Inputs/Outputs levels & symmetrical routing for a Reggae Preamp project

LLP

Hi everyone,

First, thanks for this Bela Gem Multi, it’s an amazing piece of hardware that really allows for some high-quality audio work!
I am currently working on a 5U reggae preamp project using the Bela Gem Multi, and it is working incredibly well

My preamp design features 4 inputs and 1 output. Each of them needs to support both balanced and unbalanced connections. To achieve this, I am currently using the Bela Wings and routing them through external 15V balancing/unbalancing boards.

However, looking closely at the Bela PCBs, I just realized that the Bela natively has 2 balanced outputs. This got me thinking, and I have a few questions regarding the inputs and signal levels for a live concert environment:

Are all the inputs natively balanced?
Looking at the WING connector on the Gem Multi, I see dedicated negative pins (IN0- through IN9-) for every single input. Does this mean all 10 inputs are fully balanced?

Is the output level of the balanced outputs hot enough for live gigs?
Since this preamp is designed to be used in live concert conditions, will the native balanced outputs provide a strong enough line-level signal to drive professional venue mixers or sound systems directly?

Do I need voltage dividers on the inputs?
If all inputs are indeed balanced, can I plug external pro-audio balanced gear directly into them, or will the signal be too hot?
Should I design voltage dividers on my custom PCB to prevent clipping, or can this be fully managed via software/PGA gain in case of high gain?

Thanks a lot for your help and insights!

giuliomoro

LLP Are all the inputs natively balanced?
Looking at the WING connector on the Gem Multi, I see dedicated negative pins (IN0- through IN9-) for every single input. Does this mean all 10 inputs are fully balanced?

Yes, but they have different specs. The first two go into a TLV320AIC3106 via a 1u capacitor, the remaining eight go into 2x TLV320ADC3140, DC-coupled.

LLP Do I need voltage dividers on the inputs?
If all inputs are indeed balanced, can I plug external pro-audio balanced gear directly into them, or will the signal be too hot?

Short answer: you need circuitry in-between. Attached below are a couple of relevant pages from the work-in-progress datasheet:

LLP Since this preamp is designed to be used in live concert conditions, will the native balanced outputs provide a strong enough line-level signal to drive professional venue mixers or sound systems directly?

The first two outputs are from a TLV320ADC3106, and that's the raw, DC-coupled output that is exposed: 1.414Vrms differential or 0.707Vrms single-ended centered around 1.6V. The remaining eight outputs are from an ES9080Q, fed through a MC33204 in non-inverting, DC-coupled configuration, to obtain ±5V DC-coupled outputs. These are single-ended only, no differential. They are driven from the output of the MC33205 with a series 100R, so you could reasonably set up an impedance-balanced balanced output if the voltage works for you and you need balanced.

Before you expose the on-board signals (inputs or outputs) to the 'pro audio' world, you'll want at least RC high-pass filters with a 48V-safe DC-blocking capacitors on all sides, because someone will eventually plug an XLR or jack with phantom power into it at some point.

LLP

giuliomoro Thank you so much for your reply!
Good catch on the 48V protection capacitors, I'm going to add some to all of my inputs and outputs !