Topping D50 III optical input bug with 44.1kHz files

[Roland68]

Given that my setup never had a problem using a Chord Mojo and SMSL DAC, would that not point to the Topping being the slightly dodgy item? Worth noting the problem has been fixed by changing the cable.

If using a different optical cable improves the situation, this absolutely sorts out the suspect of "too much deviation of clock frequencies".
This behaviour does rather point to a broken optical cable or dirt on one of the fiber end surfaces.
Of course the Toslink transmitter or receiver can be faulty (or dirty) as well, such that the intensity of the light is marginal and a small difference between cables makes a difference.

Usually you can retract the fiber connector by a couple of mm on the receiver side when you maintain pointing onto the receiver on axis. At some point the protection lid will close and this will shut down the transmission of course.
Retracting the fiber a couple of mm will reduce the amount of light shining onto the receiver photodiode. This way you can check if there's some margin with respect to intensity.

Edit: What I basically want to say with my posts above is, that if you invest money in a better fiber, this may just turn the optical transmission from "marginally not working" into a "marginally working" one.

POF fiber optic cables have 100 times the attenuation of quartz fiber optic cables. This isn't really a problem over such short distances, but as @nanook already mentioned, it also depends on the quality of the LEDs, and with inexpensive Toslink connectors, that's precisely where the greatest savings potential for the manufacturer lies.

In some cases, replacing this connector with a higher-quality one may be sufficient for a device with problems.

 

[nanook]

@VientoB: In case the optical cable really makes a difference (it's worth the effort to double check), I would check the cable if it's broken and if all optical surfaces including transmitter and receiver are clean.
As for the cable, you can just hold one end towards "the sky" and look onto the other end. Comparing the two you should see a difference if one of them is seriously damaged.

Even a cheap transmitter / receiver should manage 44.1 properly, so it's hard to believe they cause a problem.

What's actually the fiber length you are using?

 

[VientoB]

@VientoB: In case the optical cable really makes a difference (it's worth the effort to double check), I would check the cable if it's broken and if all optical surfaces including transmitter and receiver are clean.
As for the cable, you can just hold one end towards "the sky" and look onto the other end. Comparing the two you should see a difference if one of them is seriously damaged.

Even a cheap transmitter / receiver should manage 44.1 properly, so it's hard to believe they cause a problem.

What's actually the fiber length you are using?

About 1m. I think ai threw the old cable out. Definitely made a difference changing the cablesm