24 channel mixer the "Stereotype"

[funkmuffin]

Looking good funkmuffin!!

GARY

Thanks Gary!  I'd just like to extend my thanks to Don for putting together a great set of boards to build this project around.

I've been mixing through it for about a week now and I'd like to relay that this thing sounds VERY nice.  It has removed a layer of "crud" from all of my mixes!  I was going to wait to put it together until I finished the album I'm currently mixing, but I can't tell you what a blessing in disguise it was to have my old board decide to start dropping channels.  The album is going to sound loads better through the Stereotype than it would have otherwise, and I'm a happy camper!

Thanks again Don, and also, thanks to Jeff and Gary for the other important bits of the project!

P.S.  A public service announcement: when you put together your DB25s (what a pain in the ass!), make sure to double check the pinouts before you solder up!  I had to flip the order of all 24 channels at my patch bay because I wired the DB25s backwards...  Coulda rewired it inside the mixer, but that's just too many cables -- the patch bay was much quicker, and I wanted to make some damn music with it.

 

[hakanai]

ok so i just emailed the fab house and I will hopefully be receiving a pile of revised boards in a little over 2 weeks. I did order switch boards as well. also since I ordered quite a few more this time, so the price should also come down per board. I will post the list of revisions soon, for now i need to figure out if this will be a white or black market thing.

thanks for all the interest
don

 

[fenchelteefee]

Hi don, im in for two boards and switch pcbs. Let me know when you're ready.

Thanks

 

[grubbyliver]

I'm in for 16 switch boards if you have enough, thanks Don.

Ben

 

[hakanai]

I should be seeing boards early next week. I'll keep you guys posted.

don

 

[mrcase]

great!  ;D
do you have an idea how much the pcbs are?

 

[fenchelteefee]

Don,

Please count 24 channels with pan pcbs.

Don, other forum fellas,

I'd like to take advantage of the fader option (penny giles) and 8 channels of S800 EQs. In addition, a bypass push button to exclude the fader + eq section, keeping the signal path as clean as possible would be nice. Any mods needed to do this or is this straightforward to implement? PSU extension for additional Eq eeded?

Thanks for advice for any sugestions.

 

[GregNey]

Hello, I'm in for 24 channels worth (so 3 PCBs), no pans. Thank you so much for putting this together!

 

[anjing]

What is new on the revised board? Is it just fixing the fader option? I'm interested in a few boards with pans also.

 

[hakanai]

The new boards changed by:
1. caps added in parallel to R3 for better CMRR
2. smaller caps used for DC blocking, allowing for a much less cramped layout
3. revised trace layout

I had an EE friend look over the board and give me feedback. Functionally it can be built exactly the same as my original version, but these tweaks should allow for better performance overall. The fader option was fixed in the last revision, so it didn't change for this one.

Talked to the PCB fab guy today and he said they are in production now. That means I should see them early next week.

I think the prices will end up at 40 USD for the 8 channel main board and 3 USD for the switch board (or 20$ for 8 boards). There will be a white market thread as soon as I have them in hand and confirm they are up to snuff.

I have had some questions regarding PSU's and opamp compatibility.

PSU - there are kits available on this forum for various projects. Alot of these will work. What you need is a bipolar supply capable of +/-15v-17v (a larger range is fine as well). Remember, the opamps give their power specs for what they want at their pins not what the supply puts out. So if you are using the blocking diodes (if you don't understand what these are doing please use them, if you do then I'll leave it to you to make your own informed decision) then you are losing a volt there. Meaning you will want to trim your supply to +/-16v instead of 15. Jeff's summing board uses the same blocking diodes, so if you are confident you will not wire the supply lines backwards you can skip these diodes on both boards and have no need to compensate. As for draw (Amp capacity) you need to look at the spec of your desired opamp and multiply it by the number you will have in the box. So a SL Red Dot, for example, draws 60ma MAX. If you have a 24 channel box then you have 28 (channels+summing) opamps potentially drawing 60ma (this is the totally over mic'd drumkit crushing mix down). So that is 28*60=1680ma. So unless I am completely burnt out right now, that is 1.7A potential load. This mixer needs a PSU with more capacity than 1.7A. How much more? That's your call. I used my own 3A PSU and my box, 24 Gar2520's and 4 SL Re Dots, always seemed happy, but that was my mixer, in my studio. I think the guys who have shared their builds in the thread have mentioned what they are using for a supply, so be sure to go through the thread.

Opamp Compatibility - The circuit was designed from the original 2520 application sheet and then tweaked based on the input section of an old API desk. Anything designed to be a drop in replacement for the API 2520 SHOULD work. I have only personally used the Gar2520's I made from Gary's kit. If you want to use another opamp with the same footprint (990, gar1731, Forsell, or any of the many other) I would send the stereotype schematic to the designer and ask if any values should be adjusted. If you do that, please be sure to report back any info here in the thread. I am excited to see some of the mutations people will inevitably be building.

ok, that's enough typing for this post
don

 

[funkmuffin]

Just dropping in to back up Don's power supply info above, which is spot on.

It is supposedly very simple to knock together a simple bipolar supply, but I didn't trust myself, so I went with a GDIY51x PSU, and only built out two of the rails.  I'll gladly recommend that approach, as it is a really solid board, very well documented (and several board members offer parts kits to make it even easier!) and can be built out to different specs, based on your needs with just simple value changes.  In my case, I went way overboard and built a 3 amp supply using LM350 series regulators, and have it putting out 18 volts.  Works great, plus I've got 3 more rails I could build out for different purposes at a later date.

Just make sure you provide adequate heat-sinks!  I had thermal shutdown issues with the dinky little ebay sinks I tried first.  Beefed those up, and this thing is more or less bullet-proof.

Ryan

 

[fenchelteefee]

Friends, what about my question about adding the S800 EQs (or Sontec 8) to the boards? Both have a a build in bypass function as far I see, but I'm uncertain @ which point to interconnect them. Any mods needed anwhere?

the chain would be be:

line receiver (2520) - fader - pan - EQ (with built in bypass) - 2 ACA

Thanks for your feedback,

 

[hakanai]

I am not sure what you would need to do to get that particular circuit to sit happily inside this one, but your signal flow would be more like - line receiver>EQ>fader>pan -. the fader point in the board is right after the DOA.

don

 

[fenchelteefee]

Thanks don for your chain suggestion. Maybe anyone else can give insights on how to link individual channels of the summing board with S800 or Sontec 8 EQ's?

I believe, this would be killer mixer project incorporating high quality EQ's with gain pots/faders and active API summing. Anyone else interested who might support this idea?

I recently discovered a mixer chassis that would make perfect fit:

http://www.elcal-system.com/de/Standardgehaeuse/Kleinpult-Gehaeuse-

Thanks guys!

 

[Pliplo]

im in for 24ch worth of everything

first post yay !

 

[anjing]

Thanks don for your chain suggestion. Maybe anyone else can give insights on how to link individual channels of the summing board with S800 or Sontec 8 EQ's?

I believe, this would be killer mixer project incorporating high quality EQ's with gain pots/faders and active API summing. Anyone else interested who might support this idea?

I recently discovered a mixer chassis that would make perfect fit:

http://www.elcal-system.com/de/Standardgehaeuse/Kleinpult-Gehaeuse-

Thanks guys!

That mixer chassis would make me very happy, looks like it's only available in germany!

I am thinking of inserting a passive EQ as well, i was thinking of using one board of 8 channels for 4 inputs. The first 4 as input from the fader insert point to the eq and then the next four as makeup gain then to the fader and pan...

 

[fenchelteefee]

Anjing, this is a german company, but im confident they communicate english. If not, i speak german and will help you if nessecary.

The s800 and sontecs im focused on are both active. Am i right in saying that because of the active design, i dont need to have the stereotype boards twice each channel, like you describe?

Again, is there anybody out there, who may help me clarifying how to link the eqs and the boards with faders together? Simply daisy chain? Is it that straight forward? Thanks to everybody for chiming in.

 

[anjing]

Using twice the boards is just an idea like that, more like brainstorming. Is the sontec balanced in and balanced out? If so why not just put it before the stereotype input.
 

 

[mrcase]

great I´m in for 2-3 Boards plus some Switches PCBs

 

[hakanai]

Ok the new boards are in hand. I am waiting on a part to make sure everything is kosher with the boards and then I will open the white market thread. Should be at the end of the week.

thanks
Don