Building my own live mixer

[Re-Pete]

I know you are doing this to serve your own purpose but have you considered, if it turns out great, doing it in 500/Lunchbox format and selling modules?

I know your manufacturer days are over after the Vox-ish amps finished up, but yeah, there's a market out here for streamlined down electronics that are made to purpose without bells & whistles, I bet.

 

[Logrinn]

I know you are doing this to serve your own purpose but have you considered, if it turns out great, doing it in 500/Lunchbox format and selling modules?

I know your manufacturer days are over after the Vox-ish amps finished up, but yeah, there's a market out here for streamlined down electronics that are made to purpose without bells & whistles, I bet.

Hear, Hear!

 

[mayfly]

I know you are doing this to serve your own purpose but have you considered, if it turns out great, doing it in 500/Lunchbox format and selling modules?

I know your manufacturer days are over after the Vox-ish amps finished up, but yeah, there's a market out here for streamlined down electronics that are made to purpose without bells & whistles, I bet.

Well, I have built a few 500 series type modules, but the problem is that now everyone and their dog is doing it.  Case in point:

The barrier to entry is low, and there is a lot of competition even in the DIY space.  And of course every flavor is already available.  Nothing I could do would add any differentiation to what's already out there.

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!

 

[mayfly]

More updates.  Another box from Mouser, and another bare board.  Time to get stuffing:

 

[mayfly]

Well that was easy.  The line pre lit up with no issues.  However, I think I won't put in the gain switch: the -10dbu seems to work with everything.

Here's two mic pres and two line pres all together with the power supply and summing mixer.  Looks cool, but how does it perform?

 

[mayfly]

Here's the other side

 

[Logrinn]

Looking cool, indeed! :icon_thumright:

 

[Axkoa]

That's actually awesome, looks really clean. Super inspiring.

 

[Cagey]

So, have you figured out what you're going to do about packaging all that stuff up yet?

 

[mayfly]

So, have you figured out what you're going to do about packaging all that stuff up yet?

Yep - I'm going to mount everything to an aluminum top plate, probably from Front Panel Express. More testing needs to be done though - I need to verify the unbalanced performance of the line pre and then decide on the HPF in the mic pre.  I thought I'd like the toggle switches on the line pre, but I'm thinking of switching them out for push button switches (which you can get in the same form factor).

 

[rgand]

This is looking really outstanding.  :icon_thumright: :icon_thumright: :icon_thumright:

 

[mayfly]

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.

 

[bagman67]

I know the smell.  Thank goodness you detected it BEFORE your component blew and your board got burned beyond rescue.

 

[Cagey]

Mmm... the dreaded smell... Been there, done that. Never forget it. It's like your first lover's perfume, etched in your memory as indelibly as... something indelible.

 

[Axkoa]

I think I sorta know the smell...I haven't done much work with electronics before but is it sorta like if you accidentally, somehow, forget to put water in with your 2 minute noodles in the microwave and it breaks the microwave...?

Not speaking from first hand experience of course...

 

[Logrinn]

I think I sorta know the smell...I haven't done much work with electronics before but is it sorta like if you accidentally, somehow, forget to put water in with your 2 minute noodles in the microwave and it breaks the microwave...?

Not speaking from first hand experience of course...

I guess that would be the smell ... topped with noodle seasoning of course :toothy12:

 

[swarfrat]

Yeah, any time you need to dissipate more than a half watt or so you really should do a dissipation check. Just think if instead of almost working, it worked pretty darn well.... for a couple years.

 

[BigSteve22]

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

A good dose of thermal compound, (I like Arctic Silver), is also a good idea....

 

[mayfly]

ok!  Let's do some thermal analysis.  The good old 78xx and 79xx series regulators are well understood.  Here's the thermal rise charts as published by ON semi for the 7815:

As you can see, when running with no heatsink, you can only get about 2 watts of power out of it at 25 deg C.  Doing the math, this turns out to be 133mA.  Doing some measurements, each strip seems to be pulling about 50mA out of each rail, which means that 4 of them would be pulling down 200mA.  Hence the thermal rise over time leading to the smell.

Ultimately, I want to run a fully loaded mixer with 8 strips (which includes the compressor side chains).  Assuming 50mA each, this leads us to 400mA of current, which implies 6 watts of dissipation.  From the chart, this means we need to use a heat sink of at maximum 15Deg rise per watt, and it would be nice to be even lower for reliability.

A search on mouser turns up this little guy:

http://ca.mouser.com/ProductDetail/Wakefield-Vette/265-118ABHE-22/?qs=sGAEpiMZZMttgyDkZ5WiuqOKhVZf43mJV9bYA6ECl8w%3d

Which at 7deg/watt would do the job nicely.

 

[Cagey]

This reminds me of a brief period where I was able to make some money on Bugera's engineering department's refusal to acknowledge that they didn't do what you just did - analyze the circuit. They just ballparked it, and installed these 7805 regulators without heatsinks. Math said it was close, but ok. Thing they didn't take into account was the regulator was installed inside dead airspace in a tube-type amp, where temperatures are normally high when everything is working right. So, the rise curves were NFG as ambient was way off to start with. Regulators stopped regulating after a while, and the sfx/control circuit would stop working. People were returning their amps left and right, or in some cases putting them on ebay for a song. I was buying them up, installing a heatsink or maybe even a new regulator + heatsink, and increasing the value of the amp by $150 with a $5 investment. Fun while it lasted, but eventually they wised up and started putting the sinks on in production, putting the brakes on my gravy train. So, if you ever come across a Bugera V22 or V55 that isn't being used because it's flakey, offer 'em $25 for the thing and you can fix it for next to nothing and flip it. They're actually pretty nice amps when they work.

Anyway - doesn't Mouser have a $25 minimum order? I know Allied does. Maybe you need a roll of solder and a stand to go along with that heatsink. Or, maybe you have an old piece of electronic gimcrackery laying around that you could poach a heatsink of of. Those things are common as dirt. I think I've got several here left over from the amp repair days.

What am I thinking of? You're buying gobs of components already, so you're covered.

Never mind!​