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RF Noise - Optical vs Coax (Source to DAC)

ash87

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Feb 1, 2022
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Hi,

Wanted to ask if there is any merit to the thinking at Sonore about having a streaming endpoint separated from the music server via an optical cable. The idea being that the fiber line prevents transmission of any RF noise from the "dirty" computer server to the streaming endpoint / DAC. This would be in comparison to a PI hat streamer, where everything is sandwiched in a box and is usually outputting Coax.

If there is merit to the thinking, would it be much different running a PI Streamer that outputs optical? It's sort of the same concept, although the streaming endpoint is getting the "dirty" RF, but at least the DAC isn't?

Thanks!
 

EdTice

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Hi,

Wanted to ask if there is any merit to the thinking at Sonore about having a streaming endpoint separated from the music server via an optical cable. The idea being that the fiber line prevents transmission of any RF noise from the "dirty" computer server to the streaming endpoint / DAC. This would be in comparison to a PI hat streamer, where everything is sandwiched in a box and is usually outputting Coax.

If there is merit to the thinking, would it be much different running a PI Streamer that outputs optical? It's sort of the same concept, although the streaming endpoint is getting the "dirty" RF, but at least the DAC isn't?

Thanks!
I am of the firm belief that there would be no benefit. When you say outputting Coax do you mean Analog via RCA or SPDIF? Yes a Raspberry Pi probably does emit some small amount of RF noise. But not enough to interfere with the DAC components. If DACs were so easily "degraded," there wouldn't be any such thing as an AVR which has much more circuity than a Raspberry Pi. It's hard to imagine that a microprocessor (especially one subject to FCC class B regulations) would emit RF that caused the DAC in the same box to fail but didn't interfere with it's own operation.

If the DAC is outputting Coax SPDIF it's not a DAC. If its outputting RCA, there is some possibility that you will get RF interference if using absolutely awful cables. There is, of course, the potential for ground loop issues but those can be solved the way any other ground loop issue would be solved.

I feel like you must have listened to some very impressive (even if factually challenged) marketing.

Streaming DACs (such as the ones from topping) are putting out 120dB SINAD signals over analog RCA while being connected to high-power PCs via USB. AVRs are putting out 100dB SINAD. Clearly having modern electronics in close proximity to DACs is not (generally) a problem. That doesn't mean that particular implementations can't be awful, of course.

I have no idea what DAC would be in the Pi streamer. So you might want to consider a USB Topping DAC not because of "RF noise" but because its a high quality DAC!
 

AnalogSteph

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If you just want galvanic isolation between the server and streamer, using UTP network cable between them should get the job done well enough for audio purposes - the only direct connection with Ethernet is the shielding. Given the permissible cable lengths, its design had to account for considerable potential differences. If a few hundred volts is not enough, you can buy dedicated network isolators, or go WiFi, of course.

While there commonly is merit to galvanic isolation when dealing with unbalanced audio connections, this usually is for much more mundane reasons to do with issues in the audible range rather than RF, like power supply leakage currents or plain ground loops.
 
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ash87

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@EdTice I'm thinking my thread title is not quite representative of my question.

My main question was referring to the digital connection between the music server and the streamer. With Sonore, they separate it with a fiber cable in order to "filter out" the noise from the music server computer, whereas in a Pi setup the server and streamer are in the same box connected with a pin slot. The Sonore explanation is that the RF from the server computer pollutes the streamer and thus the DAC.

When I mentioned output coax, I was referring to coax digital output to the DAC, like you see with a DigiOne or Pi2AES. I was considering getting one of these to go into something like an El Dac II+ (I'm leaning toward US made product when it seems suitable for my purposes).

The Pi2Aes has an optical digital out, which can feed to the El Dac. I suppose I'm trying to understand if the optical digital out on the Pi2AES would be less "noisy" than the SPDIF on the DigiOne. But again I remember reading something about optical being inferior to SPDIF on the DigiOne marketing, which is "why" they don't have an optical digital out on their streamer.

@AnalogSteph Thanks for the info. I need to do more homework on power supply leakage, ground loops, network isolators, and galvanic isolation
 
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