Differences in sound: DAC vs. DAC + Pre-amplifier

[The Computer Audiophile]

On 2/5/2020 at 1:19 PM, plissken said:

Preamps can obviously color the sound. They can't however improve the fidelity of the inputs.

Technically a preamp could improve the signal to noise ratio with a powerful output stage, correct?
 

That’s a serious question, no snark. 

[STC]

1 hour ago, The Computer Audiophile said:

Technically a preamp could improve the signal to noise ratio with a powerful output stage, correct?
 

That’s a serious question, no snark. 

No. There is no perfect preamp. 

[Matias]

2 hours ago, The Computer Audiophile said:

Technically a preamp could improve the signal to noise ratio with a powerful output stage, correct?
 

That’s a serious question, no snark. 

I don't think that is possible, because that would mean only the signal gets amplified and the noise floor does not, which is not possible. Unfortunately the best thing an analog preamp can do is not to raise the noise floor further, or prevent adding more distortion (if that is what one wants, thinking of people looking into deliberately adding distortion = tubes), while hopefully adding more current output and lower impedance.

 

But then there are reviewers who prefer adding preamps after their dCS DACs, which have the lowest output impedance I have seen, so in theory preamps should not be necessary. I guess some people just like the sound of adding a little harmonics. Nothing wrong with that.

[The Computer Audiophile]

52 minutes ago, STC said:

No. There is no perfect preamp. 

Did someone suggest there was a perfect preamp?

[The Computer Audiophile]

3 minutes ago, Matias said:

I don't think that is possible, because that would mean only the signal gets amplified and the noise floor does not, which is not possible. Unfortunately the best thing an analog preamp can do it not to raise the noise floor further, or prevent adding more distortion (if that is what one wants, thinking of people looking into deliberately adding distortion = tubes), while hopefully adding more current output and lower impedance.

 

But then there are reviewers who prefer adding preamps after their dCS DACs, which have the lowest output impedance I have seen, so in theory preamps should not be necessary. I guess some people just like the sound of adding a little harmonics. Nothing wrong with that.

That doesn’t make sense to me. Setting the output of my DAC to 6 volts raises the signal to noise. It should do similar with a preamp. 

[Matias]

2 minutes ago, The Computer Audiophile said:

That doesn’t make sense to me. Setting the output of my DAC to 6 volts raises the signal to noise. It should do similar with a preamp. 

Don't ask me, it is what I read on reviews. Again maybe those reviewers prefer the "flavor" that their preamps add? I don't know.

[STC]

1 minute ago, The Computer Audiophile said:

Did someone suggest there was a perfect preamp?

 

still no. Amplifier job is to amplifies all signals. Be it noise or music. The ratio will be the same plus additional noise of the preamp itself. in the case of preamp, it reduces the level. 

[The Computer Audiophile]

Just now, Matias said:

Don't ask me, it is what I read on reviews. Again maybe those reviewers prefer the "flavor" that their preamps add? I don't know.

Understood :~)

[Matias]

On 3/1/2020 at 3:29 PM, barrows said:

With preamp, higher noise floor, a little less transparency, but better dynamics and fuller, more robust sound.  I preferred with preamp, but wanted to figure out DAC direct as it was clear there was an advantage in transparency with DAC direct.

 

Then, the designer of the Legato output stage changed it, tripling its output current capability.  I now tried DAC direct vs. preamp again:

 

DAC direct: lower noise floor, better detail retrieval, and now, no loss of dynamics either.  So now that the DAC was driving the input stage of the amplifier optimally, there was only loss by adding the preamp.

 

After about 3 weeks of testing, i sold my Ayre preamp, and have not looked back.

 

It is clear to me that DAC direct, for those who do not need source switching. results in the best fidelity to the source, as long as the DAC's output stage is capable of driving the amplifier input stage robustly.  Additionally, most DACs have the capability to drive most amplifier input stages entirely adequately.  Look for a DAC with low output impedance (less than 100 ohms is nice, but up to a couple hindered ohms is going to be OK for most amps) and enough output voltage.  Most IC opamps in DAC output stages can drive amps directly with no problem.  Occasionally there might be a DAC with a bit weaker output stage, but these are rare.

 

I am no expert so correct me if I am wrong, but from what I have researched, looking the system as a whole, I would like to add that there is a 3rd option.

 

1. Fixed gain(s), digital attenuation on DAC.

2. Fixed gain(s), analog attenuation (potentiometer or resistor ladder).

3. Variable gain.

 

Usually preamps are a buffer (gain=1) and/or have a fixed gain (>1), and add analog attenuation. This should add noise and distortion.

 

A few preamps have variable gain output stages (Accuphase and Mola Mola Makua for example), which on lower volumes (gain <1) do not amplify the signal needlessly, preventing noise and distortion. Still the DAC has an output stage with some fixed gain before it, so 2 gain stages in series.

 

Makua goes further by having a top performing DAC inside it, and I think (not sure) it does not duplicate output stages and gains needlessly (DAC+preamp). It only ads the gain it needs (variable gain) and once. So I think this is a very clever system approach.

 

An all in one system (Devialet, Bel Canto Black, digital active speakers, etc) could in theory have only 1 gain stage, ideably variable, between DAC and the output stage of the power amplifier, to have the lowest noise floor and distortion possible.

[barrows]

7 hours ago, ro7939 said:

Yes, as someone stated, one can err Re. an analog VC.  The difference is that with many preamps, a visual glance can confirm the volume setting, whereas in the digital realm some invisible software setting can be off, and take a lot longer to find and fix than a glance across the room.  

 

Well this really depends on set up...  I would submit that many people only have to glance at a tablet in their hands when using digital volume control, and not a small screen across the room.

Digital volume control can work with DSD player, as HQPlayer does it, and so does the ESS chip when playing back DSD.  And i would not claim either approach turns it into "PCM" although the debate would be on semantics.  Of course if one wants DSD to playback with absolutely no processing, then an analog volume control in the DAC will be required, as is done in the newer Bricasti DACs like the M21,  Which sounds fantastic direct into an amplifier (especially a Bricasti amplifier).

[barrows]

3 hours ago, The Computer Audiophile said:

Technically a preamp could improve the signal to noise ratio with a powerful output stage, correct?
 

That’s a serious question, no snark. 

Chris that would only be relevant if one used a higher level during playback:  So, say we made a preamp capable of outputting 10 volts, and then based our SNR test off of full output.  Well yes, then the SNR spec could look better.  But in use we woudl have no better performance, because we would not be using the preamp at 10 volts output.  So, in actual use we probably are only runinng the preamp at a level which produces 2 V output, where the SNR would be much lower.

 

As SNR is a ratio: signal/noise, where the "noise" element is basically a constant (noise floor), the only relevance to performance in actual playback is the SNR at the level one uses during playback.  Inflated numbers based on high playback levels (which are never actually used) is misleading as a "spec" or measurement.

 

We can then see how a adding a preamp degrades performance: no matter what, any preamp (even a passive) will add to the noise of a system.  All noise elements are additive.  So we see from our consideration above, that adding a preamp, at the least, adds more noise, and there fore reduces SNR in use.  Look at the ratio, our amp always requires the same level input foe our listening level, so "S" is constant, and "N" is increased, back to our ratio Signal/Noise one can see that the actual SNR i use will be lower becasayuse of the additional noise of the preamp.,

 

 

[fas42]

What a preamp can do is buffer the output of the DAC, so the current drive demanded by the power amplifier doesn't load the DAC circuitry to the point that the SQ suffers; this only gets worse, the higher the gain is set - audio friend down the road has this very problem, has spent huge amounts of time trying to get the cleanest solution; and still hasn't achieved a peak performance trying this.

[motberg]

Is it required to oversample the file (say Redbook 16/44) to get the best performance for using a digital software volume control, using HQPlayer for example ?

[Miska]

8 minutes ago, motberg said:

Is it required to oversample the file (say Redbook 16/44) to get the best performance for using a digital software volume control, using HQPlayer for example ?

 

It depends on the DAC too, but it certainly helps since it allows more resolution and especially with noise shaping curves increase of dynamic range beyond that of output word length within the original bandwidth.

 

[motberg]

On 3/7/2020 at 9:11 PM, Miska said:

 

It depends on the DAC too, but it certainly helps since it allows more resolution and especially with noise shaping curves increase of dynamic range beyond that of output word length within the original bandwidth.

 

 

OK!  I am testing this with my NOS DAC, HQPlayer 3, dual PC, just got a Windows NAA working on Server 2019 GUI and it is sounding great so far.. For HQPlayer, how is best to manage the "gain staging" of the digital volume control? I am upsampling to 384, within the rate family, and have Min Vol set at -60 and Max Vol set at -3.. would this be optimal ?

 

 

 

[Miska]

1 hour ago, motberg said:

For HQPlayer, how is best to manage the "gain staging" of the digital volume control? I am upsampling to 384, within the rate family, and have Min Vol set at -60 and Max Vol set at -3.. would this be optimal ?

 

Suitable range setting depends on how you use the volume control...

 

[ericuco]

2 hours ago, motberg said:

 

OK!  I am testing this with my NOS DAC, HQPlayer 3, dual PC, just got a Windows NAA working on Server 2019 GUI and it is sounding great so far.. For HQPlayer, how is best to manage the "gain staging" of the digital volume control? I am upsampling to 384, within the rate family, and have Min Vol set at -60 and Max Vol set at -3.. would this be optimal ?

 

 

 

 

I started using HQP volume control a few weeks ago. Currently, my settings a -25 max and -60 min. When playing music, I am in the -30 to -40 range. The -25 max helps prevent sending a blast to my system if for some reason the volume control accidentally gets turned up all of the way.

 

At your current -3 and -60 settings, turn the volume down very low. Start playing music and gradually raise the volume to normal level and see where you are. Then adjust the max volume slightly greater, just beyond the max setting in normal listening (for me -30 is max normal listening, so max setting is at -25).

 

Just be careful when raising volume!!

[Allan F]

2 hours ago, Miska said:

 

Suitable range setting depends on how you use the volume control...

 

 

I believe that Miska means that it depends on whether you are using the digital volume control to control playback volume or you are using fixed fixed settings in HQPlayer and controlling the playback volume through a pre-amp or a volume control on the DAC. The -3db setting is to avoid clipping. On my system, I experienced clipping with some music files at a max setting of -4 while upsampling everything to DSD512. So I now use a max setting of -5. You may not hear clipping but if the volume control in HQPlayer turns red, that indicates that you went into clipping and should use a lower setting. If that doesn't happen, -3 should be fine.

 

You may want to follow the suggestion from @ericuco if you are concerned about accidentally turning or leaving the preamp or DAC volume control at maximum. Personally, I have never experienced that with my pre-amp. At worst, the previous volume setting on my pre-amp may be too loud for the recording I am now playing and I can easily turn it down.

[ro7939]

A state of the art preamp w/analog volume control allows users to swap DACs without consideration for the DAC's output current capacity, without consideration for the existence of nor quality of digital volume within or in front of the DAC, and without consideration for any existing or potential sum total input impedance of the load amplifier(s), which might include sub amps with very low input impedance (the norm for such amps).

 

A state of the art analog preamp is positively always required for maximum system flexibility, not a luxury nor performance impediment.  This is always true, even while certain users assemble one particular system with fixed, hand picked DAC and amp that may perform best without a preamp, especially a lesser preamp.  

 

For any poster here who prefers his DAC direct without a preamp:

1. What is the input impedance of your total amplifier load?
2. What is your DAC's output impedance? (The higher the ratio the better is audio performance, a low ratio is considered 10-1.)
3. Do you maintain DAC direct would outperform a state of the art preamp even if the load impedance was 8k ohm?  (Sum total of my sub amps and main amps.)

 DAC direct always and only minimizes choices, period.  The fact that certain users prefer this option does not make this statement false.   

[The Computer Audiophile]

A preamp definitely enables one to make changes upstream without too much worry. I guess one could look at it as a convenience over quality thing as well. A well matched DAC and amp just can't be beat by placing a third component in the middle. I say "well matched" and I really mean it. Not all DACs drive all amps well. 

[Miska]

4 minutes ago, ro7939 said:

A state of the art preamp w/analog volume control allows users to swap DACs without consideration for the DAC's output current capacity, without consideration for the existence of nor quality of digital volume within or in front of the DAC, and without consideration for any existing or potential sum total input impedance of the load amplifier(s), which might include sub amps with very low input impedance (the norm for such amps).

 

Preamp can only worsen the quality that comes out of the DAC, not improve it. Generally it increases noise and distortion, more or less.

 

Input impedance of a pre-amp shouldn't differ from input impedance of a power amp.

 

Pre-amp is of course useful when you want to switch between multiple inputs.

 

[barrows]

11 minutes ago, ro7939 said:

A state of the art analog preamp is positively always required for maximum system flexibility, not a luxury nor performance impediment.  This is always true

The above is false.  the statement: "nor a system impediment" is what I am referring to.

 

A preamp in the signal path does this:

 

Losses of fidelity from:

 

Preamp input switching devices

Preamp gain stage

Preamp analog volume control

an additional interconnect

At least two additional connections per channel (XLR or RCA jacks and plugs, plus their soldier joints to wires)

 

All of the above mentioned items are lossy, noise and distortion sources which can only add noise and distortion and reduce fidelity.  Remember, that distortions and noise are additive throughout the system.  Removing the preamp (and this applies to any preamp, no matter how good) removes these sources of noise and distortion.

[Kimo]

1 hour ago, barrows said:

The above is false.  the statement: "nor a system impediment" is what I am referring to.

 

A preamp in the signal path does this:

 

Losses of fidelity from:

 

Preamp input switching devices

Preamp gain stage

Preamp analog volume control

an additional interconnect

At least two additional connections per channel (XLR or RCA jacks and plugs, plus their soldier joints to wires)

 

All of the above mentioned items are lossy, noise and distortion sources which can only add noise and distortion and reduce fidelity.  Remember, that distortions and noise are additive throughout the system.  Removing the preamp (and this applies to any preamp, no matter how good) removes these sources of noise and distortion.

 

Benchmark will tell you that you will get better performance using their DAC 3 at a fixed setting and inserting their preamp.

 

ESS will tell you analog volume controls are better than digital.  I think there is a paper online from them with measurements.

 

That being said, I don't run a preamp in my system, and doubt that I would go back to one.  I guess I would, if I switched to an all Benchmark System.  I might consider one if I went back to a tube amp.

[Miska]

5 minutes ago, Kimo said:

ESS will tell you analog volume controls are better than digital.  I think there is a paper online from them with measurements.

 

Problem is that for example ESS has inherent series resistance of 600 ohm which defines the thermal noise limits. With analog volume control you are going to have hard time finding one that has equal or less inherent resistance. In addition you'll need additional analog buffer/impedance converter sections which also will have some noise and distortion.

 

7 minutes ago, Kimo said:

Benchmark will tell you that you will get better performance using their DAC 3 at a fixed setting and inserting their preamp.

 

Sure, because they can sell two devices and get more than twice the amount of money that way!

 

[barrows]

30 minutes ago, Kimo said:

Benchmark will tell you that you will get better performance using their DAC 3 at a fixed setting and inserting their preamp.

 

I would expect a manufacturer who manufactures and sells a preamp to say this.

 

31 minutes ago, Kimo said:

ESS will tell you analog volume controls are better than digital.  I think there is a paper online from them with measurements.

 

You can find Martin Mallinson's video from RMAF on Youtube.  Be careful how you interpret it though. if you pay attention, what he is saying is that analog volume control has an advantage IF you need to use tons of attenuation.  A digital volume control is demonstrably more transparent than an analog one as long as it is not used at very high levels of attenuation.  For example, the ESS chip's volume control runs at 32 bits, so, with a 24 bit source file you have 8 bits extra for volume before you lose ANY resolution.  8 bits means that you can have attenuation up to (8*6dB) -48 dB.  The other potential drawback with digital volume control is thta it does not reduce the noise floor as the volume is lowered, again, this is a non-issue unless you use very high amounts of attenuation, and have a noisy source, both are non-issues in the vast majorities of real world systems.