approach without doing any measurements. If they fight you on it then you could break out the meters to see if what they claim in the spec sheet is true or not.

Thanks CJF for you comments. The new DAC's spec state 5.1Vrms on balanced output (old one was 4V). I measured hot and cold and got 2.56Vrms on each so I guess added together they are right (5.12Vrms). Perhaps the volume curve is different on the new DAC from what I have been used to and the displayed "dB" on both DACs is rather different for a typical listening level. Unfortunately I don't have the old DAC to do a comparison as it sold before the new one arrived...

[dericchan1]

Hi everyone, I have just upgraded my dac and the new dac allows xlr output voltage of 1) 4.6v or 2) 10v

 

i have a schiit Freya + preamp. I have reached out to Schiit to see if either voltage output will work with the Freya + and the response was that both output voltage will work but recommended to go with 4.6v as it is closer to the Freya + xlr voltage output around 4v as well.

 

i guess my silly question is I suppose it means because the Freya + xlr output voltage is limited to 4v it really doesn’t matter which output voltage I select on my dac it won’t give me more volume/gain ?

 

thanks

 

Deric

[GregWormald]

On 12/19/2022 at 4:19 PM, dericchan1 said:

it really doesn’t matter which output voltage I select on my dac it won’t give me more volume/gain ?

The answer also depends on the amp and the speakers/headphones.

But anyway let me suggest that you go with the voltage that gives you the best control over the listening volume.