Questions about the unbalanced output from balanced headphone amp/DAC stack

[zandm7]

Quick question regarding balanced amp/DAC stacks:

So as I understand it, the benefit of going balanced is that it will eliminate any ground loop issues you could potentially encounter, and this benefit is only applied if you feed a balanced input from your DAC into the amp (e.g. XLR from SMSL SU-8 V2 to Drop THX 789). If I'm understanding this correctly, whether or not you use the balanced headphone output from the amp does not determine whether you reap the benefits of your balanced stack (but the balanced headphone output will usually be more powerful).

Do I have this right? To illustrate my example a little more specifically, say I have an SMSL SU-8 V2 DAC and Drop THX 789 amp. I connect my computer to the SU-8 via USB, and then connect the XLR output of the SU-8 into the XLR input of the 789. From there, regardless of whether I use the XLR or 1/4" headphone output of the 789, I will still have eliminated any ground loop issues, correct?

And another question: I believe that it generally isn't safe to convert a balanced input into an unbalanced output (i.e. using an XLR to 1/4" adapter on the XLR headphone output of the 789 is a no-no); is it still safe to use the unbalanced output of an amp like the 789 if it's being fed a balanced input? If so, why is that the case but using an XLR to 1/4" adapter is a no-go?

Thanks in advance <3

 

[AnalogSteph]

From there, regardless of whether I use the XLR or 1/4" headphone output of the 789, I will still have eliminated any ground loop issues, correct?

Yep.

And another question: I believe that it generally isn't safe to convert a balanced input into an unbalanced output (i.e. using an XLR to 1/4" adapter on the XLR headphone output of the 789 is a no-no); is it still safe to use the unbalanced output of an amp like the 789 if it's being fed a balanced input? If so, why is that the case but using an XLR to 1/4" adapter is a no-go?

I think you've got your inputs and outputs mixed up.

You can always adapt an unbalanced output to a balanced input, and if the cabling is done right (which is rare enough) you'll even reap the benefits of the latter.

Adapting balanced outputs is much more tricky, as what you can do and what kind of adapter cabling you need will depend on the circuitry lurking behind the panel. (It'll often say in the specs.)
If you have a transformer-coupled output, you can pretty much wire up pin 2 = signal and pin 3 = ground and be done with it. In an electronically floating oder merely impedance-balanced output you'll want to short 3 and 1 as well.
A very common output topology, however, is not floating and just takes the unbalanced signal and generates an inverted version to complete the balanced output. Then you basically have two ground-referenced single-ended outputs with out of phase signals, and neither would be particularly happy if you were to short it out. So in that case you need pin 2 = signal and pin 1 = ground, with pin 3 going unused.
Another way of looking at the difference is that this topology has a very low common-mode output impedance, whereas floating topologies have a high common-mode output impedance, so their common-mode voltage can be shifted up and down almost arbitrarily and they won't care.

 

[raif71]

Yep.

I think you've got your inputs and outputs mixed up.

You can always adapt an unbalanced output to a balanced input, and if the cabling is done right (which is rare enough) you'll even reap the benefits of the latter.

Adapting balanced outputs is much more tricky, as what you can do and what kind of adapter cabling you need will depend on the circuitry lurking behind the panel. (It'll often say in the specs.)
If you have a transformer-coupled output, you can pretty much wire up pin 2 = signal and pin 3 = ground and be done with it. In an electronically floating oder merely impedance-balanced output you'll want to short 3 and 1 as well.
A very common output topology, however, is not floating and just takes the unbalanced signal and generates an inverted version to complete the balanced output. Then you basically have two ground-referenced single-ended outputs with out of phase signals, and neither would be particularly happy if you were to short it out. So in that case you need pin 2 = signal and pin 1 = ground, with pin 3 going unused.
Another way of looking at the difference is that this topology has a very low common-mode output impedance, whereas floating topologies have a high common-mode output impedance, so their common-mode voltage can be shifted up and down almost arbitrarily and they won't care.

I have a question that has been bugging me. Let's use the smsl su-8 v2 dac and thx 789. Both of these units have SE rca out and rca in as well as balanced xlr out and balanced xlr in. Will balanced connection between dac and amp give higher output volume at the headphone whether SE or balanced out of the amp compared to SE connection (rca) from dac to amp? Thanks

 

[AnalogSteph]

I have a question that has been bugging me. Let's use the smsl su-8 v2 dac and thx 789. Both of these units have SE rca out and rca in as well as balanced xlr out and balanced xlr in. Will balanced connection between dac and amp give higher output volume at the headphone whether SE or balanced out of the amp compared to SE connection (rca) from dac to amp? Thanks

It will appear that
a) THX AAA 789 overall gain is the same for both inputs and
b) SU-8 v2 balanced out is 6 dB louder than unbalanced.

The Massdrop amp has a crazy high maximum output amplitude but not that much gain (3.3x max), and needs ~5 Vrms to reach clipping levels. You would need the balanced connection to vaporize 600 ohm cans.

 

[raif71]

It will appear that
a) THX AAA 789 overall gain is the same for both inputs and
b) SU-8 v2 balanced out is 6 dB louder than unbalanced.

The Massdrop amp has a crazy high maximum output amplitude but not that much gain (3.3x max), and needs ~5 Vrms to reach clipping levels. You would need the balanced connection to vaporize 600 ohm cans.

Meaning that if I play a song using SE connection between dac and amp at 12 o'clock level, if I use balanced connection between dac and amp, the volume level would be lower say 10 o'clock to give the same loudness ?

 

[crossover34231]

You can always adapt an unbalanced output to a balanced input, and if the cabling is done right (which is rare enough) you'll even reap the benefits of the latter.

I really appreciate yall's discussion on this topic. Two follow up questions regarding the same hypothetical (Computer w/ USB into smsl su-8 w/ XLR into thx 789 w/ rca into headphones)
1. How do I make sure "the cabling is done right" so that I can "reap the benefits" of the balanced DAC-AMP connection without having a balanced output into the headphones?
2. Is there any danger in damaging the equipment by not having a fully balanced chain? Are the dac, amp, or headphones in danger of damage because of using too much power?

Thanks!