Stereo Line In 1U module volume really low

I upgraded my audio board in my 104hp case to the newer version so I could connect my Mixup mixers to it, so when I use the new Stereo Line-In 1U module the volume is really low. I have to crank any synth connected to it to max, and crank the module volume to max to get any usable signal. Since everything is cranked full volume there’s also a lot of noise present. I didn’t have to do this with the old audio board and Stereo Line In/Out module.

HI Huron,

Can you give me some specific examples of synths you are using? Are these unbalanced, consumer level or balanced pro line level?

I tried a Roland Alpha Juno, TE Op-1, and Arturia MicroFreak. All have very low almost unusable levels when put into the Line In module.

Please send an e-mail to with an image of how you have things connected. We’ll get you sorted out!

Yes - are you connecting these synths to 1/4" jacks (on the back of thre 104hp 7u case, for example) - and running for the 3.5mm/mini jacks on the Stereo Line In Module over to (e.g. your mixup, or a filter or etc)?

And, what are your “internal” connections (inside the case) like? What modu,ea are connected to what modules, how? (Usuing the ribbon audio cables, 3pin connectors, etc.)

I agree it could definitely do with more gain. To boost a Monotribe line out to Eurorack level, I have to plug it into the L in, then patch the L out back into R In, and use the R out.

Any update on this? I’m also having to crank anything (Nord Stage 2, Roland TD-25, monome norns, etc.) up to max and crank the knobs on the Stereo Line In 1U to max to get anything, and even then it’s still quite quiet. These are consumer line-level, but even my pro line level outputs (Apollo x8) need to be running quite hot to get anything usable.

I ended up buying a 1u mono line in which works fine with everything I have, but now I need another for stereo! I think gain is +20 dB on these, but only +15 dB on the stereo in, for some reason? Any chance of a version 2? It would save money, hp, and allow use of input jack sockets.

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Yeah I guess this is on me for assuming it’d have closer to +20dB gain (or even +30dB) like most other modules, including the earlier Audio I/O 1U. Rather disappointed.

@21echoes Are you using balanced cable outputs from your Apollo x8? You should not need to crank anything if you are using a pro line level (nominal +4dbu TRS).
If you are using a balanced output with a TS cable then you are getting a half-legged signal and losing +6dB in the process.

As for gain, it should be possible to mod the Line In module, it would just be a matter of changing one resistor per side but it could be a bit tricky to get access to them based on the mechanical assembly.

The mod to get 12db more of gain:
Change R21 and R22 to 22k (was 4.7k) they are by IC2

The way the pcbs are sandwiched together, you have to desolder the two 6 pin headers in order to separate the boards. For anyone experienced with soldering this is pretty easy, 5 minute job but it does require some desoldering skills/tools.

If you want some help with this, please feel free to reach out to


when i’m in the studio, yes. when i’m playing shows, i was hoping to be able to plug a guitar or bass or keyboard straight in. the keyboard works if i really crank it, but the guitar and bass are just too quiet. i’ll probably just end up getting a boost pedal outside the rack – i dont have soldering materials so i can’t make any mods like that. i’m sure that advice will be helpful for someone else tho!! thanks for writing it up :blush: