Building my own live mixer

[mayfly]

With Mouser (or Digikey, or Allied, or Future, or...) all I need to do is say "Ross Video" and they wave whatever fees/minimums.  I might even be able to get engineering samples of these 

 

[Cagey]

Yeah, I forgot who I was talking to for a minute there. Almost deleted the post as pointless, but left it for the story anyway.

 

[mayfly]

Come on! It's a great story - and instructional too!  :headbang:

 

[mayfly]

next day delivery from DigiKey:

 

[Cagey]

You gotta love Digikey.

They're a funny outfit. You get the impression from their ads/flyers/catalogs that they're a buncha dingbats on a par with Radio Shack, but they actually have a comprehensive stock and do a good job of getting it to you quickly at reasonable prices.

 

[fdesalvo]

Haha the smell.  Last time I smelled that, the odor was preceded by a filter cap exploding sending plastic shrapnel into my chest and poly fibers all over the room.  Caps don't like AC!

Nice work, though!  I really dig this project.

Yeahh - Digikey.  Worst user interface of all time, but they seem to have everything.

 

[Re-Pete]

Now if I were to build a, say, 16 channel console that used 500 series modules for the pre and EQ sections, then just sold the frame (which would include mix bus, faders, aux buses, power supply, optional automation etc) then that might be interesting.  Then the spiel would be to just drop in the 500 modules of your choice and build a mixer to your liking!

100mm fader modules......some of us started music in late 70s & got used to riding faders not twiddling vintage knobs.... and yes, GREAT idea about an empty mixer board waiting for 500 modules. I think there's one or two makes of those out there but usually they are SO boutique you need to mortgage your house to buy the board....

 

[Re-Pete]

So I fired up that mixer and played around with it.  It sounded so good I started to sing/play a bunch of songs.

Then it happened - I smelled the smell. Anyone who has built or dealt with electronics has smelled the smell.  The 'something is wrong and there's a piece of silicon that's on the edge of exploding' smell.  I shut it down and did some investigation.  my 78/79 series linear regulators were just on the verge of melting down on me. 

I guess those heatsinks really do something after all.  :icon_jokercolor:

So I improvised some heatsinks and fired it up again.  Things seem to be under control, but I guess I'll have to do a bit of thermal analysis after all.

 
Blew up an old amp years ago and that smell was in my bedroom for ages...... thankfully you didn't see  smoke & a blue flash.  :icon_thumright:

 

[Cagey]

Blew up an old amp years ago and that smell was in my bedroom for ages...... thankfully you didn't see  smoke & a blue flash.  :icon_thumright:

Thankfully?! I'd say you got cheated. If you're gonna blow up an amp, you should at least get to watch  :laughing7:

 

[mayfly]

ok!  the next thing to do is a line level stereo input for either an iPhone or electronic drums.  Since this input is unbalanced, I decided to not do anything fancy - just straight into op-amps (and a 10K load).  The gain of the first stage was determined by experimenting with running an iPhone (and those drums) into the instrument inputs.  volume, pan, bus, and overload circuits remain unchanged.  Well, kind of -  the volume is actually a stereo pot and I'm running both left and right into the overload circuit - why not! 

The two switches are a ground lift, and a 'mono' (runs left channel into both left and right).  Why left? Because that's the one on the tip of your TRS plug (that would be grounded if you're plugging in a mono plug).

Here's the schematic,

and here's the layout:

 

[mayfly]

Decided I should re-work the power supply / bus mix and output board at the same time.  This page shows the bus mix, a buffer stage, and the balanced output drivers.  The bus mix is essentially a text book summing mixer.  The buffer stage is after the master volume control and I'm actually not sure that I'll need it. I've got it set to a gain of '1' in the prototype.  I've got a pair zero ohm resistors in the schematic to bypass the whole thing if desired, which I may do just to try it.  For the balanced output drivers, it's THAT corp to the rescue again. 

and here's the power supply stage.  It's as simple as it gets really.  The things along the bottom are the heatsinks for the regulators.

 

[mayfly]

aaaaaaand here's the layout:

 

[Cagey]

Looks great! Very professional.

Trevor's gonna take over the mixer world!

All you have to do now is subtract the R&D, logistics, marketing, labor, insurance, regulatory fees, facilities costs, taxes, economies of scale and profit, and you could compete with Behringer!  :laughing7:

 

[mayfly]

the toughest thing is sales.  It's a full time job selling stuff like this!

 

[Cagey]

Well, that and getting somebody to work for $.25/hr. Kids won't even tell you to kiss their ass for that kind of money.

 

[bagman67]

Well, that and getting somebody to work for $.25/hr. Kids won't even tell you to kiss their ass for that kind of money.

Heck, Cagey, I'd tell you to kiss my ass for *free*!  Wait, that's not what you meant, is it?


Ducking and running now...

 

[Cagey]

:doh:

 

[mayfly]

Update:  The board shop just let me know that the PCBs have shipped.  Time to buy those parts at mouser!

 

[mayfly]

Getting bored waiting for the boards  :icon_jokercolor:

Decided to start working on the top panel.  Here's a sketch:

 

[mayfly]

Late night spent with the front panel express design tool.  The engraved circles are the size of the knobs I'll be using so I can judge how close to put text etc.

More tomorrow