if you choose method 2) it's extremely safe and there will be no disadvantage. it's called "impedance balanced" and many professional audio equipments are wired this way. it has all the nice properties balanced output has, such as common mode noise rejection, ground loop elimination, etc.
See the table in
http://www.paformusic.org.uk/gl_b.htm#Balanced
The maximum output is 2V instead of 4V. if you don't listen at that high volume a lower voltage is even better.
This means even DX5 has 6 db higher dynamic range, because 4V is 6db hotter than 2V, DX3Pro+ has the same low absolute noise level as DX5.
The RCA to XLR connector is easy to do: connect RCA+ to XLR Pin 2, RCA ground to XLR Pin 1, and a 20Ohm resistor between XLR pin 1 and 3. Then you're all set.
The method works because the 20Ohm resistor is exactly what DX3 Pro+ has in its final output circuit.
Here's the wiring from google image search:
View attachment 195336
(please replace the 100 Ohm to 20Ohm)
See it in action:
View attachment 195337
If you want to apply this solution to another unbalanced product, you have to change the resistor value.
In some rare cases, you need to get the DAC output circuit and copy more passive components to Pin3 as well.
Fortunately for DX3Pro+ only a 20Ohm resistor is needed.
Conclusion: If you don't need full 4V output, just stay with your DX3 Pro+. It's trivial to make it balanced.
Don't purchase DX5 for its balanced output.
Folks I came across this older post from Audiofun and found it very interesting and educational. It seems this method can also be adapted to most if not all RCA/Unbalanced output from a device if you want to feed it into a balanced-input device. Of course voltage output of the unbalanced output will needs to be determined if sufficient for the input device in order to work well. The key is you need to know/determine the output impedance of the unbalanced output of the source device.
I then PM'ed Audiofun and asked a few followup questions. Just wanted to post our conversation here as below so everyone can see it. Hope you may find it useful.
I have not tried such conversion yet FYI.
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Q: Would it works the same if I connect it as below? (which is simpler to do, R is the 20 ohm resistor)
Answer from Audiofun:
it works for eliminating the ground loop, but to avoid interference, you need to make sure the cable is very short.
alternative is to do a short dongle like this, and then connect to your speaker/amplifier using a long normal cable.
rule of thumb is, the closer 20ohm is to the device, the better.
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More Questions and Answers:
> One more question though. The 20 ohm value we use .. is it based on the Output impedance value of the DX3Pro+ published by Topping?? It is specified in Topping's manual/product listing BUT how do we know if it is accurate/true??
It's accurate. I measured it.
> Is it better/needed for us to measure the actual Output Impedance of our DAC and get the exact resistor value to use??
If so do you have instruction on how to measure output impedance of our DAC's RCA output??
a. You can do a tear down and find the circuit look like advertised:
https://nwzimg.wezhan.net/contents/sitefiles3604/18020413/images/4953000.jpg
the leftmost two resistors are marked with 30X, which means 20Ohm
b. You can do a tear down and measure the resistor using a multimeter. it's 20Ohm
c. You can avoid a teardown and connect output to a resistor A and then ground. Output a constant voltage. Let's say R_A = 100Ohm, and you measure the voltage it divides using a multimeter. Then change R_A to 200Ohm. Measure again. You'll get another voltage. Then you can calculate the internal resistor using simple math.
Shortcut: Let R_A = 20Ohm. You get voltage V1. Let R_A = infinity (don't connect a resistor), you get voltage V2. If V2 = 2V1, then You know internal resistor is equal to the first R_A (20Ohm).
d. You can avoid a teardown by just trusting me or Topping.
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