Input voltage for high gain amplifiers and the dream of XLR cables.

[Bird_of_Hermes]

Hello all,

I have a question about amplifier gain and the impact that XLR vs single-ended cables make.

I am in the process of buying a DAC and amp. I plan on using a NCx500 amp with the default Hypex buffers: 11.5 dB and 26.8 dB gain which respectively correspond to a voltage of 14.2V and 2.16V to reach their max power. Let's go ahead and ignore that 11.5dB gain option. If we take the normal/modern DAC spec of 2V unbalanced and 4V balanced output, is there any reason I should choose to use the XLR output for a short cable (just a few feet) run?

I am sure this is silly, but I feel like I would be doing something "wrong" not to use the balanced connection over the single-ended one, especially when the amp requires the balanced cable.

I suspect that any performance increase from using the XLR (via the reviews such as this: DMP-A6) is simply due to the 6dB higher output level of the XLR connection. I feel like all I would be doing by insisting on the balanced cable would be to reduce the total usable digital volume control of the DAC. I would need to drop 6dB of voltage just to get it to the 2V max output level of the amp/buffer, then drop another few dB because my speakers (300W at 6 ohm) certainly can't handle as much power as the NCx500 can output (probably ~500W at that impedance)... and neither can my ears... or maybe even my neighbors' ears. And even then it will be blisteringly loud.

It's worth noting that I would need to get a RCA/single-ended to XLR cable as I still need a XLR connection on the amplifier side.

I am sure this has been posted before, but the correct search terms elude me. Please forgive my first post!

PS. Perhaps someone can help me with the math, but from the streamer linked above, Amirm reduced the output by 2dB to reach a 4V output voltage. Which, if the website I found is correct, should have resulted in a max voltage output of 5V, but he had indicated that the max was above 6V!

If I change the calculation to 4dB, as if the streamer was showing power gain instead of voltage gain, the numbers seem more reasonable: 6.34V. I am not really sure what to make of this.

 

[staticV3]

If we take the normal/modern DAC spec of 2V unbalanced and 4V balanced output, is there any reason I should choose to use the XLR output for a short cable (just a few feet) run?

Yes. An XLR connection can prevent ground loops, which are largely unrelated to cable length.

I suspect that any performance increase from using the XLR (via the reviews such as this: DMP-A6) is simply due to the 6dB higher output level of the XLR connection.

No. The benefits of an XLR connection go beyond just a hotter signal.
It prevents signal interference.

PS. Perhaps someone can help me with the math

According to the user manual, the DMP-A6 has a maximum analog output voltage of 5Vrms, via the XLR output.

And indeed, Amir's measurements seem to confirm that with 2dB reduction resulting in 4.0Vrms (4*10^(2/20)≈5.0Vrms)

Accordingly, this statement from Amir doesn't make much sense to me:

Eversolo DMP-A6 Measurements
Output goes up to 6+ volts so I dialed that down to 4 volts for the measurements (-2 dB).

I took a look at the comments to see if perhaps he added a measurement of the DMP-A6 at full volume, but sadly he didn't.

For now, I would assume that the "6+ volts" was some kind of mistake.
Perhaps the APx Voltage readout hadn't settled yet when he read that value, or perhaps Amir tested a pre production unit with slightly different output.

 

[levimax]

For now, I would assume that the "6+ volts" was some kind of mistake.

Maybe RMS vs P to P ?

To OP... go balanced for all the reasons given

 

[Bird_of_Hermes]

In regards to the marketed output voltage, it’s actually stated to be 5.2V, which isn’t either of our calculated values.

That said, it’s interesting. I expected to be suggested to go with the RCA connections. The software only allows the digital meters to work at the top end of the output level.

I suppose, if nothing else, that I grab a pair of both cables and try them out for a ground loop.

Thanks!

 

[dualazmak]

Just for your reference, I assume this diagram would help your proper understandings;

 

[Bird_of_Hermes]

Just for your reference, I assume this diagram would help your proper understandings;
View attachment 301986

Sure, I understand that, but I fail to see why that isn’t related to cable length.

Assuming that I’m not going to string it along a mains AC cable or else install a HAM radio, what is going to cause noise in the cable?

There is plenty of EMR out there, so I am welcome to things I haven’t considered.

 

[dualazmak]

Sure, I understand that, but I fail to see why that isn’t related to cable length.

The longer the cable, the higher the possibilities of the noise intrusions.
The more complex of many long and/or short cables (jungle of various cables), the higher the possibilities of the noise intrusions.

This is one of the reasons that XLR balanced connections are preferred, or even the "must", in large stage/hall settings, as well as in sound recording/editing/mixing studios, where long microphone cables and long analog line level cables are needed.

Even in our home audio setups, if you would prefer as HiFi as possible, XLR balanced connections would be therefore recommended.

If you would be interested, my latest home audio setup shared here and here would be of your reference. I always stick to XLR balanced connections as much as, as far as, possible.

 

[wwenze]

is there any reason I should choose to use the XLR output for a short cable (just a few feet) run?

Because in most scenario of common-mode noise the noise doesn't care how long the cable run is. Since most of it is conducted noise and conducted noise doesn't care how long the cable run is.

 

[Bird_of_Hermes]

I suppose the the final question would be: Is there proof/math that shows the loss of signal due to a lower digital output is preferable to moving to a single-ended setup?

 

[wwenze]

I suppose the the final question would be: Is there proof/math that shows the loss of signal due to a lower digital output is preferable to moving to a single-ended setup?

None, and it isn't guaranteed either. Different situations have different results, and you can easily test which is the better situation for you in terms of noise, simply with a smartphone's mic stuck very close to your speaker's tweeter or woofer.

In your situation the final output volume is the same, with the XLR out you lose signal-to-noise ratio from lower digital volume usually by the same amount of volume you attenuated. You lose SINAD if the SINAD is noise-dominated, but in some cases you may gain SINAD if the SINAD is distortion-dominated. Nothing here really matters tho since you can't hear it. What really does matter is if your setup is prone to common-mode noise. Any noise that you ears actually picked up, electrically it will measure at least -100dB to -60dB worth of noise depending on your setup. And a balanced connection will reduce that noise to almost inaudible.

With regards to the better SINAD from balanced out

"There are also benefits to system linearity. In very low distortion applications, the headroom of the power supplies can be increased by a factor of two when compared to a single-ended signal. The inherent cancellation of even-order harmonics in a differential system, means that the 2nd, 4th, 6th, and so on harmonics will be quite low compared to the odd-order harmonics. It is important to note that a perfect cancellation cannot be achieved, but there is a clear advantage."

Differential Circuit Design Techniques for Communication Applications

Recent advances in integrated RF circuit technology and expansions of available high performance differential RF building blocks.

www.digikey.es

And indeed this seems to hold true in DACs measured by ASR, at least when we say whether it is the 2nd or the 3rd harmonic that is bottlenecking the SINAD score. But again, at a SINAD close to -120dB, this is all academic.

 

[MaxwellsEq]

I suppose the the final question would be: Is there proof/math that shows the loss of signal due to a lower digital output is preferable to moving to a single-ended setup?

There have been some tests here (I think Amir did one), investigating whether attenuation in the digital domain is worse than attenuation using a preamplifier (which, by the way is the product you need to purchase to allow variable analogue levels into your power amplifier), and demonstrated that with modern DAC/DSP implementations there is no noticeable downside relative to a good analogue attenuator.

 

[Randyman...]

RME has the same general outlook regarding digital attenuation (within reason).

 

[dualazmak]

There have been some tests here (I think Amir did one), investigating whether attenuation in the digital domain is worse than attenuation using a preamplifier (which, by the way is the product you need to purchase to allow variable analogue levels into your power amplifier), and demonstrated that with modern DAC/DSP implementations there is no noticeable downside relative to a good analogue attenuator.

I essentially agree.

The use of "right person in right place" choice/selection/utilization of HiFi "integrated amplifier(s)" having XLR balanced input and excellent gain/volume controller would be another option, I believe. If interested, please refer to my summary post here on amplifiers exploration.

 

[dualazmak]

I control the "master volume" in the most upstream digital domain (internal digital volume of software audio player JRiver MC), and I can use the volume/gain controllers of HiFi "integrated amplifiers" for safe and flexible relative gain (tone) tuning on-the-fly i.e. while listening to the music, ref. here and here;

 

[Noske]

There are available correctly constructed RCA to XLR cables. Of course there will be certain well known "issues" with RCA as documented here and elsewhere.

While my own DAC and power amp may be connected easily with XLR, I am in the process of commissioning a hand built 6SN7 transformer pre-amp with RCA in and out - 5 RMS 100ohm out, 6 dB gain. It will oulast me.

I do enjoy 2nd and 3rd harmonics.

My DACs tend to die every year or two, and they are very unforgiving should the recording be less than high fidelity.

 

[antcollinet]

Here is an alterantive approach. Start by running the amp at the lower gain. The available 5V is only 9dB down (approx half the perceived volume) on the 14V needed for full power. So you'll not have the full 700W available

Instead, you'll "only" have about 100W of easy clean power. I doubt very much you will make use of this for normal listening.

If it turns out though not to be enough, then go to the higher gain setting.

Another option would be the higher gain setting with some passive attenuators on the input, to match full volume to your maximum required listening level.

 

[dualazmak]

Another option would be the higher gain setting with some passive attenuators on the input, to match full volume to your maximum required listening level.

Although I understand this option, at least in my case (and I assume also in OP's case), complete elimination of passive LCR network and passive attenuators would be the important motivation/goal of our audio system building for much better total sound quality; I mean direct and dedicated drive of SP units by amplifier(s).

Just for your and OP's reference, during my ignition/start-up sequences (ref. here), I first set the digital master volume of JRiver MC at minimum level, then I carefully set/dial-up all the "integrated amplifiers" (or preamplifiers, if this would be the case) to their best working standard volume/gain level (usually around -17 dB or 12:15 O'clock dial position), then finally I gradually and carefully increase the "digital master volume" of JRiver MC to my required listening level; of course below the clipping level all the way through digital stage to analog amplifier stage.

In my audio system and listening environment, the master volume of JRiver MC never reached 0 dB (100%) level even for the unusually loudest full orchestral sounds. (I still have/set 4 dB margin below the clipping level in software DSP EKIO input level, and also 4 dB margin below the 0 dB maximum output level in the multichannel DAC, OKTO DAC8PRO, as shown in the signal path diagram in my above post #14.)

In other words, the standard gain levels of proper HiFi "integrated amplifiers" (or preamplifiers) should be determined beforehand so that the master volume of JRiver MC can control up to the loudest listening volume for myself/ourselves in my/our listening environments; and of course the "integrated amplifiers" (or the power amplifiers) should have enough power margine to achieve these gain/level controls.

 

[antcollinet]

Although I understand this option, at least in my case (and I assume also in OP's case), complete elimination of passive LCR network and passive attenuators would be the important motivation/goal of our audio system building for much better total sound quality; I mean direct and dedicated drive of SP units by amplifier(s).

Just for your and OP's reference, during my ignition/start-up sequences (ref. here), I first set the digital master volume of JRiver MC at minimum level, then I carefully set/dial-up all the "integrated amplifiers" (or preamplifiers, if this would be the case) to their best working standard volume/gain level (usually around -17 dB or 12:15 O'clock dial position), then finally I gradually and carefully increase the "digital master volume" of JRiver MC to my required listening level; of course below the clipping level all the way through digital stage to analog amplifier stage.

In my audio system and listening environment, the master volume of JRiver MC never reached 0 dB (100%) level even for the unusually loudest full orchestral sounds. (I still have/set 4 dB margin below the clipping level in software DSP EKIO input level, and also 4 dB margin below the 0 dB maximum output level in the multichannel DAC, OKTO DAC8PRO, as shown in the signal path diagram in my above post #14.)

In other words, the standard gain levels of proper HiFi "integrated amplifiers" (or preamplifiers) should be determined beforehand so that the master volume of JRiver MC can control up to the loudest listening volume for myself/ourselves in my/our listening environments; and of course the "integrated amplifiers" (or the power amplifiers) should have enough power margine to achieve these gain/level controls.

Who said anyting about LCR networks. A passive attenuator should be purely resistive, and so have no negative impact on the frequency response (or other sound quality aspects) of the system.

 

[pseudoid]

The longer the cable, the higher the possibilities of the noise intrusions.
The more complex of many long and/or short cables (jungle of various cables), the higher the possibilities of the noise intrusions.
This is one of the reasons that XLR balanced connections are preferred, or even the "must", in large stage/hall settings, as well as in sound recording/editing/mixing studios, where long microphone cables and long analog line level cables are needed.
Even in our home audio setups, if you would prefer as HiFi as possible, XLR balanced connections would be therefore recommended.

These two above correct statements get diluted by these two:

An XLR connection can prevent ground loops, which are largely unrelated to cable length.
-----------
Because in most scenario of common-mode noise the noise doesn't care how long the cable run is. Since most of it is conducted noise and conducted noise doesn't care how long the cable run is.

Unless they can be quantified.
EDIT: highlighted parts which require quantification: e.g. -xxdB@Fx

 

[staticV3]

These two above correct statements get diluted by these two:

Unless they can be quantified.

dualazmak is talking about induced noise, which gets worse the longer your cables are.
I was talking about transmitted noise, which does not meaningfully change with cable length.
If you have a GND loop in your system, then it doesn't matter if the cable is 1m or 10m long, the GND loop will stay.