Volume control of external amp

I have a Up2Stream Mini v4 that I’m connecting to an existing amp. I’m able to use the line out on the mini to connect to the line in on the amp and it works great but I’d like to improve the volume control. If I change the volume in the app this changes the gain on the line out and can lead to distortion at higher volumes.

Is there a way to set a fixed gain on the Up2Stream mini and have a signal on the GPIO pins when the volume changes in the app? That would allow me to control the volume via the existing volume controls on the amp. From looking at the documentation it shows GPIO1 and GPIO2 for volume control but this appears to be for input only

The GPIO pins are for the encoder board which is a digital gain control.
You will find that the internal gain control (via the app or encoder board) changes the 3.5mm jack, the PH2.0 connector and the digital out gain.
I’m not aware of any means of making this a set (fixed) level, although if another user knows of such, I’ll stand corrected.
Personally, I like the added control that the app gives as I can control all of my linked devices as one or separately.
I’ve never had any issues with saturating the input levels to distortion, not that I play music to high db.

ACP adjustment flow chart

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Would lowering the pre-gain in APCworkbench be a solution? In that way you would still be able to control volume directly via the Up2stream module.

Another solution would be setting a fixed output volume through UART commands. This works for the Pro V3 module, but hopefully also for the mini. You can set the fixed output volume by sending the message ‘VOF:100;’. This would fix the output volume at 100%. Documentation on this suggests that is only binary (1/0) on off setting, but in testing this I have found this not to be the case. In your case you could then set the fixed volume at a level where there is no audible distortion. Adjusting the volume slider will then have no effect on volume. Bonus: the module still sends UART updates on the volume settings, which you could use to set the volume by app on an external device through a MCU. I plan on using this to set the volume on an external ADAU1701 DSP so I can use more digital resolution for the digital volume control (24 vs 16 bits).

@Bas2807 using UART sounds like it could be the perfect solution, do you have a link to the documentation you where referring to?

See discussions here and here