work on new backplane

A project log for Multichannel Audio DSP Field Mixer Recorder

bluetooth app controlled professional portable DSP mixer.balanced audio IO,phantom power,flexible routing,ISO recording. timcode. AVB audio.

ben bilesben biles 11/21/2019 at 07:310 Comments

new backplane nearly finished ! 8 preamp cards fit into a smaller space.

I am using a shocking amount of SSR's ( solid state relays ) 2 for each preamp channel.

8 on top and 8 on the bottom of the board. Yuk !! Why ? because I there cheap and I know they work.

I will run wires direct to the micro controller breakout connectors on my main mixer board so I don't

need to go to 4 layer board. Its a prototype and the price difference is large.

The max 4mA required for each optoMos SSR pair ( +/- 5v ) can deliver 120mA per channel which

allows plenty of headroom to fire up the PGA2500's 

The ADC_DAC card will plug directly onto the analouge board and bridge to the main Digi board that has the ARM and DSP.

I have a separate connector card and power card that will supply the analogue power.

Also new and really exciting is the OVR connector. This will send over level signals from the individual cards 

to the micro that will be the hardware limiter. The micro can trim back the gain in an instant. hopefully within 20ms or so.

Lastly rail Voltage sense setup with divider resistors and a reference 3.3v. This will be so I can monitor the voltages

of both the +/-5v and +/-10v or whatever I set the higher rails to for Headphone and driver cards.

Theoretically I can shutoff all the preamp cards if there is to much difference in the +/-5v rails as protection !!

Eventually I'd like to experiment with making a tracking dual rail supply MC controlled !!

I'll have to see how accurate my voltage divider setup is 1st !

I found much smaller smd SSR's by Toshiba but at 2$ a go that makes 32$ just to switch the preamps on/off with

isolation. mmmm a bit to pricey for a prototype :)