[PHC1]

I wonder if the remote relay pot

Just measured impedance of the inputs.
When it turned on XLR inputs have 10 kOhm between pin 2 and 3.
When it turned off it has couple of MOhms between pin 2 and 3 (not sure how much exactly).
RCA inputs always have 47 kOhm.
No short circuit here.

I wonder if the remote relay acts differently when OFF? I mean something has to be loading my DAC output section when the V281 is OFF.

 

[zhgutov]

I wonder if the remote relay acts differently when OFF? I mean something has to be loading my DAC output section when the V281 is OFF.

I have the standard volume control, can't check this. Do you have relay?
But anyway, it is hard to believe it works this way.
Maybe it generates something back when it is turned off (just a guess, need to check this).

 

[PHC1]

I have the standard volume control, can't check this. Do you have relay?
But anyway, it is hard to believe it works this way.
Maybe it generates something back when it is turned off (just a guess, need to check this).

Yes I have the remote relay. I’ll pull the amp from the rack and measure inputs out of curiosity.

 

[zhgutov]

I’ll pull the amp from the rack and measure inputs out of curiosity.

Have you tried not just to switch the power off, but also to unplug the power cord from V281 and check your effect again?

 

[PHC1]

Have you tried not just to switch the power off, but also to unplug the power cord from V281 and check your effect again?

Yep, I just tried it. Listening to the Audeze amp, V281 ON, no problem. V281 OFF, big bass distortion. Pulled the cord from the V281, still distortion. Something about the V281 loading down the DAC while OFF. Strange.

 

[zhgutov]

Yep, I just tried it. Listening to the Audeze amp, V281 ON, no problem. V281 OFF, big bass distortion. Pulled the cord from the V281, still distortion. Something about the V281 loading down the DAC while OFF. Strange.

This amp has large capacitors, so when it is powered off it probably still can do something.
Does this effect remain after some time?

As I remember, you use the balanced power conditioner.
Have you tried to use regular power source?

 

[PHC1]

This amp has large capacitors, so when it is powered off it probably still can do something.
Does this effect remain after some time?

As I remember, you use the balanced power conditioner.
Have you tried to use regular power source?

The balanced power conditioner has nothing to do with it. This happens with or without it. At first I could not figure out what was happening with my other amps since sometimes I had the V281 ON, sometimes OFF and of course the other amps only sound distorted when the DAC output section is loaded down by the OFF condition V281. I have not tried to see if this goes away if the V281 has been off for some time. Hmm... Will try that. I'm thinking the V281 shorts the inputs when the power goes OFF for whatever reason. There is no other explanation.

 

[zhgutov]

The balanced power conditioner has nothing to do with it. This happens with or without it. At first I could not figure out what was happening with my other amps since sometimes I had the V281 ON, sometimes OFF and of course the other amps only sound distorted when the DAC output section is loaded down by the OFF condition V281. I have not tried to see if this goes away if the V281 has been off for some time. Hmm... Will try that. I'm thinking the V281 shorts the inputs when the power goes OFF for whatever reason. There is no other explanation.

In the case of the overload you will probably hear everything distorted, but you are talking about the distorted bass only.
My guess is this may probably point to the strong 50 or 60 Hz hum (maybe with the harmonics) from the inputs.
Hmm... I am still thinking how to make a good experiment to confirm if this is true.
My DAC has separately driven outputs, so I cannot see the effect here.
And my experiment with the ADC may be incorrect too (it is weird in terms of grounding, cannot trust it).

 

[PHC1]

In the case of the overload you will probably hear everything distorted, but you are talking about the distorted bass only.
My guess is this may probably point to the 50 or 60 Hz hum (maybe with the harmonics) from the inputs.
Hmm... I am still thinking how to make a good experiment to confirm if this is true.

Bass and the mids are distorted. Of course the deep bass draws the most current from the overloaded DAC output section which distorts the bass and the mids. I doubt it has anything to do with hum at all since the v281 is not affected and neither are the other amps when the V281 is ON. Turning the other amps OFF, does not affect the V281 itself.

 

[PHC1]

Another experiment. Audeze amp playing. Set the Audeze DAC and Gungnir DAC to play the same track through Roon. Simply flipping the source switch on the Audeze lets me hear the Gungnir and the Audeze DAC. Switched the V281 OFF and of course the same problem. Switch to Audeze DAC problem gone and everything is clean. It is obvious there is nothing else going on but the V281 loading the Gungnir output section when the V281 goes OFF.

 

[zhgutov]

In the case of overloads everything will be distorted, because the whole spectrum will be on the bass peaks (tops of the wave).
But if it just sums with the strong hum, it will distort the signal partially, which looks more like your case.
Your experiment still shows the possibility of both problems.
Do you have simple multimeter to confirm or exclude your guess about the shorten inputs?

 

[PHC1]

Yes, I will check with an ohm meter. I need to pull the amp out and measure.

 

[zhgutov]

Oh, you told about the rack.
Do you have the rack stand in which V281 may be placed?
Or was this just about the units connected to each other?

 

[zhgutov]

This is the spectrum of the noise normalized to 0 dBFS (click to enlarge):


It is captured from the RCA inputs of the V281 turned off using Zoom H2N running from the battery.
The hum is not so high, but it is here. The noise floor belongs to the Zoom H2N.

Don't know how much the relatively small hum from the inputs when the amp is turned off can affect another outputs of your DAC.
Don't know how much different the hum can be for the balanced inputs.
Don't know how much different this hum can be in the different environment.
Don't know if the ground-lift switches may affect this.

 

[PHC1]

This is the spectrum of the noise normalized to 0 dBFS (click to enlarge):


It is captured from the RCA inputs of the V281 turned off using Zoom H2N running from the battery.
The hum is not so high, but it is here. The noise floor belongs to the Zoom H2N.

Don't know how much the relatively small hum from the inputs when the amp is turned off can affect another outputs of your DAC.
Don't know how much different the hum can be for the balanced inputs.
Don't know how much different this hum can be in the different environment.
Don't know if the ground-lift switches may affect this.

Thanks for the great info. I still think it is a matter of the inputs being shorted (by design or less likely a problem with my unit?) I will get the amp out of my rack and measure the RCA inputs tomorrow when I have more time to look at it. It's not a big problem, I just leave the V281 ON when I listen to any other amp.