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Re: That1580/1510 mini mixer

Posted: Fri Dec 22, 2017 2:15 pm
by weroflu
side project - stereo that 1510, +-9v rails, p48, 10 way switches gain 12db-66db, mint tin size

3d render of better version not yet built

(pots were added later)

Re: That1580/1510 mini mixer

Posted: Thu May 07, 2020 5:46 pm
by weroflu
Onto version 2.0

changes from the initial prototype:

-implement wayne's excellent suggestions from post #11
current summing
his lcr pan scheme
-digital switching of pan,phantom, phase, gain control
-replace bluetooth/android interface with mini oled/5-way mini joystick
-reduce power rails to ~ +/6v
-mcu and summing section integrated onto backplane
-AT328p MCU @8Mhz 3.3v (shrinkified arduino pro mini = mcu+4 passives)
-have p/s and preamp cards properly removable with edge connector
-maybe 5v and or usb powered main supply since rails will be lower now
-fit it properly in tin this time, last go round it was slightly too large
-reduce to 5 channels in order to fit in screen/mini joystick/mcu controller on the backplane

-maybe some led level metering

I have the physical layout near where I want it. Without finding these samtec mini edge connectors I would not have been able to make these cards modular. Working with mini pitch headers was a nightmare on the last version.

There is some regret in lowering the channel count but there's no way to fit 6 channels in with these edge connectors and the mini oled screen. Also a little regret in ditching the android bluetooth interface, especially because it worked. But I'm leaning toward having everything in one box.

I checked the visibility/workability of this .66" screen and it's just about perfect. The contrast is high enough that it offsets the small characters. I'm planning on two screens: main screen for gain and pan --->>navigated to a secondary screen for phantom and phase. I can't fit everything into one screen of 64x48 characters.

The mcu runs at 3.3v, the oled runs as 3.3v, and THAT spi runs 3.3v. The screen actually wants 7v but it has an onboard charge pump that takes 3.3v and I suppose doubles it and 6.6v is close enough.

Will post schems soon. Have never done any digi controlled switches so I need to read up, and haven't figured out how or if to tie in all the device resets.

Re: That1580/1510 mini mixer

Posted: Fri May 08, 2020 11:25 am
by JR.
over the decades I have done my share of electronic switching, what do you have in mind?


Re: That1580/1510 mini mixer

Posted: Wed May 13, 2020 1:34 am
by weroflu
JR I have not ignored you, just busy working on the power supply before I get into the switches. The previous version p/s used an ltm8049 micromodule (with bga footprint) for the opamp rails and the TI tps7axx low noise +-regulators. I did have room on the board to go this way, but decided to try to eliminate one daughter board as above and also get away from the bga footprint.

Decided to use +-5v rails as 15 was way overkill for line level. And settled on 5v-9v Vss. Using LT3032 dual ldo for the rails which clock in at 20/30uV noise, a little noisier than the TPS7a3/4 series regulators, but it's more compact and I doubt it's going to make any difference in the end.

I was looking over the LT8330 (which I use for phantom) datasheet and supposedly this can take care of my rails. Inductor selection is over my head but I used the coilcraft spreadhseet tool and cross referenced that with LT's eval board to choose LPD50x0 series. A few mm's smaller footprint of coilcraft vs. Wurth (too large) makes all the difference so I can just about fit in two lt8330 blocks for the rails now. I have no idea if switching noise will creep back into audio, so we'll see what happens when it's built.

It could be interesting to make some mini lt8330 generic dc converter boards. Maybe I can work out a way to jumper in all three topologies into one board - boost, sepic, and inverting. I'm trying to stay away from more daughter boards but this would sort of solve any p/s design in the future.

I looked briefly into led metering. The only place there is room is on the preamp daughter boards, and it looks like the easiest solution is for 1 mcu per daughter board to drive the led's. Not sure if I want to make things this complicated. Maybe there will only 1 stereo output meter, if anything. Or a tiny soc monitor speaker.

Also thinking about a dead man power switch that cuts off the Vdd supply to the mcu/oled section, just in case there is too much digital noise injected. Last go round this was not the case.

Re: That1580 mini mixer

Posted: Wed May 13, 2020 9:02 am
by JR.
I don't know how many audio paths you will have but I found huge utility from a bicolor LED per path, green for signal present and red for overload (say 3dB below saturation).