DIY Active Direct Box w/ Adjustable gain

[familyortiz]

Hey All,
I'm jazzed to get and share some ideas round here.
I got a great design that I'd like to share and although I can't upload the pdf of the schematic yet, I figure I'd share the link to the heart of the design which pretty much contains great app notes to go by.
The design is for an active direct box which uses the Analog Devices SSM2142 balanced line driver. I've added an input section which consists of:
1) A stereo 1/4" input which can be used mono or stereo. Great for inputting 2 guitars or other.
2) I used an OP270 (dual opamp) for both the input stage inverting amp and then into an inverting gain stage with variable 0.1 to 2.1 gain, fed into the SSM2142.
This comprises 2 - 8 pin chips, 4 resistors and 1 pot as well as decoupling caps for both chips. Implementing this balanced line driver is a snap and I've handwired this small board on simple, ground planed protoboard.
The output connector is a male xlr. I can imagine adding a 1/4" link output.
I used an Acopian ac to dc supply +/- 12v or 15v (100mA output or better) give great headroom and are easily fused, wired, and mounted in a chassis, which was a die cast aluminum box.
Sorry for not being more prepped with pix and such but I'll post soon. This has been a really great performing device, useful, very quiet and simple to build.

http://www.analog.com/en/audiovideo-products/audio-signal-processors/ssm2142/products/product.html

[TimWaldvogel]

It's Bren awhile since you posted this. But any chance you have a schematic or a layout for your design? I would love
to build it

[familyortiz]

Tim,
  I just uploaded the schematic yesterday in the MISC section of the schematics area,  which I did see as posted, titled "2CH BALANCED LINE DRIVER WITH ADJUSTABLE GAIN."
Plz let me know if you cannot find it and if so, I could send you a pdf of the schematic, directly, and maybe a few pix of my build.
The device has been a workhorse, but what differentiates it from other direct boxes is the mono or stereo input if you would want to send, say, 2 guitars to the board or other.
If you look at the data sheet for the Analog Devices SSM2142, you will see an app note showing how to implement the driver. It was really a snap.   Regards,  Mike

[familyortiz]

Try this...


http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=44224&g2_GALLERYSID=63ca859bb0bd3c802fe4530d84325732

[Pedro26]

Hi Mike,

Could you post photos etc of your build ?

I'm in the UK Acopian, is a US company getting one could be difficult, does that power supply have special characteristics, like stability etc ?

Thanks,

Pedro

[ashcat_lt]

The input impedance on this box is too low for a passive guitar.  It'll probably work reasonably well with most pedals as a source, but at that point it's pretty much redundant.  A straight wire TS>XLR cable will accomplish the important part of what this does.

[tubegeek]

Note that the most recent info is from 2011 - you might not get an answer 

[GibsonGM]

Could up the input and feedback resistors, no?
I asked this in 2011; there was a delay in it being posted til now   

[ashcat_lt]

Could up the input and feedback resistors, no?
I asked this in 2011; there was a delay in it being posted til now   

Well, bumps is bumps. 

You could increase the input and feedback resistors, but that's supposed to also increase noise.  I guess I don't actually know how big of a deal that is, but I've always heard the trade off isn't worth it.