USB to Optical/Spdif

[Berwhale]

Ha yeah the iFi went straight back, if you're in the UK we probably had the same one!

My balanced DAC (M-DAC) is also fine, although I can use the RCA outs with no issues either.

I feel pretty confident the USB to optical is going to help so have a Douk U2 on the way from China. I will however test the Mojo via USB with my Windows PC when I'm home out of curiosity to see if it also has the high pitched squeal listening through the active speakers.

Also try running the Mac off battery (I had a similar issue with a Lenovo Thinkpad, but it only made the noise when connected to it's charger or docking station).

 

[Liberte]

Also try running the Mac off battery (I had a similar issue with a Lenovo Thinkpad, but it only made the noise when connected to it's charger or docking station).

It's an iMac/desktop so no option for battery, but thanks for the info.

 

[Ken Tajalli]

You can test for ground loop issue.
disconnect the ground wire from either the iMac or the amplifiers.
that breaks the loop.
If it turns out to be indeed a ground loop issue , then a Topping HS01 is your guy!
you get full bit rate compatibility.
The Topping is a true galvanic isolator.

 

[sam_adams]

Douk Audio U2 Pro:

USB out to TOSLINK in (on an old Mac laptop).

997 Hz (96KHz, 512K, CosineSum9-235, 87.5%):

Multi-tone (96KHz, 512K, Rectangular, 87.5%):

SMPTE 60Hz/7KHz (96KHz, 512K, CosineSum9-235, 87.5%):

19KHz/20KHz (96KHz, 512K, CosineSum9-235, 87.5%):

 

[tifune]

Of the converters in this thread, do any support multichannel? I've checked the manuals on a few, but they don't seem to say one way or the other. Hoping to bitstream as high as coax or Toslink will allow. I think for non-HDMI that's DD+ 5.1, or in that neighborhood, which is fine as long as stereo 24/192 is also an option.

 

[Liberte]

Which isolators have you tried? Some 'audiophile' ones don't really isolate (i'm looking at you iFi).

A cheap, ADUM4160 chip, isolator like this one worked for me, but it will limit your sample frequency to 96kHz...

https://www.amazon.co.uk/DollaTek-Isolator-Eliminator-Industrial-Protection/dp/B07KXRP784

The Topping HS01 is more expensive, but won't limit you to 96kHz...

https://www.amazon.co.uk/HS01-Isolator-Eliminate-Portable-Suitable/dp/B09LCRCT8T

You can test for ground loop issue.
disconnect the ground wire from either the iMac or the amplifiers.
that breaks the loop.
If it turns out to be indeed a ground loop issue , then a Topping HS01 is your guy!
you get full bit rate compatibility.
The Topping is a true galvanic isolator.

The Topping HS01 solved the issue of the high pitched squealing noise using the chain iMac > Mojo > Powered Speakers.