24 channel mixer the "Stereotype"

[kante1603]

Hello Gary,

yes,thanks for the hint.I thought about it when I bought precision types for the bus resistors.
So I went the "biasing" way,and it worked pretty well with the trim pot.Used my cmrr adapter plug that I had built/used for Jeff's preamps.It was super easy to dial in with a scope,and to give myself a proof I tried it with my old fluke dmm too.Worked fine,the "golden spot" was easy to find within say about a quarter turn on the pot.

Thanks for helping,

Best regards,

Udo.

Btw,I used one of these pcbs for testing my last 30 doas from you.

 

[prescott]

Hello!

Is there any of the summing boards available at the moment?
(Or someone want to sell?)

I'd buy 2 of them.

Thanks!
Peter

 

[JayDubrek]

Boards are available here Peter- http://www.groupdiy.com/index.php?topic=49242.0

...but I think Don may have a lot on his plate judging by the notice at the top of his white market thread....
Jay

 

[hakanai]

Ok so I am not totally recovered from the surging Gowanus Canal, but I am going to get moving forward anyway. I should have some mixer boards available in the next week or so. I will rummage through my emails but anyone who has contacted me and not heard back or been asked to wait, please contact me again. Pan boards are gone as well as my remaining stock of Elna caps. I am not sure when I will be getting more of these but I will keep the white market thread up to date.

New things! So I have been thinking of building myself a more full featured mixer for live to 2 track work. I am thinking of doing a small daughter board that would connect to the "fader" point on the current mix boards. It will have footprints for a fader pot, pan pot, and some facilities for Auxes. i am thinking 2 auxes with the second aux switchable between Aux bus 2 and a post aux fader direct out (no bus just balanced direct out). Basically I am going to try and make it simple so people who just want easy implementation of pan and fade can use it, but also have bunch taps for whatever you want to do (maybe a solo, ooh la la!).

Let me know what you guys think and if there is anything that you would like to see added. Also the physical format of the board is open to input as well. I have been going back and forth between making it a single channel board and making it a bank of 4 channels per board. I am leaning towards single channel boards as it makes things more flexible in terms of front panel layout and total project implementation.

don

ps get those .1% like Gary mentioned! I'll update the BOM...............soon-ish

 

[kante1603]

Hello Don,

nice to have you back and I hope everything will be fine soon!
About functions:A non-destructive solo would be great.

All the best,

Udo.

 

[hakanai]

Thanks Kante.
As for solo, I was thinking of adding another aux tap on the board that feeds a mono summing amp and then a "monitor source" switch which would also have your 2mix as an option. Then put a momentary switch on each channel that acts as the solo switch. It sounds a little convoluted but it is a far simpler way to solo. it could be pre or post fade depending on how you wire it and it would be non-destructive, so using it during a live to 2 mix would be ok.

oh and did I mention this daughter board will add a fader buffer? yeah so we should be able to do all sorts of nonsense with it.

 

[JayDubrek]

So this sounds like a 'slimmed down' API input card...is it using a DOA as a fader buffer in the same way? If so you could include some points to hook up an output transformer for an optional direct out.
Definitely think a single channel module for this!
Also just a simple solo solution if folk want it- people using a DAW will probably use the solo function ITB?
I would definitely be interested in several of these boards if they happen Don.
Cheers
Jay

 

[hakanai]

Jay, it's definitely happening, in fact it may be happening this week. I am going to a friends place today to talk about the schematic and decide on features. I am aiming to make this board as flexible as possible so people can do whatever they need with it. I'll post what we come up with in the next day or so.

don

 

[hakanai]

Ok so this is what the new board is looking like:

1 footprint for a fader (pot)
1 footprint for a pan (pot)
8 pre fade aux taps
1 pre fade transformer out tap
8 post fade aux taps
1 post fade transformer out tap
1 mute
1 discreet fader buffer

I am going to attempt to make this fit vertically on a 2 RU faceplate so it can just hang off the pots. Now I'm off to draw the pcb! Let's hope it all fits

 

[JayDubrek]

That sounds great to me Don- nice one!

 

[grubbyliver]

1 footprint for a fader (pot)
1 footprint for a pan (pot)
8 pre fade aux taps
1 pre fade transformer out tap
8 post fade aux taps
1 post fade transformer out tap
1 mute
1 discreet fader buffer

Holy smokes
Will it be possible to use the stepped pan boards with this?

Ben

 

[kante1603]

Hi Don,

so do I get it right and this board still connects to the fader point of the existing boards?

Udo.

 

[hakanai]

The idea is that it will pick up at the fader point and return at the pan point. The board will have footprints for a pan pot but you can of course put the existing pan switch boards on short flying leads.

the question I am wrestling with now is how to deal with the aux bus'. Do I put a footprint for ribbon cable, or do I simply leave it up to people to make bus bars? Or maybe I put the bus out holes in a standard array for a pin header and we have rigid pin headers going board to board. that sound cumbersome. Not sure how I will handle this, I'm open to suggestions.

Just to be clear the only things that will mount directly to the board are the pan pot, fader pot, buffer circuit, and maybe the mute switch. Everything else will have a footprint for molex or screw terminals. That sound good to people?

 

[kante1603]

Sounds really good Don!

Personaly I prefer bus bars over ribbon cables,but that´s my preference.
Leaving parts open and having options on molexes or whatever is a good idea,just the basics is cool for,I would even leave it open to choose pots or faders for level if that helps you designing the pcb (o.k.,one could use te pot pads as needed....).

Do you have some kind of a general overview or a rough schematic for this?

Thank you Don,very good work and ideas!

Udo

 

[JayDubrek]

Im with Udo on this - I prefer pin headers or bus bar over ribbon....
Jay

 

[Trench Recordings]

I was about to order parts from CAPI but now I dont know whats needed for this new board

Grayhill 1x12 for pan and Bourns 1K CW Audio Taper for fader pots ?

Also newbie question, whats the benefit or need for a fader buffer circuit ? Is this going to double the amunnt of DOAs needed in the build ?

 

[hakanai]

The buffer is not strictly necessary for just a fader (as you can see with some of the previous builds). What it will do is create the proper support circuitry for the fader and allow us to do a few cool things. The most notable is have all sorts of pre/post auxes and have gain in hand for the fader, or to simply make up for loss, or drive the bus harder. Amps are handy! Also you can use from 1k to 25k faders now. It's just a much more stable environment for messing with your audio.

So some more info on the evolution of the board. For auxes, it will have everything you need for 4 pre and 4 post aux sends. It will also have a tap for you add up to four more of each but you will need to hang the aux bus resistors off the pots. The boards will each have a small section to be used as a bus bar for 4 (maybe 8 ) channels. Also the amp will have a DIP8 footprint as well. So that means you can use a variety of good, but inexpensive relative to DOA's, parts. There are many good IC opamps for less than $2 a piece. Which will be important when I build myself a 16 channel version with auxes and all sorts of bells and whistles. Time and cost will become a factor.

Another thing that has not been mentioned is that I will be making another daughter board as well. This will be a dual purpose board. Stuffed one way it will be an IC based mono summing amp. Stuffed the other way it will be an IC based balanced line driver. I will be using this as my aux summing amp, as well as a direct out amp. Space, weight, and cost make an all transformer/DOA implementation unreasonable for my location work, mine will be hybrid.

So continuing micro to macro trend of my post. You guys can expect more boards and kits from me. My plan is to rebuild everything I lost in the flood from scratch and offer each thing as a kit as I go. So keep an eye on the white market thread!

don

ps did I answer everything?

 

[hakanai]

oh and there will be a resistor footprint next to the fader to slug it. So linear pots can be used. Maybe i should set up the pan this way as well to get nice schmancy S curves? that seems fun.

as for a schematic, it is all just scribble on paper, but the funny thing is it ended up being almost identical to the input buffer. Only now the common mode trim will be a gain trim. So you can have a trim pot, fixed resistor, or wire off a front panel pot for all the gain a 2520 has to offer. I'll probably just do a trim pot and give myself 6db of gain in hand, but the options will be there. Other than that the only thing of note might be that the transformer taps will have protection diodes on them, and the DIP8 will have a little extra circuitry to make it happy doing the same job as the DOA.

don

 

[hakanai]

Ok So I am looking for some input here. currently the board is 2.75"x2.75" and has all the above mentioned facilities. Three things are causing me to rethink this current layout. First at 2.75 + 9.5 for the main board that leaves you 1.75 front to back space to make all the wiring fit in a Par 14" case. after that you go to the 17" monster case. Second, I have to wonder if anyone will want to use this board without auxes. Is anyone thinking of using this without auxes? And if you are going to have a fader, a pan, and at least 1 aux I suspect you will be thinking of a 3RU faceplate anyway. am I wrong in thinking this? Is anyone thinking of having fader/pan vertical and then aux1/2 next to them (in stead of below)? That seems weird and you could really only do a 8 channel mixer like that, and it wouldn't leave room for a master section at all. And finally If I make it 3RU I can put everything for 4 auxes right on the board, and I might be able to include a mute switch, solo switch, and a small recessed toggle for pre/post on each aux. Also the board would end up being smaller in terms of square inches, which means cheaper. Let me know what you guys think, because I am really liking the sound of the 3RU version.

oh it would be 1.5x4.5" I think

don

 

[kante1603]

Hi Don,

in my opinion it's not necessary to "force" anything into a par 14" case.As a european/german builder I would go for different case manufacturers anyway.
If I decided to go for long throw faders I would house them maybe in their own bucket.
For the rest 3 ru is cool I think,having mute and solo is a must- have for me.
Auxes on them?Yes,please,where else should I attach my 480? ;D
Seriously now,I like it that way,and if the width of one channel doesn't exceed 1,5" the box could nicely line up with frontends in 51 x or 500 series format modules.
Just my 2 ct.......

Best,

Udo.