Quick answer: Yes, you can connect both an optical and a coaxial digital cable to the same device. They are separate inputs, and the device plays one at a time based on its input selector, not both together. Use each cable for a different source, or keep one as a backup path, and label the runs so the right input gets selected.
Running optical and coaxial digital inputs together
The TV has an optical output, the streamer has a coax output, and the amplifier on the shelf has one jack of each. The question that follows is always the same: can both be connected at once, or does one have to be unplugged? Nothing breaks, and nothing gets summed. The amplifier treats them as two separate inputs and plays whichever one is selected. What follows covers how that selection works, how to assign one medium per source, and the labeling habit that prevents the usual two a.m. troubleshooting session.
Both jacks, but one active input at a time
An amplifier or processor with optical and coaxial digital inputs has two independent receiver circuits, and the input selector routes one of them to the conversion stage. There is no mixing and no summing. If both cables carry audio, you hear the selected one and nothing else. That is a deliberate design choice, not a limitation to work around: two digital streams arriving at once would have unrelated clocks, and combining them would produce garbage rather than a blend. The practical consequence is that running both cables is safe, and it never doubles the audio. The selector, a remote key or an automatic priority rule decides which jack is live. Two cables, two receiver circuits, one live path, and no interaction between them.
How input selection actually works
Selection falls into two families: manual and automatic. Manual selection is a front panel button or a remote key that steps through inputs, and it is the most predictable arrangement. Automatic selection watches for a valid S/PDIF stream on each input and locks to the first one that appears, sometimes with a priority order set in a menu. Both behave the same way once a stream is locked, but they differ in what happens when a source stops. Knowing which type you own explains most surprising switching behavior, including the case where a TV that stays powered keeps an input held. Neither type knows which source you meant to hear, only which one currently has a valid stream, so the selector remains the only real control you own.
Manual selection on a receiver
Manual receivers keep the last input you chose until you change it or power cycle with a different default. That is convenient for a fixed setup and annoying when two people share the room. Most remotes have discrete input keys, so program a scene or a macro if the remote supports it. Write the input name on a label near the jack, because panel abbreviations rarely match the source names.
Automatic priority and fallback
Automatic units often scan in a fixed order, coaxial first or optical first depending on the model and menu. A stream that loses lock for a few milliseconds, during a channel change for example, can hand the input to the other jack and stay there. If switching feels random, set a fixed priority or turn automatic selection off. The manual states the order; guessing it wastes an evening.
Assigning one cable type per source
The clean pattern is one source per input. Put the TV on optical, because that run is usually longer and light does not pick up noise from the panel, and put the streamer on coax, because the run is short and the plug is robust. Then name the inputs to match. A second valid pattern is a backup path from the same source, where both cables come from one box and you switch only if the primary fails to lock. That is useful for diagnosis, since a working alternative on the same source proves the fault is in the cable or the jack rather than the source. Name the inputs to match the sources, using the same words the household uses out loud.
Why running both is worth the trouble
There are three honest reasons. Different sources offer different outputs, and using what each one has avoids extra converters. Electrical isolation matters when a TV and an amplifier sit on different circuits, and an optical link breaks the ground path that would otherwise hum. And redundancy helps in a rack that gets serviced, because a spare input of the other type costs nothing and can rescue a session when a plug or a Toslink shutter fails. What does not justify it is a belief that one medium sounds better; both carry the same S/PDIF frames within similar rate limits. Run both cables with the same tidy routing and cap the unused optical port, so redundancy stays available instead of turning into a dust path.
The ground loop case
When a TV and an amplifier sit on different circuits, the coax shield can carry a small current between chassis, and that current becomes hum in the analog stage. An optical link breaks the path because light carries no ground. This is the most practical reason to keep one optical input free. Test it by switching to the optical path with the coax still connected; if the hum stops, the loop was real.
The service and swap case
Racks get serviced, plugs get bent and Toslink shutters break. A second input of the other type turns a failed cable into a two minute switch rather than a rescheduled session. It also proves a point fast: if the alternative path plays, the source and the amplifier are both healthy. Keep the spare cable coiled loosely inside the rack, not folded into a drawer where the plugs get crushed.
Labeling, dressing and the common mistakes
Four mistakes account for nearly every call. Plugging a coax output into an optical input with an adapter that has no power, which does nothing at all. Connecting both cables from one source and expecting a level boost. Leaving an unused optical cable in place with its shutter open, which lets dust into the emitter. And selecting the wrong input on the amp, then blaming the source. Label both ends, coil the spare with a tie rather than a tight bend, and keep the Toslink connectors capped when unplugged. If a run must cross mains cable, cross at ninety degrees. None of these are cable faults, and each one costs more time than labeling the install properly would have cost in the first place.
Typical optical plus coax setups
| Setup | Optical used for | Coax used for | Selection | Note |
|---|---|---|---|---|
| Two sources, one amp | TV or disc player | Streamer or console | Manual input key | One plays at a time |
| Same source, backup | Primary path | Fallback path | Switch if no lock | Useful for diagnosis |
| Auto priority receiver | Preferred input | Secondary input | Fixed scan order | Check the menu |
| Mixed run lengths | Long run to TV | Short run to DAC | Per source | Fiber suits distance |
| Rack with monitor feed | Monitor chain | Main chain | Assigned per output | Label every cable |
Real-World Application Scenarios
Three common layouts. A living room where the TV feeds the amp over optical for ground isolation while a streamer feeds the same amp over coax, and a single input key swaps between them. A studio desk where a computer interface takes coax from a converter and optical from a keyboard, with each input named on the front panel. And a reseller build where a compact amplifier ships with two labeled digital inputs, one capped optical port and a quick start card that tells the buyer which key selects which source.
Related Guides on This Site
For the differences between the two transports, read the comparison of S/PDIF versus optical, then the short answer on whether optical is the same as S/PDIF. If you plan to convert between them rather than run both, the digital audio to optical cable page covers what a powered adapter does, and the coaxial S/PDIF digital audio guide covers the copper side in detail.
Frequently Asked Questions (FAQ)
Q: Can I connect both optical and coaxial cables at the same time?
A: Yes. They are separate inputs on the amplifier or DAC, and connecting both is harmless. The device plays only the one you select, so the second cable is silent until you switch to it. No damage results from leaving both plugged in with active sources.
Q: Will the sound play through both outputs at once?
A: No. The amplifier routes one digital input to its converter at a time. Two streams arriving together have independent clocks, so mixing them is not useful and is not implemented. If you hear both, you are listening to two different paths in one room, not one summed signal.
Q: Which input should I use, optical or coax?
A: Use optical for long runs or when the two devices sit on different mains circuits and you want to break a ground loop. Use coax for short runs where the cable may be handled or bent, since the metal plug is tougher than a Toslink connector. Both carry the same format.
Q: Why does my receiver switch inputs by itself?
A: It likely has automatic input priority. When the selected stream loses lock, the receiver scans for another valid signal and locks to it. Set a fixed priority in the menu or disable auto selection. A source that powers down briefly can trigger the same behavior.
Q: Can I use an adapter to plug coax into an optical input?
A: Not with a passive adapter. Copper and fiber need different emitters and receivers, so the conversion requires a small powered box. A passive plug that claims to do it cannot work, because nothing in it converts voltage to light. Buy a powered converter and give it its own supply.