u/martyboulders

I currently have a Behringer UMC22 outputting to two JBL 305P's.

I was gifted some (passive) speakers that have subwoofers, so I am trying to add one in to what I already have set up. I bought a small amp for the sub (Wuzhi Audio ZK-TB21), and have confirmed that this works on its own when I use bluetooth from my phone.

My issue is getting the signal from the audio interface's 1/4" two-channel output into the amp's 3.5mm input.

What I've tried so far: I got two 1/4" splitters (TRS) and plugged one each into the L and R outputs from the audio interface. I plugged the left monitor into one side of the L splitter and same for the right monitor. With an empty 1/4" female on each channel, I used a 3.5mm to 1/4" splitter (accidentally got TS; not sure how much that matters in this use case) to merge the 1/4" outputs into a single 3.5mm input.

This does produce sound through my monitors (although quieter), but there is nothing from the sub.

More importantly: The signal does successfully come through the sub, from the audio interface, if i use the 1/4" to aux adapter directly from the interface into the amp. So the problem is certainly with this adapter combo.

I've been reading that 3.5mm can play more nicely with RCA, so I ordered a few 1/4" to RCA adapters and a 3.5mm to RCA splitter (in lieu of the direct 1/4" to aux). I'll see if that works in a couple days.

I have a feeling there is something going on here with balanced/unbalanced signals and their corresponding connectors, but I don't know enough to know exactly where to go here.

Thanks so much for your help!