Unbalanced Octo card works great; balanced version not working

[mpirker]

Hi,

first things first, thanks for the incredible work building the Octo card!
Getting the unbalanced version up and running with a raspberry pi 3 was straight forward. The Octo is working like charm. All tests so far very promising. Got my RME Babyface connected and run input/output of lines through TotalMix. Even using a Jabra 410 to output the channels from the raspberry via USB.

I am struggeling with the balanced version and the preamp. No sound at all. Yes I did check the cables several times, no issues there. My principle setup is the same as the unbalanced version (same rasbian and drivers for Octo). HW: Octo board, pre-amp with extra 20V 1.7A power, balanced breakout for in- and output, connected via balanced breakout cables to RME Babyface XLR line connectors.

I haven't found any detailed setup and installation information about the balanced version. Happy to help with this once the Octo card is working. Can you please confirm I should be able to run tests a) balanced breakout boards without preamp (straight from the Octo card) and b) with preamp (same way as the other option)? Same drivers used as for the unbalanced version? Octo card working the same in unbalanced and balanced version (no HW change)? Anything else I may miss getting the balanced setup work?

Thanks for your great support!
Michael

[flatmax]

Hi there,

Great to hear from you.

Lets sort out the problems here.

Can you take a snap shot of your setup ? Perhaps a couple of shots - particularly interested in the plug between the octo card and the preamp card.

Your power supply sounds good - as long as it uses a positive tip.

Matt

[mpirker]

Hi Matt,

thanks for your reply. A long while since end of July. Sorry for my late answer. I have been to busy to setup further testing. With spare time left, I started testing a few days ago of the Octo sound card and compared unbalanced and balanced setups incl. other HW devices (RME, Behringer, etc).

Primary answer to why the balanced setup did not work:
I ran into a production error of your manufacturer! The six microchips on the input balanced breakout board are slightly off position. Those for channel 2 and channel 3 aren't correct soldered. The four pins on the left side have no connection with the board.

pins not soldered correct

pins_channel_2.jpg (236.27 KiB) Viewed 3000 times

pins not soldered correct

pins_channel_3.jpg (248.72 KiB) Viewed 3000 times

.
I repaired the board and signals now work correct.

I have successful tested unbalanced and balanced stereo setups recording with arecord and using aplay to stream the recorded files. Hint, don't pipe arecord into aplay it won't work for common reason. I also tested 6 channel input recording and verified the wav files with Audacity. All looks very well. I still fight with the correct volume levels and gain (feeding the audio streams around different software). For curiosity the Octo card works well on a Raspberry Pi 3 B and a Raspberry Pi zero W (!).

Pi zero, Octo and RME Babyface

Pi zero W and Octo.jpg (198.88 KiB) Viewed 3000 times

Final aim of my tests is a unbalanced prototype for 6 channel recording (electret microphones) in the field with a battery pack only. I do have other ideas for the balanced and pre-amp version for live mix and studio later. Also want to play around with a potential optical ADAT out solution I found on the internet.

Equipment used so far:
- MacBook Air, mainly to run Audacity, TotalMix and connect to raspberry via SSH terminal
- RME Babyface incl. TotalMix (handy to connect Octo but also Behringer ADA8000 and hardware and switch back and force to check cables)
- Raspberry Pi 3 B
- Raspberry Pi zero W (this really works even with 6 channels)
- 19V Asus power supply for pre-amp board
- various unbalanced XLR to RCA cables
- various balanced XLR to TRS cables
- amixer, alsamixer, arecord, aplay, Audacity

Hope this motivates others to share their common findings and tests in this forum.
Michael

[flatmax]

Nice work!

That is terrible, I am surprised that we didn't pick this up during QA. I will send this post to the testing/assembly team. Thank you very much for the information. I am really glad you have the skills to sort this out yourself.

Are you planning to remove the preamp when you go in the field off a battery ? Or do you plan to use a step up/down regulator ?
I wonder if you can drive everything off a 6V hobby battery - I guess it depends on the Pi's step down regulator.

Matt