How Does the Output Voltage of DAC Affect the System's Sound Quality? Does it Matter if One is Using a Quality Preamp?

[caesar]

How does the output voltage of a DAC affect system sound quality?

What is the ideal voltage if one is / is not using a preamp? Does it even matter if one is using a great preamp? Or is it a concern only for guys who want to drive the amp directly from a DAC?

How does, say, a voltage of 1.3 vs. 1.6 vs. 2.0 vs 3.2 affect the sound ? ( And what are the proper units V? V RMS?)

Thanks in advance

 

[K3RMIT]

It’s complex and there are some pros here that should answer but may be afraid to.
SE and bal have a min n max in voltage
but it’s not just voltage that effects the sound from source to preamp.
The source needs to much lower in imp then the preamp
next gain input voltage should be adjustable at the preamp. This helps in varying voltage output at source.
The plan is to get the best dynamics without going into clipping the input of the preamp.
some sources allow for adjusting there output as well.
lastly if the dAC has a volume control this is used to tune the sound with the preamp again sws inside

 

[poonbean]

Well, I've got the same question - hoping for more discussion from those far more knowledgeable than me on this subject - low bar.

 

[DonH50]

Specs for audio components are usually Vrms (and Arms for current). Power is normally average power in W (there's no such thing as rms power).

The noise floor is often a lower limit on DAC performance, so the only practical way to provide higher SNR and SINAD (~THD+N) is to increase the output voltage. However, it is harder to achieve higher linearity (and thus lower distortion) with higher voltage, so there is always a trade made for noise vs. distortion in a practical design. There are numerous other related technical trades, such as bandwidth, gain, and feedback factor, but noise vs. distortion is a biggie.

At the system level, matching signal levels for best end-to-end noise and distortion is desirable, but somewhat complex. I have a long post on ASR about that but am sure that would be unwelcome here and is not an easy read. Basically you want to optimize the interface at each component pair, that is, choose components and gain settings that optimize the noise and distortion through the signal chain. Too low a signal leads to higher noise, and too large a signal leads to higher distortion.

Example: A DAC with 1 Vrms max output feeding an amplifier with 10 Vrms max input level will likely not be able to drive the amp to full output, leading to excessive distortion from the DAC operating at its max output, and being at the low end of the amp's input range means higher noise at the amp's output. Amplifier SNR is typically specified at maximum output, so an amp with 100 dB SNR for 10 V input may exhibit only 80 dB for 1 V input. A DAC capable of 10 Vrms output driving an amp with 1 Vrms sensitivity means the DAC will be at the low end of its output, increasing noise and the chances of overdriving the amp and creating high levels of distortion in the amplifier. Always trades...

HTH - Don

 

[PYP]

Specs for audio components are usually Vrms (and Arms for current). Power is normally average power in W (there's no such thing as rms power).

The noise floor is often a lower limit on DAC performance, so the only practical way to provide higher SNR and SINAD (~THD+N) is to increase the output voltage. However, it is harder to achieve higher linearity (and thus lower distortion) with higher voltage, so there is always a trade made for noise vs. distortion in a practical design. There are numerous other related technical trades, such as bandwidth, gain, and feedback factor, but noise vs. distortion is a biggie.

At the system level, matching signal levels for best end-to-end noise and distortion is desirable, but somewhat complex. I have a long post on ASR about that but am sure that would be unwelcome here and is not an easy read. Basically you want to optimize the interface at each component pair, that is, choose components and gain settings that optimize the noise and distortion through the signal chain. Too low a signal leads to higher noise, and too large a signal leads to higher distortion.

Example: A DAC with 1 Vrms max output feeding an amplifier with 10 Vrms max input level will likely not be able to drive the amp to full output, leading to excessive distortion from the DAC operating at its max output, and being at the low end of the amp's input range means higher noise at the amp's output. Amplifier SNR is typically specified at maximum output, so an amp with 100 dB SNR for 10 V input may exhibit only 80 dB for 1 V input. A DAC capable of 10 Vrms output driving an amp with 1 Vrms sensitivity means the DAC will be at the low end of its output, increasing noise and the chances of overdriving the amp and creating high levels of distortion in the amplifier. Always trades...

HTH - Don

@DonH50 my DAC has options for outputting 0.6v, 2v, 6v. The amps (same manufacturer) have the following specs:
Unweighted Signal/Noise Ratio: 128dB
Input Impedance: 100kohm

Which DAC setting should be the best match? (I tried them all a long time ago; maybe time to try again). Thanks.

 

[DonH50]

@DonH50 my DAC has options for outputting 0.6v, 2v, 6v. The amps (same manufacturer) have the following specs:
Unweighted Signal/Noise Ratio: 128dB
Input Impedance: 100kohm

Which DAC setting should be the best match? (I tried them all a long time ago; maybe time to try again). Thanks.

What is the input sensitivity of your amplifier? The equations get a little complicated, but I'd start by choosing the DAC output that most closely matches the amp's rated input, erring on a little more voltage from the DAC.

 

[poonbean]

Wow, DonH50, that explanation is awesome - thank you

 

[PYP]

What is the input sensitivity of your amplifier? The equations get a little complicated, but I'd start by choosing the DAC output that most closely matches the amp's rated input, erring on a little more voltage from the DAC.

specs listed in manual and on website:

PERFORMANCE​

400W/8 ohm, 700W/4 ohm, 1200W/2 ohm
Gain: 28dB
Unweighted Signal/Noise Ratio: 128dB
Distortion (THD, IMD): <0.003 % (all frequencies and power levels)
Input Impedance: 100kohm
Output Impedance: <0.003 ohm (DF>4000), all frequencies
Bandwidth: >50kHz

Mola Mola

Description

www.mola-mola.nl

 

[DonH50]

specs listed in manual and on website:

PERFORMANCE​

400W/8 ohm, 700W/4 ohm, 1200W/2 ohm
Gain: 28dB
Unweighted Signal/Noise Ratio: 128dB
Distortion (THD, IMD): <0.003 % (all frequencies and power levels)
Input Impedance: 100kohm
Output Impedance: <0.003 ohm (DF>4000), all frequencies
Bandwidth: >50kHz

Mola Mola

Description

www.mola-mola.nl

400 W into 8 ohms is 56.57 Vrms and given 28 dB(25.12 V/V) gain requires 2.25 V for full-scale output. I would try the DAC's 2 V output setting. That provides 399 W, barely under rated spec, without overdriving or significantly underdriving the amplifier. Using 0.6 V only provides 28 W from the amp, and 6 V would way overdrive the amplifier at full-scale output.

HTH - Don

Power = Voltage^2 / R
Gain in V/V = 10^(Gain in dB/20)

 

[poonbean]

So :

56.57V = (400W*8R)^0.5 - I think this means that the amp delivers 56.57V into the loudspeaker at max output, which is why those with electrostatic loudspeakers (eg quad) need to be careful - yes?

25.12V/V = 10^(28db/20) - I think this parameter explains the ratio of output volts to input volts - yes?

thus 56.57V / 25.12V/V = 2.25 V input "for full-scale output"

Assuming I have this right - thanks for the education !

FWIW, my Dac max output is 3.6V, but the amps I'm currently looking at amps with input sensitivities in the range of 1-2v, so perhaps these are not a good pairing and need to broaden the search ? Or, just be prepared to deal with less subtle gains between incremental volume changes and utilizing roughly half the output V from the dac. Do I have that about right?

 

[DonH50]

So :

56.57V = (400W*8R)^0.5 - I think this means that the amp delivers 56.57V into the loudspeaker at max output, which is why those with electrostatic loudspeakers (eg quad) need to be careful - yes?

Yes to the voltage, with the caveat that amplifiers typically deliver more voltage (with higher distortion) than their rated specifications.

As for ESLs, older Quads would not handle a lot of power, but I have not kept up with their current line. Sound Labs, Sanders, perhaps other ESLs can handle higher power.

25.12V/V = 10^(28db/20) - I think this parameter explains the ratio of output volts to input volts - yes?

thus 56.57V / 25.12V/V = 2.25 V input "for full-scale output"

Correct. I put the equations at the end of my post. Amplifiers are usually specified by input voltage, sometimes gain, and output wattage, so to get to the rated input sensitivity I worked backwards. They did not provide input sensitivity in their manual.

Assuming I have this right - thanks for the education !

NP

FWIW, my Dac max output is 3.6V, but the amps I'm currently looking at amps with input sensitivities in the range of 1-2v, so perhaps these are not a good pairing and need to broaden the search ? Or, just be prepared to deal with less subtle gains between incremental volume changes and utilizing roughly half the output V from the dac. Do I have that about right?

A lot of DACs have higher output voltage than amps need these days, probably so they can specify greater dynamic range as mentioned in my first post. DACs generally have far more dynamic range than we can hear and/or use in our systems so I would not worry about the higher DAC output voltage. You give up roughly 6 dB for each having in signal from the DAC, so if the DAC's dynamic range is 120 dB, using only half its output voltage yields 114 dB, still a large number compared to most recordings. Or to what you are likely to be able to stand assuming you want to be able to hear afterwards. You could also insert a passive volume control or fixed attenuator before the amp's input to reduce the DAC's output to suit the amp.

100 mV used to be fairly common, but that number has moved up over the years, and now DACs and preamps putting out 5-10 V (formerly "pro" levels) are not uncommon. Amp designers must tread the line across technologies to suit the widest audience, and 1 Vrms or so has been a de-facto standard for years. Fortunately our hearing is logarithmic so a large change in absolute terms is not that big in the real world.

HTH - Don

 

[banpuku]

Don - great stuff. In my current system, I have a Blue Node 2 has 2.1V max output and 650ohm output impedance. This is directly connected to my power amps which use a line input transformer (see specs below) which has a max input voltage 10V. The line input transformer then connects to the tube (spud amp) which is an EML 30A. So, based upon what I gleaned from you comments above, this suggests that the the Blue Node streamer does not have enough voltage to properly drive the input transformer and tube to max output. Correct?

 

[DonH50]

Short answer: I don't know. But note the transformer's max input spec does not matter unless you are pushing it; what you need to know is the voltage required at the input of your amp to produce full-scale output. Transformers get very nonlinear (distorted) when overdriven so applying no more than 2 V or so seems like a good idea. But not reaching the transformer's max input voltage does not matter unless it is a 1:1 transformer and your amp requires more than 2.1 V to achieve full output.

A transformer presents input and output impedances based upon the source and load impedances reflected through the transformer, so that makes it hard to define, and I don't know anything about the amp. If the primary is 600 ohms as stated, that seems low for a DAC, which usually wants to see a high input impedance. (600 ohms is appropriate for a professional system where mics are often designed to drive 600-ohm loads.) But that assumes all impedances are matched on both sides, something I do not know. Ignoring that, if the input/output ratio is 1:9.2 (odd choice), then we need to know if that is the total ratio including the center tap. Finally, there is a max input, but no max output voltage spec. That's a lot of unknowns.

IF it is a step-up transformer with a 1:9.2 ratio, and your DAC can drive the input to 2.1 V (may be only about half that if the DAC's output is 650 ohms and the transformer's input is 600 ohms), then the output voltage would be 2.1 Vrms * 9.2 = 19.32 Vrms, which I would expect to drive any amp to max output. Half that is still around 9 V if it loads your DAC's output, which again I would expect to be plenty for a consumer amp.

Easy answer: If your systems sounds OK as-is, play on.