DAC Splitting Causing Treble Distortion
Jun 7, 2017 at 7:03 PM Thread Starter Post #1 of 9

DamageInc77

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I am having a very odd issue that I was hoping that someone smarter than me might know how to deal with or at least what the cause is.

I am running a DAC with two RCA y-splitters, one connection to my headphone amp, and one to a receiver.

When the receiver is turned off (as in not standby, but complete power cutoff), the upper treble on the headphone amplifier output will distort ever so slightly. I've tried switching to a different PC as main source, 2 completely different DACs, 3 different models of receivers, 2 different brands of headphone amps, and 3 different headphones. The issue persists no matter the configuration.

I could use the passthrough on the receiver instead of the y-splitter on the DAC, but I don't want to leave the receiver on all the time. And if the amp had to be on all the time, the current setup works fine.

What might be causing treble distortion through the RCA y-splitter due the receiver being powered off? Especially as the problem is consistent through a crazy number of configurations? Any help would be very much appreciated.
 
Jun 7, 2017 at 7:41 PM Post #2 of 9

007shark76

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Someone can correct me if I am wrong, but rca connections have resistance. When you have 2 sets connected all the time with y-splitters you are putting the resistances in parallel which is creating an impedance mismatch. The Schiit SYS would work in your situation of using a switch to control the rca output.
 
Jun 7, 2017 at 8:26 PM Post #3 of 9

castleofargh

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many circuits will have at least a different impedance when switched off, but it might be hard to tell more than that without some measurements. as a solution I agree with the post above, just find a switch to place at the output of the DAC.
 
Jun 7, 2017 at 11:32 PM Post #4 of 9

MindsMirror

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An amp's RCA input should be high impedance, meaning to the other circuits it's connected to it effectively looks like an open circuit, like nothing is there. If the receiver is affecting the sound from the DAC to the amp, then that must not be the case for the receiver's RCA input. Did you mean that you have 3 different receivers which each cause the same issue? I wouldn't expect so, but maybe the RCA audio inputs on your receivers are 50 Ohms terminated?

You could make a simple DC resistance measurement of the receiver input on vs off using a multimeter. That won't give you the full story if the impedance changes at AC, but it's a starting point and it might at least tell you something.

I would also try to make a quantifiable measurement of the distortion. You could use a sound card or recording interface and RMAA to make a loopback measurement of the DAC output, with the receiver on, off, and disconnected, and work from there depending on what you find.
 
Jun 8, 2017 at 3:34 AM Post #5 of 9

DamageInc77

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The receivers I've tried are:
Denon AVC-A1D
Some 20-25 year old Philips Stereo Receiver
NAD T765

The audible distortion is the same level no matter which one I use, at least to my ear. The distortion goes away in the headphone amp once any of the receivers is turned on.

I might try using my multimeter later today. A Schiit SYS has been ordered and should arrive Monday hopefully.

Thanks for the help guys. I really appreciate it.
 
Jun 10, 2017 at 8:39 AM Post #6 of 9

Speedskater

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As in post #3, powered off inputs were a big problem decades ago. Unbuffered pre-amp tape outputs would mess-up the main output when the recorder was turned off. Without power the input stage acts as a diode across the signal line.
 

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