Using two outputs on a DirectStream DAC


#1

I read in the manual that you should not use both outputs on the DirectStream DAC but it never says why. I have my DSD connected via balanced cables to my preamp. I also want to use the single ended output on the DSD to connect to my headphone amp. Volume control is not an issue as both units have their own volume control. So why can I not I the DSD this way? Most of the time when I am using the preamp I am not listening to headphones and when I am listening to the headphone amp I would not be using the preamp. I suppose there are times when I might use both simultaneously but this would not be the norm. I just want to know the why of this.


#2

Info in this thread.


#3

Interesting read but I don’t see an answer to the question of having both connected but only using one at a time. If the preamp is connected via balanced cables and the headphone amp which is connected to the single ended outputs is off does this negatively impact the balanced connection in the way described in the link? If the headphone amp is off then no load is present. I am thinking that this is like having nothing connected to the single ended output. Am I looking at this wrong?


#4

Unfortunately, the load is present whether the attached unit is powered on or off.


#5

Thank you. That’s exactly what I was wondering. Too bad.


#6

You can use both outputs simultaneously - the only thing you loose is some noise immunity on the balanced outputs, but most of the time that’s not a problem. You can’t hurt the DS even if you short the outputs indefinitely.


#7

Thanks Ted.


#8

That is how I have been doing it as well. XLR to M700s and RCA to Deckard HP amp. I have noticed zero ill effects and of course the HP amp is off when not in use.


#9

According to Elk, even when the HP Amp is off it presents a load to the DSD. I have another way to configure my system so as not to use two outputs on the DSD so that’s how I am using it.


#10

I still think there may be some misunderstanding going on so I’ll try to be more explicit (sorry if this is all obvious):

Bottom line: You should try listening with both cables connected and then again with one disconnected and see if you hear a difference. If you don’t then it doesn’t matter. If you do, you can decide if it matters vs. the inconvenience of using something down stream (e.g. a extra preamp output, etc.) to get the other output.

Details:

If you can reconfigure and loose nothing then in theory it’s best to just use one output on the DS, but that’s may be only in theory.

Elk is correct, there’s a load just by the cables being connected, it doesn’t matter what’s on the other ends of the cables (even if they are disconnected or shorted at the other end) because this load is a capacitive load and parallel capacitance (two cables instead of one) adds.

But that’s not the kind of load that most people think about when people say “load”. Usually they are talking about a resistive load (i.e. a current load.) The DS doesn’t care about how much current you try to draw and in fact the 20dB attenuator is merely a 15 ohm resistor to ground which draws much more current than any set of cables, preamps or amps (they usually are 22,000, 40,000, 100,000,… ohms which is zilch current.)

The two things that can matter in some systems when using two outputs instead of one are the capacitance of the cables and the amount of common mode noise in the system (e.g. groundloops between the DS and something downstream.)

If your cables are of a high capacitance variety and you have two sets of them connected you many affect the frequency balance on the high end. But most cables are low enough capacitance that even doubled up there won’t be any affect anywhere near the audio. (And BTW extra capacitance doesn’t all ways roll of the top end of the frequency response, it can also cause peaking, depending on the particular capacitance in question and whether the DS is in high range or low range.)

Once again, it’s simpler to listen than to try to figure it out analytically.


#11

Yep. I believe the connection to to RCA influences the grounding properties of the balanced connection if I remember right. I’m going to try going double duty on my pre… I can always go back to PC direct connection but was trying to avoid that. My pre does not have a very good HP section… Thanks

(I answered this via email w/o seeing your post Ted. Thanks for the input!)


#12

So, you won’t unbalance the trafo’s balanced connection and thus lose 6dB gain?


#13

It won’t change the gain - the transformer is center tapped which goes to the ground - so the RCA is across 1/2 of the transformer output and the balanced output is across the whole transformer. The loads of the devices on the other end of the cables is minute so they don’t affect the gain either.


#14

Thx. I guess this means that when using both outputs simultanously, the user need to be aware of that the RCA and XLR outputs may give different SPL if all four outputs are routed to amps (e.g. to subwoofers and main speakers line input). For headphone listening this will not be a problem.