Question Bass weak using optical TOS-link cable

Nov 26, 2023
I connect a TV (Sharp 65EQ3eA) to an amplifier (Pioneer VSX-817-K) using optical TOS-link audio connection.
The amplifier is driving front and rear speakers and an active subwoofer.
The speakers are fine but very little comes out of the subwoofer.
I tried from two different TV's and two different active subwoofers, no difference.

I change the cabling from the TV headphones out to the amplifier CD in.
Now there is full throttle on the subwoofer also.
How can the TOS-link be made to function with a subwoofer? A pre-amplifier maybe?
Jan 25, 2024
The optical SPDIF output can only transmit Dolby Digital or DTS sound formats for multi-channel surround playback. If the source signal is any other audio format then the optical audio output only transmits a stereo signal (2.0 ch).

I found the digital audio output on my PC very disappointing when trying to play music on my Denon AVR X-4100W AV Receiver. I have not added a subwoofer to my system yet but the playback on my Left and Right front speakers lacked bass in contrast to the many other sources I enjoy on that receiver.

When you use the headphone output from the TV you are connecting an analog audio signal that does not have discrete audio channels assigned digitally. The stereo analogue signal is interpreted by the receiver. Based on the L/R stereo mix the receiver can convert the L/R audio to multiple channels and use its crossover setting to filter out the low frequency sound and send it to the subwoofer.

Ideally you should never use a heaedphone output to playback audio on speakers. 3.5mm jacks are designed to output a very low power signal for the high impedence tiny drivers inside wired headphones (20+ Ohms). Loudspeakers have impedance values 4 ohms (car audio) to 8 ohms (A/V home theater amplifiers). Your TV may have an L/R RCA (white / red) audio output connection. Often TVs have both digital audio out (Optical TOS link) as well as analog audio out in the form of RCA stereo terminals.

For the best audio playback your source should be connected directly to your VSX receiver. Connect the device with an HDMI cable to the receiver and the receiver's monitor out to your TV. The receiver will play the audio and pass the video to your TV. Another more complex option would be to use the ARC (audio return channel) HDMI input on the TV as the audio output to your receiver. Reference the Pioneer manual to see how to set the input to ARC or TV audio on your receiver. Also make sure the TV audio settings have been changed to select ARC or eARC as the sound output. Only one of the TV inputs will have this ARC functionality and it is labeled ARC. All the other inputs on your TV can have their audio sent to the receiver over this one HDMI cable connecting the ARC on your TV to the ARC on your receiver.