Deafening hum from new DAC

[miv]

Just bought a SMSL Sanskrit 10th MKII. Replaced my Audioengine D1 in a simple desktop system (laptop > DAC > Icepower 50asx2se unit > speakers), and was assaulted with a very loud hum. "Deafening" is only a slight exaggeration. The pitch suggests a ground loop hum, even though the MKII is powered by the laptop USB, just as the D1 was. It isn't connected to the mains itself.

Tried using toslink cable and powering the MKII with a phone charger; same result - "deafening" hum. The D1 produces zero hum in this configuration if I use the 3.5mm jack out , and a relatively faint hum when connected to the computer via USB, or when connected via toslink input and the RCA outputs...

The hum with the MKII is diminished, but doesn't disappear, if I disconnect the laptop from its charger, which seems at once to suggest a ground loop issue (the decrease in volume) and something else (only one element in this case is plugged in to the mains.....)

Not even sure what my question is. Maybe one of:

-How can a component without its own power supply even cause ground loop problems, especially of this magnitude?

-Is there some design issue with the MKII - some filter left out, perhaps to keep the cost down(?) - that means it fails to resolve a problem between laptop and amplifier that the D1 can?

- Would replacing the laptop charger with a two-prong model (they exist, and seem to be properly certified) be worth a try?

-Is this clearly a ground loop issue, or do I have a dud?

Any suggestions most welcome, thanks.

 

[MaxwellsEq]

Does the hum disappear when you plug the Audioengine back in?

 

[AnalogSteph]

Usually a problem like this would indicate a bad RCA cable. In this case I would also be tempted to check whether the output jack grounds on the DAC are hooked up properly with a multimeter.

 

[threni]

Just bought a SMSL Sanskrit 10th MKII. Replaced my Audioengine D1 in a simple desktop system (laptop > DAC > Icepower 50asx2se unit > speakers), and was assaulted with a very loud hum. "Deafening" is only a slight exaggeration. The pitch suggests a ground loop hum, even though the MKII is powered by the laptop USB, just as the D1 was. It isn't connected to the mains itself.

Tried using toslink cable and powering the MKII with a phone charger; same result - "deafening" hum. The D1 produces zero hum in this configuration if I use the 3.5mm jack out , and a relatively faint hum when connected to the computer via USB, or when connected via toslink input and the RCA outputs...

The hum with the MKII is diminished, but doesn't disappear, if I disconnect the laptop from its charger, which seems at once to suggest a ground loop issue (the decrease in volume) and something else (only one element in this case is plugged in to the mains.....)

Not even sure what my question is. Maybe one of:

-How can a component without its own power supply even cause ground loop problems, especially of this magnitude?

-Is there some design issue with the MKII - some filter left out, perhaps to keep the cost down(?) - that means it fails to resolve a problem between laptop and amplifier that the D1 can?

- Would replacing the laptop charger with a two-prong model (they exist, and seem to be properly certified) be worth a try?

-Is this clearly a ground loop issue, or do I have a dud?

Any suggestions most welcome, thanks.

To rule out the "dud hypothesis" can you connect the DAC to a phone via usb, and use its phone charger? I've had nothing but trouble connecting desktops/laptops to my E30 DAC.

 

[miv]

Hi,

Thanks for the reply and suggestion: establishing whether this is a dud is obviously my most immediate concern!

To clarify: do you mean connect the phone to the usb data input (called "in 1" on the MKII), and the phone's charger to the usb "aux power" input?

 

[antcollinet]

Do you have optical out on your laptop? (Some have dual function 3.5mm jacks)

What happens if you run the laptop from battery, and no connection to mains?

Try also connecting an external PSU to the SMSL into the aux power connection.

 

[threni]

Hi,

Thanks for the reply and suggestion: establishing whether this is a dud is obviously my most immediate concern!

To clarify: do you mean connect the phone to the usb data input (called "in 1" on the MKII), and the phone's charger to the usb "aux power" input?

Yes, I had a quick look at the manual and you can't power it and provide data via the same port.

 

[miv]

Do you have optical out on your laptop? (Some have dual function 3.5mm jacks)

What happens if you run the laptop from battery, and no connection to mains?

Try also connecting an external PSU to the SMSL into the aux power connection.

Hi, and thanks for the suggestions.

My laptop doesn't have an optical output (lenovo t460s - checked the specs on lenovo website). I tried the DAC using a USB to toslink converter, with an external power supply for the DAC - result was the same very loud hum. The 5v came from a phone charger with non-polarized plug.

If I run the laptop from battery, the hum is reduced from painful to annoying. This points to the possible problem, maybe(?) - but it isn't really a solution, especially given the battery life of my old Thinkpad!

If it is a ground loop hum (checked with my guitar, and it's about the frequency you'd expect), I don't understand why two different devices powered only by the laptop usb (i.e. not from mains), between the laptop and amp, would act so differently. The cause must be some interaction between the amp and laptop, which one dac prevents and the other doesn't.

 

[miv]

Yes, I had a quick look at the manual and you can't power it and provide data via the same port.

Hi,

Tried using phone and charger. As with running from the laptop on battery, the hum is reduced from loud to annoying, and still audible when playing music at reasonable levels.....

It works without the charger as well - just running off the phone battery. The hum is gone completely.

(Note: in the original review by Amir, tests were done using only the one USB port.... )

Does the hum disappear when you plug the Audioengine back in?

Yes, completely - with toslink connection, and using the headphone jack instead of the rca to connect to the amp. (Using rca, the hum is audible, though only faintly).

 

[miv]

Usually a problem like this would indicate a bad RCA cable. In this case I would also be tempted to check whether the output jack grounds on the DAC are hooked up properly with a multimeter.

Hi,

Re the first issue: when I tried the MKII with my phone and no charger (just phone>OTG>MKII>amp) the hum disappeared completely. This was with the same rca cables that produce the truly extravagant hum when using the laptop via USB or toslink (latter with 5v external power supply).

Re the second issue: I don't know how. And I don't even know whether the perfect performance as described above makes this issue moot...... Is it an issue that relates to the MKII itself, and it's propensity to create a ground loop problem. Or does it relate to its its causing/preventing ground loop issues between the two powered devices it connects....

 

[miv]

To all (along with thanks to those I neglected to thank individually):

When I did the first set of clumsy experiments (described in my first post), the hum with the laptop on battery (disconnected from charger) was still there, if reduced. But just out of curiosity, I tried it again (since I already had everything set up to use the phone, as suggested by threni, and could just transfer the usb...).

But this time I picked the laptop up completely out of its dock, and the hum was reduced to virtually nothing; the faintest, liveable-with, suggestion of a hum.

Also, the volume of the hum, when using the phone and a charger, was reduced a bit if I touched or pressed on the charger where it was plugged into its power bar...thereby (?) providing some kind of ground....(?)

I have a bit of a mental block when it comes to anything to do with electricity, but it all suggests to me that this is down to a particularly powerful and malevolent ground loop. I still don't understand why laptop>MKII>amp produces such a massive hum, while laptop>D1>amp produces a faint hum, when both are connected the same way (with the DAC powered by the laptop) and so with neither connected to a power supply themselves.....

 

[antcollinet]

Hi,

Tried using phone and charger. As with running from the laptop on battery, the hum is reduced from loud to annoying, and still audible when playing music at reasonable levels.....

It works without the charger as well - just running off the phone battery. The hum is gone completely.

(Note: in the original review by Amir, tests were done using only the one USB port.... )

Yes, completely - with toslink connection, and using the headphone jack instead of the rca to connect to the amp. (Using rca, the hum is audible, though only faintly).

Try replacing your RCA Cables.

Also you have mentioned other kit now - eg laptop dock. Can you sketch your complete system including how items are connected to each other, and to earth, and including anything connected to the laptop and/or dock. Also include how your mains connections are made (eg all to same wall connector, or multiple multi way blocks etc.

I still don't understand why laptop>MKII>amp produces such a massive hum, while laptop>D1>amp produces a faint hum

This may be down to how the two DACs manage internal ground connections - for example if one creates separate digital and analogue grounds and the other doesn't.

 

[MaxwellsEq]

Does the hum disappear when you plug the Audioengine back in?

Yes, completely - with toslink connection, and using the headphone jack instead of the rca to connect to the amp. (Using rca, the hum is audible, though only faintly

That is significant. You may have a ground loop with your existing equipment, but the combination is less sensitive to it, so you've not needed to try and resolve it

 

[Zek]

The 5v came from a phone charger with non-polarized plug.

What does this mean?

 

[Jimbob54]

This sounds suspiciously like my issue with my rme https://www.audiosciencereview.com/...ac-fs-ground-hum-any-ideas.43713/post-1551044

Tldr

Connect the coax digital of the dx3 to a properly grounded device. (assuming you don't use the coax input)

 

[miv]

What does this mean?

Might have used the wrong term - just meant that it both arms of the plug were the same width, and it could be plugged in either way.

 

[miv]

"This may be down to how the two DACs manage internal ground connections - for example if one creates separate digital and analogue grounds and the other doesn't."

This makes sense to me, as the cause, even though I don't understand it as a process!

 

[miv]

This sounds suspiciously like my issue with my rme https://www.audiosciencereview.com/...ac-fs-ground-hum-any-ideas.43713/post-1551044

Tldr

Connect the coax digital of the dx3 to a properly grounded device. (assuming you don't use the coax input)

Do you mean the DAC? What would constitute a properly grounded device? Something with a three-prong plug, or something wired properly to avoid grounding issues?

 

[miv]

That is significant. You may have a ground loop with your existing equipment, but the combination is less sensitive to it, so you've not needed to try and resolve it

That's what it seems like. I also have a Centrance Dacport Slim that produced no hum - switched to the D1 because it seemed to provide a bit more clarity and separation. The Centrance is also a DAC-amp.....which may be significant, or pure co-incidence, or something in between (as in: perhaps Dac-amps tend to better prevent ground loop between the components they're connecting....?)

 

[antcollinet]

"This may be down to how the two DACs manage internal ground connections - for example if one creates separate digital and analogue grounds and the other doesn't."

This makes sense to me, as the cause, even though I don't understand it as a process!

Hi

Somehow you have quoted me as saying a bunch of stuff I didn't. Please can you correct.