24/2 1272 Summing Box

[Coop]

Hello,

Some months ago I started to work on my studio setup. Bought a couple of Avid/Digidesign Interfaces and an HD Native Card to finally be able to have Hardware Inserts that are timealligned properly.
When working on this setup I thought, why not implement a little summing box in this setup. Just a simple box with 24 Inputs and 2 Outputs. Nothing fancy.

So I wrote down some ideas

• 24 balanced inputs via 3 DB25 connectors
• Neve makeup gain stage
• Channels 1-8 either as Mono or as Stereo useable
• Attenuatur to either drive the output transformer harder or softer
• VU output meter
• -6dB switch at XLR out if the signal is too hot for the converter

And these are my first rough layouts of the circuit and the front panel.







The parts for making the 2 Neve 1272 preamps are already on it's way. So right now I'm working on the details. If anyone has some input, please feel free to comment.

Johannes

 

[ruffrecords]

How do you plan to do the mono/stereo switch?  Where are you going to pan the mono?

Cheers

Ian

 

[Coop]

Four switches on the front, one for each of the first 4 pairs, that sends both channels to the odd and the even bus.

 

[ruffrecords]

Four switches on the front, one for each of the first 4 pairs, that sends both channels to the odd and the even bus.

OK so the pan is to the centre and both inputs get sent there. Thanks.

Cheers

Ian

 

[Coop]

Yes, just both inputs panned to the center. First I thought about making In 1-8 Mono all the time, because I need a couple of mono inputs that are panned to the center for busses like kick, snare, bass,... anyways. But I figured that I would be more flexible if I add a simple switch.

 

[Coop]

A small update on my summing box build. DB25 PCBs and the other parts arrived last week and I have already assembled everything and tested it. Had to use two BA283 boards from my 1073s to test it, as the boards that will be installed in the summing box are still on their way.

Everything works so far, stepped pot is also working great. Still missing a case, the front switches to switch the first 4 channel pairs from stereo to mono and the output meters though.

I think I will integrated both the switches and the meters at a later stage. But I'm thinking about adding a switch to attenuate the output after the transformer. That way I can drive the unit hotter but not clip my converters.

 

[PermO]

Nice !

Big transformers, looking good man  8)

 

[Coop]

Thanks man!

Yesterday the B283 PCBs from avdaudio arrived. Already started populating them and discovered that I forgot to order some capacitors....

Hope the parts come in soon and I can finish and test this unit.

 

[ruffrecords]

Looks really good.

Cheers

Ian

 

[Coop]

Thanks Ian!
I hope I can finish it soon and really test it out. Still need to build some cables to hook all 24 channels up correctly and I hate soldering DB25 and Harting connectors...

 

[Coop]

It's almost done  ;D

Yesterday I finally got the case from Don-Audio. Took quite a while to get it delivered and there are also some screws missing which is not so cool. But anyways, I had some laying around to use and finish the case.

For now it's just a a simple 4 Mono/10 Stereo input unit with a little stepped attenuator for the 2Bus.

Some things I like to integrate in the future:

• VU Meter for L/R
• 4 illuminated pushbuttons to switch channels 1-8 from 4 stereo pairs to 8 mono channels
• a custom made frontpanel with a nice design

 

[innercityman]

I've just received an order from don-audio and guess what...? Missing screws !

I've sent them a mail them but no answer. I won't say anymore about them, I don't want to be incorrect.

That said, very interesting project !

 

[Coop]

Thanks man 

Well it is not the first time I had problems with an order. Couple of years ago I ordered parts for my 33609 build, including two ELMA switches. Only one was delivered. Called them and they had it posted the next day.

This time I got some extra screws that are not even needed with the case and the crucial ones like for the top plate and the backplate where missing....

 

[SIXTYNINER]

.....

Are the 2n3055 heatsink custom ?
cheers

 

[Coop]

@SIXTYNINER
Yes, the heatsinks are custom made out of aluminium L brackets. Couldn't find any low profile ones online.

 

[SIXTYNINER]

@SIXTYNINER
Yes, the heatsinks are custom made out of aluminium L brackets. Couldn't find any low profile ones online.

Much thanks for info ,
it is possible know the dimensions and thickness ?
more cheers .

 

[Coop]

@SIXTYNINER
You're welcome. I will take some pictures and measurements later.

 

[Golgoth]

Great build @Coop. I am waiting for all the parts I need to restore an old Neve 10x1 mixer with a similar design as yours. Do you by any chance have the BOM for the BA283s? I could not find them myself and that would be very helpful! Thanks!!

 

[Coop]

@Golgoth
Thanks!
Yes, I do have some stuff. I will attach it here. I think I should even have a mouser cart for both BA283 sections.

 

[Golgoth]

Thank you very very much! That's one precious document!