[Fiyero]

Dear all
I don't know if this is the right forum.

I have a Moondrop S8 IEM and I have bought a used Chord Mojo DAC in the last days.

When I connect the IEM to the DAC to the smartphone I hear some noise as an electric interference.

This noise increases when the USB C Plug of the OTG cable gets near the Plug of the smartphone.

The S8 is a 16ohms 122db IEM.

I have not performed other tests with different sources or different IEM or different DAC (in the past I used a Meridian Explorer 2 DAC never with problems but uctually I have it no longer)

Just tested different OTG cables.


Any idea of what it could be?

Thanks,

Maurizio

 

[castleofargh]

The S8 is a 16ohms 122db IEM.

It's for 1 volt RMS so around 104dB for 1mW(If I typed the right numbers) which isn't all that sensitive so I'd ignore the low level hiss of the Mojo as a general cause.

Are you charging either cellphone or Mojo while doing this? It's been reported a number of times that while charging, the Mojo could be noisy.
Is the noise going away if you put your phone into airplane mode? depending on cellphone's connection(3g/4g etc), I remember that some were apparently noisier than others on the Mojo.

I'm sure actual owners would be more knowledgeable, try asking here for example: https://www.head-fi.org/threads/chord-mojo-dac-amp-☆★►faq-in-3rd-post-◄★☆.784602/

 

[redrol]

Your phone is EMFing the hell out of the mojo. You will have to use something else.

 

[bigshot]

If it's the DAC, send it back for a refund. Anything that isn't designed to be used with a cell phone is poorly designed. That should be a given.

 

[redrol]

If it's the DAC, send it back for a refund. Anything that isn't designed to be used with a cell phone is poorly designed. That should be a given.

Actually no, cellphones are EMF blasters. It requires a special amount of isolation and shielding to make it not happen

 

[bigshot]

Cell phones are VERY common sources. I use a cell phone as my source and I'm sure millions of other people do too. A DAC should work with your source. You shouldn't have to go out and buy a DAP to suit the DAC. A DAC should have the requisite shielding. If it doesn't, it's poorly designed- no matter how expensive or popular it is.

"Oh garsh! We designed this DAC and never imagined someone would use a cell phone with it... Duh!"

 

[redrol]

True enough and yet, they don't care one bit. Just use BT and spend more money.

 

[bigshot]

If you're using bluetooth, why not just stream from the phone and not use a DAC?

 

[gregorio]

Actually no, cellphones are EMF blasters.

Agreed but laptops, computers, tablets, smart watches and various other things have Wi-Fi, Bluetooth and/or cellular connections and are therefore EMI blasters too. So as bigshot says, a DAC that can’t operate optimally with an “EMI blaster” nearby is a DAC that will frequently not operate optimally and is therefore incompetently designed/faulty.

It requires a special amount of isolation and shielding to make it not happen

Sort of, but if $9 dongles and cheaper DACs can manage this perfectly adequately, why can’t a more expensive DAC, unless it’s incompetently designed/faulty?

However, it’s not been ascertained for sure if this is entirely the issue. It could be some gain staging or power/impedance issue that’s raising the noise floor and making what should be inaudible interference audible.

G

 

[bigshot]

He's says he's hearing "electric interference". I'm assuming that is some sort of crackle or buzz. Impedance mismatches wouldn't create that kind of sound would they? Wouldn't it be more like a steady hiss like wind?

Perhaps it's a grounding issue if his phone is plugged in to the wall wart while he's playing. Maybe it would go away working off the phone's battery?

No matter what is causing it, if it's only a problem when using the DAC, there is definitely something wrong with the DAC.

 

[gregorio]

He's says he's hearing "electric interference". I'm assuming that is some sort of crackle or buzz. Impedance mismatches wouldn't create that kind of sound would they? Wouldn't it be more like a steady hiss like wind?

Typically it would be hiss but in some cases you might need to use a lot of gain to overcome the loss of power and so, some electrical interference or other distortion which would be inaudible at reasonable listening levels could become audible. Same thing with incorrect gain staging, more gain to overcome an output level that’s too low earlier in the chain and therefore a more audible noise floor/distortions.

G

 

[Fiyero]

He's says he's hearing "electric interference". I'm assuming that is some sort of crackle or buzz. Impedance mismatches wouldn't create that kind of sound would they? Wouldn't it be more like a steady hiss like wind?

Perhaps it's a grounding issue if his phone is plugged in to the wall wart while he's playing. Maybe it would go away working off the phone's battery?

No matter what is causing it, if it's only a problem when using the DAC, there is definitely something wrong with the DAC.

I confirm a noise like bzzzz.

 

[bigshot]

It really sounds like a grounding issue of some sort to me. Flyero is the buzz the same when you operate off the battery as when you plug in for power?

 

[gregorio]

It really sounds like a grounding issue of some sort to me.

It could be, but not necessarily. Some DACs popular in the audiophile world have relatively poor isolation (even compared to some cheap dongles). Although, by “relatively” I mean significantly higher noise and/or interference induced distortion compared with other DACs but still inaudible at reasonable listening levels. However, put a transformer near it and/or have some inappropriate gain-staging or impedance and that distortion can be well above the audible threshold (and can be an “electrical” sounding buzz).

G

 

[bigshot]

Send it back for a refund!