DAC as a pre-amp?

[mac_and_dac]

Hi

 

I am about to take ownership of a DAC that will have its own digital volume control. The attenuation is controlled through the ESS9018 chips (one per channel).

 

This is something new for me. It now gives me the opportunity to control my system's volume by the following means:

1) Digital players (Aurdivana/Amarra)

2) DAC

3) Passive pre-amp

 

Ultimately I will use my ears to decide which approach I prefer, but I would be interested to hear what you guys would theoretically opt for if given the choice?

 

My gut feel is to continue to use the pre-amp. My limited little brain tells me that low digital volumes may impact resolution due to reduced bit depth, but perhaps this is simplistic and addressed in other ways (e.g. upsampling prior to attenuation?).

 

All responses appreciated,

 

TIA

mac_and_dac

[vladimirb0b]

I would use the ESS9018's internal volume:

 

http://www.esstech.com/index.php/download_file/view/70/267/

 

For the 2nd choice if you don't want to use DAC's volume control you might A/B between CPU and preamp to see if there is a sound difference. If there isn't one, and I think there might not be, I would pick whichever can use a remote.

[wgscott]

As long as the digital volume control doesn't compress/degrade the audio, you should be fine. Most properly designed digital volume controls won't do much, if any, of that. If you can adjust the gain on your amp, set it so that full on volume from the DAC is as loud as you might ever need it, but not so loud that it damages your speakers. Ideally, you want to attenuate as little from this value for normal listening as possible.

[mac_and_dac]

As long as the digital volume control doesn't compress/degrade the audio, you should be fine. Most properly designed digital volume controls won't do much, if any, of that. If you can adjust the gain on your amp, set it so that full on volume from the DAC is as loud as you might ever need it, but not so loud that it damages your speakers. Ideally, you want to attenuate as little from this value for normal listening as possible.

 

 

Thanks both.

 

If the digital volume doesn't degrade the sound, then I might just bypass the pre-amp and go direct into the mono's (one less device and cable pair in the chain, assuming no impedance issues).

[wgscott]

What is the DAC? Can you link to the specs?

[mac_and_dac]

What is the DAC? Can you link to the specs?

 

Hi,

 

It's the LKS-MH-DA003:

MH-DA003 DAC -ES9018x2 with Femto clock | Volent

 

More detail can be found in the manual.

http://www.mu-sound.com/files/MH-DA003_20141022.pdf

 

It will get the following modifications before arriving:

LKS MH-DA002 Modification – Sound Affairs

 

Probably a bit left-field and not everyone's cup of tea, but I like the architecture of this DAC and the fact that you can easily roll the op amps plus customise the sound in other ways.

[jcn3]

i think you've gotten some good feedback already. i'll throw in my support for a passive pre-amp. i use a luminous audio axiom ii passive pre with xlr input and output. sounds great, great parts quality (for the few that there are), and not expensive at all.

[Pepsican]

Hi

 

I am about to take ownership of a DAC that will have its own digital volume control. The attenuation is controlled through the ESS9018 chips (one per channel).

 

This is something new for me. It now gives me the opportunity to control my system's volume by the following means:

1) Digital players (Aurdivana/Amarra)

2) DAC

3) Passive pre-amp

 

Ultimately I will use my ears to decide which approach I prefer, but I would be interested to hear what you guys would theoretically opt for if given the choice?

 

My gut feel is to continue to use the pre-amp. My limited little brain tells me that low digital volumes may impact resolution due to reduced bit depth, but perhaps this is simplistic and addressed in other ways (e.g. upsampling prior to attenuation?).

 

All responses appreciated,

 

TIA

mac_and_dac

 

I use my Chord Hugo also as pre-amp. The designer, Rob Watts, stated that adding a pre-amp did nothing to enhance sound. It could only degrade it as it was another component in the chain to mess with the signal. That said, in the Hugo, the pre-amp part was specifically considered as part of the design.

[mac_and_dac]

I use my Chord Hugo also as pre-amp. The designer, Rob Watts, stated that adding a pre-amp did nothing to enhance sound. It could only degrade it as it was another component in the chain to mess with the signal. That said, in the Hugo, the pre-amp part was specifically considered as part of the design.

 

I'll have to see whether my Cyrus Mono's act up when I plug my XLR's into it from the new DAC. If they play ball, then I don't see the need for a pre-amp. If they don't, then I will probably just set the DAC volume to 0db and continue with my passive pre-amp.

[ecwl]

I have in the past thought quite a bit about what makes a digital volume control better than a pre-amp. And with some experimentation, I've developed some thoughts on the matter. But then I still don't know if they are correct. So perhaps it's just an opinion, however uninformed.

 

I think the usual thoughts people have is that the preamp has to be able to drive the amp, in terms of impedance matching, power supply of the preamp, etc. so technically, those are still factors that play a role in a DAC. I have definitely heard a DAC with digital volume control sound worse than a preamp but then the moment the "better" power cable of the preamp was switched to the DAC, bypassing the preamp sounded better. Obviously, I'm opening up a can of worms with this power cable thing so like I said, just an opinion.

 

And then the other pretty standard thing people think about is signal to noise ratio and some people would say forcing the DAC to go through a preamp will always degrade the sound because the preamp has it's own SNR and acts as a filter. However, I have heard really transparent preamps with great SNR where the DAC always sounds better through the preamp, probably because once you use digital volume control, you're digitally reducing your SNR anyway.

 

I think once people settle in on digital volume control, it is usually better implemented in the DAC as you can only get up to 32-bit and usually 24-bit USB transmission to the DAC if you decide to attenuate digitally on the PC. If the digital volume control in the DAC is used, you can go beyond 24-bit/32-bit volume attenuation if that's how the DAC is designed. Whether the DAC is capable of outputting that signal with attenuation given its analog noise floor of course is another matter.

 

And now I get to the more controversial parts. Even taking everything I said above, I have heard many times dealers tell me and even show me that the high-end preamplifiers sound better than without preamplifiers. Assuming the preamplifiers are not adding second or third order harmonic distortions to begin with, I think the sonic difference is because people are not paying attention to two other factors in a DAC. First of all, most DACs left-right channels are not perfectly matched. They're close but not the same. So if you're significantly reducing the volume digitally, I suspect these subtle differences in volume is going to become more detectable. However, if you're keeping the DAC at full volume, the slight mismatch at the DAC level may not matter so allowing your preamplifier to attenuate the volume, you're relying on the preamplifier's ability to match the volume and attenuate the signal. And yes, often analog attenuation of volume is also imperfect but you're starting off with a larger signal. Maybe this is a real effect? I'm really not sure. I think the best way to see if the low-level signals of the left-right channels match in a DAC is to actually look at the Stereophile measurements of the 1kHz sine wave at 24-bit. Of course, we come back to whether this effect is truly audible because we are talking about very low level signals here.

 

Finally, I also think one factor people don't think about is the linearity of DACs in general with volume changes. Some DACs have better linearity than others and sometimes, the distortion varies significantly depending on the loudness of the sound it is reproducing. I think Hi-Fi News & Record Review usually starts off with a graph mapping increasing distortion to decreasing digital signal level. The straighter that sloped line, the lower the distortion with volume changes. I think the problem is that some DACs have more distortions at specific volume levels. At the maximal volume, and going through a preamplifier, that's the "sound" of that DAC. But if you're going to do digital volume attenuation, you have just completely altered when and where the sound is going to be most distorted. Obviously, this distortion does not only occur at the DAC chip level but probably also occurs at the Op Amp level. I noticed that OP was planning to roll various Op Amps. So I can easily imagine some Op Amps may sound great going through a passive preamplifier while others may sound better with bypassing the preamplifier.

 

Anyway, at the end of the day, I think that's why experimentation is required when one wants to decide whether to bypass the preamplifier or not. Ultimately, it depends on the DAC and the preamplifier. As to why this happens, I think the above are some hypotheses that I have developed over the years. And I think that's why you hear different people in different camps and I think they are all right. Since implementation is everything...

[mac_and_dac]

Great points, and food for thought.

 

I understand the issue with noise floor, I need to go away and do my research on how digital attenuation will impact resolution, particularly at low volumes.

[ecwl]

Of course in the digital domain, there's no loss of resolution even with say -48dB of 16-bit data because you'll just move the data into the bottom of the 24-bit space. Loss of resolution is still primarily an effect of noise floor and SNR. The issue we were talking about in terms of loss of "resolution" or quality is probably more related to linearity issues as in different DACs can have different amounts of distortions at different volumes. The distortions are small but I suspect they're audible from a psychoacoustic standpoint. I think that's why people sometimes prefer preamps because the low-level distortions sound worse.

[mac_and_dac]

Of course in the digital domain, there's no loss of resolution even with say -48dB of 16-bit data because you'll just move the data into the bottom of the 24-bit space. Loss of resolution is still primarily an effect of noise floor and SNR. The issue we were talking about in terms of loss of "resolution" or quality is probably more related to linearity issues as in different DACs can have different amounts of distortions at different volumes. The distortions are small but I suspect they're audible from a psychoacoustic standpoint. I think that's why people sometimes prefer preamps because the low-level distortions sound worse.

 

A few years ago I wrote a basic digital volume control for a software PCM/WAV sampler. The basic math on the samples always involved some rounding up or down of the output, which could be termed 'distortion' or (more arguably) 'loss of resolution'. Whether a difference could be heard at small db attenuations from 0db I don't know. (I wasn't building for SQ.)

 

Anyway, I'm sure there are smarter ways of implementing digital attenuation than the one I used.